SMITHSONIANINSTITUTION
UNITED STATESNATIONAL MUSEUMBULLETIN 233WASHINGTON, D.C.1963

MUSEUM OF NATURAL HISTORY
Host Relations
of tlieParasitic Cowbirds
HERBERT FRIEDMANN
Director, Los Angeles County MuseumResearch Associate, Smithsonian Institution
SMITHSONIAN INSTITUTIONWASHINGTON, D.C. ? 1963
Publications of the United States National Museum
The scientific publications of the United States National Museum include twoseries, Proceedings of the United States National Museum and United States NationalMuseum Bulletin.In these series are published original articles and monographs dealing with thecollections and work of the Museum and setting forth newly accquired facts inthe fields of Anthropology, Biology, Geology, History, and Technology. Copiesof each publication are distributed to libraries and scientific organizations and tospecialists and others interested in the different subjects.The Proceedings, begun in 1878, are intended for the publication, in separateform, of shorter papers. These are gathered in volumes, octavo in size, with thepublication date of each paper recorded in the table of contents of the volume.In the Bulletin series, the first of which was issued in 1875, appear longer, sepa-rate publications consisting of monographs (occasionally in several parts) andvolumes in which are collected works on related subjects. Bulletins are eitheroctavo or quarto in size, depending on the needs of the presentation. Since1902 papers relating to the botanical collections of the Museum have been pub-lished in the Bulletin series under the heading Contributions from the United StatesNational Herbarium.This work forms number 233 of the Bulletin series. Frank A. Taylor,Director, United States National Museum.
UNITED STATESGOVERNMENT PRINTING OFFICEWASHINGTON : 1963
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Contents PagePreface viiA comment on cowbird parasitism 1Brown-headed cowbird 5Discussion 5Frequency of host selection 6Changes in host selection 9Intensity of parasitism of frequent hosts 12Breeding success of host and parasite 15Hatching potential of host species 21Mutual effect of parasite and host on egg production 22Duration of parasite's interest in host nests 25Interspecific preening invitational behavior 29Foster parent-offspring relationship 31Reactions of host to parasitism 33Hosts known to have reared young of parasite 37Hosts of the brown-headed cowbird 41Bronzed cowbird 173Discussion 173Hosts of the bronzed cowbird 175Shiny cowbird 189Discussion 189Imperfections in host relations 189Frequency of host selection 192Destruction of host eggs by parasite 196Hosts known to have reared young of the parasite 196Hosts of the shiny cowbird 199Screaming cowbird 216Giant cowbird 218Literature cited 223Index 253V

PrefaceCowBiRDS are an ideal group in which to study the biology of broodparasitism; within the six included species there are displayed allstages of the development of this mode of reproduction ranging fromthat of the non-parasitic baj^-wing through those of the completelyparasitic screaming, shiny, brown-headed, bronzed, and giant cowbu'ds.The present report deals only with their host relationships, as thisis the aspect of their biology in which our knowledge has shown thegreatest increase since my initial over-all discussion was published in1929.It is assumed that the majority of users of this monograph will beinterested chiefly in the common North American species, the brown-headed cowbird, MolotJinis ater; accordingly, the more detaileddiscussion of this buxl is presented first, constituting the major part ofthe report. This is followed b}^ a shorter but similar treatment of theother North American species, the bronzed cowbird, Tangaviusaeneus; then by a discussion of the two South American parasiticspecies, the shiny cowbird, M. honariensis, and the screaming cowbird,M. rufo-axillaris ; and finally by a discussion of the giant cowbu'd,Psomocolax oryzivorus, of Central and South America. The phj'loge-netic sequence is thus ignored for the interest and convenience of thereader. For a description of the phylogenetic relations of the includedspecies, the reader is referred to pages 343-346 of my 1929 book. Iknow of no recent information that would cause me to suggest anyalteration in the picture presented there, except that which is given inthe present discussion of Psomocolax (see pp. 216-222).For the two North American species I here submit complete anno-tated catalogs of their hosts, in answer to many requests that havecome to me over the years from students and investigators of variousones of the included host birds. In the case of the South Americanshiny cowbird and the Central American giant cowbird, the unfortu-nate general lack of interest in birds in these areas has made it unneces-sary to produce a similar new host catalog at this time, although ourknowledge of the victims of both species has increased as greatly asthat of their North American counterparts. Accordingly, I haveincluded a complete tabular outline of the known victims of each ofthe races of the parasites, but I have written accounts only of newlyadded hosts and of those others of which our estunates as cowbu'dvictims have been altered by recent information. Since there hasvn
VIII IJ.S. NATIONAL MUSEUM BULLETIN 233
been little change in our knowledge of the screaming cowbird, only ashort summary is given for this species.Inasmuch as the completeness of our knowledge varies with thedifferent species of cowbirds, the detailed discussion of such biolog-ical matters as host selection, the relative frequency with whichdifferent species of these hosts are utilized, the success rate withwhich these birds serve as fosterers, and the various reactions theygive to the parasite and to the incidence of parasitism are all givenin the account of each species of cowbird. As might be expectedfrom the interest discussed above, the data are incomparably moreextensive, and thus more amenable to analysis and interpretation,for the North American brown-headed cowbird than for any of theothers. Because of this, the chief biological discussion and sjmthesisare given under that species, even though parts of the thoughts andconclusions are applicable to the others as well.The present study of the host-parasite relations of the cowbirdshas been a long time in progress. Not only has a great mass of databeen accumulating slowly over several decades, but newer insightsand better methods of evaluating and interpreting the facts havebeen brought to bear as the material permitted. Much of the presentdata is due in large measure to the kind cooperation of many observ-
ers, collectors, and custodians of collections, all of whom havegenerously sent me numerous interesting records that otherwisewould not have been available.As previously mentioned, my first discussion of the subject appearedin 1929, and short supplements, chiefly of new host species, havebeen issued at intervals between 1931 and 1949. Since acknowledg-ments were made in each publication to the individuals who con-tributed information, it is imnecessary to repeat them in the presentwork. However, those contributors subsequent to my 1949 paperare given here in alphabetical order. While it is true that manydeserve a greater measure of thanks, all sent me what they could, andit is better to express my gratitude impartially.I am indebted to the following for their contribution to the prepara-tion of this work: Mrs. F. C. K. Anderson, Georgetown, Barbados;Dr. A. J. Berger, Ann Arbor, Michigan; Mr. D. A. Boag, Edmonton,Alberta; Mr. T. D. Burleigh, Washington, D.C.; Mr. E. A. CardiflP,Bloomington, California; Mr. E. J. Court, Washington, D.C.; Dr. I.McT. Cowan, Vancouver, British Columbia; Mr. R. S. Crossin,Tucson, Arizona; Mr. A. R. Davidson, Victoria, British Columbia;Mr. W. E. Godfrey, Ottawa, Ontario; Dr. P. Harrington, Toronto,Ontario; Mr. E. N. Harrison, Los Angeles, California; Mr. F. Haver-schmidt, Paramaribo, Dutch Guiana; Gunnar Hoy, Salta, Argentina;Mr. J. B. Hurley, Yakima, Washington; Mr. J. D. Hyatt, Anniston,
PREFACE IX
Alabama; Mr. T. A, ImhofF, Fairfield, Alabama; Miss M. F. Jackson,Vancouver, British Columbia; Dr. R. F. Johnston, Lawi-ence, Kansas;Dr. M. Koepcke, Lima, Peru; Mr. R. Kreuger, Helsinki, Finland; Dr.F. C. Lehmann V, Popaj^an, Colombia; Dr. R. McCabe, Madison,Wisconsin; Dr. D. McGeen, Pontiac, Michigan; Mr. S. Marchant,London, England; Dr. C. J. Marinkelle, The Hague, Holland; Dr. J. T.Marshall, Jr., Tucson, Aiizona; Dr. T. C. Meitzen, Refugio, Texas;Mr. W. P. Nickell, Bloomficld Hills, Michigan; Mr. F. F. Nye, Pharr,Texas; Dr. R. T. Orr, San Francisco, California; Dr. Johann Ottow,Skelleftea, Sweden; Mrs, K. Paton, Oxbow, Saskatchewan; Dr. A. R.Phillips, Distrito Federal, Mexico; Mr. E. Z. Rett, Santa Barbara,California; Mr. J. Stuart Rowley, San Mateo, California; Mr. L. L.Snyder, Toronto, Ontario; Mr. R. E. Stewart, Laurel, Maryland; Mr.L. M. Terrill, Melbourne, Quebec; Mrs. S. Wakeman, Martha's Vine-yard, Massachusetts; Mr. A. Walker, Tillamook, Oregon; Dr. R. E.Ware, Clemson, South Carolina; Dr. D. W. Warner, Minneapolis,Mmnesota; Col. L. R. Wolfe, Kerrville, Texas; Mr. J. Woodford,Toronto, Ontario.

Host Relations
of theParasitic Cowbirds
A Comment on Cowbird Parasitism
IT IS OBVIOUS that the host-parasite relation is an essential aspectin the appraisal and understanding of any given example of aparasitical mode of life. What is less obvious is the equal importanceof the delimitation of the requirements involved in these relations.It is necessary to determine the degree and the frequency with whichindividual host species are parasitized and to ascertain not merelyhow amenable they may seem to be as victims but how successfulthey are as fosterers. The results of such a survey should make itpossible to deduce which factors tend to make certain species suc-cessful hosts from the standpoint of the parasite and others unsuc-cessful?or, to view it from the opposite side, which factors tend toprotect certain potential hosts, and not others, from the attentions ofthe parasite.Inasmuch as the cowbirds are altricial birds?hatched naked, blind,and helpless?they could not succeed with precocial birds as hosts
?
which are hatched down-covered, seeing, and active?as I stressedin my first (1929, pp. 189-190) description of the situation. At thattime I listed three other requu'ements in addition to the need for analtricial host: the host species should lay eggs that are not muchlarger, if at all, than those of the cowbird; its manner of feeding itsyoung should not depart greatly from the normal passerine method;and it should feed its young on more or less typical passerine foodinsects, worms, soft seeds.The cowbirds are not specialized for a parasitic existence in thesense that some cuckoos and honey-guides are. They have no adap-tive structures, functional gradients, or innate reactions that may belooked upon as oriented especially toward survival at the expense oftheir nest-mates. While more often than not the nestling cowbird islarger than its nest-mates, which gives it an advantage in competing1
2 U.S. NATIONAL MUSEUM BULLETIN 233
with them, it is not unduly rapid in its growth or especially aggressivetowards its food rivals in the nest. As Nice (1932, p. 47) has put itin the case of the brown-headed cowbhd, the nestling cowbird "doesnot grow faster than its nest-mates purely through greed; it has tomake nearly twice as big a bu'd in the same short space of nine orten days." While the young cowbird is frequently found to becomethe sole occupant of the nest, this is not because it evicts its nestmates the way some cuckoos do. The expired, unsuccessful competi-tors for food are removed by the adult hosts, not by the young parasite.The range of host selection by the parasitic cowbirds reveals twotrends. The most primitive of the parasitic species, the screaming cow-bird, Molothrus rufo-axillaris, is parasitic wholly on the very closelyrelated and ancestral form, the non-parasitic bay-winged cowbird,M. badius. Both are very late breeders in the Ai'gentine summer,chiefly from January to March, and the mere circumstance that othersmall passerine bkds have finished nesting by then may be the factorwhich helps to maintain such a stringent, seemingly obligate, hostspecificity. From this basic, exclusive selection two trends branch out.One, developing through the shiny cowbird, M. bonariensis, andthe brown-headed cowbird, M. ater, is characterized by extremelywide host selection, the known victims including small passerine birdsof all sorts and families, ecologically and geographically sympatricwith the parasite. As might be expected in parasites with broadhost tolerance, not a few unsuitable and improbable species of birdshave been utilized by them, but such instances are no more meaningfulthan casual or accidental occurrences are in plotting the normal inclu-sions of a local fauna.The second trend is toward a more restricted host selection, althoughnot nearly as much as that in the screaming cowbird. Here again,two species of parasites are included, the bronzed cowbird, Tangaviusaneus, and the giant cowbird, Psomocolax oryzivorus, both of whichtend largely to utilize nests of related icterine species. In the caseof the bronzed cowbird, about half of all the recorded instances ofits parasitism involve hangnests of the genus Icterus, but the otherhalf shows that the species has extended its range of hosts to includenumerous other birds as well, some of them frequently. Its hostcatalog includes 52 species in all, of which 1 1 are species of Icterus.The giant cowbird, less weU observed and less perfectly known thanthe bronzed, is known to restrict its choice of brood victims to largerbirds of the oropendola-cacique portion of the Icteridae, but there is arecord on one occassion of its parasitizing a jay.On the whole, the survey of the host relations of all the cowbirdsreveals that the hosts have exerted a surprising lack of selective effecton the development of the cowbird's brood parasitism. It is true
HOST RELATIONS OF PARASITIC COWBIRDS 3
that, while the cowbhds do have host species which are most frequentlyused by them, the parasites show little tendency to ignore otherpotential victims. On the other hand, a small but appreciablenumber of hosts responds adversely to the intrusions of the parasite,although not to a degree that has become critical m an evolutionarysense. Even here, the adverse responses (which constitute desertionof the nest, covering over the parasitic egg with a new nest floor,or actually throwing out the intruder) are not behavior patterns thatappear to have been developed as defenses against parasitism. Theseresponses are not specifically "anti-cowbird" in their organizationbut rather are generalized types of reaction to something foreignentering the nest. As far as I know, no bird has actually developeda special defense against parasitism. In fact, it is difficult to imaginea clearly defined defense against an unspecialized parasite. In mostcases, the normal fecundity of the host species enables it to survivethe inroads of the parasite.There is no evidence which suggests the existence in any of thecowbirds of what have been called gentes in some species of parasiticcuckoos?infraspecific units mtermediate in nature between truepolymorphic types and the more usual, geogi'aphically delimited,subspecies. The chief, indeed the only visible, characters of thesegentes are the color and pattern of their egg shells and the corre-sponding degi'ee to which they resemble the eggs of their usual hosts.As Southern (1954, p. 220) has rightly concluded, if this egg mimicryhas evolved from an originally wide range of variations under theoperation of natural selection, the most probable selective agentmust have been, and still is, the discrimination shown by the fosterers.It follows that such adaptive evolution could only have taken placewith parasites with a marked tendency to individual host specificity,and, for the existence of such traits in some of the species of Cuculus,there is good supporting evidence. In the brown-headed and inthe shiny cowbu'ds, however, the evidence (see pp. 14-15) is sporadicin nature and gives the general unpression that individual hostspecificity is the exception rather than the rule, although such casesmay be expected to increase in number as field studies become morecritical and more intensive.Furthermore, if we tabulate the frequency of nest desertion afterparasitism by the cowbirds, and then compare the dissimilarity(to human eyes) of the eggs of the deserting hosts and those of theparasites, we find no correlation. The most frequent deserters amongNorth American victims of the brown-headed cowbird, such as theyellow-breasted chat and the cardmal, lay eggs quite similar tothose of the parasite. Desertion seems due more to "nervousness"about alien interference with the nest than to any obvious incon-
4 U.S. NATIONAL MUSEUM BULLETIN 23 3
gruities in the eggs themselves. Sunilarly, many hosts which regularlyaccept and incubate the parasitic eggs lay eggs readily distinguishablein size and coloration from those of the cowbird. Examples, tonote but a few, are the eastern phoebe, red-eyed vireo, and chippingsparrow.While the brown-headed and the shiny cowbird parasitize birdsof a considerable range in size (from Polioptila and Empidonax toToxostoma in the case of the former species; from Myiophobus andSporophila to Mimus in the latter), the parasites do not lay notice-ably small eggs for birds then* size, as do some species of Cuculus.There has been no evolution in size or in coloration tending to makecowbird eggs more readily acceptable to their hosts, as we find insome cuckoos.The data presented in this report on the several hundred speciesof hosts of the various cowbirds are not only of interest from thestandpoint of the habits of the parasites, but also serve as a digestof all that is laiown of this aspect of the natural economy of eachof the victimized species. In not a few instances, the parasitismof the cowbirds forms an important element in the breeding successrate, and hence, in the population dynamics of the host.
Brown-headed Cowbird
Molothrus ater (Boddaert)
Discussion
There are several reasons at the present time for presenting anew and comprehensive host catalog for this species. The amountof information brought together here is much gi'eater than whatwas available at the time of my earlier (1929) account: thousandsof additional instances of cowbird parasitism have been noted andcorrelated with the thousands of cases previously reported. More-over, the additional information pertinent to, or even tangential to,the problem, as well as the actual discrete bits of new data on manyof the previously included species, permits much more satisfactoryanalysis and mterpretation than formerly were possible.The rise in the number of known hosts is due to several factors.For one, the brown-headed cowbird has increased its range and its num-bers in some areas, such as parts of the Gulf and southern Atlanticstates, California, and parts of Canada. In Alabama, for example,Imhof (in htt., 1960) informed me that it now breeds throughout thestate, whereas only 10 years earlier its range was restricted largelyto the coastal belt. Monroe (1957) produced e\idence that thebird was breeding in Florida. Webb and Witherbee (1960) havecollected and summarized data establishing the extension of itsbreeding range across the western half of Georgia, as well as intonorthwestern and northern Florida. Grinnell and Miller (1944, p.437) noted that the bird had "increased phenomenally in southwest-ern California since about 1915, in the San Francisco Bay regionsince about 1922, and in the Sacramento Valley since 1927, if notearlier . . . ." In Ontario, Snyder (1957, p. 35) concluded that
"unquestionably the species has moved northward 200 miles or moreduring the present century." Such geographic expansions havebrought the parasite into contact with additional potential victims.Furthermore, since the number of observers has increased greatlyin the older ranges of the bird, many additional data have been placedon record?tliis in spite of the decline of egg collecting, which wasonce the primary source of information. Still another factor in theincrease of the host hst is the great change in our understanding ofthe specific and subspecific status of many of the birds involved.Although I have brought out a number of supplements since my6
6 U.S. NATIONAL MUSEUM BULLETIN 233
1929 list (1931, 1934, 1938, 1943, 1949), it has become exceedinglydifficult to present the data for the use of the reader who does nothave the time or facilities to correlate the various records. This isdue largely to the many changes in nomenclature that have beenintroduced into the literature. Two completely revised editions(1931 and 1957) of the official check-list of North American birdshave been published by the American Ornithologists' Union sincemy first catalog. Many additional races of birds have been recog-nized, a fact which has necessitated critical reallocations of manyhundreds of the older records, and in some instances forms that werepreviously considered species are now united as conspecific races.In the present catalog I have adhered strictly to the last (fifth)edition of the check-list and have not included any deviations fromit no matter how justifiable they may have seemed. Over the yearsmany students have written me about birds they were studying, asthey found it difficult to put together the pertinent cowbird data forthese particular host species. This has been especially the case withindividuals contributing life history accounts to the series of Bentvolmnes, and this continuing source of inquiries, together with otherqueries, as I stated in the preface, has led me to think that a needexisted for the present catalog.In the annotated catalog of hosts of the brown-headed cowbirdthe species is taken as a unit and is discussed as such, althoughreference is made to the race or races involved in each case. Tomake the total mass of records immediately available to investigatorsinterested in a particular race of either the host or the parasite, acomplete tabular summary precedes the catalog. Inasmuch asthe racial differentiations of the various host species occur alongmany different geographic patterns, frequently quite dissimilar tothat of the parasite, it follows that a single race of a given speciesof victim may be imposed upon by more than one race of the parasite,and also that several races of a species of host may be parasitizedby the same race of the cowbird. The tabulation (pp. 41-44) revealsthat the eastern race, ater, of the cowbird is known to have parasitized138 species (174 species and subspecies) of birds; the northwesternrace, artemisiae, to have affected 101 species (139 species and sub-species) of birds, and the small southwestern race, obscurus, to havevictimized 86 species (122 species and subspecies) of birds. Thetotal for the brown-headed coAvbird, as a species, is 206 species (333species and subspecies) of victims.
Frequency of Host SelectionOf the total number of birds included in the present catalog,more than half are uncommon, rare, or even accidental victims. No
HOST RELATIONS OF PARASITIC COWBIRDS 7
fewer than 42 species have been reported but a single time as hosts.Another sHghtly larger group have been noted more than once butnot more than five times apiece. In my extensive compilation ofdata, I find only 17 species have been recorded as cowbird victims100 times or more; these must be looked upon as the chief fosterersalthough at times, and in some locahties, still other species may befound to be as important, if not more so, to the parasite. In descend-ing order of frequency of parasitism, these 17 are: yeUow warblerand song sparrow, with about 1,000 instances each; red-eyed vireo,875+; chipping sparrow, 650+ ; eastern phoebe, 375; rufous-sidedtowhee, 300; ovenbird, 280+ ; yellowthroat, 250+ ; American redstartand indigo bunting, with about 200 records each; yellow-breastedchat and red-winged blackbird, about 180 each; Kentucky warbler,150; Traill's flj^catcher, 150; BeU's and yellow-throated vireo, and fieldsparrow, with approximately 100 to 125 records each.The next group of frequently imposed upon victims comprises some17 species, for each of which there are on record more than 50 butless than 100 instances. In descending order of frequency these are:veery and Kirtland's warbler, with about 80 records each; woodthrush, chestnut-sided warbler, and Louisiana waterthrush, with about75 apiece; cardinal and vesper sparrow, with about 70 each;warbling vireo and myrtle warbler, with over 60 each; easternwood pewee, prothonotary warbler, scarlet tanager, painted bunting,dickcissel, American goldfinch, clay-colored and swamp sparrow,with over 50 instances each.Of lesser frequency, but still important as cowbh'd hosts, are thefollowing birds, for each of which between 25 and 50 records areavailable. Listed in descending order of frequency they are: rose-breasted grosbeak, with 40 instances; Acadian flycatcher, white-eyedvireo, black-and-white warbler, worm-eating warbler, blue-wingedwarbler, and white-throated sparrow, with 34 to 40 apiece; easternbluebird, prairie warbler, blue grosbeak, and lark sparrow, with over30 apiece; and catbird, brown thrasher, hermit thrush, blue-graygnatcatcher, and savannah sparrow, with 25 to 30 records each.These 50 hosts account for approximately 7,800 records out of atotal of about 9,000 instances of cowbird parasitism. It would seemthat the proportionate role they play in nature is, if anything, evengreater than these figures would suggest, since many instances ofparasitism upon common hosts are left unrecorded because of theirrepetitive nature, while most cases involving uncommon victims arepubhshed as records of particular interest.In much of the literature one finds statements to the effect thatcertain species are "commonty," ''frequently," or even "invariably"parasitized. Such statements of course cannot be translated quanti-630590?63 2
8 U.S. NATIONAL MUSEUM BULLETIN 233
tatively into the figures here presented, but they do establish that theactual hsted instances form only a portion of the total experience of
all the observers. In my first compilation (1929) I did attempt to esti-mate them and added the resultant figures to the records, but they arenot included in our present totals as there is now enough data to beable to afford to disregard the earlier estimates.Aside from the frequency with which they are parasitized, somehost species are important to the brown-headed cowbird in terms oftheir unusually extensive geographic ranges, as contrasted to someothers that are much imposed upon in relatively limited areas.The comm.on hosts of great geographic availabihty to the parasiteare, in descending order of importance : song sparrow, yellow warbler,red-ayed virco, chipping sparrow, rufous-sided towhee, yellowthroat,yellow-throated vireo, yellow-breasted chat, redwinged blackbird,warbhng vireo, American goldfinch, and lark sparrow. Even amongthese, there are geographical and ecological differences; for example,in the eastern areas, where it nests chiefly in cattail swamps, theredwinged blackbird is seldom molested, whereas in other areas inwhich it nests in bushes, it is a frequent host, and, in an over-allpicture, by virtue of its abundance over a vast range, it has beenreported as a host a great many times. Similarly, the Americangoldfinch, while aval] able geographically, is often unavailable season-ally since it is a late nester. The prime example of an extremelylocalized, but locally very important, host, is Kirtland's warbler;the golden-cheeked warbler is another case, but it appears to be lessintensively parasitized.Inasmuch as data are still relatively sparse and incomplete south ofthe Mexican border, the following breakdown of the cowbird's hostsis restricted to the area covered by the official checklist of NorthAmerican bu'ds, comprising the United States and Canada and includ-ing Baja California but not the Mexican mainland. In North Americathe bulk of the cowbird's victims are found in eight families?thetyrant flycatchers, the thrashers and their allies, the thrushes, thevireos, the wood warblers, the orioles and blackbirds, the tanagers,and the finches.Of the 32 species of flycatchers in North America, 17 are known tobe parasitized. Of the remaining 15, about half do not nest withinthe breeding range of the parasite, or they are birds whose nestsseldom have been observed, or they are hole-nesters and are therebyrelatively immune to the attentions of the cowbird. Two flycatchers,the eastern phoebe, and Traill's flycatcher, are important, frequenthosts.The thrashers are somewhat infrequently imposed upon, but 7 ofthe 10 North American species have been found to be so affected;
HOST RELATIONS OF PARASITIC COWBIRDS 9
however, the catbu'd and the brown thrasher are the only speciesfor which there are numerous records.Of the 18 North American members of the thrush family, 8 areknown to be parasitized; 6 of the others do not breed in the cowbird'srange. Some of the brown thrushes (Hylocichla) are importanthosts.The vireos are severely parasitized. There are 12 species in NorthAmerica, one of which, the black-whiskered vireo, is allopatric withthe cowbu'd, but all the others are imposed upon, many of themextensively.The near relatives of the vii'eos, the wood warblers, are also veryimportant as hosts and include some of the most frequently victimizedbi'"ds. There are records of parasitism on 45 of the 57 species ofwood warblers m North Ajuerica, and of the unused minority, abouthalf are protected by theu" geogTaphic or ecologic allopatry withthe parasite.The blackbirds and orioles of North America comprise 18 species,not counting the 2 species of cowbii'ds, and of these 18, 13 are includedamong the victims of the brown-headed cowbird. The redwingedblackbu'd is the only member of the family that is generally andfrequently parasitized; some of the others are local in their sympatryand availability.The tanagers are a small group in North America, comprising onlyfour species, of which thi"ee are known to be victimized by the parasite.The largest avian family in North America, the finches and their
allies, comprises 84 species, of which 56 are known to be parasitized,including a good number that are used extensively. Of the remaining28 species, 5 are only accidental in North America, not counted asbreeding birds, and 16 others are allopatric with the cowbird. It ispossible that, as the range of the parasite expands, some of thesemay become sympatric and may then be imposed upon. The north-western extension of the cowbu'd's breedmg range in British Columbiahas resulted recently in the addition of the redpoll to the list of itsvictims.In their comprehensive summary of the bu'ds of Maryland and theDistrict of Columbia, a very well-studied area, Stewart and Robbins(1958, p. 329) noted 223 cases of cowbird parasitism. Of these, 74involved species of fuiches, 53 were with warblers, 44 with vireos, 12with thrushes, 10 with blackbirds and orioles, 10 with flycatchers, 8with tanagers, and 12 with various other hosts.Changes in Host SelectionComparison of the host preferences of Molothrus ater with those ofits neotropical relative, M. bonariensis, shows some interesting differ-
10 U.S. NATIONAL MUSEUM BULLETIN 233
ences. The latter bird parasitizes species of the following famihes,arranged in descending order of number of included host species:finches and their allies, 41 species; tyrant flycatchers, 27; blackbirdsand orioles, 24; tanagers, 10; wrens, 7; and mockingbirds, 6. It alsouses wrens and mockingbirds much more frequently than does M. ater.A number of purely neotropical families, absent from North America,such as ant-thrushes, spinetails, woodhewers, cotingas, and honey-creepers, are affected to some extent, but the real difference betweenthe two cowbirds is found in their relation to the vireos and the woodwarblers.The South American M. bonariensis seldom uses nests of vireos andwood warblers, two families that are heavily parasitized by M. ater.It is not altogether valid to compare data on the two since the pictureis about as incomplete in South America as it is complete in NorthAmerica, but it may be noted that only 2 species of vireos and 2 ofwood warblers are known to act as hosts for the shiny cowbird despitethe fact that there are resident in South America some 18 species ofthe former family and 30 of the latter. (Figures compiled fromHellmayi''s Catalogue of the Birds of the Americas.) To emphasizethe difference involved here, one should recall that M. ater has beenfound to affect every North American species of vireo (11 in all) thatbreeds within its range. Moreover, the brown-headed cowbird isrecorded as parasitizing 45 of the 50 North American species of woodwarblers that are sympatric with it.The shiny and the brown-headed cowbirds are similar in theirfrequent use of fringillids as hosts. In this family M. ater is knownto impose upon 56 of the 63 species that breed sympatricaUy with itin North America. M. bonariensis is recorded as victimizing 41 ofthe 181 fringUlid species listed by Hellmayr as breeding in SouthAmerica. The figure 181 probably includes some species allopatricto the parasite, but the present state of knowledge makes it difficult,if not impossible, to determine this in many individual cases. Thisstatement possibly applies also, and to a lesser degree, to the vireosand warblers discussed above.Since the brown-headed cowbird appears to be a more recentevolutionary entity than the shiny cowbird, the differences betweenthe two in host selection should be examined more closely. Aspointed out in the discussion (pp. 192 ff .), the shiny cowbird's interest indomed nests has some of the attributes of atavism, a lingering of paststages in the history of that species; conversely, it is in keeping withthe newer, if not necessarily more advanced, status of the brown-headed cowbird that this bird evinces much less tendency to enterand parasitize nests with dark interiors, such as domed structures orholes in trees. This could account for the fact that the North Ameri-
HOST RELATIONS OF PARASITIC COWBIRDS H
can bird seldom uses wrens as fosterers, but it does not explain themarked diminution of interest M. ater shows in the open and readilyavailable nests of mockingbirds. The latter difference between thetwo species of cowbirds?^and it is a marked difference?still remainsa puzzling change in host selection.Throughout its enormous range, the brown-headed cowbird hasshown very slight alterations in its major host relations. Expandinginto additional breeding areas, it has necessarily come into contactwith, and made use of, host species not previously available to it,such as Kirtland's warbler in the jack-pine areas of northern Alichigan,and the redpoll in northern British Columbia. In other areas ofrecent occupancy there is some evidence that suggests AI. ater hasmade more frequent use of certain fosterers than it regularly does inareas of older cowbird equilibrium. An example is the blue grosbeakin southern California (p. 139). In all these instances, however, no ob-vious change in the general pattern of habits is involved. In aU casesthe hosts are fairly similar to other, previous hosts in their nest con-struction and in their main ecological choice of nesting sites. When awide-ranging host shows a marked ecological difference in variousparts of its range, its status as a cowbird victim may change accord-ingly. Perhaps the best example of this is the redwinged blackbird.In the eastern portions of its range it nests almost entirely in thecattail swamps, where it is rarely molested by the parasite. Else-where it builds its nests frequently in bushes, and there it is commonlyparasitized.The broad spectrum of host choice and the general lack of speciah-zation within this wide latitude seem to have made it unnecessaryfor the parasite to develop any strildngly differential host relation-ships. That some such may be formed eventually is suggested bythe data presented in our discussion of the prothonotary warbler, ahole-nesting bird for which a surprisingly high frequency of parasitismhas been recorded in the vicinity of Burlington, Iowa (see p. 92).While our present knowledge of the wide-ranging shiny cowbirdis much less complete than is that of the brown-headed species, theformer does offer some evidence which is suggestive of geographicalchanges in host selection. For example, the wren, Troglodytesmusculus, is parasitized in Argentina, but not nearly as frequentlyas are some sparrows, mockingbirds, and flycatchers, whereas inSurinam and adjacent areas it appears to be the chief fosterer. InChile, where the shiny cowbird may be a fairly recent intruder, theprimary host is the diuca finch, Diuca diuca, although the chingolo,Zonotrichia capensis, by far the most frequent victim in Argentina,Uruguay, and Brazil, occurs in Chile as well and is not disregardedcompletely by the Chilean cowbirds.
12 U.S. NATIONAL MUSEUM BULLETIN 233One cannot avoid the general conclusion that the brown-headedcowbird, biologically a very successful species, both in terms of itsgreat population numbers and of its wide geographic range, is asuccess by virtue of its lack of specialization. This success may bedue to the fact that throughout its range there are no discontinuitiesof any significance; consequently, no opportunities are present forlocally restricted and inbred groups to express themselves in differ-ential host preferences. In terms of host relationships the brown-headed cowbird seems to bear out Mayr's (1954, p. 178) statementon morphological changes: "Successful species are usually widespreadand rich in genetic variability, but they tend to be rather conservativefrom the evolutionary point of view. . . ."
Intensity of Parasitism of Frequent HostsOf aU the parasitized nests recorded with full data as to the numberof eggs present, approximately 60 percent contained but a singlecowbird egg apiece; in many of the others, however, 2, and lessfrequently 3, or even more, of the parasitic eggs were present.These figures are composites, based on aU available records, but ifwe restrict our considerations to the more recent, more carefully madestudies, the data from which were recorded in greater detail, we find
actuall}'- the opposite phenomenon?a slightly greater number ofnests with multiple cowbird eggs than with single ones. Includingeven the old "scattering" records made largely by unsystematic eggcollectors and not by careful students of the birds concerned, wefind, for example, in the case of one host, the Louisiana waterthrush,that multiple cowbird eggs were discovered more frequently thansingle ones. Of 55 parasitized nests, 25 held 1 cowbird egg apiece,20 had 2, 7 had 3, and 3 had 4.For an example of results from newer, more fully investigated andmore completely documented source materials, we may note that inHofslund's study of the yellowthroat (discussed on pp. 118-119 of thepresent report) about three-quarters of the parasitized nests containedmore than one cowbird egg apiece. While this condition is true inthe area he studied, it is not certain that a similar degree of parasitismis general throughout the range of the yellowthroat.In 1960 Ussher found an unusual situation in the nest of a woodthrush in Rondeau Provincial Park, Ontario; this nest contained asingle egg of the thrush and 12 of the brown-headed cowbu'd. I wasinformed by W. P. Nickell that the park area had been sprayed earlierwith DDT, which greatly decreased the population of nesting birds,thereby reducing the number of nests available for the cowbirds.This may have been a cause behind the excessive use by the cowbirdsof this particular nest. A similar conclusion was expressed by Hann
HOST RELATIONS OF PARASITIC COWBIRDS 13
(1941, p. 220) ill his study of the ovenbird, wherein he found thatthe cowbu'd usually laid but one egg in a nest "unless nests are scarce;in that case she lays more. ..."As a matter of record, it may be noted that as manj^ as 9 cowbirdeggs have been reported from another nest of a wood thrush byHofslund (1950) in Minnesota, where apparently no DDT sprajnnghad been done. As many as 8 have been recorded from single nestsof the black-and-white warbler, the veery, the rufous-sided towhee(several such instances, ranging from 1 to 5 of the hosts' eggs), andthe ovenbird. Seven cowbird eggs have been found in one nest of ared-eyed vireo, in one of a scarlet tanager, and in one of a song sparrow.Six cowbird eggs were recorded from individual nests of a yellow-breasted chat and of a yellow-headed blackbird, and 5 from single nestsof the scarlet tanager, the indigo bunting, and the veery. Berger(1955, p. 84) described a six-storied nest of the yeUow warbler with atotal of 1 1 cowbird eggs in its various levels.The number of parasitic eggs that may be accepted by a hostordinarily appears to be limited to not more than its own maximumclutch number. In the case of many of the smaller hosts, however,such a number of cowbird eggs would overcrowd the nest to the pointof physical discomfort to the covering bird and might lead to desertion.In these cases a smaller number seems to be the effective limit. Whatwe are concerned with at this point is merely the acceptance of theegg situation, quite apart from the very different question of thehost's ability to hatch and rear this number of young cowbirds.Current understanding and information suggest that what we havehere is not a matter of latent counting abihty in the hosts, enablingthem to sense a "correct" number of eggs in the nest, but moreprobably a reaction to the visible proportion of the combined massof eggs to the available space in the nest, or even the amount ofsurface stimulation the eggs of a given clutch size produce on thebrooding surfaces of the body of the host birds.Furthermore, as indicated by Tinbergen (1951, p. 45; 1954, pp.246-247) it is conceivable that additional eggs or larger eggs, suchas often result in a parasitized nest, may actually enhance thereleased incubatory response of some birds. For example, he mentionsthat, when given the choice in experimental cases, oyster-catchersseem to prefer clutches of one or two eggs above their usual clutchnumber and to prefer eggs of double, or even more than double,the size of their own. I am not aware that similar reactions havebeen tested critically in small passerines, but if they were foundto behave in similar fashion, it might help to explain some of theirotherwise surprising acceptances of parasitism.
14 U.S. NATIONAL MUSEUM BULLETIN 23 3
While it is true that cowbu'd eggs show no tendency toward adap-tive resemblance to those of their frequent hosts, the fact that suchsimilarities have been evolved in some of the Old World cuckoossuggests that there may be, and often probably is, an advantage tothe parasite if its eggs are not too readily distinguishable by thehosts from then* own. However, that such similarity is not alwaysessential is amply shown by the success of the cowbirds.In some cases, more than one egg is laid in the nest by the same hencowbird, as Savary (1936) discussed in his account of Bell's vii-eo;in others, more than a single bird is responsible. Byers (1950, p.136-138) judged from the differences in size and coloration of the8 cowbird eggs he found in one nest of a black-and-white warbler,that four female cowbirds had been involved, and Mulliken (1899)concluded that five different birds had laid one egg each in a scarlettanager's nest that he described.At Nickelsville, Virginia, F. M. Jones (1941, pp. 117-119) had theopportunity to study the egg-laying of a female cowbird which laid avery distinctively colored, hence easily recognized, egg. He found atotal of 8 eggs from this bird between May 5 and June 15 m eight nestsof four different species?two white-eyed vireos, tln-ee praude warblers,two field sparrows, and one summer tanager. In my own field studies(Friedmann, 1929, p. 183) I found that one hen cowbhd had laid 5 eggsin fom" nests of the veery, the chestnut-sided warbler, and the redstart.Another individual had laid 2 eggs in a redstart's nest, and 3 in onenest of a red-eyed vireo; stUl another bu-d had laid 4 eggs in nestsof the veery, the red-eyed vireo, and the redstart. These casesindicate that ordinarily the parasite is not individually host-specific.Yet there are some data that suggest that at times and in particularsituations some hen cowbirds may show incipient, if not developed,specificity in their choice of victims.Such a case is described in our account of the prothonotary warbler(see pp. 91-92). At Burlington, Iowa, J. P. Norris (1890, pp. 177-182) found 35 nests of this warbler within a period of two weeks,and of these, 18 contained 1 or more cowbird eggs. Since thiswarbler nests in holes in trees and since the cowbird ordinarily showslittle interest in nests in such a concealed situation, it appears thatsome individual hens at Burlington must have had an appreciablyconsistent tendency to choose the prothonotary warbler as a host.Another, and in some ways even more striking, example is Walkin-shaw's series of observations on a cowbird consistently parasitic ona field sparrow in Michigan (see pp. 164-165).Further evidence of host-specific tendencies was found by Dr.and Mrs. D. McGeen, who very kindly sent me a summary of theresults of their intensive study of the cowbirds and their hosts near
HOST RELATIONS OF PARASITIC COWBIRDS 15
Otter Lake, west of Pontiac, Michigan. They followed very closelythe breeding activities of several female cowbirds, each of which wasreadily distinguishable by the consistent size and coloration character-istics of its eggs. One of these laid 18 eggs, all in nests (18 in number)of the yellow warbler. Another cowbu'd was responsible for 6 eggsfrom May 18 to May 27, also all in yellow warbler nests; a thirdindividual laid 6 eggs between Ma}^ 18 and 28, 5 of which were de-posited in as many nests of yellow warblers and one in a song sparrownest. On the other hand, another cowbird laid 19 eggs betweenMay 9 and June 19, using as its depositories 11 song sparrow, 6yellow warbler, and 2 Traill's fl^^catcher nests.
Breeding Success of Host and ParasiteWliether the same cowbu'd scatters her eggs in different nests ortends to deposit more than one in the same nest, the resulting fre-quency and degree of parasitism makes one ask what the damage isto the hosts and how they are able to stand up under it. In manyaccounts, the impression is that the imposition on the host is exces-sive, and yet the situation continues year after j^ear. In only onespecies, the Kirtland warbler (see pp. 108-111), however, does thesituation become alarming for the continued welfare of the host.In attemptmg to estimate the effect of cowbird parasitism upon themost frequently used, or at least the most often reported, host species,we may take as a basis for our discussion the data compiled by Nice(1957, pp. 317-318) on altricial birds. The success rate of open nestsof altricial birds in the north temperate zone, as recorded in 24 studieson 7,778 nests, ranged from as little as 38 percent to as much as 77percent, with an average of 49 percent. In 29 studies, involving atotal of 21,951 eggs, fledging success (that is, success to the point ofresulting young developed to the stage wherein the}^ leave the nest)ranged from 22 percent to 70 percent, with an average of 46 percent.Possibly because of the lesser exposure to predators, hole-nestingspecies averaged a higher degree of success; 33 studies involving 94,400eggs showed fledging success of from 26 to 94 percent, with an averageof 66 percent. Lack (1954, p. 87) gave almost the same percentages.Although they are included in the above summaries by Nice, it isof interest to review the breakdown by species given in Kendeigh'spaper (1942, pp. 19-26). He studied the outcome of 2,725 nestingattempts by 51 species, mostly of forest-edge passerine birds, in thecentral United States. Considering only species for which he had 7or more nest records, the percentage of nesting successes was 80 to90 percent in the Baltimore oriole, barn swallow, house wren, andcardinal; 70 to 80 percent in the starling, flicker, phoebe, and purplemartin; 60 to 70 percent in the catbird, yellow warbler, song sparrow.
16 U.S. NATIONAL MUSEUM BULLETIN 233
wood thrush, and red-eyed vireo; 50 to 60 percent in the chimneyswift, bkiebird, chipping sparrow, brown thrasher, field sparrow, andgoldfincli; 40 to 50 percent in the mourning dove, black-cappedchickadee, cedar waxwing, and crested flycatcher; and less than 40percent in the house sparrow.While no percentages based on such ample data are available forthe brown-headed cowbkd, it may be noted that Norris (1947) reportedon 237 nests of various passerine host species at Preston Firth, Penn-sylvania. In these nests the hosts laid a total of 668 eggs, of which383, or 57.3 percent, hatched; cowbirds laid 108 eggs, of which 46, or42.6 percent, hatched. The fledging success was 37.7 percent for theeggs of the various hosts, and 26.8 percent for those of the cowbird.Of the host eggs that hatched, 64 percent produced fledglings; of thecowbird eggs that hatched, 63 percent produced fledglings. All but 4of the parasitized nests that produced fledglings produced at leastone host fledghng. The 35 successful non-parasitized nests produced2.94 fledglings per nest; 19 successful parasitized nests produced 2.05host fledglings per nest?from which it follows that each young cow-bird was raised at the expense of approximately one host young.These figures agree very closely with those given by Nice (1937, p.200) for cowbird parasitism on the song sparrow (see p. 170).Another study, on a smaller scale, by Betts (1958, p. 143), of thepasserine birds on a farm in southern Michigan, revealed that, of 39cowbird eggs laid in 34 nests of 12 species of open-nesting hosts, 20hatched and 14 survived to leave the nest?a fledging success of about36 percent. However, this is about three times the fledging successof cowbirds in ovenbirds' nests, mentioned below (pp. 112-113), andthis, in turn, is better than the fledging success of cowbirds in nests ofyellow-throats studied by Hofslund (see below, and pp. 118-119).On the other hand, the rate of cowbkd success is higher in thecase of larger, less susceptible hosts. For example, Nice's data onthe song sparrow showed that 30.7 percent of the cowbird eggs sur-vived to the fledging stage, as compared with 35.8 percent of thesong sparrow eggs.In other words, the general breeding success of the cowbu-d, likethat of so many other parasitic animals, is often much lower thanthat of its chief victims. This is the saving factor in the picture. Ithelps to allow for the smwival of the host population in sufficientnumbers for its continuing availability and usefulness to the parasite,even though at times this seems to be made difficult by the verydegree to which the hosts are successful as fosterers. If the commonhosts were to suffer too drastically in a numerical sense from theparasitism of the cowbird, there would result a scarcity of hosts,which in turn would cause a diminution in the possible number of
HOST RELATIONS OF PARASITIC COWBIRDS 17young cowbirds reared. But this, again, might give the fosterers theopportunity to increase?and so on, in endless waves of depletion andincrease of the population, both of the parasite and of its usual victims.The natural fecundity of almost all the frequent hosts is sufficientto stand the losses due to cowbird parasitism. The idea that thetwo factors are necessarily mutually counteracting forces involvedin maintaining or upsetting the so-called ''balance of nature" is sup-positious. What we may have here is another, if somewhat special,type of predator-prey relationship. In a study, of which only asummary has been pubHshed, Darling (1959, pp. 62-63) minimizedthe supposed importance of predation in maintaining the "balance ofnature." He pointed out that recent, critical, analytical studieshave indicated that predation is, in itself, quite unimportant as afactor in regulating the size of the populations of the prey speciesand that the latter are, to a large degree, self-regulating. He sugges-ted that the effects of predation?and it seems that brood parasitismmay be looked upon as a form of predation on the next generation(the eggs), if not the present one (the adults), of the prey species
?
will be found to vary with the degree to which the population of theprey species is experiencing "optimal conditions in its ecological niche.The complex of predation may be important in conservation of habitatand consequently of the prey, by softening zenith and nadir of popula-tion oscillations and so lessening the percussive effects on habitat."At a meeting of the American Ornithologists' Union at Ann Arbor,Michigan, in August, 1960, the McGeens reported on a study of theeffect of parasitism by the brown-headed cowbird upon several of themore frequently chosen species of hosts. The McGeens correlated theincidence of parasitic successes and of host losses due to the parasitewith the population density of the cowbird. In areas where the cow-bird was more numerous, it was observed that not only were more nestsvictimized, but also that a larger proportion of these nests containedmor-3 than a single parasitic egg. To express the "cowbird pressure"as a factor in these correlations, the McGeens used the average of thepercent of host nests parasitized and the percent of multiple cowbirdeggs as compared with single ones in these nests. It was assumed, andcorrectly so, that even though it was not possible to find all the nestsof a given host species in a study area, the sample observed, if not toosmall, should give a proper picture of the degree of parasitism sufferedby that host.The "pressure" which cowbirds exert was divided by the McGeensinto two phases: the size of the affected segment of the entire nestingpopulation of a given host (in other words, the percentage of itsnests parasitized), and the degree or intensity of parasitism inflictedupon this segment. The reasoning was that a parasitized group
18 U.S. NATIONAL MUSEUM BULLETIN 2 33
of nests, each containing a single cowbird egg, was under less
"pressure" than a similar group with 2 or 3 cowbird eggs apiece.On this basis the McGeens concluded that these multiple eggswere a readily usable key to the pressure rate: the higher the pro-portion of multiple eggs to single ones in the total parasitized nests,the greater the cowbhd pressure. By averaging these two partsof the picture, it was possible to arrive at a single "pressure index"for the whole host population in a study area, and this index couldthen be used in correlating parasite successes and host losses.It seems to me, however, that multiple cowbird eggs, beyond a totalof three, are almost always lost or wasted eggs. From tliis it followsthat any cowbird "pressure" of more than 3 eggs in a nest may nothave more effect on the host than does the "pressure" of just 3 eggs,a situation which, in itself, usually speUs disaster to the entirenest contents. If the presence of 3 cowbird eggs in a nest is fatalto the outcome of the nest, 4 or 5 eggs cannot be more so. Theonly effect these extra eggs can have is that the parasite is Hterallyexpending its reproductive resources in the one way that cannotfurther harm its victims.It may be explained, at this point, that whereas the McGeensappeared to be thinking of the cowbird "pressure" as a descriptiveelement in the demographic situation, the concept of "pressure," asI am using it here, applies directly to the degree to which, or theintensity with which, the host is caused to feel the effect of the popu-lation density of the parasite. This would account for the differencein the significance attached by them or by me to the matter of multipleeggs above three in a nest. The difference is important, but actuallyit applies only to a smaU percentage of the instances of parasitismbecause, in the great majority of cases, less than 3 cowbird eggsare involved.One other thought may be introduced here. As Lack (1954b,p. 155) has expressed it in his study of the evolution of reproductiverates, the clutch size in nidicolous birds is limited by the number ofyoung that the parents can feed. "With broods above normal size,fewer, not more, young are raised per brood. . . . The decline infecundity with rising population density, found in both birds andinvertebrates, is primarily a response to a dwindling food supply forthe young, and not to population density as such. . . ."Within the total range of resultant host-parasite relationships whichemerge from the McGeens' study, at least two balanced situations,or balanced economies, were found to exist. Host species of smallsize or of relatively slow incubation and rate of nesthng developmentwere very susceptible to the presence of eggs or young of the parasite.
HOST RELATIONS OF PARASITIC COWBIRDS 19
and a considerable percentage of these cases failed to come throughto the fledging stage. They gave a low success to the parasite;consequently, they were rated as poor hosts from its standpoint.Examples include such frequent victims as Traill's flycatcher, Bell'svireo, the yellow warbler, and the field sparrow. Larger hosts, orhosts with more rapid growth gradients, proved less susceptible tothe cowbirds and consequently resulted in a notably higher parasitesuccess rate, even at higher pressures, and these the McGeens ratedas good hosts. Examples of these included the song sparrow, theovenbird, the yellowthroat, and the red-eyed vireo.The importance that the relative size of the host species may haveis shown in the case of two frequently parasitized species of vireos,the red-eyed and Bell's. The two are similar in their general nesting,egg-laying, incubation, and feeding habits, and yet Bell's vireo is apoor host, with a high frequency of loss to the parasite, while thered-eyed vireo is a good one. The latter is nearly half again as largeas the former, which fact appears to be the chief determining factorin the red-eyed vireo 's relations wdtli the parasite. For a furtheranalysis of what may be correlated with mere body size, see mydiscussion of the hatching potential of the host species (p. 21).As is indicated in my account of Kirtland's warbler (pp. 108-111),based on Mayfield's detailed study, this host is an instance of anunbalanced economy, and it suffers perilously because of it. Hereagain the large size of the warbler?as large as, if not larger than,any of its congeners?makes it a good host to such a degree that it isin danger of depleting its own population in serving its parasite.The frequency "with which the brown-headed cowbird parasitizessome of the poor hosts is one of the main checks on its increase andspread, since a poor host is a major factor of loss for the parasite.The egg and nestling mortality are correspondingly higher than theywould be if the cowbird restricted its attentions to potential fostererscapable of rearing its young with a higher rate of success.In an evolutionary sense, this inefScient host range might con-ceivably be looked upon as an indication of the imperfection and evenof the relative recency of the parasitic habit. If the degree of lossit causes the parasite were of critical importance, it might be expectedthat natural selection would tend to eliminate those individuals thatlaid their eggs more often in unpropitious nests. However, thiswould be possible only if there were a marked tendency for eachparasitic hen to be more or less host specific. As we have alreadyseen (pp. 14-15), the available evidence for actual or even incipienthost specificity is hardly more than a number of isolated instancesin a much larger mass of data, either quite devoid of any specificity
20 U.S. NATIONAL MUSEUM BULLETIN 23 3
or positively opposed to it. It appears conceivable, however, thatadditional detailed (as opposed to relatively "loose") field studiesmay increase the evidence for host specificity.One might speculate that the low survival rate between the eggstage of the cowbird and the fledging stage might be due to a selectivemechanism which residts in something partaking of the nature ofdifferential reproduction. If this were the case, it could easily leadto a relatively rapid adaptive evolution of the parasite with respectto its frequent host relations. Something of this sort appears tohave transpired in the case of the European cuckoo, Cuculus canorus,the Indian koel, Eudynamis honorata, and some other cuckoos, inwhich the degree of adaptive similarity in egg coloration achievedand the concomitant development of individual host specificitycan hardly be explained on any other basis than the selective pressurebrought to bear by the hosts. In the cowbirds, however, evolutionarychanges in the parasitic habit, after its original appearance, seem tohave been influenced surprisingly little by the hosts. The changesin the habit from the screaming cowbird through the shiny cowbirdto the brown-headed species are chiefly a widening of the choice ofhosts used, a trend towards egg removal, and, after a relatively highpercentage of waste of eggs (in AI. honariensis) , a more economicaldisposition of the eggs (in M. ater).We may note at this point some of the better quantitative dataavailable on a few of the frequently used host species. Since all ofthese are discussed in greater detail under each of the species in ourcatalog, only a brief statement is given here.In the case of the song sparrow (see pp. 169-170), Nice (1937, p. 200)asked whether each cowbird raised was reared at the expense of abrood of sparrow young. The data showed that, while 66 successfulunparasitized nests raised an average of 3.4 song sparrows each, 28successful parasitized ones averaged 2.4 song sparrows. In otherwords, each young cowbird was reared at the expense of one youngsparrow, not of a whole brood.The red-eyed vireo (see pp. 87-89) was carefully studied by Southernin Michigan. He found 104 nests, of which 75 were parasitized. Thenesting success of the vireo was 87.49 percent in unparasitized nests,66.66 percent in parasitized ones. The last figure is not as differentas one might have expected on the basis of Lawrence's study (1953)of this vireo in an area where there were no cowbirds and wherethe nesting success in 35 nests was 63 percent. Southern concludedthat the local vireo population he studied did not suffer serious deple-tion even though it was heavily victimized. He considered the cow-bird a necessary check on the undue increase of the vireo althoughhe admitted that, if the parasite were equally successful with most
HOST RELATIONS OF PARASITIC COWBIRDS 21
of its other hosts, it might become too numerous. He suspected,however, that the parasite has few other hosts with which it is equallysuccessful.Another frequently imposed upon victim is the ovenbird (see pp.112-113). Hann (1937) estimated that 52 percent of all the active nestshe watched were parasitized. The loss due to the cowbirds was 18percent of the eggs and young of the ovenbird. The chief loss wasdue to the removal of eggs by the cowbird. Out of a total of 40cowbird eggs, only 22 hatched and only 10 of these lived to thefledging stage, and not more than 5 survived to independence of theirfoster parents.In the case of the yellowthroats (see pp. 118-1 19), studied by Hofslundover a period of four years, 152 eggs were laid m 52 nests, 20 of whichwere parasitized. Of the 152 eggs, 52 were lost; and of these, theloss of 30 seemed to be due to the cowbird. The 20 parasitized nestsproduced only 0.6 cowbird each; 9 of the 20 produced young cowbirds,or an average of 1.3 each.As noted in my discussion of the field sparrow (p. 165), cowbirdparasitism at times may reduce the percentage of nest-success for thehost without producing any parasitic young.With each of these host species, the survival rate of the cowbirdsin their nests is relatively low. Even in species that seem to beoverly burdened, the results are not especially disastrous as a rule.In the case of the Kirtland warbler (see pp. 108-111), however, thesituation is other\vise. The survival rate of the cowbird with thishost is high, about 41 percent, and approximately 55 percent of allKirtland v\^arbler nests are parasitized. It is estimated that thewhole Kirtland warbler population would produce annually about60 percent more fledglings of its own species if the cowbh-d menacewere not present.
Hatching Potential of Host SpeciesAnother factor that limits the degree to which a species can be asuccessfid host to the parasite is what may be termed its hatchingpotential. A word of explanation may be in order, as the conceptinvolved is seldom used in studies of wald birds. Incubation nnpliesmaintaining a fairly constant temperature in a clutch of eggs, thebody of the incubating bird being the source of the heat. It impliesthe warming of the whole volume of each egg, not merely the portionthat happens to be on top at any given moment of incubation. Theamount of heat that the Vjird is able to give off is limited by its metabo-hsm, which is, or more properly, is thought to be, fairly constant foreach species. If a species usually lays 4 eggs of an average volume
of, for example, 2 cc. each, incubation cannot succeed unless the bird
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is able to produce heat sufficient to keep 8 cc. of eggs at a given tem-perature. The volume of an egg may be derived from its externalshell measurements, according to a formula worked out by Schonwetter(1924). Using this method, the eggs of most vireos and small woodwarblers (not the larger Ideria or Seiurus), some of the smallerbuntings, and some flycatchers are found to have a volume of from1.6 to 1.9 cc, while an average cowbird egg is just over 3 cc. Thus,the volume of a 4-egg set of a smaU warbler would be about 6.4 to7.6 CO., or shghtly to significantly more than that of 2 cowbird eggs.If the nest of a warbler were parasitized so that it held 3 warbler eggsand 1 cowbird egg, the clutch volume would be about 8 cc. If 2of the warbler eggs were replaced by cowbird eggs, the resultant clutchvolume would be 9.3 cc. ; if 3 replacements were involved, the finalegg volume would be 1 1 cc.Hann (1947, p. 174) estimated that the ovenbird could incubatesuccessfully an egg volume of between 1.3 and 1.8 times the volumeof its usual laying of 5 eggs, and probably nearer the lower than thehigher figure. Hofslund's (1957) observations indicated that 1.3times the normal clutch volume was the limit that a yellowthroatcould ordinarily incubate to successful hatching.It follows that, while a host species such as the rufous-sided towhee,with eggs as large as, if not larger than, those of the cowbird, couldincubate successfully 4 or even 5 of the parasitic eggs in place of itsown, the smaller hosts could not. By and large, within passerinespecies, the hatching potential is correlated, with some exceptions,with the general size of the egg, which usually is related to the sizeof the bird.
Mutual Effect of Parasite and Host on Egg ProductionThe exact number of eggs produced in one season by one cowbirdis still uncertain, and without this information it is diflScult to estimatethe overall percentage of egg success in the parasite to compare withthat of each of the common hosts. In my own field studies (1929,p. 188) two cowbirds laid 5 eggs each and one laid 4, but it was notestabhshed whether these numbers represented a whole season's layingor merely the equivalent of a clutch, of which there might be morethan one in a season. As a matter of fact, I quoted one instance of acowbird in captivity reportedly laying 13 eggs in 14 days, a case thatcould not be checked for its accuracy. Nice (1937b, p. 164) concludedthat the species laid three or four sets of up to 5 eggs per set, with aninterval of from 6 to 12 days between sets. D. E. Davis (1942)rearranged the data and concluded that the interval between setsshould be shorter, about three days. He also made sections of entireovaries of several species of cowbirds (shiny, screaming, and bay-
HOST RELATIONS OF PARASITIC COWBIRDS 23
winged) and found evidence for 5 eggs to a clutch (or set) for each butno histological evidence indicating whether there was but one clutchor several per season.Jones (1941, pp. 117-119) studied one cowbird that laid a verydistinctively colored egg, and he found 8 eggs, ostensibly of this onebird, from May 5 to June 15. How many others may have beenlaid by this hen and were not found by the observer cannot be stated.As described in my accomit of the field sparrow (pp. 164-165), Walkin-shaw (1949) reported that a single cowbird laid no less than 25 eggsbetween May 15 and July 20. Nice (1949, p. 233) showed that thedates in Walldnshaw's records suggested clutches of 5 eggs at dailyintervals, with a break of several days between clutches.That the individual cowbird studied by Walkinshaw was not asexceptional in its fecundity as it might seem is suggested by evidencesent me by Dr. and Mrs. Daniel McGeen, who found two cowbirdsthat had laid at least 18 and 19 eggs, respectively. The first bird laidits eggs in clutches of 3 (one each day from May 23 to 25, inclusive),of 7 (one each day from May 31 to June 6, inclusive), of 4 (one eachday from June 9 to 12, inclusive), of 1 on June 18 (this is probablyan incompletely recorded clutch that may have extended beyondJune 18 by as many days as there were eggs laid), and of 3 (on June27, July 1, and July 2). The other individual's 19 eggs similarly weregrouped in "clutches."In his general survey of the biology of avian populations andfecundity, Gibb (1961, p. 422) pointed out that the number of eggslaid by parasitic birds could be assumed to be governed, or at leastlimited, by the number of suitable nests in which to lay. Thisis an overly simplified statement inasmuch as there is evidencethat parasitism at times may actually increase the number of nestsprovided by certain host species.Thus, aside from providing evidence that a cowbird could produceas many as 25 eggs in one summer, Walkinshaw's data indicates acomphcating factor which may well affect the total egg productionof the parasite, which may well occur occasionally, and for whichthere is no adequate method of evaluation. He found that 25 eggslaid by one cowbird* were deposited chiefly in nests of one species,the field sparrow. These eggs were laid in 20 nests, 15 of whichwere deserted when the parasite laid an egg in them and removeda host's egg. A good many years earlier, Chance (1940) found thatthe European cuckoo, Cuculus canorus, could and did adjust the
? The evidence as to the Identity of the parentage of all the eggs is as follows: all were found within alimited area; all were very similar in coloration, the length of 11 similarly colored eggs had significantlyless variability than the length of 22 not similarly colored eggs; and no 2 of these eggs were laid on the sameday. 630590?63 3
24 U.S. NATIONAL MUSEUM BULLETIN 233
number of eggs it laid to the opportunities presented in the favoredhosts' nests which were in the proper stage of construction andreceptivity. In commenting on Waikinshaw's data, Nice (1949,p. 233) pointed out that, since the particular field sparrows involvedusually deserted their nests when parasitized, the continued attentionsof the cowbird unwittingly may have caused the sparrows to buildmore nests?which, in turn, tended to increase the egg productionof the parasite in a way quite comparable with what Chance achievedby manipulation of the available nest supply in the case of the Euro-pean cuckoo. From a consideration of this cause-and-effect situation,Walldnshaw's data are not merely 20 more instances of cowbirdparasitism on the field sparrov*^, each case no more significant thanother randojn records, but they are a reflection of a local intensifi-cation of the host-parasite relations. Since there is no sure wayof knowing how often and in how many host species similar situationsmay arise, i-t is impossible to allow for such situations with reasonableaccuracy when quantitatively interpreting the total data for eachspecies of common victim. It would follow that a host species,known to desert easily when parasitized, might thus inadvertentlytend to increase the egg production of the parasite, provided thatthe latter persevered in using the same host species. Conversely, theeffect of continued cowbird parasitism might serve thus to increasethe nesting activities of the host. A comparable case (p. 171) isBerger's data on the song sparrow as a cowbird host.This is actually and essentially the case in the numerous instancesof multiple-storied nests of the yellow warbler, the lower stories ofwhich each held buried cowbu'd eggs.On the other hand, it must be kept in mind that, in the case ofmany of the single-brooded species of hosts, these birds may succeedin raising young of theu* own by renesting after the desertion or thedestruction of the fu'st parasitized nests. Parasitism may thuscause an extension of the hosts' breeding season. It follows that amere calculation of the percentage of parasitized nests of these speciesgives only a partial picture of the situation. The critical point,namely the effect of parasitism on the total fledging success of thehost species, is not accurately described by such percentage figures.Cases of repetitive visits to the same host nest may be due to twofactors. They may involve multiple hens of the parasite or tlsey maybe due to successive visitations of the same individual. The dataessential for determinmg which may be the case are almost alwaysleft unrecorded, but the general question of continued attention toa host nest by an individual cowbird presents points worth consid-ering, especially in connection with the problem of egg removal bythe parasite.
HOST RELATIONS OF PARASITIC COWBIRDS 25
Duration of Parasite's Interest in Host Nests
In his detailed study of the relations of Kirtland's warbler with thebrown-headed cowbird, Mayfield (1960, pp. 144-181; 1961, p. 166)brought together evidence that the cowbirds involved had a con-tinuing, almost proprietary, interest in the nests they parasitized.Individual females tended to return to the same nests, to remove eggsfrom them or to lay eggs in them, and did not molest other unpara-sitized nests indiscrimmately. Mayfield found that the parasites didnot remove eggs on the pre-dawn visits when they laid their own butdid so several hours later, a day before, or, less often, a day later. Thecowbhd would not merely lay an egg and take one out; it would layseveral and remove one; it would lay one and take several; but ifthere was only a single egg in the nest, the parasite would not removeit. The interest in individual nests begins when the cowbird intentlywatches the nest construction by the warblers. This interest con-tinues as the parasite inspects and looks into the nests at intervals.Later, as it repeatedly visits the nests to remove eggs from them, itshows its definitely localized concentration by the fact that it removeseggs only from nests it is using or is about to use, or that it removesonly eggs of the host and not its own, or that it destroys severaleggs at one visit to a crowded nest. In Mayfield's studies, the cow-birds were not banded or otherwise individualized, but his observa-tions were close and careful, and they may be looked upon as anaccurate indication of the actual state of affairs. He concluded thatthe cowbird has an impulse to lay an egg and an impulse to steal orremove an egg, and that it has a continuing and proprietary mterestin the nests it uses.Although evidence for similar contmuing interest in host nestshas not been recorded or documented from other portions of thebrown-headed cowbird's range, one must admit that this may be areflection of inadequate observation; the absence of such evidencedoes not prove the nonexistence of such continued attention. Some-thing akin to Mayfield's experience seems to have been present inHann's work (1941) with the cowbu-d and the ovenbird in Michigan.He noted that the female cowbird made regular trips of inspectionto the nests dm'ing the absence of the owners, between the time shefirst discovered the nests and the time she laid eggs in them, and thatshe seemed to be aware in advance of ovulation where the egg wasto be laid. Parasitized nests had one or more eggs of the ovenbirdremoved by the female parasite. The eggs were removed, not atthe time of ovulation, but during the forenoon of the previous day,or the day of laying, or, more rarely, the following day. The cow-
26 U.S. NATIONAL MUSEUM BULLETIN 233
bird has not been known to give any attention to parasitized nestsafter laying in them, other than to remove eggs from them. Ordinarily,eggs are not removed from nonparasitized nests.However, whether the matter of continuing interest may be ageneral or an unusual situation, the concept of such durable attentionhas interesting phylogenetic aspects. We may recall that the non-parasitic bay-winged cowbird, M. badius, the most primitive of theexisting cowbirds, usurps or adopts a nest of another bird, from whichit then proceeds to evict any eggs or other contents, after which it goeson to use it as its own?a clear case of proprietary interest. It laysits eggs there and incubates, hatches, and rears its young in the ac-quired nest. The most primitive of the parasitic species, the scream-ing cowbird, M. rufo-axillaris , is parasitic on its close relative, thebay-mng, and in the parasitized nests of the latter, one finds multipleeggs of the former more often than single ones. Of 51 nests of thebay-wing found in Tucuman in northwestern Argentina by PabloGirard, 46 were parasitized by the screaming cowbird. Out of these46 cases, 6 nests contained 1 egg each of the screaming cowbird,19 contained 2, 10 held 3, 5 had 4, 4 had 5, and 1 nest held 6 scream-ing cowbird eggs. While these multiple eggs suggest repetitive visitsby their depositore, it must be admitted that no evidence was pre-sented as to whether one or several M. ruJo-axiUaris hens were involvedin the various cases. However, my own observations in the samegeneral area indicated that the screaming cowbird was less numerousthan the bay-wing, which would suggest (but only suggest) thatthese multiple eggs may well have been the result of successive visitsof the same hen, at least in many cases. Successive visits is essentiallywhat Mayfield referred to as continuing or even proprietary interest.In my account (1929, pp. 48-49) of the screaming cowbird, which,unfortunately, no one has enlarged or emended in the decades since itwas wi'itten, I suggested that, while I never found more than 2 eggs ofthis parasite in any single nest and while I knew of one hen that laid2 eggs in each of two nests, the fact that the species appeared to bestrictly monogamous and territorial implied that normally only onepair of screaming cowbirds (and, hence, only one female), would be aptto parasitize any one nest.The matter of egg removal by the brown-headed cowbird meritsfurther comment. In my experience, the primitive parasite, M.rufo-axillaris, does not remove eggs from its hosts' nests (although thebay-wing does so if any are present when it firet takes possession of anest), but the more advanced parasites, M. bonariensis and M. ater,frequently, if not regidarly, do remove eggs of their hosts. In thecase of M. bonariensis, the year-old birds tend to remain in flocks to afair degree and to come into breeding condition late in the Argentine
HOST RELATIONS OF PARASITIC COWBIRDS 27
summer. At this time many may lay together in old deserted nests,as many as 13 hens using the same nest and as many as 30 or 35 eggsbeing deposited in single nests. In these cases, the laying birds do notremove eggs from the nests. It looks as though egg removal in thisspecies is an adult habit, not one found in subadult (year-old) birds.The fact that the nests used are deserted ones may have something todo mth this, but more data are needed to clarify the situation.The lack of egg removal, however, in the screaming cowbird and inits evolutionary descendant, the red-eyed cowbird, makes it possibleto conclude that this habit is not an essential portion of a proprietaryinterest in a host nest although it is closely associated with such aninterest. In the brown-headed cowbu'd egg removal is one manifes-tation of interest in the nest, one that becomes more readily interpretedif it is connected with a continued and proprietary interest.While the cowbu'd may have an interest of some duration m someof the nests it has parasitized, this usually terminates long before theeggs hatch. Ordinarily, it shows no interest in the subsequent fateof the nest, eggs, or young, but there are in prmt a few observationsof attention paid by female cowbu'ds to young of theh- own species.Bonwell (1895, p. 153) reported seeing a hen cowbird feeding a j^oungone in a rose-breasted grosbeak's nest. "Nearly every evenmg shewould come and feed the young cowbird, but if the young grosbeakswould open their mouths for food, she would peck them on the headand refuse them food. . . ." This account implies gi'eater discrimina-tion on the part of the cowbuxl than of the gi'osbeak, which seemshighly unlikely. The whole incident reads as if it were "improvedupon" by subsequent recollections, and, on the whole, it seems toofar from the plain, unembellished record to be acceptable, and it maywell be ignored. However, Forbush (1927, pp. 424-425) mentionedtwo other cases. He cited Al. A. Walton's experience (1903, pp. 211-214) with a hen cowbu'd "which, as he believed, visited from time totime the nest in which her egg was laid, and finally fed and cared forher yoimg one . . . ." From his acquaintance with Mr. Walton,Forbush was "inclined to believe that his observations were reportedaccurately, but that his deductions from those observations oftenwere unwarranted by the facts. He 'believed' that this Cowbirdmade frequent visits to the 'Yellow Bird's' nest in which her egg wasdeposited but did not say that he saw this. However, he wi'ote thathe saw her feeding her own young and assisting the male 'Yellow Bird
'
in feeding it, but he had no way of identifying the feeding Cowbu'dwith the bird that laid the egg and no way of proving that the bu'ddoing the feeding at different times was always the same individual."To date, Walton's observations have remained unique, but they doestablish that, in at least one instance, a brown-headed cowbu'd did
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show interest in a host nest at a stage considerably later than thetime of egg-hiying. However, as Forbush correctly stated, it is notclear that this was a case of prolonged duration of such an interest.The other case, also cited by Forbush, an observation by L. B,Fletcher (1925, pp. 22-24), had to do with a fledged cowbird alreadyout of the nest. Fletcher trapped an adult female cowbird with arecently fledged young one, saw the former feed the latter, bandedboth birds, and released them. Later he saw the two together, thehen still feeding the young one. She fed only the banded fledglingand no others although there were other young cowbhds present. AsForbush correctly said, this is a reliable observation but affords noevidence to prove actual mother-and-child relationship. Such maybe inferred, but not more than this, as many birds occasionally feedyoung other than theh own. "It shows, however, that the adultcared for one particular j^oung, which may have been her own."Although of questionable pertinence here, an observation by Wiestnear Butler, Pennsylvania, recently published by Preston (1961) ina local newspaper, should be mentioned. Wiest found a chippingsparrow's nest containmg two eggs of its own and two cowbird eggs;he showed it to Preston, who removed the latter eggs. This was onMay 18. The sparrows deserted the nest soon afterward. OnMay 30 Wiest saw a female cowbird visit the nest. She flew to it,fluttered her wings, flew down to the ground and again up to thenest in what seemed to the observer to be a state of excitement.Then she left but soon returned with four other cowbirds, two malesand two females. (Wiest assumed that the original female was oneof this party.) The five cowbirds tore the nest apart, eventuallyknocking it to the ground, and then flew off. In his report of thisincident Preston felt it noteworthy that the time between the firstobservation on May 18 and the second on May 30 was ''just aboutthe time needed to hatch cowbird eggs, and if we surmise that thefluttering female was the mother of the eggs, or of one of them, thenit looks as if she had come back to see if her offspring had hatched.Finding neither young cowbirds nor cowbird eggs, she seems to havecalled in her friends to destroy the nest of the negligent foster-parent.It is easy to read human motivation into bird behavior, and this isregarded as a deadly sin by ornithologists, but it is hard to avoidthe conclusion that the fluttering female was the mother of at leastone of those eggs, continued to be interested in it, and was greatlyupset by what she found out."It is obviously impossible to judge this case because there is nocertainty that the "fluttering female" was the parent of one or bothof the eggs or that she was even present in the aggressive action ofthe flock of five cowbirds. It should be mentioned that this destruc-
HOST RELATIONS OF PARASITIC COWBIRDS 29
tive aggression against nests is something that has been noted in thecase of captive female (and male) cowbirds when a nest was placedin the cage as a laying inducement. Certainly, in the case of thecaptive birds, there were no cowbird eggs involved and thus no possi-ble question of parentage or of continuing interest in the nest.Quite apart from an interest of shorter or longer duration in specificnests is the fact that very occasionally the brown-headed cowbirdmay reveal some nest-building atavisms. Lasky (1950, p. 160)twice noted a courting male bird "toying with a dead leaf or a pieceof debris while bowing to a female," a residual "symbolic" nest-building act comparable to similar behavior in some self-breedingbirds. There are m the literature two older statements involvingmuch more than symbolic tokens of an earlier nest-building behavior.Although they are so contrary to the experience of all other observersas to seem doubtful, they should be mentioned here. Swain (1899)saw a pair of cowbu'ds carrying nesting material to a hole under theeaves of an old building. He noticed them doing this day after dayfor an unspecified number of days, but they disappeared soon after-ward and made no attempt to use the nest structure. Here it ispossible that there may have been a misidentification of the birdsalthough this cannot be proved. The question of correct identificationseems not to be mvolved in Honecker's (1902) statement, which iseven more difficult to reconcile with what we know of the cowbirds.He kept a pair of these birds in a large cage and he wi'ote that thefemale built a nest in which she laid 4 eggs, incubated them, andreared all four young birds! Not only has no one else had this experi-ence, but in recent years a number of investigators have been keepingcowbirds in aviaries, deliberately designed with facilities and conditionsto induce breeding, and none of the mvestigators have had any suchresponse. In fact, the most that any of them have reported is thatoccasional mdividual hens laj^ed a few eggs in old nests supplied themas "mducers," but m no case did a cowbird attempt to incubate.In some cases, the only interest the cowbirds showed in the old nestswas to tear them to pieces or to toss out of them any eggs, real orfalse, that had been placed in them to increase their possible suggestivevalue. An earl}^ instance of this adverse interest in nests by captivecowbirds was that reported in 1926 by Luttringer.
Interspecific Preening Invitational BehaviorSelander and La Rue (1961) recently have shown that brown-headedand bronzed cowbirds approach individuals of other bird species and
solicit preening from them. The cowbirds do this by giving a specialdisplay which involves bowing their heads and ruffling somewhat thefeathers on the back of their necks (where much of the preening takes
30 U.S. NATIONAL MUSEUM BULLETIN 233
place). The observers found that the persistent repetition of thisdisplay often evoked preening behavior from a variety of birds,including redwinged blackbirds, meadowlarks, house sparrows, andshell parakeets (m captivity). Some birds, such as the common andgreat-tailed grackles, the inca and mourning doves, did not respondto the invitation to preen the cowbu'ds. Invitation to preening be-tween cowbirds themselves is uncommon, and it appears to have noplace in the provocation of interspecific preening. This display isgiven by adults and by birds of the year, by males and by females.The extent to which preening may go is sometimes surprising.Baird in Rhode Island and Behrendt (1960) in New York are cited bySelander and La Rue as having noted cases wherein invited housesparrows actually hopped onto the backs of the inviting cowbirds inorder to preen them more effectively.The authors suggest that the interspecific preenmg invitationaldisplay may be an adaptation for brood parasitism. This suggestionis based on the assumption that such behavior may lessen the possiblehostile reactions of potential hosts to their would-be parasites. Thereis no evidence, however, to indicate that a female cowbird, about tolay in a nest, makes any effort to establish contact with its potentialvictim. It usually(?) enters the nest while the owner is away, laysits eggs as quicldy as possible and leaves thereafter. Moreover, theinvitation to preen is not given only, or even chiefly, to species thatare frequently parasitized.It is not clear what advantage could accrue to the cowbirds if, asadults, they became more acceptable to even the more frequentlyimposed upon species of their hosts. Such advantage appears un-necessary since there is evidence of hostility toward them on the partof only a small number of their victims (see pp. 33-34). In most casesthere seems to be little need for greater acceptability, especially sincethe social contacts are short and relatively infrequent. Even inspecies wherein hostility to adult cowbirds is not noticeable (or, atleast, has not been noticed), the individuals are apt to show excitement,possibly of an aggi'essive nature, when mtruders come to their nests.Although it seems questionable whether or not there is any meas-urable advantage to the intruders to have had earlier preening associa-tion with the intended victims, this possibility cannot be ruled outarbitrarily: even slight differences of response in short and infrequentcontacts may at times be critical.In the light of present Imowledge, it is not too safe to evaluate suchbehavior. It seems more in accord with the total evidence to interpretthis relative ease with which cowbirds solicit preening from otherbirds as a result of brood parasitism, as a possible "memory induced"reaction based on early experience of care by adults of other species.
HOST RELATIONS OF PARASITIC COWBIRDS 31
than as an adaptation to make the parasites more readily acceptableto theu' intended victims. Selander and La Rue themselves admitthat they had no observations of cowbu'ds actually using this preen-ing mvitational display in an attempt to appease hostile hosts neartheir nests. They do cite Chapman's report (1928) of seemg afemale giant cowbird, Psomocolax oryzivorus, tmce bow her headand present the fluffed feathers of the nape to a female Wagler'soropen-dola, Zarhynchus wagleri, at the latter's nest, but even here there wasno evidence of immediate intended parasitism.One fiu-ther thought should be expressed. Selander and La Ruewrite that the invitation to preen is "all the more unusual in thatcowbirds only infrequently dh'ect the invitational display to membersof then* own species and do not themselves indulge in social hetero-preening." This suggests that we have here something akin to what,in human beings, might be looked upon as a "childhood memory,"even though in each case the species invited to preen might be otherthan the actual fosterer of the inviting bird. The lack of identityof the invited preener with the origmal fostering species thus mightbe looked upon as an mdication of a general absence of specific hostimprinting on the parasite while a nestling. This would be not at allinconsistent with the general picture we have of cowbird-host relations.
Foster Parent-Offspring RelationshipIn the discussion of the cowbird's invitational display for preenmgby other birds, it was suggested that such behavior might reflect,although faintly, some earlier experience with the alien species or,in broader terms, with "birds other than cowbirds." This suggestionnaturally leads to the speculation as to whether or not nestling cow-bu'ds become imprinted on their specific, individual fosterers; andthis speculation, in turn, makes it advisable to review the entire ques-tion of imprinting, with special reference to parasitic birds.So far as the behavior of the foster parent is affected, the hatchmgof a cowbird egg in its nest is no different from the hatching of oneof its own, and from then on, until the j^oung parasite is ready to flyand become independent, the adult host reacts to the chick just as itwould to its own young. The fosterer acts, and seems, completelyunaware of the substitution, even in cases wherein the young parasitegrows to a size beyond that of the host's own typical offspring. Thisapparent unawareness or indifference is probably one of the conditionswhich permits brood parasitism to succeed.On the other hand, the young cowbird differs from the 3'oung ofits victims and of many other birds in that it reveals little or no evi-dence of becoming imprinted on its foster parents as a particularspecies. On the contrary, once it has fledged and has left the careof its foster parents, the young cowbird joins others of its own kind
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even though its own species has been foreign to its experience untilthen. In effect, if the young parasite is imprinted at all, it is im-printed on its own species, without the need for external experientialstimuli.In the past few decades, much work has been done on the behaviorof bu'ds in earliest post-hatching stages. From these investigationsthe concept of imprinting has emerged as one of the most importantbasic factors in the formulation of behavior?-both in the immediatelife of the nestling stage and even, by a supposedly ineradicableresidual effect, in the future adult stage. In almost all discussions ofthis widespread phenomenon of imprinting, one thing, curiously, isoverlooked: some brood parasites such as cowbirds show no signs ofbecoming imprinted on their foster-parents, certainly no signs whichpersist for any appreciable length of time after the bird leaves thenest. Since imprintmg of the young on the parent has been foundto be the case in an increasing list of bird species, the unusual absenceof it in young cowbirds deserves further examination.To begin with, we may take Emlen's definition (1955, p. 132) as acarefully considered expression of what is meant by the concept ofimprinting. He considers it to be "a term applied to the rapid forma-tion of stable primary stimulus-response associations or fixationsduring early infancy. It involves the selection of a stimulus situationfor a newly developed and as yet unexpressed motor pattern and,once formed, may affect a wide variety of motor patterns. . . .Imprinting resembles conditioning but differs from it in that theassociation formed is not a substitution but an original creation, aprimary association. It resembles the sign learning of Kellogg (1938),but again differs from it in being independent of previously establishedassociations. It differs from trial-and-error learning in that it is anadditive process and not used in problem solving. . . ." We may addto this the more descriptive definition given by Eibl-Eibesfeldt andICramer (1958), who write that imprmting is "an early and non-selective or not discriminating innate response toward a particularobject or individual, and is generally characterized by the fact ittakes place only during a very early and very brief period in the lifeof the animal and that it appears to have a remarkably lasting andirreversible effect. The object fixation thus estabhshed by imprintingpersists even after long periods in which that object is kept out ofthe animal's experience."Imprinting was first detected in precocial birds: they were foundto become fixed in their reactions by following the first moving objectwhich they encountered with any degree of intimacy; subsequently,they were found to maintain a fixation upon the same object. Inthe case of nestlings of altricial birds, imprinting is ordinarily difficult
HOST RELATIONS OF PARASITIC COWBIRDS 33
to determine for the simple reason that usually no birds other thanthe parents come to the nest and have any contact with the youngbirds. However, Hinde (1961, pp. 171-172) showed that the feedingbehavior of altricial nestlings is originally responsive to quite diverseobjects. "Once the eyes are open, young passerines will gape to awide variety of objects?forceps, spatula, fingers and so on?as wellas to the parent. . . . The stimuli evoking anxiety responses fromyoung bullfinches are equally generalized . . . and the precociousadult behaviour of young birds ... is often directed towards func-tionally inappropriate objects. . . ." Hinde uses the term imprintingsimply for the learning of parental (for parasitic birds: the foster-parental) characteristics by young birds.In the case of some brood parasites such as the European cuckoo,it is assumed generally that the host-specific egg-laying bird depositsits eggs in the nests of the same species of fosterer by which it origi-nally was reared. In the absence of any more testable explanation,it has been assumed that each cuckoo becomes imprinted on its ownfoster-parent species. ^Miether or not this is true, the assumptionhardly applies to the cowbu'ds; in these birds, the evidence for suchspecific host fixation is miore in the nature of occasional rather thangeneral occurrence. Even in cases of apparent host specificity,there is no corroborative evidence to make the possibility of imprint-ing anything more than an inference.
Reactions of Host to ParasitismOn the whole, the majority of American species of passerine birdsdo not act as if they recognize an enemy in the cowbird. At least,they do not attack or mob cowbirds on sight as some Palearctic birdsattack the Em'opean cuckoo. Many wi'iters have described theactive hostility with which some of these potential victims react tothe mere sight of a European cuckoo; other writers have recordedhow certain African species resort to "mobbing" attacks on some ofthe small African glossy cuckoos or how the former drive oflp honey-guides. These accounts give the impression that the parasites arerecognized as unwelcome intruders on sight, but this does not applyto most Am.erican birds when confronted with one or more cowbirds.There are exceptions, such as the tendency of redwinged blackbirdsto repel cowbirds from their nesting areas (see pp. 128-129), but thisantagonism holds only during the breeding season, whereas in someof the Old World birds, the hostility appears to be a fixed year-roundpattern. Redwings and cowbirds certainly flock and roost togetheramicably in the autumn and winter months. Hann (1937, p. 201)studied the ovenbird, a very frequent victim of the brown-headedcowbird, and found no evidence of any innate hostility between them.The same lack of antagonism is the case in South America with the
34 U.S. NATIONAL MUSEUM BULLETIN 233
shiny cowbird and its various hosts. The reactions of the hosts tothe cowbu'ds is, then, not usually to the adult parasites but to theactual interference in the hosts' nests.On several occasions Nice (1943, p. 158) noted song sparrows usinga threat-posture against cowbu'ds and even striking them. A "threatnote" was given against cowbu'ds, but not against them exclusively,as it was given also when the intruders were juncos, cardinals, andonce even a young rabbit. Nice (p. 262) found that, if a hen cowbirdcame close to a nest, the pair of sparrows frequently attacked her.The antagonistic reactions of the sparrows to the cowbird seemed todepend on some conditioning in their past experience, either in earlylife or later; recognition of the cowbird was something learned, notinnate, in the sparrows. Thorpe (1956, p. 121) considered thatrecognition of the parasite as an enemy might be based on an instinc-tive mechanism in some host species, but, in others, was probablysomethmg handed down from generation to generation, "not so muchby the experience of the dire results of attack but by the alarm dis-played by the parent birds or by members of other species when theysee one of these enemies."Birds react in several ways to the intrusion of cowbird eggs intotheir nests: they may accept them as if unaware of the eggs beingdifferent from their own (whether they are aware or not, we usuallydo not Icnow); they may desert the nest and build a new one; theymay build new nest linings over the strange eggs, thus effectivelyflooring over or burying them; or they may throw out the parasiticeggs. The same species may show more than one of these fourreactions. In many species the reaction depends on whether ornot the bh'ds have already laid some eggs of their own prior to themoment of parasitism and also whether or not the cowbird removedone or more eggs or damaged the nest.Many of the records, especially the older ones, have little or nosupporting data; they are merely statements of sets of eggs collected,with places and dates. The following summaries of the three non-accepting reactions of the victims are based only on such cases aswere reported with the pertinent observational data.Nest desertion.?The reaction observers call actual desertionof the nest is frequently an inferred rather than an ascertained fact.In the following summary I have included only those species whereinthe evidence points to a cause-and-effect relationship between para-sitism and desertion. While accurate and detailed observationsare still needed for proof, apparently nest desertion is more apt tooccur when the parasite lays before the host has laid its first eggor at least when the host is still early in its own laying schedule.The birds listed below have been observed at least once to desert
HOST RELATIONS OF PARASITIC COWBIRDS 35
theii' nests when parasitized by the brown-headed cowbird. Theirpresence in this hst should not be taken to imply that this is theirregular response or even a fau'ly frequent reaction. In those speciesthat tend to desert readily the word "frequently" is added. Intwo species the observational evidence suggested but did not provethat desertion was due to cowbird parasitism; to these the word
"uncertain" has been added.
verdin Maryland yellowthroatBewick's wren (uncertain) yellow-breast chat (frequently)eastern bluebird redwinged blackbirdBell's vireo scarlet tanager (uncertain)red-eyed vireo cardinal (frequently)yellow warbler painted bunting (frequently)myrtle warbler field sparrow (frequently)Burying cowbird eggs under new nest-lining.?Several kindsof cowbird hosts have been found which disposed of the parasitic eggsby bur}dng them under new nest linings and then proceeded withfurther egg lajdng on the new floor. Because this has the appearanceof clever resourcefulness, it has been described many times and hasoften been overinterpreted in some anthropomorphic accounts.The explanation of this "flooring over," fu'st advanced by F. H.Herrick (1910), still seems very plausible, and is, in fact, the onlyone which presents the picture on its proper behavioristic level.Herrick studied the cj^clical instincts of birds; i.e., migration, court-ship, matmg, nest-building, egg-laying, incubation, etc. He foundthat, if the cycle were disturbed at any point, the birds would goback one stage in the cycle and start again from that point. Thus,if the egg-laying stage was disturbed by some cause, the birds wouldgo back to nest-building: they would build a new nest and thenresume egg-la;^Tag. In the case of a cowbird victim, the egg-layingis disturbed by the introduction into the nest of a cowbird's egg.According to Herrick's analysis, the bird should desert?as manybu'ds do?and build another nest. However, the victimized bu'dmay be so attached to its nestmg site that it cannot easily breakaway. At the same time, the interference it has suffered promptsit to build another nest. There is then a conflict between the twoinstinctive drives?the one tending to hold the bird to the nesting-site,the other tending to pull it away to build a new nest. The forcesappear to be fairly equal, and the outcome is not predictable in anyone case. The presence of eggs of its own in the nest strengthensthe attachment of the bird to the site and nest, and it is this forceprobably that wins out in many cases. The new floor, coveringthe parasitic eggs, is thus to be interpreted as comparable to a newnest, such as the sequence of the cyclical instincts would demand,but placed directly in or on the old one, due to the strong site attach-
36 U.S. NATIONAL MUSEUM BULLETIN 233
ment. However, the presence of the host's own eggs in the nesttends to make the contest more unfavorable to the cychcal sequence;in such a situation the cowbird's eggs are frequently accepted alongwith the host's eggs which are already present.As might be expected of a purely instinctive behavioral reaction,the victimized bird may at times cover over the wrong eggs. Mousley(1916, p. 178) reported a yellow warbler's nest containing 4 eggs of itsown. and 1 cowbird egg, while 1 of the warbler eggs was covered overby nest-lining. He removed the cowbu'd egg and raised the embeddedwarbler egg, freeing it of the materials placed over it. Revisiting thenest three days later, he found that the warbler had embedded 2 ofher own eggs. The interference caused by his well-intended actionshad the same effect as if a cowbird had deposited another egg in thenest.In some species of hosts, the "flooring over" behavior has beennoted frequently, chiefly in the yellow warbler, which has been knownto follow this pattern repeatedly in cases where the parasite persistedin revisiting the nest. This would often result in two-, three-, foiu-,five-, and even six-storied nests, in the lower stories of which wereburied cowbkd eggs with or without some of the warbler's own. Inother species, this reaction behavior has been recorded less often,sometimes only once or twice. However, the fact that it has beenfound to occur indicates the wide distribution of the pattern. This,in turn, seems to bear out Herrick's concept that what is involved isan interruption of a basic cyclical pattern and not something peculiarto one or a few host species. In still other frequently imposed-uponhosts, such as the eastern phoebe, wood thrush, veery, ovenbird,Maryland yellowthi"oat, rufous-sided towhee, and chipping sparrow,flooring over has not been reported as yet.The following species have been fomid to bury cowbird eggs beneathnew nest linings:
eastern kingbird chestnut-sided warblereastern phoebe prairie warblerAcadian flycatcher Kentucky warblerTraill's flycatcher yellowthroatbush-tit American redstartcatbird eastern meadowlarkblue-gray gnatcatcher redwinged blackbirdBell's vireo Baltimore orioleyellow-throated vireo cardinalsolitary vireo indigo buntingred-eyed vireo American goldfinchwarbling vireo clay-colored sparrowprothonotary warbler white-crowned sparrowyellow warbler song sparrowmyrtle warbler
HOST RELATIONS OF PARASITIC COWBIRDS 37
Birds that evict the parasitic eggs.?Throwing the parasiticeggs out of the nest is the least frequent reaction recorded in cowbirdhosts. Most of the smaller species of victims probably would beunable to do so if they wanted to, and some of the larger ones seemto vary individually in this reaction. Egg eviction has been recordedfor the following hosts:
eastern kingbird (evidenceinconclusive)purple martincatbird (regularly)robin (regularly)
wood thrush (locally frequently)Bell's vireoBaltimore orioleBullock's oriole
Hosts Known To Have Reared Young of ParasiteThe mere fact that a cowbird lays an egg m the nest of a givenspecies of bhd does not imply that the chosen victim is necessarilyable to act as a successful fosterer. The parasite frequently depositseggs in nests of unwilling or unsuitable bird victims. From thestandpoint of the cowbhd, these are lost eggs: the maintainance of itsspecies depends on its placing enough eggs in nests of the right Idndsof bu'ds and in having enough of these eggs hatch young which reachmaturity.In compiling the list of successful fosterers, I have used as a mini-mum criterion of success the situation of a nest containing a healthynestling cowbird which is more than half grown and largely feathered,i.e., within a few days of fledging or leaving the nest. The degree ofdevelopment attained at this stage seems a fau'Iy safe indication thatthe foster parents were able to feed properly and care adequately forthe growing cowbird chick.If we were to be more exactmg and require actual fledging as ameasure of success, our list would suffer unduly from the effects ofexternal causes, such as predators that frequently take young birdsout of nests regardless of whether they are parasites or rightfulyoung. Since our interest at this point is to determine the innatesuitability of the foster species, it seems overcritical to reject evidencethat is short of full fledging success. The ability to continue to thefledguig stage may be safely deduced from a bird which has developedrapidly and well, even if the observation does not continue to thetime of leaving the nest. There is no good reason for thinking thatany given host species which could hatch and rear a young cowbird forthe first week or more of its nestling stage could not be able to completethe task. Any later factors of interference, such as predators, storms,or accidents to the foster parents are outside the concept of hostsuitability.
38 U.S. NATIONAL MUSEUM BULLETIN 233So far, we have been discussing merely the ability of the varioushosts to feed and take care of a young cowbird. Other factors alsoplay a role in determining the suitability of a host. One is the acces-sibility of its nest to a cowbird about to lay. Birds nesting in cavitieswith very small entrance holes are not ordinarily "available" butoccasionally are parasitized, probably when the entrance to the nestis unusually large or has been tampered with. Such a case is that ofthe brown creeper listed on page 39.Another factor is the intended victim's alertness or pugnacity thattends to protect it from being imposed upon by the parasite. Onegroup of passerine birds, the nests of which are suitable but which havenot been known to be parasitized, is the slirike family. I have longago attributed the immunity of the shrikes to their pugnacious, ag-gressive nature, which would cause them to attack and to drive off, ifnot actually kill, any intruding, would-be parasite. Many years ago Iexpressed this opinion to a correspondent, L. B. Potter of Eastend,Saskatchewan, who decided to test the white-rumped shrike, Laniusludovicianus, as a potential foster-parent of a cowbird. Potter (1939,pp. 219-220) published a brief account of what he found, which maybe supplemented by the following, taken from his letter of August1934.He placed a partly incubated cowbird's egg in a slirike's nestcontaining 6 eggs, one of which he removed. A week later, revisitingthe nest, he found that the cowbird had hatched but the shrike'seggs had not. The shrikes obviously had been feeding the youngparasite as it was m good condition. Tliree days later, the cowbirdhad grown appreciably and the shrike's eggs remained unhatched.The adult shrikes, busy with caring for their parasitic young, hadstopped incubating. Mr. Potter concluded that the shrikes treatedthe young cowbu'd just as they normally would one of theu^ own chicks.This crude experiment makes it seem all the more probable that it isthe pugnacity of the shrikes toward an approaching adult cowbird andnot an inability to hatch and feed a young cowbhd that is the reasonthe shrikes have remained free from the attentions of the parasite.The following list contains 101 species, or a little less than half of
all the species known to have been imposed upon by the brown-headed cowbird. While other birds undoubtedly will be added in thefuture, it seems that the percentage of the total host catalog thatmay be considered "successful" choices for the parasite will remainabout as given here.One further thought might be expressed before listing the rearinghosts. From the standpoint of the population economy of the para-
site, there is a great difference between a host species that occasionallymanages to bring up one young cowbhd and a host that does so
HOST RELATIONS OF PARASITIC COWBIRDS 39
regularly and, at times, rears multiple young of the parasite. As anexample of an extremely successful host, we might mention the songsparrow, of which species Salmon (1933, p. 100) recorded an instancewherein three j^oung cowbirds were reared, and Lees (1939, p. 121)reported a case wherein no less than five young cowbirds were seenattended by a pair of these sparrows.In the list given below I have attempted to evaluate the variousspecies on the basis of the actual records of theii" having raised youngcowbirds. This has resulted in some cases in a rather deceptivedefiniteness, which merits explanation at this point. In compilingthe data for this list, I have often come across published statementsto the effect merely that a given species was parasitized, withoutany further details. These I have concluded were probably eggrecords and I have not used them here. In addition, the absencefrom this list of some species which are included in the total hostcatalog may be due to the fact that many of the actual publisheddata were contributed by egg collectors, who took the eggs they found,rather than let them hatch; or the absence may be due to the factthat the data were reported by passing observers who did not havethe time, opportunity, or interest to revisit the nests to learn theeventual outcome of each,A consequence of this, reflected in the comments given after eachspecies, has been to present as equally valid quantitative estimatesthe data from casual observations with the results from much fullerknowledge in other species. In order to show the scope of the infor-mation from which I have deduced the degree to which each hosthas been a success for the parasite, I have added, where it seemeddesk-able, the total number of records of cowbird parasitism knownto me. In such cases, the accounts of the individual species in thecatalog may be consulted for fm-ther details.
mourning dove : one instance (with an black-capped chickadee : once (out ofelement of doubt) 4 records of parasitism)eastern kingbird: once (out of 15 brown creeper: one instance (onlyrecords of parasitism) record of parasitism)scissor-tailed flycatcher: once (out of a wrentit: once (out of 4 records ofvery few records of parasitism) parasitism)eastern Phoebe: frequently 1^?"^^ ^'^^n: three times (out of 6Acadian flycatcher: several times ^ ^^^,.^ , ,_ r ,
_, .?, ? , , , ,. Carolina wren: once (out of a dozenIraill s flycatcher: several times j r -i.- \or so records of parasitism)western flycatcher: twice (out of 6 eatbird: twice (out of 22 records ofrecords of parasitism) parasitism)eastern wood pewee: frequently i^j-q^.^ thrasher: several timestree swallow: at least once (out of a ^ood thrush: several timessmall number of records of para- hermit thrush: twice (out of aboutsitism) 20 records of parasitism)630590?63 4
40 U.S. NATIONAL MUSEUM BULLETIN 233
veery: frequentlyblue-gray gnatcatcher: frequentlyblack-tailed gnatcatcher: twice (outof 10 records of parasitism)ruby-crowned kinglet: once (out of6 records of parasitism)cedar waxwing: several timesphainopepla: once (out of 2 records ofparasitism)black-capped vireo: once (out of 11records of parasitism)white-eyed vireo: frequentlyButton's vireo: twice (out of 5 rec-ords of parasitism)Bell's vireo: infrequentlyyellow-throated vireo: frequentlysolitary vireo: frequentlyred-eyed vireo: frequentlyPhiladelphia vireo: once (out of 2records of parasitism)warbhng vireo: frequentlyblack-and-white warbler: severaltimesworm-eating warbler: twice (out of37 records of parasitism)golden-winged warbler: several timesblue-winged warbler: several timesTennessee warbler: once (out of 6records of parasitism)Nashville warbler: once (out of 16records of parasitism)Virginia's warbler: once (only recordof parasitism)Lucy's warbler: twice (out of 5 recordsof parasitism)yellow warbler: frequentlymagnolia warbler: once (out of 17records of parasitism)black-throated blue warbler: twice(out of 9 records of parasitism)myrtle warbler: frequentlyblack-throated gray warbler: once(out of 2 records of parasitism)black-throated green warbler: severaltimesgolden-cheeked warbler: twice (out of
-
_ 8 records of parasitism)hermit warbler: once (only record ofparasitism)cerulean warbler: once (out of 12records of parasitism)Blackburnian warbler: twice (out of afew records of parasitism)
Grace's warbler: once (out of 2 recordsof parasitism)chestnut-sided warbler: frequentlypine warbler: several timesKirtland's warbler: frequentlyprairie warbler: several timesovenbird: frequentlyLouisiana waterthrush: frequentlyKentucky warbler: several timesmourning warbler: several timesMacGillivray's warbler: twice (out of8 records of parasitism)yellowthroat : frequentlyyellow-breasted chat: frequently insome areas; not at all in othershooded warbler: twiceCanada warbler: twice (out of lessthan a dozen records of parasitism)American redstart: frequentlyhouse sparrow: twice (out of 7 recordsof parasitism)bobohnk: twice (out of 22 records ofparasitism)redwinged blackbird: once (out of 180records of parasitism)orchard oriole: several timesBaltimore oriole: twice (out of 14records of parasitism)hooded oriole : twice (out of a few rec-ords of parasitism)Bullock's oriole: once (out of 4 recordsof parasitism)western tanager: once (out of 3records of parasitism)scarlet tanager: several timessummer tanager: several timescardinal: several timesrose-breasted grosbeak: several timesblue grosbeak: once (out of about 30records of parasitism)indigo bunting: frequentlypainted bunting: several timesevening grosbeak: once (only instanceof parasitism)pine siskin: twice (out of 10 recordsof parasitism)American goldfinch: several timesrufous-sided towhee: frequentlySavannah sparrow: twice (out of 27records of parasitism)LeConte's sparrow: once (out of 6records of parasitism)
HOST RELATIONS OF PARASITIC COWBIRDS 41
seaside sparrow: once (only record ofparasitism)vesper sparrow: several timeslark sparrow: twice (out of about 30records of parasitism)white-winged junco: twice (out of 2records of parasitism)slate-colored junce: several timesOregon junco: once (out of 2 recordsof parasitism)
chipping sparrow: frequentlyclay-colored sparrow: frequentlyBrewer's sparrow: twice (out of 3records of parasitism)field sparrow: several timeswhite-throated sparrow: several timesfox sparrow: at least once (out of afew records of parasitism)swamp sparrow: several timessong sparrow: frequently
Hosts of the Brown-headed GowbirdSummary
42 U.S. NATIONAL MUSEUM BULLETIN 23 3Summary?Continued
HOST RELATIONS OF PARASITIC COWBIRDSSummary?Continued 43
44 U.S. NATIONAL MUSEUM BULLETIN 23 3Summary
HOST RELATIONS OF PARASITIC COWBIRDS 45
Although the record stands, it hardly warrants looking upon theblue-winged teal as anything but an accidental "host" of the cowbird.Indeed, there is no evidence that the teal was still in possession of itsnest when the first cowbird egg was laid. The cowbird involved inthis record is of the race artemisiae.
Ferruginous HawkButeo regalis (Gray)This very sizeable hawk cannot be looked upon as anything but apurely accidental host of the brown-headed cowbird. The only loiownrecord, which involves the northwestern race, wasnoted near Bottineau,North Dakota, May 3, 1894, by Alfred Eastgate, who found a nestwith 4 eggs of the hawk and 1 of the cowbird.
KilldeerCharadrius vociferus (Linnaeus)The killdeer is in our catalog solely on the basis of its inclusion in alist of cowbird victims in Oberholser's unpublished manuscript on thebirds of Texas. As I stated in my book (1929, p. 205), the datasupporting this inclusion were not placed on record, and from conver-sation with the compiler I find that at this late date it is highly unlikelythat the data will come to light. The bird is obviously inappropriateas a host species, and it cannot be looked upon as other than anaccidental victim of the parasite. Even the word "victim" hardlyapplies ; if the eggs had been left to hatch, the kiUdeer still would havesuffered no inconvenience. Upland PloverBartramia longicauda (Bechstein)The upland plover is another accidental host, for which there is buta single record?^a nest found in Minnesota, containing 4 eggs of theupland plover plus 1 of the^brown-headed cowbird. According to infor-mation received from the late J. H. Bowles, in whose collection theeggs were at the time, the cowbird egg was almost buried in the bottomof the nest. Wilson's PhalaropeSteganopus tricolor VieillotAt Bear River Refuge, Utah, June 3, 1938, Wilhams and Trow-bridge (1939, p. 77) found two nests of this bird parasitized by thenorthwestern race of the brown-headed cowbird. The nests wereabout 25 yards apart and were fairly well concealed in damp salt-grasson a small, artificial island in the lower marshes. "Each containedfour phalarope and two cowbird eggs. Since these instances seemedfrom available information to constitute a new host record, subsequentvisits to the nest were made to learn the ultimate fate of the eggs.
46 U.S. NATIONAL MUSEUM BULLETIN 233On June 21, it was found that all the phalarope's eggs in one nest hadhatched and the two cowbird's eggs were left. These were laterflooded. In the second nest, on June 28, three phalarope's eggswere found hatched. The remaining phalarope's egg was pipped buthad been destroyed by flooding along with the cowbird's eggs. Oneof the cowbird's eggs in the first nest was evidently infertile, but theothers were advanced in development."
California GullLarus californicus LawrenceThere is but one record for this unusual and apparently accidentalvictmi. Alfred Eastgate wrote me many years ago that in June 1899he found a nest of this gull containing several eggs of its own and oneof the cowbird in an area that "later became the National Bird Re-serve of Shrimp Lake." I was never able to locate "Shrimp Lake,"and only recently have I found that it was a miswriting for "StmnpLake," which is a national bird reserve in North Dakota, the state inwhich Eastgate is known to have done most, if not all, his field work.A gull is obviously unsuitable as host for a cowbird, and all that canbe said for this record is that on at least one occasion a cowbird madethe mistake of laying in a nest of this bird. The cowbird here in-volved is the race artemisiae.Mourning DoveZenaidura macroura (Linnaeus)The mourning dove is decidedly an uncommon victim of the brown-headed cowbird, but it has been recorded as a host at least six times,four records of which refer on geographic grounds to the eastern,nominate race of the dove and of the cowbird, and one to the westernrace Z.m. marginella. We may dispose of the latter one quickly as nodata concerning it are available. It is based solely on the fact that,in the hst of cowbird victims in his unpublished manuscript on Texanbirds, Oberholser included the western mourning dove, but he gaveno supporting information as to the source or conditions of his record.The other five are as follows: E. H. Bang informed Coues (1884, p.293) that he found the mourning dove to be parasitized in easternIowa, probably near West Liberty; Hicks (1934, p. 396) noted asimilar case in Franldin County, Ohio; A. J. Berger (1960, p. 118)found a nest near Ann Arbor, Michigan, which contained a youngmourning dove and a fresh cowbird egg (when first seen, it had held 2dove eggs and 1 of the cowbird); Dr. Richard F. Johnston (in litt.)informed me that, out of 1,010 nests of the mourning dove found inKansas, one contained an egg of the brown-headed cowbird; and C. D.Kellogg (1900, p. 121) observed a parasitized nest at Rock Hill,Pennsylvania, on May 25, 1899.
HOST RELATIONS OF PARASITIC COWBIRDS 47Only in the last case are there any details; the observer left thefollowing account. He found 15 or more doves' nests in one orchardon May 25, and he noticed a cowbird flutter off a large graclde's nest,which, on examination, was found to contain only a single cowbirdegg. Three days later, he noted that a mourning dove had deposited2 eggs in this nest. He was unable to visit the nest again until threeweeks later, when it contained a young cowbird almost ready to fly.Although he waited for some time, he did not see the doves return tofeed the young parasite.This account is accompanied by a photograph of the nest, showingthe young cowbird and the 2 dove's eggs, but it is not as completelyconvincing as it might appear to be. Kellogg did not actually seethe doves at the nest, and, secondly, the original builders of the nest,the gracldes, might have taken over the nest and hatched and rearedthe cowbird. Thirdly, it would be theoretically diflBcult for a doveto rear a cowbii'd because of the lack of attunement in their feedinghabits. The cowbird chick agrees with nestlings of most otherpasserine birds in its mode of feeding. At the approach to the nestof the adult food-laden bird, the nestlings open wide theu- bills andthe adult thrusts the food with its bill into the throats of the young.The dove, however, reverses the process: the adult opens its mouth,into which the young thrust their bUls for food. It would seem thata young cowbird and an adult mourning dove might have difficultiesin adjusting to this difference. This is w^hat raises a question as tothe proper interpretation of Kellogg's record.A possible sixth record is the following. Watkins (1900, p. 71)writes that cowbird eggs have been found in the nests of severalspecies of birds that nest in open meadows in Michigan, among whichhe lists the mourning dove. However, in his account of the dove, hementions only a single instance of ground nesting by this bird in openmeadows, and in that one no mention is made of any cowbu'd eggs.It is, therefore, not clear if Watkins knew of a Michigan record, ormerely mentioned the mourning dove because of the then fau'ly recentIowa record published a few years earlier by Coues. Other writerswho have listed the mourning dove as a cowbird victim, such asBendire (1893) and Davie (1889), obviously were merel}^ compilingearlier statements. Ground DoveColumbigallina passerina (Linnaeus)This dove is a rarely victimized species, for which there are onlytwo records, both from near Brownsville, Texas, and both having todo with the dwarf race obscurus of the brown-headed cow^bird. InMay, 1925, I examined about a dozen nests of the ground dove, oneof which, found on May 23, contained 1 cowbird egg in addition to
48 U-S. NATIONAL MUSEUM BULLETIN 23 3
the usual 2 of the host. The late K. D. Camp told me at the timethat once he had found a similar case in the same area years earlier.The ground dove in these two cases is of the subspecies C.p. pallescens.
Yellow-billed CuckooCoccyzus americanus (Linnaeus)This bird has been reported as a victim of the brown-headed cow-bird on three occasions. W. E. Loucks found a cowbird's egg in ayellow-billed cuckoo's nest near Peoria, Illinois, some time prior to1893. Trautman (1940, p. 273, 393) recorded a nest containing 5eggs of the cuckoo and 1 of the cowbu'd at Buckeye Lake, Ohio. Inthe collections of the Museum of Natural History of the Universityof Minnesota is another record?a parasitized set of eggs taken atFarmington, Connecticut, by Franklin Benner, on June 8, 1875. AsI stated m an earlier paper (1949, p. 158), the Loucks record is thebasis for the inclusion of this cuckoo in Bendire's list (1893) of cow-bird hosts, presented therein without any supporting evidence. Theparasite in both cases was of the typical race M.a. ater.
Black-billed CuckooCoccyzus enjihrophthalmus (Wilson)Three parasitized nests of this cuckoo have been reported. One nearBuffalo, New York, was found by Morris and Fames (Friedmann,1943, p. 353); one in Maryland was reported by Stewart and Robbins(1958, p. 329). The data on the latter instance, kindly sent me byR. E. Stewart, are that the nest contained 1 egg of the cuckoo and1 of the brown-headed cowbird; it was observed in Anne ArundelCounty, Maryland, May 26, 1932. The third case, a nest with 2 eggsof the cuckoo and 1 of the cowbird, was found at vSte. Dorothee, LavalCounty, Quebec, June 15, 1938, by Wm. J. Brown of Westmount,Montreal. I am indebted to Mr. L. M. Terrill for sending me thisrecord. In all tlu-ee cases the typical, eastern race of the cowbird isinvolved.
Ruby-throated HummingbirdArchilochus colubris (Linnaeus)The ruby-throated hummingbird is in this catalog on the basis ofone record, unfortunately without supporting details. According toF. B. Webster (1891, p. 109), M. S. Culver of Medford, Massachusetts,in July, 1890, found a nest of this bird containing a single cowbird'segg. I commented earlier (1929, p. 207) that I could not help butwonder if the nest might have been a wood pewee's, but it seems betterto assume that the observer correctly identified what he saw, especiallysince he noted that the egg completely filled the nest.
HOST RELATIONS OF PARASITIC COWBIRDS 49
Red-headed WoodpeckerMelanerpes erythrocephalus (Linnaeus)The red-headed woodpecker is a rarely victimized bird. It ismentioned in the lists of cowbird victims by Bendire and by Daviewithout any supporting details. The late Lynds Jones wrote memany years ago that he had taken a cowbird's egg from the nest of ared-headed woodpecker in Ohio, Whether this was also the basis forDavie's and Bendire's listings, I cannot say.
Eastern KingbirdTyrannus tyrannus (Linnaeus)The Idngbird is an uncommonly used host; onl}^ 15 actual instanceshave come to my notice. Several writers have listed it as a cowbirdvictim, possibly on the basis of the same few published cases. Theactual records involve two races of the parasite, ater and artemisiae;the geographic spread of the records extends from Ontario, RhodeIsland, and New York, to Ohio, Michigan, Iowa, Kansas, Nebraska,North Dakota, Montana, Saskatchewan, and Alberta.The pugnacious disposition of the kingbird probably accounts forits relative freedom from the attention of the cowbird, but once theparasitic egg is laid in the nest, the kingbird takes care of it as do theother victims. Kells (1885) found j^oung cowbirds in Idngbirds' nests;Posson (1890) found a parasitized nest at Medina, New York; andGregg (1891, p. 26) reported a kingbird feeding a young cowbird alongwith its own offspring in Chemung County, New York. A. J. Berger(1960, p. 118) near Ann Arbor, Michigan, on June 30, 1956, found anest containing a j^oung kingbird in pin feathers and a fully featheredyoung cowbird, which fluttered out of the nest at his approach butwhich remained in the nest after being banded. R. M. Anderson(1907, pp. 299, 300) wrote that in Iowa he found the kingbird to be theonly species which "objected" to the cowbird, but he did not sayexactly what he meant by this term. Possibly he was referring toSavage's (1897, p. 6) note of a parasitized nest from which the cowbirdegg disappeared, presumably removed by the kingbird. Coues (1878,p. 608) recorded an instance of "objection" in his description: thetwo-storied nest of a kingbird, with a cowbird's egg buried in the lowerpart and 2 eggs of the Idngbird on top, was found near Frenchman'sRiver, Montana, July 9, 1874.
Western KingbirdTyrannus verticalis SayThis Idngbird is in the present catalog solely on the strength of itsinclusion in a compiled list of brown-headed cowbird victims in Ober-holser's unpublished manuscript on the birds of Texas. No actual
50 U.S. NATIONAL MUSEUM BULLETIN 2 33
cases or other data supporting its inclusion are on record but, judgingfrom the geographical range of the western Idngbird, the race of cow-bird involved must be artemisiae.
Cassin's KingbirdTyrannus vociferans SwainsonI know of only a single instance of this species being used as a hostby the brown-headed cowbird. A nest with 3 eggs of Cassin's king-bird and 2 of the dwarf race of the brown-headed cowbird was found inthe Santa Rita Mountains, Arizona, June 29, 1884; it is now in theC. E. Doe collection in the Florida State Museum, Gainesville.
Scissor-tailed FlycatcherMuscivora forficata (Gmelin)The scissor-tailed flycatcher is a rarely imposed upon victim of theeastern and the dwarf races of the brown-headed cowbird. Fitch(1950, p. 158) found a nest in Brazos County, Texas, with 3 eggs ofthe scissor-tail and 4 of the dwarf race of the parasite. Before this,
all that was known of the species as a molotlu"ine host was the barefact that Simmons (1925, p. 172) listed it as one of the birds para-sitized in the region around Austin, Texas. In the files of the U.S.Fish and Wildlife Service are two mipublished records, both fromDecatm', Texas, reported by John A. Donald in 1890 and 1892.Recently Pulich (1961, p. 52) recorded that on June 29, 1959, a scissor-tailed flycatcher was observed caring for a fledged cowbird in TarrantCounty, Texas. This is the sole record for the nominate race of thecowbird using the species as a host. It would seem that by now a largeenough number of nests of this flycatcher would have been found togive some idea of the frequency with which it is victimized. Sinceno other instances have been reported, it becomes evident that thespecies is seldom bothered by the cowbird. This is diSicult to under-stand, as the South American counterpart, the fork-tailed flycatcher,Muscivora tyrannus, is a frequent host of the shiny cowbird, M.bonariensis, in Argentina.
Great Crested FlycatcherMyiarchus crinitus (Linnaeus)Like so many hole-nesting species, the great crested flycatcheris relatively unmolested by the brown-headed cowbird. Five recordshave come to my notice, two from Maryland, and one each fromMassachusetts, Michigan, and Illinois. The data are as follows: thelate J. Hooper Bowles informed me that once he had found a para-sitized nest of this flycatcher in Massachusetts; Blocker (1936) listedit as a victim of the cowbird near Amboy, lUlnois; E. J. Court (in litt.)
HOST RELATIONS OF PARASITIC COWBIRDS 51found a cowbird's egg in a nest of this flycatcher in Ciiaiies County,Maryland; Stewart and Robbins (1958, p. 329) mention two instancesin Maryland, one of which is the E. J. Court record mentioned above;A. J. Berger (1960, p. 118) examined 11 nests near Ann Arbor, Mich-igan, during four summers of 1956-1959 and found that one of themwas "parasitized" five days after it had been deserted. This nest wasin one of a series of nesting boxes placed by Berger for the flycatchers.When using this type of box, the flycatchers would cover the entirefloor with nesting material to the depth of an inch but would makethe nest cup for the eggs at the rear of the box. The parsite did notlay her egg in the nest cup but on the nesting material halfway backfrom the entrance hole. Since the nest had been deserted by the timethe cowbird layed in it, one may ask whether, in a strict sense, this isreally an instance of parasitism on the crested flycatcher.In all the above cases the race boreus of the host and the nominaterace of the parasite are involved.
Eastern PhoebeSayornis phoebe (Latham)The eastern phoebe is a very common victim of the brown-headedcowbird. Over 375 records have come to my attention, reports thatrange from Quebec, Massachusetts, Connecticut, New York, NewJersey, Pennsylvania, Delaware, Maryland, and Virginia westwardthrough Ontario, Manitoba, Saskatchewan, to Alberta; throughWest Virginia, Ohio, Indiana, Illinois, Michigan, Wisconsin, intoMinnesota, Iowa, and Kansas. The records from Minnesota, Sas-katchewan, and Alberta refer to the northwestern race of the cowbird,M.a. artemisiae; the others, to the nominate subspecies, M.a. ater.The degree to which the phoebe is affected varies locally. At Ithaca,New York, in my own field experience, out of 22 nests found, 16, or75 percent of the nests, contained from 1 to 3 eggs apiece of thecowbird. At Amboy, Illinois, Blocker (1936, p. 133) reported 50percent of the phoebes' nests had cowbirds' eggs in them. In southernQuebec, in TerriU's experience (1961, p. 3) the percentage of para-sitism was 26 percent, out of 100 nests; in the neighborhood of BuckeyeLake, Ohio, Trautman (1940, p. 393) found that 9 out of 134 nests, oronly 7 percent, were parasitized. In Kansas, Johnston (in litt.)informed me that 8 out of 79 phoebe nests, or roughtly 10 percent,were parasitized. In the Ithaca area, the first cowbird eggs of theseason were found usually in phoebes' nests, and, until other speciesbegan nesting in numbers, this flycatcher was the chief host of theparasite. Later in the breeding season it was less frequently para-sitized than it had been earlier. In southern Quebec, Terrill alsonoted that "early in the season, nests of the Phoebe may be the only
52 U.S. NATIONAL MUSEUM BULLETIN 233
suitable ones ..." and that some cowbirds seemed to show a trendtoward host specijficity on the phoebe "whether the nest site be shed,culvert, rock ledge, or sugar shanty, in the latter case often followingthe Phoebe deep into the woods."Not infrequently the cowbird deposits an egg in a nest before thephoebe has laid any of her own, but this does not seem to affect thelatter. In at least two cases wherein I knew the cowbird had laidfii'st, the nest was not forsaken; the phoebe laid her clutch of eggs asthough no strange eggs were present. On two other occasions,however, I found cowbird eggs partly buried in the bottom of thenest; in one case there were, in addition to the buried egg, anothercowbird's egg and 2 phoebe's eggs on top. Bendire, years before(1895, p. 274), had also noted occasional attempts by the phoebe tobury the cowbird eggs under a new floor in the nest.While some phoebe eggs are more or less speckled, most are un-marked white and, as such, they are in strong contrast to the darker,mottled eggs of the parasite. Crude experiments have been made totest the latitude of egg coloration tolerated by the phoebe ; the resultwas that all of the eggs which were tried?from the larger, bluish-green eggs of the robin to the smaller, heavily dotted, cinnamon-reddish eggs of the house wren?were accepted and incubated, and, inthe case of house wrens, were hatched and reared by the phoebes.
Black PhoebeSayornis nigricans (Swainson)A single instance of the nominate race of this flycatcher as a host ofthe small, southwestern race of the brown-headed cowbird has cometo my attention. E. A. Stoner (1938) found a nest about a mile anda half north of Manka, Solano County, Cahfornia, on June 26, 1937;it contained 3 eggs of the black phoebe, 1 of the cowbird, and 3 of thewestern flycatcher. The nest was obviously built by the phoebealthough at the time of discovery the western flycatchers seemed tobe in charge of it. While there is no certainty that the parasitic eggwas laid either before or after the change in ownership of the nest,it appears that it was deposited after the western flycatchers were inpossession since there was a scanty lining of fine hairs over the phoebe'seggs, over which, in turn, were the eggs of the western flycatcher andof the cowbird. The case merits discussion here, nevertheless, be-cause it involves the parasitism of the cowbird on the nest of a blackphoebe in spite of the fact that the occupancy of the nest, in themeantime, had been taken over by another species. It recalls a caseI came upon many years ago in Argentina wherein a shiny cowbird(Molothrus bonariensis) laid in the nest of a rufous ovenbird (Furnariusrujus) although the nest had been taken over by a tree toad.
HOST RELATIONS OF PARASITIC COWBIRDS 53
Say's PhoebeSayornis saya (Bonaparte)Six instances of brown-headed cowbii'd parasitism on Say's plioebehave been reported, five from Kansas and one from Oldahoma. Allrefer to the nominate race of the host and of the parasite. Two parasit-ized nests were found by Guy C. Love in Decatur County?one onMay 30, the other on June 19, 1915?both of which were collectedand eventuallj^ were incorporated into the J. P. Norris collection. OnJune 6, 1941, H. L. Heaton found another parasitized nest in thesame part of Kansas. The fourth record, Idndly sent to me by Dr.R. F. Johnston, concerns a nest with 3 Say's phoebe eggs and 1 of thecowbird, found at Concordia, Cloud County, May 13, 1951, by Dr.J. W. Porter. The fifth record reported a parasitized nest collectedat Oberlin May 30, 1909, by L. R. Wolfe. The Oklahoma record wascollected in Pa^vnee County, June 18, 1921 ; it is now in the collectionsof the Western Foundation of Vertebrate Zoology.Without further data it is not possible to evaluate this flycatcheras a cowbird host; the paucity of records, however, is suggestive ofthe probability that Say's phoebe is not of much importance to thecowbird and that the latter, in turn, is not an important factor in theeconomy of the former.
Yellow-bellied FlycatcherEmjpidonax flaviventris (Baird and Baird)Rarely victimized or, at least, rarely reported as a cowbird victim,the yellow-bellied flycatcher is in our catalog on the strength of threeparasitized nests found in Alberta?two by T. E. Randall and oneby A. D. Henderson. The cowbird in aU three cases is the subspeciesartemisiae. Acadian FlycatcherEmpidonax virescens (Vieillot)In the more than 30 years since my first appraisal (1929, p. 209)of this flycatcher as a cowbird victim, only a small amount of addi-tional data has come to hght and these new records do not altersignificantly the earlier findings. The Acadian flycatcher is generallyan uncommon host though, at times and locally, it may be imposedupon rather frequentl}^ by the parasite. In CarroU County, Indiana,Everman (1889, p. 23) found it to be one of the chief hosts of thecowbird; and in Pennsylvania, Jacobs (1924, pp. 52-54) noted 12instances. I have heard of some 59 records, an increase of only 34in the 30 or more years since ni}^ 1929 compilation; they range fromNew England, New York, Pennsylvania, Maryland, and Virginia,westward to Ohio, Indiana, Illinois, Michigan, and Kansas. In thelast-named state, Brandt (1947) described in considerable detail the
54 U.S. NATIONAL MUSEUM BULLETIN 233
rearing of a young cowbird by a pair of these flycatchers. Occasion-ally the Acadian flycatcher may build a new floor over a cowbkd's egg,especially if the parasitic egg is laid before any of the hosts' eggs arelaid. Bendire (1895, p. 304) mentions such a case, which was foundin Illinois by Loucks. AU the records relate to the nominate race ofthe cowbird, M.a. ater.In Michigan it has been the experience of Walkinshaw and othersthat, in nests of Empidonax {virescens, traillii, and minimus) whichproduce fledghng cowbirds, none of the young flycatchers survive.Walkinshaw (1961, p. 268) examined 67 Acadian flycatcher nests insouthern and western Michigan; of these, 16, or 24 percent, wereparasitized. Traill's FlycatcherEmpidonax traillii (Audubon)Both races of this flycatcher {brewsteri and traillii) are known to bevictimized by the brown-headed cowbird, all three races of which areinvolved in the total number of records. In all, I have learned of over150 instances of cowbird parasitism, in addition to several loose state-ments which implied still other cases. The records range from BritishColumbia, Saskatchewan, and Ontario to southern Quebec in Canada;and from New England to Ohio, Illinois, Michigan, Wisconsin, Minne-sota, Iowa, Colorado, New Mexico, Washington, and California inthe United States. The largest number of records comes from southernCalifornia (41 cases), but it is not known what percent of the totalnumber of nests found by the observers is represented by this figure.This flycatcher also appears to be a somewhat commoner victim inthe Nipawin area of Saskatchewan than in many other areas, ac-cording to the experience of M. G. Street (1943, p. 7), who statesthat he has seldom found an unparasitized nest of this species. InOhio, Hicks (1934, p. 386) noted that, of 108 nests found, 23, or 21percent, were parasitized; in Michigan, Berger and Parmelee (1952,p. 37) found that the ratio of parasitized nests was 20.8 out of 48nests observed; in the next eight summers, Berger observed 216nests, of which 17, or 8 percent, were parasitized. Walkinshaw(1961, p. 268) found that 4 out of 53 Michigan nests were parasitized.At Buckeye Lake, Ohio, Trautman (1940, p. 296) found cowbu^deggs or young in 9 out of 16 nests, or over 50 percent. In Wisconsin,McCabe (in litt.) found 418 nests of this flycatcher during a periodof 17 years. Of these, 29, or 6.9 percent, w^ere parasitized. Theincidence of parasitism varied from year to year, ranging from 3 to10 percent of the nests exammed. If we add the results of these 6studies (Hicks, Berger, Walkinshaw, Parmelee, Berger, Trautman,and McCabe) made in Ohio, Michigan, and Wisconsin, we get atotal of 859 nests, of which 92, or almost 11 percent, were parasitized.
HOST RELATIONS OF PARASITIC COWBIRDS 55
In Colorado, Bendire (1895, p. 307) found "several" parasitizednests; King (1954, pp. 150-154) noted two instances in WhitmanCounty, Washington. In southern Quebec, TerriU (1961, p. 4)found cowbird eggs in 9 out of 146 nests of this flycatcher, a per-centage of 6.2. He felt that the rather late nesting of this bird mayhave accounted for the low frequency of parasitism.In Whitman County, southeastern Washington, an area where thecowbird was not very abundant, King (1955) found that the hatchingsuccess of eggs of this flycatcher was very high?84 percent in 1952,98 percent in 1953. In the latter year, fledging success was 44,6percent. These figures suggest that Traill's flycatcher is a speciesreadily able to survive a considerably greater frequency of cowbirdparasitism than our present compilation indicates.J. K. Cruttenden (in litt.) writes me that he has a remarkable setof 4 eggs of Traill's flycatcher with one of the brown-headed cowbud,taken in Cook County, lUinois, July 5, 1947. The nest was con-structed in three sections: the cowbird egg was in the lowest section;a new floor had been built over it and in this the flycatcher had laidan egg, and then for some unknown reason she had built anotherfloor, this time over her own egg, and had laid 3 more eggs in thenew nest above. Cases of flooring over cowbird eggs, with or withoutone or more eggs of the host, are weU known for the yeUow warblerand several other birds, but this appears to be the first such instancerecorded for this flycatcher.
Least FlycatcherEmpidonax minimus (Baird and Baird)The least flycatcher appears to be molested rather seldom by thebrown-headed cowbird. I have noted only 19 records in all, distrib-uted from Quebec, New England, New York, Pennsylvania, andMaryland to Michigan, Iowa, Utah, North Dakota, Montana, Alberta,and British Columbia. These records involve two races of the para-
site, ater and artemisiae. The old statement in the literature by Baird,Brewer and Ridgway (1874, pp. 154-157) that this is one of the com-monest victims in New England strangely is unsupported by sub-sequent observations, and what records they may have had havesimilarly not appeared in print. In Michigan, Walkinshaw (1961, p.268) found that this species was victimized less frequently by theparasite than was either the Acadian or Traill's flycatcher.
Western FlycatcherEmpidonax difficilis BairdSix cases of cowbird parasitism on the western flycatcher havecome to my notice, all from California and all concerned with the630590?63 5
56 U.S. NATIONAL MUSEUM BULLETIN 233
southwestern subspecies of the parasite, M. a. obscums, together withthe nominate race of the host. These records are: a set of 2 eggs ofthe flycatcher and 1 of the dwarf race of the cowbird, collected onMay 12, 1941, in Santa Clara County, California, by G. Brown, Jr.,and now in the R. Kreuger collection, Helsinld, Finland; a fledglingcowbird seen by Legg to be attended by and fed by a western fly-catcher at Point Lobos, California, July 15, reported by Pray (1952,p. 298) and later by Legg (1954, p. 314); a nest containing 1 egg eachof the host and of the parasite, found at Eel River Bar, HumboldtCounty, California, in June 1941, by R. R. Talmadge (1948, p. 273);a fledged dwarf cowbird attended by a western flycatcher at Berkeley,noted by Benson and Russell (1934, p. 219) ; a nest with 2 eggs of thehost and 1 of the parasite, found near Gilroy, April 28, 1932, byEschenberg (Friedmann, 1943, p. 353); and two other parasitizednests reported in another paper (Friedmann, 1943, p. 353), one foundnear Gilroy, April 28, 1932, by Eschenberg and one at Betebel byUnglish.A possible seventh instance, reported by E. A. Stoner (1938),concerns the nest of a black phoebe, taken over apparently by a pairof western flycatchers a nest which, when found, contained 3 eggsof each of the two birds plus 1 of the cowbird. This instance is discussedunder the black phoebe. Unknown as a cowbird host until 1934, thewestern flycatcher appears to be in process of becoming a fairlyregular victim in California, where the parasite is extending its range.
Eastern Wood PeweeContopus virens (Linnaeus)The wood pewee is a fairly regular but not a favorite host of thebrown-headed cowbird. In my 1929 summary (p. 209) I knew ofabout three dozen instances; in over 30 years since then, I have notedonly two dozen more. While these probably represent only a portionof all the cases which have been found, the fact remains that, insome areas where both the wood pewee and the cowbird are commonbreeding birds, no such records have been reported. Stewart andRobbins (1958) do not include the wood pewee as a molothrine host inMaryland and the District of Columbia; similarly, there are norecords for this flycatcher in the extensive host lists of the annual sur-veys of the Detroit region which the Detroit Audubon Society madefrom 1952 through 1954. The records culled from the literature, frommuseum collections, and from correspondence range from Massa-chusetts, Connecticut, New York, New Jersey, and Virginia westwardto Ohio, Indiana, Illinois, Michigan, Iowa, and southern Ontario. AUhave to do with the eastern race of the cowbird. As many as 4 cow-
HOST RELATIONS OF PARASITIC COWBIRDS 57
bird eggs have been reported from a single nest of this species (Greene,1917, pp. 193-194). Western Wood PeweeContopus sordidulus SclaterThe western wood pewee is known to be parasitized by two races ofthe brown-headed cowbird, obscurus and artemisiae?hoth, however,on the basis of very few records. The race obscurus is involved in aparasitized set of eggs taken at Prescott, Arizona, May 31, 1891, asrecorded by Bendire (1895, p. 293), and in another set, collected byStephen Barlow "in Cahfornia" (probably near San Diego). Therace artemisiae is involved in four records of parasitized nests found inAlberta by T. E. Randall, and one nest found at Trout Creek Point,British Columbia, by E. M. Tait. In all of these cases the subspeciesof the pewee is C.s. veliei Coues.
Olive-sided FlycatcherNuttallornis borealis (Swainson)The olive-sided flycatcher is a rarely reported victim of the brown-headed cowbird (race M.a. artemisiae). I know of three records
?
two from Alberta and one from California. Each of the Albertarecords involves a nest with 3 eggs of the flycatcher and 1 of theparasite, one nest found near Belvedere, June 27, 1925, by A. D.Henderson; the other, at Boyle, June 7, 1934, by T. E. Randall.The third record involves a nest with 2 eggs of the host and 1 of theparasite, taken at June Lake, Mono County, Cahfornia, June 19,1952, by J. B. Dixon, and now in the R. Ki'euger collection in Helsinki,Finland. I am indebted to Mr. Kreuger for the data on this set.
Vermillion FlycatcherPyrocephalus ruhinus (Boddaert)This flycatcher is an uncommonly reported host of the small,southwestern race of the cowbird, M. a. obscurus, but there is reasonto believe that it is parasitized more frequently than the recordsindicate. Two races of the vermillion flycatcher are involved
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P.r.Jlammeus in Arizona and California and P. r. mexicanus in the lowerRio Grande vaUey of Texas. Near Brownsville, Texas, J. C. Merrill(1878, p. 142) found a parasitized nest on May 10, 1877; Bendu-e(1895, p. 324) found two such cases in southern Arizona; otherArizona records have come since from Nogales (Dille, 1940, p. 87),from Phoenix (A. M. Ingersold), and from Tucson (N. K. Carpenter).In the collections of the Santa Barbara Museum of Natural Historythere is a set of 3 eggs of the vermiUion flycatcher with 1 of the dwarfcowbird which was coUected south of Tucson, Arizona, June 2, 1917.
58 U.S. NATIONAL MUSEUM BULLETIN 233W. J. Sheffler informed me that he had noted many instances ofcowbird parasitism on this flycatcher in Arizona. Hanna (1936, p.174) recorded two parasitized nests from Coachella Valley, RiversideCounty, California. Horned LarkEremophila alpestris (Linnaeus)The horned lark is an infrequent victim of the brown-headedcowbird, but at least three of the lark's geographic forms are knownto have been imposed upon by the parasite
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enthymia, practicola, andleucolaema. Two races of the cowbird, ater and artemisiae. areinvolved. Of the race enthymia there is one record?a parasitizednest found at Cypress HiUs, Saskatchewan, June 8, 1920, by S. J.Darcus. Of leucolaema there are two records?one found in Albertaby T. E. Randall and one from Fergus County, Montana, reportedby W. Raine (1894, p. 120). The subspecies practicola is the onlyone for which there are a fair number of records?14 definite onesand an indefinite number of others which are referred to loosely bysuch statements as "locally commonly parasitized" around GrantPark, lUinois (A. E. Price, in Htt.), or "I often find one or moreeggs of the cowbird in the nests of this species" in Marshall County,Iowa (A. P. Godley, in Savage, 1895, p. 34). Although it can beauthenticated that in some places the horned lark is a fairly frequenthost, Pickwell (1931, pp. 106-109) found, out of 32 nests under obser-vation in Illinois and New York, only one which was parasitized.Moreover, in the annual nesting surveys of the Detroit Audubon Soci-ety, numerous horned lark nests are reported each year but none havebeen found which contain cowbird eggs or young. Price (1934, p.107) noted two parasitized nests at Pajnie, Ohio, but he consideredit very unusual to find cowbirds' eggs in horned larks' nests. Wilhams(1950, p. 153) fisted the prairie horned lark as a cowbird host in theCleveland, Ohio, region. Apparently, there must be considerable localvariation in the frequency of cowbird parasitism of this victim. Theabove records come from southern Quebec, Ontario, Ohio, Illinois,Iowa, Wisconsin, Kansas, and Minnesota. At Lake Crystal, Min-nesota, Peabody (1899, p. 118) found 2 cowbird eggs in the samenest of a horned lark; at Loganville, Wisconsin, Robbins (1949)reported a nest with 4 cowbird eggs and 2 of the host; all the otherrecords involved single eggs.Generally speaking, the cowbird does not lay to any extent lq nestsof the horned lark. Pickwell pointed out that, in lUinois and in someother areas, more than half of the lark's breeding season is over beforethat of the cowbird begins. He suggested that the early nestingtime, the exposed nature of the nest and the habitat, as well as theearly termination of the nestling period (10 days) may mitigate also
HOST RELATIONS OF PARASITIC COWBIRDS 59
against successful parasitism by the cowbird. Experimentally hefound that the lark will tolerate strange eggs or young in the nestand that in the second half of the lark's breeding season, the foodsupply is adequate and ample; thus it appears that other factors, asyet undetermined, operate against the occurrence of cowbird parasit-ism. In a period of many years in southern Quebec, Terrill (1961,p. 4) found 201 nests of the horned lark and, of these, only 3 wereparasitized. Tree SwallowIridoprocne bicolor (VieiUot)The tree swallow is a rarely imposed upon victim but one which,Kumlien and Hollister (1903, p. 105) wrote, "often becomes thefoster parent of the cowbird" in Wisconsin. Still earlier, also inWisconsin, F. L. Grundtvig (1894, p. 122) wi"ote of having seen afemale brown-headed cowbu'd looking into the nest of a tree swallowon May 28 and, on July 19, of seeing five yomig cowbirds among alarge flock of young tree swallows. More recently, Robbins (1947,p. 135) reported a nest with 7 eggs of the swallow and 1 of the cowbird,found on Jime 13, 1947, by Carl Richter in Oconto County, Wisconsin.Years ago I suggested (1929, p. 234) that, if the brown-headed cowbirdparasitizes tree swallows in Wisconsin to any extent when it still isnot known to do so elsewhere, the case might be that the swallowsthere used shallower and wider-mouthed nesting cavities (possiblynest boxes) than in other areas; however, this is not known to be so.It is strange that every one of the few records should come from asingle area, especially since the tree swallow is not parasitized in theremamder of its ranges. The parasite in aU these cases is the easternform, M.a. ater. Bank SwallowRiparia riparia (Linnaeus)The bank swallow is an unusual and unlikely victim of the brown-headed cowbird. There is one record. In the R. M. Barnes collec-tion, presumably now in the Chicago Natm'al History Museum, is aparasitized set of 6 eggs of the bank swallow and 1 of the cowbird(race M.a. ater), collected in Illinois by W. E. Loucks. This recordinvolves the nominate race of the host.
Barn SwallowHirundo rustica LinnaeusThe barn swallow is a very infrequent victim. The known instancesare as follows: Anderson (1907, p. 299) listed it as a cowbird host inIowa, a listing which he based on the record of a parasitized nest foundby J. V. Crone and originally reported by Savage (1895, p. 36); aparasitized set, consisting of 4 swallow eggs and 1 cowbird egg, col-
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lected at La Anna, Pennsylvania, Jime 30, 1914, was in the collectionof the late J. Hooper Bowles; Poole (1930, p. 41) wrote that in BerksCounty, Pennsylvania, two parasitized nests of this swallow had beenreported; Wells (1934, p. 130) found "several" parasitized nests atColony, Kansas. A fifth instance of the barn swallow as a cowbirdhost has been noted in Maryland by Stewart and Robbins (1958, p.329). The exact data, for which I am indebted to R. E. Stewart, isthat a nest containing 1 egg of the swallow and 1 of the cowbird wasfound in St. Mary's County, Maryland, May 30, 1932. All of thesecases involve the nominate race of the parasite and the subspecieserythrogaster of the host. What might have become still anotherinstance was observed at North Eastham, Cape Cod, Massachusetts,by O. L. Austin (1932): a female cowbird was seen trying to enterthe nest of a barn swallow but was driven off by the pair of swallows.
Cliff SwallowPetrochelidon pyrrhonota (Vieillot)Of all the swallows in the present catalog, this one, because of thedifficulties of entrance imposed by the narrow openings of its retort-shaped nests, seems the least likely to be parasitized by the brown-headed cowbird. At La Anna, Pennsylvania, however, on June 30,1914, three nests were found with cowbirds' eggs in them, accordingto the late J. Hooper Bowles (in litt.), who acquired one of these setsfor his collection. Poole (1930, pp. 41, 50) recorded four parasitizednests of the cliff swallow in Berks County, Pennsylvania. Many yearsearlier. Poling (1890, p. 92) mentioned a cowbird's egg found in a cliffswallow's nest near Chicago by George L. Tappan. This is probablythe basis for Bendire's inclusion of this species in his list of cowbirdhosts. It is the same record that I erroneously mentioned (1929, p.234) as being by an unsigned, and hence anonymous, observer. Theabove records all refer to the eastern race of the parasite, M.a. ater.
Purple MartinProgne subis (Linnaeus)The purple martin has never been reported in print as a cowbirdhost. One record, which has been in my files for many years, shouldbe reported now. In 1929 Mr. C. A. Barnum of Detroit, Michigan,wrote me that he had built a martin house and placed it on a pole about20 feet high. When the martins nested in it, he noted that brown-headed cowbirds often came and entered nest compartments for a fewmoments at a time. He was unable to get up to the nests to examinethem, but on several occasions he found broken cowbird eggs aroundthe base of the pole. He did not observe any fledgling cowbirds laterwith the martins. The fact that he saw cowbirds enter the nest
HOST RELATIONS OF PARASITIC COWBIRDS 61
compartments and the fact that later he fomid broken cowbird eggson the gromid below certainly suggest that the eggs were deposited inthe nests and then subsequently ejected. Because Mr. Barnumactually had not seen the cowbird eggs in the martin nests, I have with-held this record for many years. Inasmuch as no additional instancesof the cowbird parasitizing the purple martin have come to my noticesince then, I can assume only that this swallow is molested rarely bythe parasite but that such a situation did occur at the time of theoriginal observation. The nominate races of both the swallow and thecowbird are involved here.
Blue JayCyanocitta cristata (Linnaeus)The blue jay is an uncomm.on victim quite unsuitable as a potentialfosterer for a brown-headed cowbird. The eggs of the former are somuch larger than those of the cowbird that any eggs of the latter in anest would hardly have sufficient contact with the body of the incu-bating host to allow them to develop and hatch. There are a fewrecords, which can be listed as follows: Blocher (1933, p. 58; 1936,p. 132) found the blue jay to be parasitized at Amboy in northernIllinois ; in the first of his two papers he reports a nest on May 22, 1932,containing 4 eggs of the jay and 1 of the cowbird; in the secondpaper he records what appears to be a similar instance in 1934, in thesame locality, but his wording is too inexact not to rule out the pos-sibility that both refer to the same case; F. B. Webster (1890, p. 31)stated that he had a parasitized set of blue jays' eggs in his collectionbut gave no details; finally, the late T. S. Roberts (inlitt.) informedme many years ago that he had a distinct recollection of finding, atleast once, the egg of a cowbird in the nest of a blue jay. The easternrace of the parasite, M.a. ater, and the northern race of the jay, C.c.hromia, are the forms involved in all of these records.Common CrowCorvus brachyrhynchos BrehmOne indefinite record of this unexpected host?unfortimatelywithout details?should be mentioned here. In Feathers, the journalof the Schenectady Bii'd Club, in the issue of February 1941 (p. 15),there is given a list of "cowbird-raisers" in the vicinity of Buffalo,New York. Among the 41 listed species is the crow. The statementis made that all of the species listed are in "the records of the BuffaloOrnithological Society." Some years ago, however, the late JamesSavage tried in vain to fuid anything further about the basis for theinclusion of the crow in the list. While it obviously is possible that abrown-headed cowbird, with an egg ready to be laid, may be forced
62 U.S. NATIONAL MUSEUM BULLETIN 233by circumstances to use an unlikely but available nest, such a recordmeans no more than a record of the accidental occurrence of a birdoutside its usual range. The fact that the crow was listed as a "cow-bii'd-raiser" cannot be taken as evidence that it reared a youngcowbird; the most that can be assumed is that an egg of the latterwas found in a crow's nest. The geographical location of the "record"implies that the cowbird involved was typical ater and the crow,typical brachyrhynchos.
Black-capped ChickadeeParus atricapillus LinnaeusThe black-capped chickadee is a rarely imposed upon victim. Outof many hundreds of nests reported on, only four instances of para-sitism by the brown-headed cowbird have come to my notice?fromIowa, Massachusetts, and Michigan. Goelitz (1915, p. 152) found anest with 4 eggs of the chickadee and 1 of the brown-headed cowbu'dat Ravina, Illinois, May 8, 1915. The record as published specifiedthe Carolina chickadee but, on geographic grounds, the bird is muchmore likely to have been the black-capped species. Blocher (1936,pp. 131-133) found it to be parasitized at Amboy, Illinois. Packard(1936) found a nest on May 25 at North Eastham, Cape Cod, Massa-chusetts, containing 4 eggs of the chickadee and 2 of the cowbird. OnJune 6 the 2 cowbird eggs hatched and 1 chickadee egg was missing.Two days later 2 chickadee eggs hatched but 1 young chickadee wasdead. On June 10 the second young chickadee was missing; the otheregg of the host never hatched. That same date the young cowbirdswere removed for parasitological study. Recently, one other recordof this unusual fosterer has been reported. Nickell (1956, p. 136), ina willow stump in southeastern Michigan, found a nest in which acowbird egg had been laid about 13 inches from the entrance on anarrow ledge of rotten wood, which was just broad enough to preventit from rolling off. This egg was laid on June 12, 1952, at a time whenthe nesthng chickadees were already 10 days old; thus it almostcertainly would have been abandoned and not hatched by the chick-adees. In Nickell's discussion of the few instances of cowbird para-sitism of this bird, he states that this was the only parasitized nest hehad discovered, out of 38 nests observed during 14 years of study inthe area. However, in the 1952 survey of the area, the DetroitAudubon Society (1953, p. 70) lists a nest containing 5 eggs of theblack-capped chickadee and 1 of the cowbird which had been foundby Nickell at Cranbrook. In spite of the discrepancy, I am convincedthat these refer to the same instance.AH of the above records involve the nominate races of both host andparasite.
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Carolina ChickadeeParus carolinensis AudubonThis species parallels the black-capped chickadee in its relationto the brown-headed cowbird. The similarity in appearance and inhabits of the two chickadees probably reduces them to a single entityas far as the parasite is concerned. Only two records have come tomy notice, both from Maryland and both recorded by E. J. Court:a nest with 5 eggs of the host and 2 of the cowbird, collected at PineyPoint, St. Mary's County, April 25, 1934, and another with 5 eggsof the chickadee and 1 of the cowbird in the same area on May 25,1934. In the case of the first record. Court informed me that hecaught the female cowbird on the nest about half an hour after day-light. Stewart and Robbins (1958, p. 329) list only the secondrecord, a circumstance which raises the question as to whether ornot the two records may be really a single instance with an errorin reporting. The nominate race of the cowbird and the subspeciesextimus of the chickadee are involved here.
Tufted TitmouseParus hicolor LinnaeusThe tufted titmouse is an uncommon victim of the brown-headedcowbird, but it has been noted in that capacity in Pennsylvania,Ohio, and Illinois. In Bendire's early list (1893) of cowbird victims,he included this species, but what evidence he had is not clear. Ogilvie-Grant (1912, p. 374) listed a cowbird's egg in the British Museum,an egg reported to have been taken from a tufted titmouse's nest byP. M. Whealer, but no date or locality was given. Goehtz (1915)recorded two parasitized nests in Illinois, one containing 7 eggs ofthe host and 1 of the parasite, the other with 3 eggs of the titmouseand 2 of the cowbird. Jacobs (1888, 1823) noted a parasitized nestin Pennsylvania on May 7, 1887, early enough to have been thebasis for Bendire's inclusion. Price (1934) found another at Sher-wood, Ohio. Sutton (1928, p. 163) discovered a tufted titmousethat was parasitized on one occasion in the Pymatuning Swamp area,Pennsylvania. All the records relate to the eastern race of theparasite, M.a. ater. Black-crested TitmouseParus atricristatus CassinOne subspecies of this titmouse, P.a. sennetti, has been recordedas a victim of the dwarf race of the brown-headed cowbird. A, J.Kirn informed me some years ago that once at Somerset, Texas, hecollected a set from this bird with 2 of its own eggs and 1 of the cow-bird's. He wrote that evidently there had been a disturbance atthe nest: one of the host's eggs was punctured, the nest was some-
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what disarranged, and it had been deserted. This is the same instancementioned by Bent (1946, p. 191) and by me in another paper (Fried-mann, 1949, p. 158). Apart from this one case, the only other recordis that of Simmons (1925, p. 172) in his hst of cowbird victims for theAustin, Texas, region. VerdinAuriparus flaviceps (Sundevall)The eastern race of the verdin, A.f. annexus, has been reported ona few occasions as a victim of the dwarf race of the brown-headedcowbird. At Brownsville, Texas, in May 1924, I found five nests ofthis little bird, one nest of which contained an egg of the parasiteas well as 4 of the host. The entrance to the nest was larger thanthe entrances of the others; it may have been disarranged somewhatby the cowbird when attempting to enter the nest. R. W. Quillinwrote me many years ago that he had found a few similarly para-sitized nests, all of which were in poor condition, with the neck orentrance torn away, and all of which were deserted.
Bush-titPsaltriparus minimus (Townsend)Two races of this bird, one of the smallest victims of the dwarf raceof the brown-headed cowbu-d, have been found to be parasitized inCalifornia?the coastal form minimus and the inland race californicus.Bradford (1928) at Rincon, Riverside County, June 24, 1926, found anest of 2 eggs with 1 cowbu'd egg partly buried under a new nest lin-ing. This record I referred to calijornicus (1929, p. 256) but, on thebasis of present laiowledge of the ranges of the races of the bush-tit,the report seems to be allocated better to minimus. H. W. Carrigerinformed me that he found a parasitized nest of minimus at Irvington,Alameda County, May 15, 1932, containing 8 eggs of the host, 2 ofwhich were punctured, and 1 of the parasite. Of the race calijornicusthere is the following record: Ashworth (1930a, p. 43; 1930b, p. 122)found a nest in Ventura County, March 29, containing 7 eggs of thehost, 1 of which was partly buried under the feather lining of the nest,and 1 Qgg of the dwarf cowbird.
White-breasted NuthatchSitta carolinensis LathamAs might be expected from its habit of nesting in holes, this bu'drarely is parasitized. Only five records have come to my attention
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three from Pennsylvania, one from Illinois, and one from New York.In the last state, Reinecke (1912, p. 536) found a parasitized nestnear Buffalo. In Pennsylvania, two of the records were made atState CoUege by R. C. Harlow, one on May 16, 1910, and one on
HOST RELATIONS OF PARASITIC COWBIRDS 65May 5, 1912. The other instance was found by Jacobs (1923, pp.19-20), presumably near Waynesburg. All four records involve thesubspecies cookei of the host and the nominate race of the parasite.The Illinois set, taken in Knox County, May 12, 1942, by H. M.Holland, is now in the egg collection of R. Kreuger, to whom I amindebted for the data.
Red-breasted NuthatchSitta canadensis LinnaeusThis species is a recent addition to the list of parasitized birds, andit is one that is not likely to be molested frequently by the parasite.Houston and Street (1959, p. 176) Hst the red-breasted nuthatch as avictim of the brown-headed cowbird (subspecies artemisiae) at Nipa-win in the valley of the Saskatchewan River, Saskatchewan. Whenthe nest first was found, apparently it did not contain a cowbird'segg. At that time the opening was enlarged to allow the observer toreach inside and then the "portion that had been removed was replaced.Later it was noted that the replaced portion had fallen away and thenest was now found to contain an egg of the cowbird in addition tothose of the Nuthatch." The logical question arises, therefore,whether or not the cowbii'd would have used, or would have been ableto use, this nest for its egg were it not for the enlargement of the open-ing; and thus the question remains as to whether or not this birdlegitimately can be considered a natural host of the parasite.Brown CreeperCerthia familiaris LinnaeusA single instance of cowbu'd parasitism on the brown creeper hasbeen reported. Kumlien and Hollister (1902, p. 124) noted that atMeridan, Wisconsin, late in June, 1897, J. N. Clark observed a pair ofbrown creepers feeding a recently fledged cowbird. Since noisy youngcowbirds occasionally attract the attention of food-laden bu'ds inaddition to their own foster-parent, one may ask if Clark's observa-tion constitutes a defuiite record of parasitism. Because of this andalso because most nests of the creeper would be inaccessible to theparasite, an element of doubt cannot be eliminated?although theprobabilities are that the creepers were the actual fosterers. Thesubspecies americana of the host and the nominate race of the parasiteare involved here. WrentitChamaea fasciata (Gambel)Two races of this little bird have been found to be victimized by thesmall southwestern race of the brown-headed cowbird. The recordsrest upon five occasions, all in California. Four of these instancesconcern the pallid subspecies CJ. henshuvn. M.C. Badger informed
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me that he once found this bird victimized at Santa Paula on June 13,1917, when he collected a set of 1 egg of the victim and 1 ofthe parasite. These eggs later went to the collection of the lateJ. Hooper Bowles. In the collections of the Western Foundation ofVertebrate Zoology there is another set: 4 eggs of the wren tit and 1 ofthe dwarf cowbird, taken at Santa Paula on May 8, 1936. Kowley(1930, p. 131) put on record a similar instance of cowbird parasitismin the San Gabriel River district, May 8, 1927, with a nest containing3 eggs of the wrentit and 1 of the cowbird. Mr. N. K. Carpenterwrote to me of still another instance. In a record from Inverness,Marin County, Williams (1957, p. 428) reported that on July 22 oneof these wrentits was seen attending and feeding a recently fledgedcowbird. This last record refers to the race rwfula of the host.House WrenTroglodytes aedon VieillotThe house wren is parasitized very infrequently, partly because ofits habit of nesting in holes and partly because of its pugnaciousnature, which may be a deterrent to visiting cowbirds. An unex-plained mystery, however, is involved here: the South Americanhouse wren, T. musculus, with essentially similar habits, is imposedupon far more often by the shiny cowbird, Molothrus bonariensis.Only six actual instances, distributed from Ontario, New York,Michigan, and Iowa, to North Dakota and Alberta, have come tomy attention, A few authors, such as Bendire and Davies, haveincluded the house wren in their lists of cowbird victims, but withoutany supporting data. The cases known to me are as follows. Kells(1885, p. 106) found the race haldwini of the wren to be parasitizednear Listowel, Ontario, in 1884. Alfred Eastgate informed me manyyears ago that he once found an egg of the cowbird (subspeciesartemisiae) in a nest of the western race of the wren ( T. a. parkmanii)in North Dakota. Later, T. E. Randall sent me a second record forthe western house wren, involving a nest with 5 eggs of the wren and1 of the cowbird taken at Boyle, Alberta, June 10, 1934. Finally, onJuly 12, 1947, James Hodges saw a pair of western house wrens feedinga recently fledged brown-headed cowbird at Duck Creek, Scott County,Iowa. In this instance I deduce, on geographic grounds, that theparasite must have been of the nominate race, M.a. ater. Hamerstrom(1947) noted a house wren feeding a recently fledged cowbird inMichigan. In this case there was some question as to whether or notthe young cowbird came from an earlier brood, as at the time theonly pau* of wrens present had a nest with eggs. The cowbird mighthave been reared by some other species, and, as a result, the observa-tion involved only its begging from and being fed by a wren.
HOST RELATIONS OF PARASITIC COWBIRDS 67
Evidence of still another instance of a young cowbird being rearedby a house wren is afforded from a photograph of such an incident,probably in New York State, taken by A. A. Allen and reproduced inArmstrong (1955, opp. p. 217, fig. b).Of comparative interest is the fact that the European wren {Troglo-dytes troglodytes)?a species more like the North American winterwren {T. hiemalis) than it is like the house wren, but yet not too dis-similar in habits?is parasitized frequently by the European cuckoo, abird larger than the cowbird. Armstrong (1955, pp. 240-242) con-cluded that, in Britain, wrens' nests are parasitized occasionally,apparently only when the nests of other fosterers are not available, buthe noted that there were numerous records from continental Europe.As he stated, "it would be difficult to believe that the popularity ofthe wren with the cuckoo as a fosterer had not been exaggerated didnot the evidence of so many authorities concur." In Germany, onmore than one occasion, as many as three cuckoo eggs have beenreported from a single wren's nest.
Bewack's WrenThryomanes bewickii (Audubon)Bewick's wren is an infrequent victim. Only six actual instances,involving three races of the wren and two of the parasite, have cometo my notice. Of the nominate T.b. bewickii, there is a single record,from Missouri, where Nehrhng (1893, p. 244) found a brown-headedcowbird's egg in this wren's nest, which was in a nest box he hadprovided. He noted that "the entrance hole was very small so thatno Bluebird and not even the Tufted Titmouse could enter. Never-theless the cowbird deposited its egg in the nest." Henninger (1902,pp. 400-401) found a parasitized nest of the subspecies T.b. aliusin southern Ohio, containing 5 eggs of the Wren and 1 of the parasite.The other four records refer to the Texas race T.b. cryptus and thedwarf form of the brown-headed cowbird, M.a. obscurus. R. W.Quilhn wrote to me many years ago that in the summer of 1925 hecollected two sets of eggs, each containing 5 eggs of the wren and1 of the cowbird. In both cases the wrens were flushed from the nest.Quilhn previously had found cowbird eggs in a number of this wren'snests but they were deserted and in most cases did not contain anyeggs of the wren. AU the nests used by the parasite were in holesthat had been broken or otherwise enlarged so that the rim of thenest was visible. Recently, Air. E. J. Court sent me a card writtenat San Angelo, Texas, in April 1954, by Fred Nye, describing anincomplete set, which comprised 2 eggs of the host and 1 of the cow-bird. The nest was in a cavity in a rotten stmnp eight feet abovethe ground; the cowbird egg was on the rim of the nest about four
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inches inside the hole, a factor which suggested to the collector thatthe parasite may have been unable to enter very far into the nestcavity. Nye (in litt.) wrote to me about yet another parasitized sethe collected in Texas, containing 5 eggs of the wren and 1 of thecowbird. Carolina WrenThryothorns ludovicianus (Latham)The Carolina WTen is an uncommon victim in most parts of itsrange, but apparently less so in Oldahoma than elsewhere. All of therecords involve the nominate subspecies of the wren and all but one,the eastern form of the parasite. The known instances are as follows.Dickey (1914, pp. 158-160) records four parasitized nests in south-western Pennsylvania, one, "found April 22, 1905, was built behindsome overhanging sod, in a bank bordering a public road. . . . Thebird laid but three eggs when a cowbird deposited one of hers. . . .April 24, I found a nest built in a depression of the sod, at the base ofan old apple sprout, which grew on a bank at the roadside. The fe-male incubated three eggs of her own and one of the cowbird's. Someyears later two more nests of this wi^en, containing eggs of the cowbird,came under my observation." Jacobs (1924, pp. 52-54) describesanother case, also from Pennsylvania. The late R. M. Barneswrote to me that he had a set of eggs from this wren with a brown-headed cowbird's egg, but he gave no locahty. Nice (1931, p. 136)hsts four parasitized nests from Copan and Vinita, Oldahoma, thesefour comprising one-fourth of all the nests of this species found there.At Radnor Lake, near Nashville, Tennessee, on July 9, 1933, Crook(1934) found a nest containing 3 eggs of the Carolina wren and 1 ofthe cowbird. Johnston (in litt.) informed me that, of 11 nests foundin Kansas, 2 were parasitized by the brown-headed cowbird. In thevicinity of Austin, Texas, Simmons (1925, p. 172) listed the Carolinawren as a local victim of the dwarf race of the cowbird, M.a. obscurus.Pulich (1961, p. 60) reported the same thing, possibly on the basis ofSimmons' statement. Rock WrenSalpinctes obsoletus (Say)The rock wren has been recorded as a brown-headed cowbird hostin Kansas and in Colorado. The Colorado instance, recorded byBendire (1895, p. 437) on information received from W. G. Smith,refers to the western race of the parasite, M.a. artemisiae; this recordremains the sole case for the subspecies. In Kansas the eastern,nominate race of the cowbird is the breeding form. In that area L. R.Wolfe wrote to me that he collected a set of 4 eggs of the wren and 2
HOST RELATIONS OF PARASITIC COWBIRDS 69
of the cowbird on June 17, 1914. Herr Schonwetter informed me thathe has m his collection a parasitized set taken in Kansas, May 12, 1913,and Mr. Guy Love wrote to me that he had collected no less thantwelve parasitized sets in Decatur County, where Col. Wolfe hadobtained his set. It appears from this that the rock wren (nominaterace) must be a fairly frequent victim in Kansas.
MockingbirdMimus polyglotlos (Linnaeus)The mockingbu'd is molested by the brown-headed cowbird infre-quently, in sharp contrast to the situation in Ai-gentina where theseveral species of the genus are among the regular hosts of the shinycowbird. Both the eastern and the western subspecies of the mocking-bird have been reported as victims, and two races of the cowbird, aterand obscurus, are involved in the several records, which come fromMaryland, Arkansas, Kansas, Oklahoma, and Texas. The actualrecords are as follows. E. J. Court informed me that he once found aparasitized nest in St. Mary County, Maryland. This and one otherMaryland record are noted by Stewart and Robbins (1958, p. 329).Plank (1919, p. 18) found a similar case near Decatur, Arkansas.According to R. F. Johnston (in litt.), of 49 nests found in Kansas,1 was reported as having a cowbird egg in it. Nice (1931, p. 138) listsanother instance, discovered by T. R. Beard at Sapulpa, CreekCounty, Oklahoma. This record is the same as one which earlierand tentatively I had allocated (1929, p. 252) to the western race ofthe host, M.p. leucopterus, but it turns out that the nominate easternrace is the form involved. The western race is, however, the onerecorded as a cowbird victim in McLennan County, Texas, by Old-right (1890a, p. 58) and at Austm, Texas, by Simmons (1925, p. 172).Oldright (1890b, pp. 33, 34) wi'ites that dwarf cowbirds' eggs seldomare found in mockingbirds' nests but that in 1890 several were found.E. J. Court informed me that he once found a parasitized nest nearSan Antonio, Texas. CatbirdDumetella carolinensis LinnaeusThis bird is an infrequently used host and one with which the cow-bird is generally unsuccessful because, in the majority of cases, thecatbird throws out the cowbird's eggs. Many years ago at Ithaca,New York, I conducted some crude experiments to see whether ornot this reaction of the catbu'd was correlated with ability to distin-guish its own eggs from those of other birds, specifically those eggsdiffering in coloration and in size from its own. House sparrow andchipping sparrow eggs were placed in two catbird nests, and in each
70 U.S. NATIONAL MUSEUM BULLETIN 233
case both kinds of eggs were ejected by the catbh'ds. More recently,I have tried the same experiment with a robin's egg and a mourningdove's egg, and again the catbird threw them out while, at the sametime, another catbird's egg was accepted. A catbird's egg, however,on which small specks and blotches were painted was rejected. Nut-tall (1840, p. 380) observed more than a century ago that other birds'eggs Avere "almost instantly ejected" from catbird nests.Nickell's studies (1958, p. 286) of about 3,000 nests of the catbirdin southern Michigan, over a period of 30 years, revealed that onlyeight nests were parasitized, or about 1 in every 375. "Six nests heldone cowbird egg each at the time of discovery, and one held two eggsof the parasite. . . . All cowbird eggs had disappeared from five nestsin less than a day from the time they were laid, one egg disappearingin less than an hour after being deposited."A relatively few species of victims have been reported to bury cow-bird eggs by building a new nest floor or wall over them. Amongsuch species is the catbu'd; one occurrence, a nest with a cowbird eggcovered over in the lining, was found at Cranbrook, Michigan (DetroitAudubon Soc, 1953, p. 74). More recently, the McGeens (1962, pp.116-117) reported another instance, also in Michigan.Occasionally, however, cowbird eggs are accepted and the parasiticchicks are reared by the catbird. Elder (1921, p. 185) reported thathe had known a catbird to raise one or two of its own young alongwith a young cowbird. Recently, Nickell (1958, p. 286) reported acowbird reared to the fledgling stage by a catbu'd in Michigan.Some 26 actual instances of cowbu'd parasitism on this species havecome to my attention, in addition to a number of indefinite statementsor mere listings. These records come from Quebec, Maine, Massachu-setts, New York, New Jersey, Pennsylvania, Maryland, Indiana,Michigan, Minnesota, Iowa, Kansas, Missouri, and North Dakota.Two subspecies of the parasite, the nominate race and the northwesternM.a. artemisiae, are involved, the latter race in the North Dakotarecords, the former in all the others. In the great majority of thesecases, only 1 cowbird egg was found in the nest, but in Nelson County,North Dakota, on June 14, 1901, A. C. Bent collected a set containing1 egg of the catbird and 4 of the cowbird, the latter apparently laidby two different individuals. Van Winlde (1890, p. 48) found a nestwith 4 eggs of the catbird and 2 of the cowbird. A similar set, alsoin Michigan, was found by Berger (1951c, p. 117). This was the onlyparasitized nest out of 71 examined by him.If the proposed races of the catbird, rujricrissa and meridianus,should be accepted by the next checklist, the present records wouldinclude both the nominate carolinensis and meridianus.
HOST RELATIONS OF PARASITIC COWBIRDS 71
Brown ThrasherToxostoma rufum (Linnaeus)Both subspecies of the brown thrasher, rufum and longicauda, areparasitized occasionally by the brown-headed cowbird (subspeciesater and artemisiae). This species is the largest passerine bird molestedby the parasite?except for accidental victims?and it is the largestbird definitely known to have hatched and reared a young cowbird.Thirty-one actual records of cowbird parasitism have come to mynotice, reports that range from Quebec and Ontario to Saskatchewanin Canada, and from Connecticut, Pennsylvania, Maryland, Illinois,Michigan, and Iowa to Minnesota, Wisconsin, Kansas, North Dakota,Nebraska, Missouri, Tennessee, and Oklahoma in the United States.For many years J. A. Allen's observation of a female brown thi-asherfeeding a nearly full-grown fledgling cowbird in western Iowa in1868, a report which was discussed by Baird, Brewer, and Ridgway(1874, p. 155), remained unique. In recent years, however, similarcases have been reported. Bent (1948, p. 371) noted an observationby T. Moore concerning a thrasher feeding three young fledged cow-birds, the details of w^hich were published later by the observerhimself (Moore, 1956, p. 558). More recently, Nickell (1955, pp.90-91) has noted three nests of the brown thrasher containing chicksof the cowbird, indicating that the greater size of the host does notpreclude the eventual success of the parasite. In two of the nests,young thrashers were developing together with the cowbird chicks;in the third, the cowbird chick also had nest-mates but it did notsurvive to the point of leaving the nest.
Long-billed ThrasherToxostoma longirostre (Lafresnaye)All that is laiown of this species as a cowbird host is a report fromthe late R. D. Camp, who informed me that he had found the thrasher(subspecies sennetti) to be imposed upon by the dwarf race of theparasite near Brownsville, Texas.
Bendire's ThrasherToxostoma bendirei (Coues)In the collections of the U.S. National Museum there is a set of3 eggs of Bendire's thrasher with 1 of the dwarf brown-headedcowbird collected by E. A. Mearns near Red Rock, Arizona, April 3,1885. This is the only instance of cowbird parasitism known to me.Although a great number of the nests of this bird have since beenexamined, the above record has remained unique, a fact which sug-gests that Bendire's thrasher ordinarily is unmolested by the cowbird.Brown (1901) wrote that over a nimiber of years he had examined630590?63 6
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about 500 nests?but he made no mention of a cowbird egg in anyof them. This apparent immunity to parasitism may be due partlyto the early start of the thrasher's breeding season; eggs have beenfound as early as February 24, more than seven weeks before thefirst cowbird eggs are laid in the same region. However, since fromlate April until mid-July both birds are breeding, some as yet unknownfactor may keep them apart.
Curve-billed ThrasherToxostoma curvirostre (Swainson)The curve-billed thrasher is still known as a victim of the dwarfrace of the brown-headed cowbird on the strength only of informationgiven me (1929, p. 254) by the late R. D. Camp, who had found thebird parasitized near Brownsville, Texas, sometime prior to 1924.The local race of the thrasher is oberholseri.Sage ThrasherOreoscopies montanus (Townsend)The sage thrasher has been recorded a single time as a victim ofthe western race of the brown-headed cowbird, M.a. artemisiae.In the smiimer of 1937, Twomey (1942, p. 456) found a parasitizednest in the Uinta Basin, Utah.
RobinTurdus migratorius LinnaeusThis familiar bird is an uncommon victim. It is possible, however,that the brown-headed cowbird may lay in robins' nests more oftenthan the records indicate; the robin's habit of throwing out strangeeggs necessarily would do away with the evidence. All in aU, Ihave learned of only 26 records, ranging from Quebec, Connecticut,New York, Maryland and the District of Columbia, to Ohio, Michigan,Wisconsin, Iowa, Missom^i, North Dakota, Utah, and Alberta.Three races of the robin are involved : propinquus in the Uinta Basin,Utah (Twomey, 1942, p. 456) and Wahpeton, North Dakota (Jensen,1918, p. 347); achrusterus in Marj'land with four records (Stewart andRobbins, 1958, p. 329); and typical migratorius in the other listedareas. Two forms of the parasite are involved: artemisiae in NorthDakota, Utah, and Alberta; and ater in all the other records. Whenone considers that hundreds of robins' nests are found each year, it isobvious that a total of merely 26 instances of cowbird parasitismover man}^ years can mean only that the robin generally is unmolestedby the cowbird. To mention a single example of the evidence: inthe files of the British Columbia Nest Records Scheme there aredata on 486 robins' nests, not one of which has been parasitized.
HOST RELATIONS OF PARASITIC COWBIRDS 73Many years ago I conducted some experiments to determine whetherthe robin distinguished foreign eggs from its own by differences incolor or size or both, and it was fomid that color was the most decisivefactor. Chipping sparrow eggs, which are even smaller than cow-bird eggs, were accepted by the robins, in whose nests sparrow eggswere inserted along with their own, whereas larger eggs, more nearlythe same size as robin eggs but dissimilar in color, were rejected.Nice (1941) made similar tests, using house sparrow eggs, and foundthat the majority were rejected (although some were accepted).Howell (1942, p. 560) independently tried similar experiments andfound that alien eggs were removed but that an addled robin egg wasaccepted. Although cowbird eggs usually are not tolerated byrobins, the latter will accept and rear very young nestlings of theparasite. On one occasion I put two very young cowbirds in arobin's nest which at the time contained only eggs. The robins tookcare of and reared the young cowbirds. An early case of a robintolerating only the parasitic eggs was mentioned by Walton (1879,p. 78), who recorded an instance wherein the female robin was foundsitting on a nest containing a cowbird's egg in addition to threeof her own.The robin's relative immunity from parasitism is due not solelyto its ejection of the cowbird eggs; Leathers (1956, p. 68) observedan incubating robin vigorously attacking and driving from its nestan intruding female cowbird. Wood Thru8hHylocichla mustelina (Gmelin)The wood thrush is a frequent victim of the brown-headed cowbird.Although it is not the commonest host in any one area, in some regionshalf or more of the nests of this bird are parasitized. The thrush isnot as abundant as some of the hosts which outrank it in these areas,such as the song sparrow, the red-eyed vkeo, or the yellow warbler.Over 75 records have come to my notice, ranging from Ontario, NewYork, Massachusetts, Rhode Island, Connecticut, New Jersey,Pennsylvania, Delaware, Maryland, Vu-ginia, and West Virginia toOhio, Indiana, Michigan, Mmnesota, Wisconsin, Iowa, Illuiois,Missouri, Kansas, Tennessee, Arkansas, Oklahoma, and Texas. Thetypical eastern race of the cowbird is involved in all the recordsexcept one from the vicinity of Houston, Texas, where the breedingform of the parasite is the subspecies obscurus.When I fu'st compiled the data on this host (1929, pp. 257-258), Inoted that Iowa seemed to be the region of greatest parasitism forthe species; two-fifths of aU the records came from that one state.I assumed that, as more records were published, this ratio would
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change. Green, at Des Moines, Iowa, wrote (1887, p. 91) that one-half of the nests of this thi'ush which were found contained 1 or morecowbird eggs and that, in a single nest, he had discovered as many as6 of the parasitic eggs with 2 of the thrush's. Similarly, Keyes andWilliams (1888, p. 48) recorded the observation that this thrushfrequently was parasitized, with from 1 to 4 cowbird eggs per nest.Stoner, also in Iowa (1919, pp. 80-81), recorded 12 parasitized nestsof this bird. Since 1929, the total number of records of parasitismhas increased by 50 percent, but so has the number of Iowa records.R. F. Johnston (in litt.) informed me that 6 out of 28 nests which hefound in Kansas were parasitized.In Minnesota, Hofslund (1950) noted 14 parasitized nests, one ofwhich contained the surprismg number of 9 cowbird eggs in additionto 2 of the thrush. He noted two different wood thrushes, eachfeeding three fledgling cowbirds.A stdl more astonishing record is that of a nest found in the RondeauProvincial Park, Ontario, in 1960, by Garry Hanes, and reported tome by R. D. Ussher; the nest contained 1 egg of the thrush and noless than 12 of the cowbird. Walter Nickell informed me that thearea had been sprayed with DDT, a fact which may have reduced thenumber of nesting biixls and may have forced the cowbirds to "con-centrate" on fewer nests. In repl}'' to my queries, Mr. Ussher wroteme that the eggs were of four distinct types: 3 were rather narrowand pointed with very heavy specklings; 2 were large eggs, coarselyspeckled with heavily blotched wreaths at the large end ; 4 were lightlyand uniformly speclded; and 3 were rather coarsely but uniformlyspeckled. The appearance of the eggs suggested that four hencowbirds may have been involved.The late Lynds Jones informed me many years ago that he laiew ofa case wherein a wood thrush threw a cowbird's egg out of its nest,just as the robin does regularly. This remains only an exceptionalinstance because the thrush usually accepts the parasitic egg; in fact,Langille (1892, pp. 162-164) even found a wood thrush sitting in anest containing a solitary cowbu'd egg.Simmons (1915, p. 329) found a parasitized nest six miles west ofHouston, Texas, April 9, 1911. This is the only recorded instance ofthe dwarf cowbird parasitizing the wood thi'ush.
Hermit ThrushHylocichla guttata (Pallas)Four races of the hermit thrush (guttata, auduboni, faxoni, andpolionota) have been reported as hosts of two races of the brown-headed cowbird (ater and artemisiae) . As far as published informationindicates, the species is rather uncommonly imposed upon, but it
HOST RELATIONS OF PARASITIC COWBIRDS 75
should be noted that A. O. Gross {in Bent, 1949, p. 160) found thebu-d to be a fairly frequent victim. He writes that, although he hadseen less than 15 nests of this thrush, four of them had been para-sitized?two in Maine and two in Michigan. Furthermore, Cowan(1939, p. 44) at Tupper Lake, Peace River, British Columbia, reportedthat seven out of eight nests found were parasitized. These TupperLake records probably are better allocated to the nominate form of thehost than toJaxoni as I previously thought (1943, p. 354). In southernQuebec, over more than a half century of observation, Terrill (1961,p. 5) found 120 nests of the eastern hermit thrush, Jaxoni; of these,only six, or five percent, contained eggs or young of the cowbird.Other reports of parasitism on the eastern hermit thrush are on recordfrom Alberta (Godfrey, 1952, p. 170), Montreal (Wintle, 1896, p. 90),Michigan (Swales, 1892, p. 45), and New York (Short, 1894, pp. 255-256; Burtch, 1910, p. 139). There is a single record for the subspeciesauduhoni: a set taken in Valley, Utah, June 12, 1912, comprising 3eggs of the host and 1 of the parasite, now in the R. M. Barnes collec-tion of the Chicago Natural History Museum. There must havebeen an earlier record, since Bendire listed H.g. auduhoni as a cowbirdhost in his 1895 list. A parasitized set of eggs of the host race polionotawas taken in Mono County, California, June 6, 1933; it is now in thecollections of the Western Foundation of Vertebrate Zoology.
Swainson's ThrushHylocichla ustulata (Nuttall)Swainson's thrush has been reported very seldom as a cowbii'd host;less than a dozen instances have come to my notice. The datainvolve two races of the host and thi'ee of the parasite. Smith (1926,p. 245) found a nest of the nominate race of the thrush near San Jose,California, containing 2 eggs of the host and 1 of the brown-headedcowbird (obscurus); another parasitized set, taken near Riverside,California, June 26, 1950, is now in the San Bernardino Countj^Museum; these are the only instances for each of the foregoing sub-species. Horsbrugh (1918, p. 495) noted three cases of parasitism ofthe eastern race H.u. swainsoni at Sylvan Lake, Alberta; to this maybe added a fourth case from Edmonton, a set now in the Rowancollection at the University of Edmonton. Stansell (1907, p. 120)recorded another from Alberta. All the Alberta records involve thenorthwestern race of the parasite, M.a. artemisiae, as do also two fromMinnesota (Cass and Kjttson Counties) Hsted by Roberts (1932, p.129), one from Minnesota listed by Sparkes (1953), and one from ReevesLake, TurnbuU Refuge, Spokane Coimty, Washington (from the filesof the British Columbia Nest Records Scheme). The eastern formof the cowbird, M.a. ater, is involved in two instances of parasitism
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on Swainson's thrush in Michigan, as reported by Swales (1893,pp. 100-101). VeeryHylocichla fuscescens (Stephens)All three of the currently recognized races of the veery are para-sitized by the brown-headed cowbird, two races of which, in turn,are involved in the various records. The veery is a fairly commonvictim, but the degree of frequency seems to vary considerably indifferent parts of its range. The records, approximately 80 in num-ber, are from southern Quebec (subspecies H.f. fuliginosa);Ontario, Maine, Massachusetts, Connecticut, New York, Pennsyl-vania, Ohio, and Illinois (the foregoing, H.f. fuscescens); Michigan,Wisconsin, Minnesota, North Dakota, Manitoba, Saskatchewan,Alberta, and British Columbia (the foregoing, H.f. salicicola). Thegreatest frequency of cowbird parasitism has been reported fromCharlevoix County, Michigan, where Nickell (1942, pp. 99-108)found that 16 out of 29 nests which were studied were parasitized.Since then he has added other local instances. At Ithaca, New York,in my own field work, 7 out of about 30 nests which were observedcontained cowbird eggs or young. As many as 5 cowbird eggs havebeen found in one nest of this thrush. One such nest was found byB. W. Cartwright near Winnipeg, Manitoba, June 18, 1932, contain-ing a single egg of the host together with 5 cowbird eggs, whichappeared to have been laid by two different individuals. Anothercase, reported by Schorger (1931, p. 39) from Bayfield County,Wisconsin, contained 2 eggs of the thrush and 5 of the parasite.In southern Quebec, Terrill (1961, p. 5) reported 17 parasitizednests out of a total of 128 nests examined. He found that the veerywas a very tolerant host; he never saw any evidence that it attemptedto eject or to bury the parasitic eggs.
Eastern BluebirdSialic sialis (Linnaeus)The eastern, nominate race of the bluebird is known to be para-sitized by all thi-ee races of the brown-headed cowbird. Nowhereis it a frequently used fosterer, but it is probably one of the mostoften victimized of all hole-nesting birds, the most affected in thisregard being the prothonotary warbler. About 30 instances havecome to my attention, ranging from Quebec, Alassachusetts, RhodeIsland, Connecticut, New York, Pennsylvania, and West Virginiawestward to Ohio, Illinois, Michigan, Wisconsin, Iowa, Missouri,Arkansas, Oklahoma, Texas, and Wyoming. Simmons (1925, p. 172)lists the bluebird as a cowbird host in the area of Austin, Texas,where the breeding form of the parasite is the small race ohscurus.
HOST RELATIONS OF PARASITIC COWBIRDS 77One Wyoming record (near Laramie) refers to the northwesternform of the cowbird, artemisiae, while all the other records refer tothe nominate race of the parasite. In one case in Illinois, as many as3 cowbird eggs were found in one nest with 6 eggs of the bluebird.From Wisconsin and Missouri there are records of nests with 2 cow-bird eggs each in addition to the rightful eggs. In all the remainingcases there was but a single egg of the parasite.In her detailed study (1946) of the bluebird in Arkansas, Thomasfound one nest which was deserted because of cowbird parasitism.This is the only instance of desertion by this host which has beenrecorded definitely as such.
Western BluebirdSialia mexicana (Swainson)The western bluebird, subspecies bairdi, is in the present catalogsolely on the basis of its inclusion by Bendire in his list of victims ofthe dwarf race of the cowbird. It is obviously a very rare fosterer;Bendire gave no specific case, and none has come to attention else-where. Mountain BluebirdSialia currucoides (Bechstein)One record, a nest found by T. E. Randall, at Boyle, Alberta,May 29, 1934, containing 4 eggs of the bluebird and 1 of the brown-headed cowbird, subspecies artemisiae, first reported by me in anearher paper (1938, p. 47), is still the only instance wherein this speciesis known to have been used by the parasite. The absence of addi-tional records is not due to a lack of frequency with which nests ofthis bluebird have been found. In the files of the British ColumbiaNest Records Scheme there are data on 115 nests of this bird, notone of which has been parasitized. In addition. Bent (1949, p. 288)mentions 107 "egg dates," none of which apparently involve eggs ofthe brown-headed cowbird.
Blue-gray GnatcatcherPolioptila caerulea (Linnaeus)The blue-gray gnatcatcher is not an uncommon host, and in someareas it is even a fairly common victim. Two races, caerulea andamoenissima, are known to be victimized, the former by two racesof the brown-headed cowbird, ater and ohscurus, the latter by artemisiaeand ohscurus. Due to a change in the accepted nomenclature of thegnatcatchers, the name P.c. obscura, used in my 1929 book (p. 257)for the western form, is now restricted to the race of Baja California;the records formerly referred to this name now must be groupedunder P.c. amoenissima. All in all, some 39 records have come to
78 U.S. NATIONAL MUSEUM BULLETIN 233my notice, distributed among the following areas: Ontario, Pennsyl-vania (eight records), New Jersey, Maryland, Virginia, North Caro-lina, Tennessee, Illinois, Michigan, Iowa, Alabama, Oldahoma, Texas,New Mexico, Colorado, California, and Michoacan, Mexico. Lowe(1917, p. 455) found that in Pueblo County, Colorado, the cowbirdappeared to rely extensively on the gnatcatcher; there "the youngmay be seen yearly fed by gnatcatchers. It is rather strange thatI have never laiown them (the cowbirds) to lay their eggs in thenest of any other species though they doubtless do so." In a similarfashion, Ligon (1961, p. 235) reported that, in New Mexico, thisgnatcatcher was one of the frequent victims of the parasite; in Cali-fornia, Ashworth and Thompson (1930, pp. 122-124) also foundthese gnatcatchers rearing young cowbirds. In one case the hostsraised one of their own chicks together with one of the parasite'schicks. A noteworthy southern record is the one reported by Davis(1953, p. 95) from Tzitzo, Michoacan, Mexico.Donald (1888, p. 26) reported a parasitized nest in Texas, andrecently Nye (in litt.) found another in the same state, containingno less than 3 eggs of the dwarf cowbird and 1 of the gnatcatcher.This is the largest number of parasitic eggs yet recorded for a singlenest of this small host.Occasionally, this species may cover over the strange eggs?if thelatter are laid before any of the host's eggs are present. Spicer(1887, p. 38) at Goodrich, Michigan, found a pair of gnatcatchersbuilding a nest; eleven days later he examined the nest and foundthat a cowbird had deposited an egg before "the owners, and thatthey had put in more lining and covered it entirely over, and hadthen buUt up the sides of the nest about three quarters of an inchhigher. ..."Despite the lesser frequency with which the gnatcatcher is para-sitized, as compared with some of the vireos, warblers, and sparrows,it has been noted as a cowbird host by such early writers as Wilson andAudubon and by numerous others since then, many of whom merelylisted it as a known victim but gave no new instances.
Black-tailed GnatcatcherPoUoptila melanura LawrenceThree races of the black-tailed gnatcatcher are known to be im-posed upon by the dwarf race of the brown-headed cowbird in Arizona,California, Baja California, Sonora, and Chihuahua. There are,in all, only 13 records with data in my fJes but, from discussion withobservers of long experience, it is clear that these are only a fractionof the total number of such cases found and otherwise not placed onrecord; thus, it is not possible to appraise adequately this species
HOST RELATIONS OF PARASITIC COWBIRDS 79
as a cowbird fosterer. No reason exists, however, for assuming thebird will be very different in this respect from the better known andmore completely documented P. caerulea. This should be truedespite the fact that Hanna (1934, p. 89) has suggested that theearlier breeding season of P. melanura (the extreme egg dates atRiverside being April 10 and May 30) may help it to escape excessiveparasitism, especially early in the season. He also suggested thatthe usual habitat of this gnatcatcher, the dry bush-covered hillsidesor dry gullies, might have an isolating effect so far as cowbirds areconcerned, but this is not at all certain.Baird, Brewer, and Ridgway (1874, p. 157) noted that at CapeSt. Lucas, Baja California, Xantus found cowbhd eggs in nests ofthe black-tailed gnatcatcher, the local race of which is P.m. margaritae.This is all that has been recorded for the race.The Arizona-northwestern Mexican form. P.m. lucida, is knownas a cowbu'd host from the following records. G. Bancroft informedme that he collected two parasitized sets of eggs, one at Santa Eulalia,Chihuahua, and one at Guaymas, Sonora. A. R. Philhps (in litt.)noted a recently fledged cowbhd being attended and fed by a maleblack-tailed gnatcatcher near Granados, northeastern Sonora, onAugust 10. Swarth (1905, p. 79) found a fledgling cowbird beingattended and fed by a black-tailed gnatcatcher in the Santa RitaMountains, Arizona. At Sacaton, Arizona, Gilman (1915, p. 88)found a parasitized nest, and at Alamo Ranch, near Tucson, Brandt(1951, pp. 80, 133, 684) reported two more parasitized nests. Monson(1949, p. 248) found a fledgling cowbird being attended by one ofthese gnatcatchers, at Tucson, Arizona. Brewster (1882, p. 77)reported a parasitized nest which was found at Yuma, Arizona, byStephens. W. J. Sheffler informed me that in Aiizona he foundmany parasitized nests of this host; in fact, at times he was led towonder how the gnatcatchers were able to withstand the pressureof cowbird parasitism and to raise enough of their own young tomaintain their population.Bent (1949, p. 371) quoted Rowley, who observed that "alongthe Colorado River area, cowbirds parasitize the nests of these birdsrather abundantly ..." and who noted that he had "found a femalesetting on three eggs of a cowbhd and none of her own, with manynests containing one or two cowbird eggs."For the California race. P.m. californica, there are fom* records:Woods (1930, p. 126) saw a pair of these birds feeding an almostfully grown cowbird at Azusa in June 1928; Cl5^de L. Field founda parasitized nest at National City, April 24, 1929; N. K. Carpenterfound another in San Diego County; Hanna (1934, p. 89) found
still another at Riverside in May 1933.
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Ruby-crowned KingletRegulus calendula (Linnaeus)The ruby-crowned kinglet is rarely victimized; only six records,five for the nominate race of the kinglet and one for the race R. c.cineraceus, are known to me. Davie (1889, p. 428) reported a nestwith 9 eggs of the owner and 1 of the cowbird taken at Lennoxville,Quebec, May 15, 1882, by Montague Chamberlain; Terrill, also insouthern Quebec, found two nests with cowbird eggs in them; Holt(1942, p. 589) found a ruby-crowned kinglet feeding a very recentlyfledged cowbird at Scarboro Beach, Maine, July 22, 1941 ; A. D.Henderson informed me that he once found a parasitized nest nearBelvedere, Alberta. In the collections of the Western Foundationof Vertebrate Zoology there is a set of 7 eggs of the western raceof this kinglet with 1 of the brown-headed cowbird, collected inMono County, California, June 23, 1948. This and the Albertarecord involve the northwestern race of the parasite, M.a. artemisiae;the others are all of the nominate subspecies.
Sprague's PipitAnthus spragueii (Audubon)Sprague's pipit has been recorded as a victim of the northwesternrace of the brown-headed cowbird a single time. A nest containing3 eggs of the pipit and 2 of the parasite was found by Albert C. Lloydat Last Mountain Lake, southern Saskatchewan, May 29, 1932, andwas reported by Todd (1947, p. 417).
Bohemian WaxwingBombycilla garrula LinnaeusThe Bohemian waxwing breeds largely in regions where the brown-headed cov/bird does not breed, but in at least one area of symipatry onone occasion it has been recorded as a host of the parasite. The record,Idndly sent me from the files of the British Columbia Nest RecordsScheme, reports that a deserted nest, containing 3 eggs of the host and2 of the cowbird, was found on June 27, 1957, at Grand Forks, BritishColumbia. The host is the North American race B.g. paUidiceps,and the parasite, M.a. artemisiae.
Cedar WaxwingBombycilla cedrorum VieillotThe cedar waxwing seldom is parasitized, but it has been recordedas a host in Ontario, Quebec, New York, Connecticut, Ohio, Michigan,Wisconsin, Minnesota, Montana, Alberta, and British Columbia. Ihave learned of only 18 actual cases. Those from Montana, Alberta,and British Columbia refer to the northwestern race of the cowbird,
HOST RELATIONS OF PARASITIC COWBIRDS 81
M.a. artemisiae] the others, to the typical subspecies M.a. ater. Thefact that the waxwing is a late breeding bird and that usually it doesnot begin to nest until the laying season of the cowbird is well past itsheight probably explains its relative immunity from the attentions ofthe parasite. Over a period of 50 years in southern Quebec, Terrill(1961, p. 5) found 329 waxwing nests, of which only 4 had been para-sitized by the cowbnd.One new item of information about this uncommon victim of thebrown-headed cowbird has been brought to light recently by Nickell(1955, pp. 91-92). He points out that the waxwing, unlike many birds,begins to incubate after the laying of the fh'st egg and that, as a result,the eggs may hatch at intervals rather than all together. Nickellfound a nest with 2 young waxwings about four or five days old and 2young cowbu'ds?one about six days old, the other three days old
?
plus 1 waxwing egg. He attributes the early hatching of the oldercowbird to this peculiar mode of incubation.This fact leads to the following consideration. In the majority ofcases, cowbird eggs are laid in nests already containing eggs of thehosts and, in many cases, the cowbird eggs develop slightly morerapidly than do their nest-mates, giving them the advantage of earlierhatching. It would appear, therefore, that, in a species with theincubation habits of the waxwing, such a pattern might offset theparasite's advantage?or at least make it more likely that one or moreof the host's young would survive with it and compete with it.
PhainopeplaPhainopepla nitens (Swainson)This bird has been reported only twice as a victim of the dwarf raceof the brown-headed cowbird. Strong (1919, p. 181) reported aphainopepla's nest containing 1 egg of the parasite which was foundby Frederick Dunham at Tucson, Ai-izona, on May 20, 1897. Rowley(1930, pp. 130-131) recorded a nest containing a young cowbird aswell as a young phainopepla on June 2, 1929, near Alhambra, southernCalifornia. "The cowbird actually was forcing the young 'Pep' fromhis rightful cradle, and the adults were simply gorging the hoggishyoung cowbu'd with all the food it could hold, seemingly forgettingabout their own 'child' that was ... in the bottom of the over-crowded nest." Both records refer to the subspecies lepida of the host.
StarlingSturnus vulgaris LinnaeusThe hole-nesting habits and the pugnacious disposition of thestarling probably are the reasons for its being molested very seldomby cowbirds. Only two records of parasitism on this introduced
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species, out of many hundreds of nests examined by various observers,have come to my notice. Mr. E. J. Court informed me that A. H.Hardisty once found a cowbird's egg in a nest with eggs of the starlingnear Beltsville, Maryland. Blocher (1933, p. 157) reported a para-sitized nest at Amboy, Illinois.
Black-capped VireoVireo atricapilla WoodhouseThe black-capped vireo is an infrequently reported and probablya fairly uncommon victim. Twelve instances of cowbird parasitismon this vireo have come to my notice, involving two races of theparasite, ater and obscurus. Four records from Oklahoma, three ofwhich were mentioned by Nice (1931, p. 150) and observed by G. W.Morse at Tulsa, concern the nominate subspecies of the cowbird,while seven from Texas (Comal and Travis Counties) involve thedwarf race. One of the latter records, from Austin, includes the ob-servation of a fledgling cowbird reared by a black-capped vireo; theothers are all egg records. White-eyed VireoVireo griseus (Boddaert)The white-eyed vireo is a fairly frequent host, first recorded in thiscapacity by Alexander Wilson (1810, p. 166) in the early days ofAmerican ornithology. The general scarcity of published data on thisbird is reflected in the fact that, in my first summation (1929, p. 237),I was aware of about 20 records; in the 30 years or so since then, Ihave been able to add only 37 more. The records range from Con-necticut, New York, New Jersey, Pennsylvania, and Virginia toIllinois, Tennessee, Georgia, Alabama, Louisiana, Texas, Oklahoma,Kansas, and Tamaulipas, Mexico. Many years ago Mr. S. J. Darcusinformed me that he had found two parasitized nests of this vireo atFredericton, New Brunswick, in 1909 and 1910. This information Ipublished (1934, p. 34) because of its far northeastern locality, butat present I prefer to consider the record somewhat doubtful for thevery reason of its location. Bent (1950, p. 235), nevertheless, statesthat the breeding range of the white-eyed vireo extends to "Gasp6County, Quebec (L'Anse Pleureuse); New Brunswick (Frederictonand St. John, probably) . . . ."Although few actual cases have been put on record since Singley'soriginal instance (1888) in southern Texas, Mr. R. W. Quillin andthe late E. D. Camp found the local race of this vireo, V.g. micrus,to be very commonly parasitized. The southernmost instance in-volves a nest with 4 eggs of the vireo and 1 of the dwarf race of thecowbird found at Reynosa, Tamaulipas, Mexico, May 4, 1941, and
HOST RELATIONS OF PARASITIC COWBIRDS 83
now in the Cruttenden collection, Quincy, Illinois. The records fromOklahoma northward all refer to the host subspecies V.g. novehoracensisand all involve the nominate race of the parasite.Since most of the records are based on eggs found in nests, the factshould be pointed out that the white-eyed vireo has been known torear young cowbirds. Such was observed by Stone (1937, p. 877) onthree occasions at Cape May, New Jersey. In one of these instancesthe pair of vireos was feeding two young cowbirds.
Hutton's VireoVireo huttoni CassinHutton's vu*eo seldom is reported as a victim. Eight records havecome to my attention, six from California, involving the nominaterace of the host, and one each from Texas and New Mexico, involvingthe race stephensi From California, Hanna (1928, p. 161) listed onenest containing 2 cowbird eggs in the San Bernardino Valley andanother (1938) in Kiverside County; M. C. Badger informed me thathe had found a parasitized nest at Santa Paula, and H. W. Carrigerwrote to me that he had found two more cases near Oakland (in oneof the latter the nest contained a large young cowbird, almost readyto leave); Grinnell and Wythe (1927, p. 104) recorded Hutton's vireoas a cowbird victim in Cahfornia on the basis of a parasite nestlingtaken from a nest between Niles and Irvington, June 15, 1923, byH. V. LaJeunesse. From New Mexico, Mitchell (1898, p. 309) notedstephensi as a cowbird victim in San Miguel County; in my firstaccount (1929, p. 189) I rejected this record on the basis of the local-ity, which is considerably north of the known range of the vireo, butlater I noticed that Ridgway and others had accepted it; the A.O.U.Check-list, however, still includes only southern New Mexico in itsrange. From Texas, Fred F. Nye, Jr., \vrote me that on May 22,1951, nine miles west of Hot Springs, Brewster County, he found anest of stephensi containing 4 eggs of its own and 1 of the dwarf raceof the cowbird. The California records also refer to the small raceof the parasite, but the New Mexico report involves the nominaterace, M.a. ater. Dwarf VireoVireo nanus NelsonPreviously unknown as a cowbird host, this vireo now may beadded to the list of victims of the dwarf race of the parasite. In theMoore Collection, Occidental College, there is a set of 4 eggs of thevireo and 2 of the cowbird, taken on June 17, 1943, five miles north-east of Irapucto, Guanajuato, Mexico.
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Bell's VireoVireo bellii AudubonBell's vireo is a frequent victim of the cowbird in an area thatextends from Illinois, Wisconsin, Iowa, Nebraska, Kansas, Oklahoma,and Texas to Ai-izona and southern California. All four races of thisbird recognized within the United States are loiown to be affected
?
typical bellii from Ilhnois to north-central Texas, medius in BrewsterCounty, Texas, arizonae in southern Arizona, and pusillus in southernCaHfornia. The first of these is parasitized by the eastern form ofthe cowbird, M.a. ater; the other three, by the dwarf race, M.a.obscurus. In the course of many years I have learned of 82 actualcases of cowbird parasitism, but these constitute only a fraction ofthe number that lie back of the nimierous estimates put forward byvarious authors. Attwater (1892, p. 237) considered it a rare occur-rence to find an unparasitized nest in Bexar County, Texas. Bendire(1895, p. 442) found it "almost impossible to obtain a full set of eggsof the Least Vireo, nearly every nest containing one or two eggs ofthis parasite, and usually only one or two of its own, and the latterwere frequently punctured." R. W. QuiUin wrote me that, in SanAntonio, Bell's vireo is a very frequent victim; he added that it some-times covers over the parasitic eggs with a new lining to the nestand that it occasionally may "push the foreign eggs from the nest, asI have seen many, many eggs of the Cowbird on the ground under anest of this species. Yet the Bell's Vireo will hatch the eggs in themajority of cases." Other observers have had different experienceswith this bird. Lantz (1883, p. 95) concluded that parasitized nestswere usually deserted. Moore (1928) came to a similar conclusion,suggesting, as a result of his observations, that the vireo leaves itsold nest when molested by the cowbird and builds a new one near theoriginal site. He foimd 10 such nests within about a hundred yardsand only one pair of vireos in the vicinity. Since only two of thenests showed evidence of parasitism, the explanation he offered,however, does not fit the case too well. Pitelka and Koestner (1942)described an instance wherein the evidence indicated that cowbirdparasitism was the probable cause of desertion of the first two, andpossibly three, nests of a pair of these vireos. At each of the neststhe desertion took place after the removal of an egg of the host.Dawson's statement (1921, p. 31) that "one irate vireo I saw whoseized a cowbird three times her size and dragged her off the nest bymain force" may be discounted as highly inaccurate. The most thata vireo could do would be to hover about excitedly and possibly peckat a visiting cowbird which was on its nest.Barlow's recent work (1962, pp. 291-292) in Kansas has revealedthat the incidence of cowbird parasitism is greater in the case of
HOST RELATIONS OF PARASITIC COWBIRDS 85
Bell's vireo than in that of any other local host. Out of 35 occupiednests of this bird, 24, or 68.6 percent, were parasitized, whereas, outof 43 nests of other parasitized passerine species, 14, or 32.6 percent,were so affected. Barlow found that, with this species as host, thepercentage of cowbird eggs which hatched as compared to the numberthat were laid was relatively low. He considers that Bell's vireo isless tolerant of cowbird parasitism than are many of the other fre-quently chosen victims.The study by Nice (1929, pp. 13-20) suggests that the nest mor-tality of this vireo is often very high and, since the cowbird is oftena factor in the mortality, the parasite's importance in the populationdynamics of the host is heightened thereby?although difficult toestimate. Of 17 nests studied by Nice, the outcome of two was un-known, but the other 15 came to untimely ends. In tliree cases thecowbirds seemed to have caused desertion, in three others there werecowbu'd eggs, but only in one case was a young cowbird raised success-fully. Nice pointed out that Bennett (1917) reported on 13 nests,of which nine were failures, three were successes, and one remainedincomplete for study purposes. Of the nine failures, seven ostensiblywere due to cowbirds.Savary (1936, p. 64) reported one parasitized nest of a Bell's vheocontaining 4 cowbhd eggs and none of the vireo. He considered theeggs to be so similar that they were almost certainly the product ofone cowbird. Gray VireoVireo vicinior CouesThis is a frequently imposed upon victim, for which I have noteddwarf race of the brown-headed cowbird: at Cajon Pass, northwestof San Bernardino, California, on June 4, 1944, Hanna (1944, p. 244)found a nest containing 2 eggs of the vheo and 1 of the parasite. Inthe collection of the San Bernardino County Museum, however, thereare two additional records?one from near Hesperia, San BernardinoCounty, and the other from Sheep Creek Canyon, San Gabriel Moun-tains. Yellow-throated VireoVireo flavifrons VieillotThis is a frequentl}^ imposed upon victim, for which I have notedabout 100 records. They are distributed am.ong the following areas:Ontario, Quebec, Massachusetts, Rhode Island, Connecticut, NewYork, New Jersey, Pennsylvania, Maryland, and Ohio to Indiana,Michigan, Minnesota, Iowa, Illinois, Kentucky, Tennessee, Alabama,Arkansas, Oklahoma, and Kansas. In some places this vheo is re-ported as a common host while in others, even where both it and the
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cowbird are numerous, it is relatively unmolested by the parasite.Occasionally this host may bury the cowbird's egg under a new nestlining if it has no eggs of its own at the time; such a case was reportedby Jacobs (1903, p. 19). The j^ellow-throated vireo has been knownto rear cowbirds successfully to the fledging stage. All the recordsof parasitism on this bird involve the typical race of the cowbird.
Solitary VireoVireo soliiarius (Wilson)The solitary vireo is parasitized less commonly than the white-eyedand the yellow-throated and much less so than either Bell's or thered-eyed vireos. I know of 20 records, involving four races of thisbird: solitarius (in Massachusetts, New York, Michigan, and Minne-sota), alticola (in West Virginia), plumbeus (in Alberta, Montana, NewMexico, and Arizona), and cassinii (in Oregon and California). Allthree races of the parasite are involved : ater is the form parasitic onsolitarius, plumbeus, and alticola; artemisiae and obscurus both vic-timize plumbeus and cassinii. Although a majority of the reportedinstances are egg records, the fact is known that the solitary vireosuccessfully may rear young cowbirds, A. H. Miller (1948, p. 92)saw solitary vkeos with young cowbirds in the open pine woods ofPowder Kiver County, Montana, in June, 1947; similar observationsalso have been reported from Minnesota by Roberts (1932, p. 176).However, judging by not very abundant data, it seems that the soli-tary vireo is somewhat more prone to cover over cowbird eggs withnew nest lining than to allow the young to hatch ; this habit the vireoreveals more than the other species of its family. Allen (1913, pp.296-300) and Greene (1892, pp. 8-9) have published accounts of suchbehavior.Since the records for the races alticola, plumbeus, and cassinii are
still few in number, they can be itemized here, V.s. alticola so faris known from two instances, Dickey (1941, pp. Ill, 112) found anest with 3 eggs of the vireo and 1 of the cowbird near Cheat River,West Virginia, and another nest with a cowbird egg embedded in itswall at Point Mountain, Randolph County, West Virginia. Thewestern subspecies, V.s. plumbeus, is known as a victim in the follow-ing localities: Power River County, Montana (Miller, 1948, p. 92);Grassland, Alberta, where a parasitized set of eggs was collected June8, 1935, a set now in the William Rowan collection at the Universityof Alberta; Boyle, Alberta, where a set of eggs was collected May 28,1934, by T. E. Randall; New Mexico, according to Bailey (1928, p.661) on information received from Stokley Ligon; and Arizona, whereAlex Walker found a nest with 3 eggs of the vireo and 1 of the dwarfrace of the cowbird on June 15, 1932, in Montezuma Canyon in the
HOST RELATIONS OF PARASITIC COWBIRDS 87Huachuca Mountains at 5400 feet elevation. Finally, the subspeciesV.s. cassinii was found to be parasitized at Yosemite, California, by-Michael (1935, p. 178) and near MUton, San Joaquin County, Cali-fornia, by W. B. Sampson. The latter informed me that on May 30,1932, he found a nest containing 2 eggs of the cowbird together with2 of the vireo. Kebbe (1954, p. 51) found another parasitized neston May 6, 1954, at McKay Creek near North Plains, WashingtonCounty, Oregon. Bent (1958, p. 453) noted that J. Stuart Rowleyhad found a parasitized nest at Lake Arrowhead, San BernardinoCounty, California. Two similar sets, collected in the same county,are now in the San Bernardino County Museum. In the collectionof the California Academy of Sciences there is a cowbird egg takenfrom a Cassin vireo nest in Alameda County, May 13, 1934, by H.W. Carriger. Yellow-green VireoVireo flavoviridis (Cassin)This vireo is a very poorly known victim; only a single observationhas been reported. Lawrence (1874, p. 280), quoting Grayson, wrotethat, near Mazatlan, Stnaloa, Mexico, the yellow-green vireo is "thepreferred host" of the dwarf race of the brown-headed cowbird.Lawrence's statement is the basis, in turn, for that of Salvm andGodman (1886, p. 451). Red-eyed VireoVireo olivaceus (Linnaeus)The red-eyed vireo is one of the commonest hosts used by thebrown-headed cowbird. No species is molested more?either in thetotal number of cases or in the percentage of nests that are para-sitized. The cases are so numerous that it is possible only to estimatethem; a total in excess of 875 was noted finally, at which point thereseemed no reason to accumulate any more. The records range fromAlberta, British Columbia, New Brunswick, Ontario, Quebec, andSaskatchewan, in Canada, to the following states in the United States
:
Alabama, Arkansas, Colorado, Connecticut, Delaware, District ofColumbia, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky,Maryland, Massachusetts, Michigan, Minnesota, Montana, NewJersey, New York, North Dakota, Ohio, Oklahoma, Pennsylvania,Rhode Island, South Dakota, Tennessee, Texas, Virginia, Washington,West Virginia, Wisconsin, and Wyoming. All three races of theparasite are involved: obscurus in the San Antonio area of Texas,artemisiae in the region from British Colombia east to Saskatchewanand south to Colorado and Wyoming, and ater in the remaininglocalities.
630590?63 7
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In recent years, data of higher quahty, especially in their significantlyquantitative aspects, have been put on record by observers such asSouthern, who made an extensive study (1958) of this vireo in theDouglas Lake region of Michigan. Out of 104 nests which he found,no fewer than 75, or 72.17 percent, were parasitized. Of the 69nests which contained cowbird eggs when the nests first were found,32, or 46.38 percent, contained more than a single cowbird egg apiece.In several nests, the cowbird eggs were similar enough in size andcoloration to suggest that they were laid by one female, but in caseswhere there were as many as 3 parasitic eggs, two cowbirds wereinvolved.Southern found that the incidence of survival of the nestling vireosin parasitized nests was greater than earlier observational data hadindicated. There were 24 parasitized nests which produced fledglingsand, in these, the success of the cowbird was 87.08 percent. "Of thenests fledging no vireo young, two produced three cowbirds; and fourproduced two cowbu'ds. On the other hand, six fledged one vireo andtwo cowbirds ; nine nests fledged one cowbird and no vireos ; and threenests fledged one of each species. These figures indicate that the cow-bird is highly successful after hatching occurs; the young usuallysurvive whereas those of the host do not." Still, nine nests did pro-duce fledglings of both species?which is more than might have beenexpected. Southern states that "the cowbu'ds were probably toblame for the loss of many vireo eggs and young as well as causing theactual desertion of vkeo nests by laying too many eggs in them. Ofthe 19 vireo nests deserted, 17 contained cowbird eggs; four containedeggs of the host and cowbird in equal numbers; 11 contained fromone to seven eggs of the parasite only; and two nests contained fewereggs of the cowbird than of the vireo. These figures substantiatemy contention that an excessive number of cowbird eggs caused thedesertion of many vireo nests." The nesting success of the vireo,based on the number of eggs laid in the 32 nests producing vireoyoung, was 87.49 percent; the nesting success of the vu-eo, withreference to the 48 nests that fledged young vireos and/or youngcowbirds, was 66.66 percent. The total nestmg success of the vireoin 78 nests, observed tlirough fledging, destruction, or desertion, was41.03 percent.We should compare these figures with those published by Lawrence(1953) from a study m central Ontario, a forested area where, becausethe cowbii'd is locally absent, the vii'eo is unmolested. He found thatthe nesting success of 35 nests was 63 percent and that the hatchingsuccess of eggs in 30 nests was 60 percent.In his summary of cowbird parasitism in Ohio, Hicks (1934) notedthat, out of 231 observed nests of the red-eyed vireo, 84, or 36 percent,
HOST RELATIONS OF PARASITIC COWBIRDS 89
were parasitized. In southern Quebec, Terrill found that 26 out of 63nests, or 41 percent, were so affected.In its surveys of the nesting birds of the Detroit region, the DetroitAudubon Society (1953, p. 72; 1954, p. 85; 1956, p. 90) reports thatthe red-eyed vireo is one of the most heavily parasitized bhds in thatarea. This conclusion, however, is a comment more upon the vireo asa cowbird host than upon the cowbird as a vireo parasite. Theyellow warbler and the song sparrow were the most frequent hosts inthe locale; far more of their nests were found with cowbird eggs oryoung than was the case with the red-eyed vkeo. Only in the per-centage of parasitism of the total number of observed nests did thevireo emerge as a more frequently victimized species.In southern Quebec, Terrill (1961, p. 6) examined 64 nests, of which27, or 42.2 percent, were parasitized. He concluded that the red-eyedvireo was victimized more regularly in that area than any other hostspecies.To return to Southern's study, we should note his concluding obser-vation that, although both the vireo and the cowbird were commonbirds in the study area, if "the vireo population were in any way being
'harmed' by the cowbird, it was not apparent. Possibly parasitismby the cowbird was a natm'al device for preventing an over-productionof vireos. ^Vlien considering the number of species parasitized bj^ thecowbtrds in my study area it does seem possible that, if the cowbirdenjoyed equal success with other hosts, it might become too numerous.But I strongly suspect that the cowbu'd has few other hosts in theregion that it parasitizes with any comparable success."Occasionally, the red-eyed vireo covers over or buries the parasiticeggs in the manner of the yeUow warbler and some other birds, butit has been known to accept and to incubate cowbird eggs even whennone of its own were present. Uusally it is an extremely tolerant host.Although in the majority of cases only 1 parasitic egg was present,there are numerous instances of 2, and fewer instances of 3 and even 4,cowbird eggs in a single nest. An extreme case of multiple parasitism,mentioned by Bent (1958, p. 438), was a nest containing 6 cowbii'deggs and none of the vireo, a phenomenon reported by F. A. E. Starr,who found the vireo, nevertheless, sitting on this unusual clutch.
Philadelphia VireoVireo philadelphicus (Cassin)The Philadelphia vireo is a rarely reported victim: only two recordshave turned up. T. E. Randall wrote me that he found a nest of thisvireo with an egg of the cowbird (subspecies artemisiae) in Alberta.Bailhe and Harrington (1937, p. 239) recorded that in the Sudburydistrict, Ontario, on July 18, 1937, C. E. Hope saw a Philadelphia
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vireo attending and feeding a recently fledged cowbird (subspecies
ater). Warbling VireoVireo gilvus (Vieillot)The warbling vireo is a frequent host of the brown-headed cowbird
;
64 records have come to my attention, involving three races of thevireo, gilvus, swainsonii, and leucopolius, plus all three subspecies ofthe parasite. The records range from British Columbia, Alberta, andWashington eastward to Minnesota, Wisconsin, Illinois, Indiana,Ohio, Ontario, Quebec, Connecticut, New York, New Jersey, andPennsylvania and southward to California, Oklahoma, Iowa, andTennessee. In my own field work at Ithaca, New York, I observedonly two cases, but in other localities this vireo seems to be imposedupon to a greater extent. Eaton (1914, p. 227) lists the warblingvireo as one of the most frequent victims in New York State. Asimilar estimate was made in southwestern Pennsylvania.Since there are still relatively few records for the two western racesof both the vireo and the cowbird, these can be listed here. Thesubspecies V.g. swainsonii has been recorded as a host of Al.a. obscurusin California by Sherwood (1929, p. 3) and by H. W. Carriger nearOaldand, June 2, 1929; a third record is a parasitized set of eggs fromSan Diego County (G. Bancroft Collection) ; a fourth, from the SanGabriel Mountains and now in the San Bernardino County Museum;and a fifth, from the same area and now in the collections of the Wes-tern Foundation of Vertebrate Zoology. Coues (1878, p. 513) statedin an indefinite way that the host race V.g. swainsonii was victimized,but he gave no actual instances. Nice (1931, p. 171) recorded thisrace as a victim of M.a. ater in Oklahoma, with a record from Kenton,Cimarron County. Mr. T. E. Randall informed me that he hadfound swainsonii to be parasitized by M.a. artemisiae in Alberta, andE. M. Tait found three victimized nests at Trout Creek Point, BritishColumbia.For the subspecies V.g. leucopolius, there are the following tworecords, both involving M.a. artemieiae. Jewett, Taylor, Shaw, andAldrich (1953, p. 551) mentioned that, at Spokane, Washington,May 30, 1924, Sloanaker found a nest containing 3 eggs of the vireoand 1 of the cowbird. Schultz (1958, p. 435) recorded an instance ofa pair of these vireos feeding a recently fledged cowbird near Seattle,Washington. Slaty VireoNeochloe brevipennis (Sclater)A single instance of the slaty vireo as a host of the smaU south-western race of the brown-headed cowbird has been recorded by
HOST RELATIONS OF PARASITIC COWBIRDS 91Rowley and Orr (1960). On June 13, 1958, in a pine-oak forest threemiles east of Cuernavaca, Morelos, Mexico, Rowley found a nestcontaining 3 eggs of the vireo (nominate race) and 1 of the parasite;the eggs are now in the collection of the California Academy ofSciences. Black-and-white WarblerMniotilta varia (Linnaeus)The black-and-white warbler is a somewhat uncommon victim ofthe brown-headed cowbird; only 38 instances have come to my notice.The cases range from Alberta eastward to Ontario and Quebec, andsouthward to Massachusetts, Rhode Island, Connecticut, New York,Pennsylvania, Ohio, Illinois, Michigan, Missouri, Iowa, Kansas, andSouth Carolina (with one instance). There is also only one recordfrom Alberta?a parasitized nest found there by T. E. RandaU andinvolving the northwestern race of the parasite, M.a. artemisiae. Allthe other records refer to the eastern race M.a. ater. Although inmost places this warbler is imposed upon rather infrequently by theparasite, it should be noted that Kells (1902, p. 230) considered it tobe seriously molested at Listowell in south-central Ontario. Insouthern Quebec, Terrill (1961, p. 6) reported four cases of parasitismout of 14 nests that were observed. Although most of the recordedinstances involve cowbird eggs in nests of this bird, Morden's observa-tions (1884, pp. 193-194) show that the black-and-white warblermay, and does, rear the young parasites. He found two well-nourished young cowbirds in a nest and underneath them there werean addled cowbird egg and two young warblers nearly dead fromstarvation or suffocation. As many as 5 cowbird eggs, together with3 eggs of the warbler, have been reported from a single nest (Trippe,1868, p. 171-172); Byers (1950) found 8 cowbird eggs in a nest, with2 eggs of the warbler, near Half Moon Lake, Michigan. The SouthCaroUna record, a set of 3 eggs of the warbler and 1 of the cowbird,taken in Anderson County, May 1, 1893, by C. B. Crayton and nowin the Bent collection in the United States National Museum, is ofinterest as a far southeastern record.
Prothonotary WarblerProtonotaria citrea (Boddaert)Because of its habit of nesting in holes?frequently in dead trees inswampy places and even in standing water?to find this species oftenparasitized by the cowbird is somewhat surprising. No less than 54definite records have come to my notice from Ontario in Canadaand from Alabama, Arkansas, Delaware, Illinois, Indiana, Iowa,Minnesota, Missouri, New Jersey, Ohio, Oklahoma, and Virginia inthe United States. AU of these cases involve the eastern, nominate
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subspecies of the cowbird. The degree to which the warbler is im-posed upon in certain areas is demonstrated by the fact that, in theJ. P. Norris collection alone, 18 out of 70 sets of prothonotary eggscontain 1 or more eggs of the cowbird and that all of these 18 victim-ized sets were collected within two weeks at Burlington, Iowa,where a total of some 35 sets of eggs were taken. In other words,the incidence of parasitism at Burlington during that period was aUttle over 50 percent.In his detailed study of the prothonotary warbler, Loucks (1894,pp. 31-32) wrote that to find 1 or more eggs of the cowbird in nestsof this bird was not unusal. As many as 4 eggs of the parasite,together with 4 of the host, have been reported from a single nest;Bent (1953, p. 27) mentions a nest containing 7 cowbird and nowarbler eggs. Several instances of double-storied nests of this bird,with a cowbird egg buried in the lower part, are on record; however,the warbler usually accepts and incubates the strange eggs. I amnot aware of a definite record of this bird actually rearing one of theparasitic young, but we can assume that it not only can but does do so.
Swainson's WarblerLimnothlypis swainsonii (Audubon)Swainson's warbler is loiown to be parasitized by the cowbird inCopan County, Oklahoma. A. J. Kirn (1918, pp. 97-98) reportedthat, "during the season of 1917, six different nests were found in astrip of woods a mile long and a little over a quarter of a mile in width,built by at least four different pairs of birds; two held eggs, one withCowbird's, two were deserted, one held a punctured egg of the owner,the other a Cowbird's and a punctured Warbler's egg and a brokenWarbler's egg on the ground beneath. Tlu-ee or four eggs are laid orif Cowbirds are present, and they usually are, sometimes three eggsare laid." This statement, quoted by me in an earlier publication(1929, p. 239), is still the only pertinent observation on record. Thefact that in more than 40 years since the record was made no one hasadded to it, although not a few nests of the warbler have been found,suggests that, at best Swainson's warbler is a very local host. Sincemost of its breeding range lies outside that of the parasite, v/e are safein concluding that neither bird plays an important role in the economyof the other. Worm-eating WarblerHelmitheros vermivorus (Gmelin)This is an uncommonly reported host. When I fii-st (1929, p. 239)compiled the available data on the worm-eating warbler as a cowbu'dhost, I knew of 21 definite records. In more than 30 years since thenI have been able to add only 16 more. In some places, however, such
HOST RELATIONS OF PARASITIC COWBIRDS 93
as Green County, Pennsylvania, the incidence of cowbird parasitismis very high, as shown by Jacobs (1924, pp. 52-54) and S. S. Dickey(1934, pp. 179-184), who together found no fewer than 17 parasitizednests. In the experience of the latter observer, 8 out of 23 nestsfound near Waynesburg had been molested. In no other area hasthis warbler been reported to this extent as a cowbird host. NearWest Chester, Pennsylvania, Ladd (1887b, pp. 149-151) found 24nests, 3 of which contained eggs of the cowbird. The total availablerecords range from Connecticut, Nev/ York, New Jersey, Maryland,and Pennsylvania to Indiana, West Virginia, Kentucky, and Iowa.This warbler has been found to hatch and rear young cowbirds.Ladd (1887a, p. 110) noted a nest containing one young cowbird,nearly fully fledged, plus an addled cowbu'd egg and 5 eggs of the host.Dickey (loc. cit.) near Blacksville, West Virginia, observed a nestwith three young warblers and two young cowbirds.All the records for this host involve the eastern, nominate race ofthe parasite. The latter may be said to be important only locally inthe demography of this warbler; even here it is not apparent that thishost plays a great role in the economy of the cowbird.
Golden-winged WarblerVermivora chrysoptera (Linnaeus)The golden-winged warbler is an occasional victim of the bro^vn-headed cowbu'd. I have been able to learn of 17 definite recordsin addition to mere statements in the literature that this warbleris a cowbird host. The records come from Massachusetts, New York,New Jersey, Pennsylvania, Alichigan, and Wisconsin. In GreeneCounty, Pennsylvania, Jacobs (1904, pp. 19-21) found 20 nests,of which 6 were parasitized. This, together with the fact that atleast four more parasitized nests recently have been reported fromMichigan (Wallace, 1945, p. 174; Detroit Audubon Soc, 1953, p. 72;1954, p. 86; 1956, p. 86), qualifies our concept and points to theconclusion that, where it occurs in any numbers, this warbler is aregular victim. As many as 4 cowbird eggs have been found ina single nest. Not only have eggs of the cowbu'd been found innests of this species, but also young of the parasite have been rearedby golden-winged warblers in at least three cases?in two of v/hichthe young of the host survived together with the young parasite.In one of these cases, a nest found in Springfield Township, therewere 3 eggs of the warbler and 2 of the cowbird when the nest wasdiscovered on May 30, 1952; by June 8 there were two young ofeach. The other instance was an observation m Clyde Township,July 3, 1954; a pair of golden-wmged warblers was in attendanceupon two recently fledged young of their own and one of the cowbird.
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Elsewhere in its range, the golden-winged warbler has been reportedas a \dctim on the basis only of single or very few records. In Massa-chusetts, J. A. Allen (1870, p. 576) recorded one instance. I havelearned of but one other case from that state since then. Green(1928) reported one nest with 6 eggs of the warbler and 1 of thecowbird; he supplemented his record with the statement that heoccasionally found cowbird eggs in nests of this species with smallernumbers of warbler eggs present. In Wisconsin P. R. Hoy (1885,pp. 102-103) reported a lone instance of cowbird parasitism. Nofurther records for this state were published until 1947, when Robbins(1947) reported two parasitized nests discovered by Richter; a sub-sequent report (1949) gave still others. The cowbird involved inall the records is the typical race, M.a. ater.
Blue-winged WarblerVermivora pinus (Linnaeus)The blue-winged warbler is a fairly frequent victim of the easternrace of the brown-headed cowbird, M.a. ater. Thirty-five definiteinstances have been noted, rangmg from Connecticut, New York,New Jersey, Pennsylvania, Maryland, and Virginia to Ohio, Indiana,Michigan, Minnesota, Iowa, Missouri, and Alabama. In thesummer of 1927 at Cold Spring Harbor, Long Island, New York,I found at least three pairs of blue-winged warblers feeding recentlyfledged cowbh'ds. As many as 4 cowbird eggs together with 2 ofthe host's, have been found in one nest: Bailey (1913, pp. 198-201)considered the former similar enough to have been laid by one female.Reiff (1893) reported a nest in Pennsylvania also containing 4 cowbirdeggs and only 1 of the warbler.One of the hybrids between this warbler and the golden-wing,the so-called Brewster's warbler, has been found to be a victim in atleast one instance. Eames (1893, pp. 89-90), who removed the 2cowbird eggs from the nest, reported this case from Connecticut.
Tennessee WarblerVermivora peregrina (Wilson)This northern breeding warbler is a very uncommon victim of thecowbird. Two races of the latter, ater and artemisiae, have beenknown on a few occasions to lay in the warbler's nests. Brodkorb(1926, p. 249) noted a Tennessee warbler feeding a fledghng cowbirdat Duck Lake, Muskegon County, Michigan, on July 12, 1923.T. E. Randall wrote to me many years ago that he had collected aparasitized set of eggs in Alberta. Rowan collected another parasit-ized set at DonatviUe, Alberta, on June 17, 1935, a set now in thecollections of the University of Alberta. A third case was found
HOST RELATIONS OF PARASITIC COWBIRDS 95
also in Alberta by Donald Wilby. Street (m Houston and Street,1959, p. 176) discovered that this warbler was parasitized at Nipawin,Saskatchewan. Although these are all the records I have located,it appears that some earlier cases (or at least one) must have beenreported but not published, since Oberholser included the Tennesseewarbler within his list of cowbird hosts in his unpublished manuscripton the birds of Texas?a work written long before any of the aboveinstances were observed.
Orange-crowned WarblerVermivora celata (Say)The orange-crowned warbler has been recorded but once, to myknowledge, as a host of the brown-headed cowbird. A. R. Davidson(in Utt.) informed me that on August 18, 1959, he saw one of thesewarblers (race V.c. lutescens) feeding a fledgling of the parasite (raceM.a. artemisiae) in Vancouver Island, British Columbia. (For an-other, possible record see Wilson's warbler, p. 123.)
Nashville WarblerVermivora ruficapilla (Wilson)The Nashville warbler and the brown-headed cowbird are rela-tively unimportant to each other as host and parasite. I have beenable to learn of only 16 instances of cowbird parasitism on this species.The records come from Quebec, Massachusetts, New York, Michigan,Ontario, Minnesota, and Manitoba. In southern Quebec, over aperiod of nearly 60 years, TerriU (1961, p. 6) found 83 nests of theNashville warbler, 6 of which, or a Uttle over seven percent, wereparasitized. While the total number, 6 nests in 60 years, is small asfar as the cowbird is concerned, the percentage of victimized nests ishigh enough to be a factor, at least locally, in the economy of thewarbler. In no other part of its range, however, has anyone found acomparable frequency of parasitism. In Masspxhusetts, a state wherea great many observers have been working continuously for over acentury, only three instances have been noted: J. A. Allen (1864,p. 60) found the first set of eggs near Springfield on June 5, 1863; onJune 8, 1888, another set was collected near Farmington for theJ. P. Norris collection; and on June 15, 1907, F. H. Carpenter col-lected the third set, now in the U.S. National Museum (Bent collec-tion). From New York, another weU worked state, I know of but asingle record, a set collected at Holland Patent, on June 2, 1888, andnow in the U.S. National Museum.In Ontario, Lawrence (1948) watched a parasitized nest and foundthat eventually it produced a young cowbird together mth two youngwarblers. This is the only observed case which resulted in the rearing
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of the parasite by this host; the others were all egg records, collectedwhen they first were found. Other Ontario records were reported byBailUe and Harrington (1937, p. 242) and by Snyder (1938, p. 203).Macoun (1909, p. 614) listed another Canadian record, near Ottawa,for June 1, 1899. All of these records refer to the eastern race, bothof the host and of the parasite. Cartwright (1931, p. 185) reporteda nest with 2 eggs of the warbler and 3 of the cowbird in Manitoba;there the parasite is of the race artemisiae.In the Itasca State Park area of Minnesota, Hickey, Hofslund, andBorchert (1955) found two instances of cowbird parasitism on thiswarbler. Virginia's WarblerVermivora virginiae (Baird)This species only recently has been found to be molested by thebrown-headed cowbird. A single record reports a nest seen by Cross(1950, p. 138) near Daniels Park, Colorado, in July 1949. Originally,when first found by Niedrach, the nest contained several eggs of thewarbler and 1 of the cowbird (subspecies artemisiae), but whenCross was shown the nest on July 13, it contained only a well-grownyoung cowbird and a single, weak, little warbler. This is the sameinstance as the case mentioned by Bent (1953, p. 124).Since the altitudinal range of Virginia's warbler largely is abovethat of the cowbird, such general allopatry probably reduces theincidence of parasitism on this host.
Lucy's WarblerVermivora luciae (Cooper)The published data on Lucy's warbler indicate that, while thereare very few records of cowbird parasitism on the species, locally thiswarbler may be imposed upon rather frequently. In the report on acollection of birds from Arizona, Brewster (1882, p. 85) mentions ayoung Lucy's warbler which was taken from a nest that also held ayoung cowbird (subspecies ohscurus). Bendire (1895, p. 442) liststhis warbler as a cowbird host?probably on the basis of Brewster'srecord. For a long time this was all that was laiown until Dawson(1923, p. 458) listed three cases in California and referred to thecowbird as a prominent enemy of this species. "Sometimes thewarblers are able to entrench themselves behind apertures so narrowthat the Cowbird cannot get in; and once we saw the Cowbird'sfoundling resting unharmed, but also harmless, upon the doorstep'not less than two inches distant from the warbler's eggs. Anothernest, more exposed, contained three eggs of the arch enemy, and hadbeen deserted by the troubled owners." More recently. Bull (1958,p. 394) observed a fledgling dwarf cowbird being fed by Lucy's warbler
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in Hudspeth County, Texas, on June 8, 1958. R. S. Crossin (in litt.)informed me that on May 24, 1959, along San Pedro River, St. David,Cochise County, Arizona, he collected a set of 2 eggs of Lucy's warbleralong with 1 of the dwarf cowbird. In the collections of the SantaBarbara Museum of Natural History there are two more parasitizedsets of eggs, which were taken in 1917 near Tucson, Arizona; threesimilar sets formerly were in that museum.
Parula WarblerParula americana (Linnaeus)The parula warbler seldom has been reported to be molested bythe brown-headed cowbird. While this may be due in part to theobserver's difficulty in finding the dainty, pensile nests of the hostwithin the drooping masses of Spanish moss it prefers as a breeding
site, the total number of the warbler's nests which have been foundis large enough to indicate the low percentage of cowbird parasitism.It follows that neither the warbler nor the cowbird are importantin the economy of the other. Altogether, only 12 records have beennoted, distributed among the following states: Massachusetts,Connecticut, New York, New Jersey, Pennsylvania, Maryland,Virginia, Indiana, Alabama, Oklahoma, and Texas. The easternrace of the parasite, M. a. ater, is involved in aU the records exceptfor one instance: a parasitized nest collected by H. P. Attwater inKerr County, Texas, in 1895, and now in the U.S. National Museum;in this case, it is the dwarf race, M. a. ohscurus, which is involved.Many years ago, the late J. P. Norris informed me that he had anunusually large "set" of eggs taken in Northampton County, Vir-ginia, May 27, 1890, by G. B. Benners, comprising 3 eggs of thewarbler and 3 of the brown-headed cowbird.
Yellow WarblerDendroica petechia (Linnaeus)The yeUow warbler has been known for a long time as one of themost frequently imposed upon cowbird victims. The actual recordswhich have been observed must be well over a thousand. I stoppedaccumulating them after I had noted more than 900 instances. Allthree races of the brown-headed cowbird and five races of the yellowwarbler
?
aestiva, amnicola, rubiginosa, morcomi, and sonorana?are involved. The great mass of records come from practicallyevery province of Canada and every state of the United Stateswhere the warbler and the cowbird both occur as breeding bhds.In recent years, studies of the yellow warbler have yielded importantquantitative data on the relations between it and the cowbird.Hicks (1934, pp. 385-386), in Ohio, found 62 out of 146 nests to be
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parasitized, a percentage of 42. Berger (1951a, p. 29), in Michigan,recorded 18 parasitized nests out of 44 nests, or 40.9 percent. Terrill(1961, p. 6) found that 42 out of 307 yellow warbler nests in southernQuebec were parasitized, an incidence of parasitism of 13.6 percent.The data assembled in the Detroit area in 1954 (Detroit AudubonSoc, 1956, p. 90) reveal that, of 208 nests of the yeUow warblerreported in 1954, 74, or 35.6 percent, were parasitized. In the pre-ceeding year the percentage of parasitism had been 31.2 percent.The percentage varies locally within the "Detroit area," whichincludes eight counties of southeastern Michigan and adjacentOntario. For example, in the Cranbrook Area in 1953, 21 of 49nests, or 42.8 percent, were parasitized, but in 1954, 29 of 49 nests,or 59 percent, were affected; at Rondeau Park in 1953, 6 of 45nests, or 13.3 percent, had cowbird eggs or young, whereas in 1954,27 of 84, or 32.1 percent, were so recorded; at Otter Lake in 1953,15 of 42 nests, or 35.7 percent, were parasitized, but in 1954, 7 of23, or 30.4 percent, were affected; at Pontiac Lake in 1953, 7 nestswere found, not one of which had been molested, but in 1954, 1 nestout of 18, or 5 percent, was parasitized. The overall average fre-quency of parasitism for five years in the "Detroit area" was 37.1percent of the nests which were found.The situation at Pontiac Lake is of interest. The apparent freedomfrom cowbird attention which the yellow warblers seem to enjoythere appears to be explained by the fact that nearly all the nestswhich were found were situated in, or close to, colonies of redwingedblackbirds. The latter, with their aggressive dispositions, act as adeterrent to intruding cowbirds, and, furthermore, cowbirds are lessliable to use nests in marshy areas, where the redwings nest. Sutton(1928, p. 163) found at Pymatuning Swamp, Pennsylvania, thatredwings refused to tolerate cowbirds in their breeding area. Hesaw "a flock of Red-wings once pursue a female Cowbird until shewas utterly exhausted and plunged into the water to escape. Herpursuers chased her to the edge of the Swamp then headed her offand forced her to the opposite bank."Although the yellow warbler is, in many cases, a tolerant host,accepting the parasitic eggs and rearing the emergent young, itoften does eliminate the foreign eggs by building a new lining or anew nest floor over them and leaving them buried in the structure.Perhaps an extreme instance of this tendency is a case reported bySchrantz (1943), who studied 41 nests of this warbler in two successivesummers at West Okoboji Lake, Iowa. Of the 41 nests, 12 wereparasitized, and 11 of the 12 had cowbird eggs buried under the nestlining. In some of these nests the foreign eggs were so deeply buried
HOST RELATIONS OF PARASITIC COWBIRDS 99
that it seemed they probably were deposited before the completionof the original nest lining.Other species of victims have been known to do this also, but noneto the extent of the yellow warbler. The situation may be describedas follows.If a cowbird's egg is deposited in an empty nest before the warblerhas laid any of its own, the strange egg frequently is buried under anew floor, but not infrequently the nest may be deserted and a com-pletely new one built. If, however, the warbler has laid even 1 eggprior to the cowbird's egg being introduced into the nest, the hostusually accepts and incubates the strange egg along with its own.Sometimes it buries the eggs, its own included, in what seems aneffort to get rid of the foreign egg. The bird also may desert the nest.It sometimes happens that, after building a new floor to the nest,the warbler again is parasitized. A great deal of variation arises inthe reactions of the victim to such conditions. Usually, if there areseveral eggs of its own in the nest, the warbler will tolerate the cowbirdegg and will incubate. If the cowbird should lay first, the warblereither may desert or build a new nest floor. There are numerousrecords of two-, three-, four-, and even five-storied nests of the yellowwarbler, each of the lower stories containing eggs of the cowbird and,in some, eggs of the warbler as well. Berger (1955, p. 84) has reportedwhat must be a record case: a six-storied nest with a total of 11 cow-bird eggs buried in the various layers. As many as 4 eggs of thewarbler, a complete set, have been found buried with 1 of the cowbird,but such extreme cases are rare. It is very uncommon to find morethan 1 or 2 eggs of the warbler covered over in this manner.Near Pontiac, Michigan, the McGeens (in litt.) found 40 parasitizednests of the yellow warbler. In 13 of these, the warblers had coveredover the alien eggs with new floor lining; in 13 others, the nests weredeserted after being parasitized; of the other 14, 6 met with failurebecause of predation and 9 carried through to fledging success.Recently, Berger (1961, p. 273) reported that, in the McGeens' study,the synchronization of the cowbird eggs with those of the yellowwarbler (i.e., the time of deposition in the nests) was important;it was found that 86.5 percent of non-synchronized cowbird eggswere covered over or deserted, but only 22.5 percent of well-syn-chronized ones were treated thusly.One of the older records of cowbird parasitism on the yellow warblermerits some mention. Savage (1895, p. 13) reported one of thesewarblers feeding a fledged cowbird in Iowa on October 2, 1893. Ifthis is correct, which is highly doubtful, it is an unusually late datefor both the parasite and the host. Bent (1953, p. 182) gives no eggdates for the warbler later than June 8 in the central United States.
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Magnolia WarblerDendroica magnolia (Wilson)The magnolia warbler has been recorded rather seldom as a cow-bird victim, a fact which suggests that probably it is parasitizedinfrequently. Eaton (1914, p. 410), however, wrote that the cow-bird "seems to make a specialty of presenting this Warbler with oneor more of its eggs, generally punctm-ing the eggs of the Magnoliabefore leaving the nest." Unfortunately, Eaton did not support thisstatement with explicit data, and such evidence has not been foundin the literature. Higgins (1894, p. 106) collected a parasitized nestnear Cincinnatus, New York, and a second set that later becamepart of the J. P. Norris collection. Other parasitized sets of eggs arein the collections of the American Museum of Natural History andthe Chicago Natural History Museum. The late H. Mousloy wrote tome that he had found a cowbird's egg in a magnolia warbler's nestnear Hatley, Quebec. All in all, only 17 records have been noted,ranging from Quebec, Prince Edward Island (Mills, 1958), Ontario,and Saskatchewan to Massachusetts, New York, Pennsylvania,Michigan, and Minnesota. In southern Quebec, in the course ofalmost GO years, Terrill (1961, p. 7) found 147 nests of this warbler,of which 6 contained cowbird eggs.All the records refer to the nominate, eastern race of the brown-headed cowbird, except one from Saskatchewan, wherein the raceartemisiae is involved. This was found by Street {in Houston andStreet, 1959, p. 159) at Nipawin, Saskatchewan, on June 27, 1934.Cape May WarblerDendroica iigrina (Gmelin)Many years ago, the late J. H. Bowles wrote to me that he had adistinct recollection of having seen a set of eggs of this warbler con-taining one of the cowbird, but he could not recall where or when itwas collected or in whose collection it was when he saw it. Becauseof this lack of precise data I have kept this statement in my unpub-lished notes, waiting for a more completely documented case, butno other instance has yet been reported. Without a specified locality,one cannot say which of the two possible races of the cowbird wasinvolved. Since the Cape May warbler nests high up in evergreentrees, it is not likely to be recorded to any extent as a cowbird host.
Black-throated Blue WarblerDendroica caerulescens (Gmelin)This is a very infrequent host of the brown-headed cowbird. Only10 records have been noted?distributed from Ontario and Quebec toRhode Island and New York. Hathaway (1913, p. 557) saw a female
HOST RELATIONS OF PARASITIC COWBIRDS 101
black-throated blue warbler feeding a young cowbird much larger thanshe was. Kells (1887, and 1902) recorded two parasitized nestsin Ontario; another Ontario record is a parasitized nest found bySaunders at Durham, Gray Count}^, on June 22, 1909, and reportedby BaiJhe and Harrington (1937, p. 245). In New York, W. L. Ralphcollected three such nests, which are now in the U.S. National Museum.Terrill (1961, p. 7) discovered three instances of cowbu'd parasitismin seven nests which were found in southern Quebec in the course ofnearly 60 years of observation in that region. All the records involvethe nominate race, both of host and parasite.
Myrtle WarblerDendroica coronata (Linnaeus)The myrtle warbler is a commonly utilized host in southern Canada,but seldom has it been recorded elsewhere in this capacity. Ithas been noted as a victim of the cowbird in Alberta, Saskatchewan,Ontario, Quebec, Maine, Michigan and Wisconsin. Dr. Paul Harring-ton wrote to me that near Wasaga Beach, South Georgian Bay,Ontario, he examined 38 nests, no less than 25 of which contained eggsof the cowbird; 20 nests had 1 parasitic egg; three had 2 each; andtwo had 3 each. One nest had a cowbird's egg imbedded in its side,where the warbler had built a new nest lining over the egg. Bent(1953, p. 250) quotes Harrington that "it would not be exaggeratingto say that two-thu*ds of the initial nests are parasitized. The egg oreggs of the cowbird are often deposited before the nest is completed,leading to many a deserted nest. Twice I have found a cowbird'segg imbedded, as so often happens in the yellow warbler's nest, butin both cases yet another was in the nest with the owner's. Twelvepercent of the nests with eggs of the cowbird were deserted, but nonein which the owner's eggs were also present. Generally but one ofthe parasite's eggs was found, occasionally two and rarely three."Bent cites F. A. E. Starr as saying that, of 30 nests examined, hehad yet to find one which did not contain from 1 to 3 eggs of thecowbird. In southern Quebec, out of a total of 33 nests examined,Terrill (1961, p. 7) noted two instances of cowbird parasitism on thiswarbler.In Maine, Knight (1908, pp. 341-342) hsted the myrtle warbler asa local cowbird host, and C. H. Morrell collected a parasitized set ofeggs at Pittsfield, on May 26, 1891. This set, now in the U.S. NationalMuseum, may have been the basis for Knight's statement. In Michi-gan, Van Tyne (1924, p. 169) found a parasitized nest near Hessel,Macldnaw County, on June 20, 1919, and Root (1942) observed apair of myrtle warblers feeding a fledgling cowbird. The foregoingrecords all involve the eastern race of the cowbird.
102 U.S. NATIONAL MUSEUM BULLETIN 2 33The northwestern race, M.a. artemisiae, has been found to parasitizethe myrtle warbler in Alberta and Saskatchewan. T. E. Randallinformed me that on May 27, 1934, he found a nest at Boyle, Alberta,containing 4 eggs of the warbler and 1 of the cowbird. At Winterburn,Alberta, a set of 3 eggs of the warbler with 1 of the cowbird wascollected ; the set is now in the Rowan collection at the University ofAlberta. Godfrey (1950, p.79; 1952, p. 166) noted fledgling cowbirdsattended by myrtle warblers at Grimshaw, Alberta, and at FlattenLake, Saskatchewan. Gunn (1956, p. 88) noted that a pair of myrtlewarblers at Spirit Lake, Saskatchewan, raised 2 of their own youngand 1 cowbird. Street {in Houston and Street, 1959, p. 176) foundthis warbler to be victimized at Nipawin, Saskatchewan. Bent (1953,p. 250) records two Alberta records sent to him by A. D. Henderson.It now appears that the molestation of the mj^rtle warbler occursregularly throughout its range without regard to the subspecies of theparasite.All records refer to the typical race of the myrtle warbler.
Audubon's WarblerDendroica auduhoni (Townsend)This warbler is known as a cowbird victim on the basis of onlyfour instances. E. M. Tait (Friedmann, 1934, p. 36) found that itwas parasitized at Trout Creek Point, British Columbia. Cowan (inlitt.) wrote to me that a parasitized nest had been found at Lumby,British Columbia. Rogers (1955, p. 392) recorded a similar instanceat Cromwell Island, Flathead Lake, Montana. Finally, an egg ofthe brown-headed cowbird taken from a deserted nest of this warblerat Mammoth Camp, Mono County, California, on July 3, 1922, wassent to the Santa Barbara Aluseum of Natural History. All fourrecords involve the cowbird race artemisiae, but they refer to tworaces of the host
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auduhoni in British Columbia and California, andmemorahilis in Montana.
Black-throated Gray WarblerDendroica nigrescens (Townsend)The black-throated gray warbler is a species that has been studiedvery little; correspondingly, its relations with the brown-headed cow-bird are documented poorl3^ There are three pertinent observations.Marshall (1957, p. 112) found this warbler to be a victim of the localrace of the cowbird, obscurus, in the pine-oak woodlands of southernArizona, and Bent (1958, p. 454) noted that Hanna had collecteda parasitized set of eggs in San Bernardino County, California.Recently, T. D. Burleigh has informed me that at Oakley, CassiaCounty, Idaho, on July 20, 1958, he noted a male black-throated
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gray warbler feeding a fledgling cowbird; this record, on geographicgrounds, must refer to the cowbird race artemisiae.
Black-throated Green WarblerDendroica virens (Gmelin)This warbler appears to be a very infrequent victim of the brown-headed cowbird. Only 15 definite records have been reported, fivefrom Michigan, two each from Ontario, Quebec, Maine, and NewYork, and one each from Minnesota and Ohio. All the records referto the nominate race of both host and parasite. Bicknell (1882, p.159), on the authority of John Burroughs, listed the black-throatedgreen warbler as a cowbird victim in the Catskill Mountains of NewYork. A little to the northwest, at Ithaca, New York, on July 3,1922, I watched a recently fledged cowbird being fed by one of thesewarblers. Mendall (m Palmer, 1949, p. 515) found a parasitized nestat South Thomaston, Knox County, Maine, on July 13, 1936. Swain(1899a, p. 33) found several nests of this warbler in Maine, of whichone was parasitized by the brown-headed cowbird. In southernQuebec, TerriU (1961, p. 7) reported two cases out of a total of 16nests examined; in Ontario, Harrington found two cases near WasagaBeach, South Georgian Bay, which I reported in an earlier paper(1938, p. 48). Wikerstrom (1953, p. 147) saw a pair of these warblersfeeding two recently fledged cowbirds at O'Reilly, St. Clair County,Michigan, on July 12, 1953; Wallace (1945, p. 174) and Pitelka (1940)recorded still other cases of cowbird parasitism on this species inMichigan. Guttman (1956, p. 136) noted one of these warblers feed-ing two recently fledged cowbirds in Clearwater County, Minnesota,on August 7, 1955. The first naturalist to record the black-throatedgreen warbler as a cowbird host was Krider (1879, p. 51), who, un-fortunately, gave no locality for his record.
Golden-cheeked WarblerDendroica chrysoparia Sclater and SalvinThe golden-cheeked warbler has a very hmited breeding range, com-prising a few counties in south-central Texas, but there it has beenrecorded as a victim of the small race of the brown-headed cowbird,M.a. obscurus. In all, nine definite instances of parasitism have cometo my notice. These nine do not include a statement by Strong (1919,p. 181), who noted a parasitized nest, supposedly of this species, col-lected on June 6, 1894, at Fort Small, Arizona, -with 3 eggs of thewarbler and 1 of the cowbird. Since the golden-cheeked warbler isnot known to breed in Arizona, there seems to be a misidentification here.In the J. P. Norris collection there were three parasitized sets of eggstaken in Comal County, Texas. Three other instances?from the630590?63 8
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files of the U.S. Fish and Wildlife Service?were reported by H. Laceyfrom his ranch at Turtle Creek, Kerr County, Texas: on June 14, 1900,two warblers were seen feeding a young cowbird in a wall nest near ahouse (a very young golden-cheeked warbler in the same tree probablywas reared with the cowbird although the adult warblers were notseen actually to feed it); on May 15, 1905, a nest with 2 eggs of thewarbler and 1 of the cowbird was found; on April 26, 1915, anothernest with similar contents was discovered. Brewster (1879, pp. 77-79), reporting on Werner's data from Comal County, Texas, mentionsa nest with 3 eggs of the warbler and 1 of the cowbird. A few daysearlier, the same collector had seen a pair of golden-cheeked warblerswith a brood of fledglings, among which were young cowbirds. Nye(in Htt.) collected a set with 1 egg of this warbler plus 3 of the dwarfrace of the cowbird. Hermit WarblerDendroica occidentalis (Townsend)It is not possible to estimate the relations between the hermit war-bler and the brown-headed cowbird. Not only is the former a seldomstudied species, but also only a single instance of cowbird parasitismhas been reported. Reynolds (1942, p. 28) saw a fledghng cowbird(race obscurus) being attended and fed by a pair of hermit warblers atCamp Augusta, three miles from Nevada City, California, on June 2 1
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1942. Cerulean WarblerDendroica cerulea (Wilson)The cerulean warbler is an uncommon victim of the brown-headedcowbird. Because it builds high in trees, its nests rarely are discovered.While this fact may tend to keep down the recorded number of in-stances of cowbird parasitism, enough nests have been collected overthe years to make meaningful the paucity of cowbird records. Only 12instances have been noted. They are distributed from Ontario toMichigan, Indiana, New York, Pennsylvania, and Virginia. Samiders(1900, p. 361) reported two parasitized nests from western Ontario.The late J. P. Norris informed me many years ago that there werethree parasitized sets of eggs from Ontario in his collection, butwhether these included any of those listed by Saunders is not clear.Dickey (1912, p. 302) noted a case in Greene County, Pennsylvania.In the Bent collection in the U.S. National Museum there is a para-sitized set collected at Tonawanda Swamp, New York, on June 1, 1900.In the same collection there are two similar sets?one from Saginaw,Michigan, taken by R. A. Brown, on June 23, 1900, and one fromBeaver County, Pennsylvania, collected by W. E. C. Todd. FHnt(1892) recorded a set of eggs of the cerulean warbler with a cowbird's
HOST RELATIONS OF PARASITIC COWBIRDS 105
egg but, unfortunately, he gave neither locality nor data of collection.On June 28, 1952, at Pontiac Lake, Michigan, a female cerulean war-bler was observed feeding a recently fledged cowbird along with afledghng warbler (Detroit Audubon Soc, 1953, p. 72). The southern-most record comes from southwestern Virginia, where Jones (1936,p. 88) found a parasitized nest. The nominate race of the cowbird isinvolved in all these records.
Blackburnian WarblerDendroica fusca (Mxiller)This is a very uncommon host of the brown-headed cowbii'd. Inmy first account of the bird (1929, p. 245), I listed four cases; in morethan 30 years since then, I have learned of only six others?testimonyin itself, to the very slight incidence of parasitism on the blackburnianwarbler. The records are from New York, Michigan, Minnesota, andOntario.Apparently on the basis of a note from Dr. Brewer, Audubon (1839,p. 491) was the first to record this warbler as a victim of the cowbird.Brewer (in Baird, Brewer, and Ridgway, 1874, pp. 154-157) includedthis bu'd in a list of species in whose nests he had found cowbkd eggs.Merriam (1885, p. 103) reported a nest, 84 feet from the ground in atall tree in the lower Hudson Valley, New York, containing 4 eggs ofthe warbler and 1 of the cowbu'd. This is the "altitude record" for acowbird's egg.According to Roberts (1932, pp. 229-231), S. A. Grimes found a nestin Cass County, Minnesota, on June 22, 1929, with 2 eggs of the warblerand 2 of the cowbird, and another nest with 3 eggs of the host and 1 ofthe parasite. Another Minnesota record (from a note in files of U.S.Fish and Wildlife Service) states that E. D. Swedenborg watched ablackburnian warbler feeding a recently fledged cowbird near Minne-apolis on July 15, 1928.A similar record from an area near Ottawa, observed by Taverner,was mentioned by Lloyd (1944, p. 169); Snyder (1942, p. 144) noted aparasitized nest found by Shortt in the Sault Ste. Marie Region ofOntario.Preston (1889) recorded a nest with 2 newly laid eggs of the ownerand 1 of the cowbird, and "at the foot of the tree were fragments of twomore eggs which had been crowded from the nest by this parasite."He also recorded another nest with 3 eggs and "with one of theinevitable cowbird."Wood (1957, p. 394) reported a nest with 4 eggs of the warbler and 1of the cowbird, near Kalamazoo, Michigan.The records all refer to the eastern race of the cowbird.
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Yellow-throated WarblerDendroica dominica (Linnaeus)The yellow-tliroated warbler is known as a host of the cowbird(typical race) only in Oldahoma and on the basis of single record:a parasitized nest found by T. R. Beard {in Nice, 1931) at Sapulpa,Creek County. The warbler involved is the race alhilora. Theabsence of additional instances is difficult to explain as this warblerseems to be a suitable host and the cowbird is common in the sameareas. Grace's WarblerDendroica graciae BairdThis is another rarely reported cowbird victim about which it ispremature to form an estimate. Three instances of cowbird para-sitism have been reported. The late J. P. Norris informed me thatin his collection he had a set of 3 eggs of the warbler and 1 of thecowbu'd, taken by O. W. Howard in the Chiricahua Mountains,Cochise County, Arizona, on June 23, 1900. Marshall (1957, p. 112)saw Grace's warbler feeding a fledgling cowbird in the pine-oak wood-lands of southern Aiizona. Sheppard (1959) found a cowbird's egg ina nest of this warbler in McKinley County, northwestern New Mexico.This record, on geographic grounds, must be referred to M.a. artemisiaethe two Arizona instances are M.a. obscurus.
Chestnut-sided WarblerDendroica pensylvanica (Linnaeus)The chestnut-sided warbler is a frequent victim of the brown-headed cowbird (races ater and artemisiae). Over 75 definite recordshave been reported, distributed among three provinces of Canada
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Saskatchewan, Ontario, Quebec?and the following of the UnitedStates : Maine, Massachusetts, Connecticut, New York, New Jersey,Pennsylvania, and Maryland to Ohio, Michigan, Minnesota, Iowa,and Nebraska. The one record from Saskatchewan, a nest containing1 egg of the warbler and 1 of the cowbird, which was found atNipawin, on June 24, 1941 by Street {in Houston and Street, 1959,p. 161, 176), is the only record for the cowbird race artemisiae; allthe others involve typical ater. In southern Quebec, Terrill (1961,p. 7) found 55 nests of this warbler during about 60 years of fieldobservation, and of these, 16, or 29 percent, contained eggs of the cow-bird. This is a higher incidence of parasitism than has been reportedin most other parts of the common range of the warbler and the cowbird.In a much smaller series of nests in Ohio, Hicks (1934) found fourcases of parasitism in 12 nests, or 33.3 percent.At Ithaca, New York, I observed three parasitized nests and foundthe chestnut-sided warbler to be a tolerant host, accepting, incubating,
HOST RELATIONS OF PARASITIC COWBIRDS 107
and rearing the parasites. Occasionally, however, it has been knownto bury cowbird eggs if the latter are laid first. Sage and Bishop(1913, pp. 110-111) in Connecticut recorded such a case: a nest con-taining 4 eggs of the warbler and 1 of the cowbhd, which was buriedunder a new nest lining. The nest had been observed previously forover a week, and the cowbird's egg was known to have been laidbefore any of the warbler's. Mercer (1911) reported a double-storied nest of this M^arbler with a buried cowbird egg in the lowerportion. Terrill found that, while this warbler was a frequent host,it was not always submissive. Six nests, in which the cowbird hadlaid before the owner, were destroyed, and in a seventh, the parasiticegg was buried partly in the nest lining.
Bay-breasted WarblerDendroica castanea (Wilson)This northern breeding warbler is geographically and ecologicallysympatric with the brown-headed cowbird only to a limited degree, afactor which undoubtedly helps to protect it from parasitism. Thereare, however, two records?both observed by F. Napier Smith, whoreported the first (1951, p. 44) from Kamouraska, Quebec, about 150miles north of the latitude of Montreal, on July 2, 1951; the nestcontained 2 eggs of the warbler and 1 of the cowbird. The second nest,from the same area, was found on June 18, 1952, about 60 feet from thesite of the first one, according to Terrill (1961, p. 8).
Pine WarblerDendroica pinus (Wilson)The brown-headed cowbird seldom inflicts its eggs upon the pinewarbler. Only 10 records?from Ontario, New York, New Jersey,Michigan, Wisconsin, and Minnesota?have been noted. At Ithaca,New York, on June 29, 1921, I watched a pine warbler feeding ayoung cowbu'd at the foot of a tree in which there was a nest some 60feet from the ground. Since only one pair of pine warblers was inthe immediate vicinity and previously I had heard cowbird-likefood cries from the upper part of this tree, it seemed fairly certainthat the young cowbird came from that nest. No young pine war-blers were seen. Eaton (1914, p. 429) reported a nest, also in NewYork, with 3 eggs of the host, 1 egg of which was punctured, and 1of the cowbird. Ord (1836, p. 59) found a parasitized nest in NewJersey in May, 1813. Wood, Smith, and Gates (1916, p. 14) saw apine warbler feeding a fledged cowbird in Cheboygan County, Mich-igan. Recently, other Michigan records have become available.Wickerstrom (1953, p. 147) noted one instance in the Port Hurongame area on July 5, 1953, and Walkinshaw (1952, p. 96) found two
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parasitized nests. The Ontario records, two in number, were foundnear Wasaga Beach, South Georgian Bay, by Dr. Paul Harrington.All the records refer to the nominate race of both warbler and cowbird.
Kirtland'B WarblerDendroica kirtlandii (Baird)Bjrtland's warbler is a species, perhaps the only one, the survivalof which is seriously threatened by the parasitism of the cowbird.As is well known, the breeding range of Kirtland's warbler is extremelysmall, being limited to stands of small jack-pine in a few counties ofnorth-central Michigan ; the cowbird probably extended its range intothis area after 1875 and it has increased rapidly there ever since.The earliest record I have found involves a parasitized nest dis-covered in Crawford County on May 31, 1908, by Strong (1919,p. 181). Barrows (1921) in Iosco County found a parasitized nestcontaining 1 egg of the warbler and 3 of the cowbird while a 4thcowbird egg lay on the ground just outside the nest. Subsequently,the warbler laid another egg, and 1 of the cowbird eggs disappeared.Shortly thereafter. Barrows wrote me that his "correspondence withseveral collectors indicates that bird is frequently victimized ; in fact,I believe the cowbird is one of the most serious enemies of this species."A. K. Fisher collected another heavily infested nest, with 1 egg of thewarbler and 4 of the cowbird, about 15 miles east of Grayling, onJune 13, 1923; the set is now in the U.S. National Museum. Leopold(1924, p. 53), like Barrows, concluded that the brown-headed cowbirdwas a major reason for the numerically low status of Kirtland'swarbler.The recent publication of Mayfield's meticulous and exhaustivestudy (1960) of this warbler not only makes incomplete all earlierstatements about its relations with the cowbird, but also provides uswith the most critical evaluation of host-parasite relations we havefor any of the cowbirds' hosts. The interested reader should consultMayfield's book (especially pp. 144-181) for fuller details than canbe given here.Kirtland's warbler has this peculiarity as a cowbird host: it isvictimized very frequently, but the area in which it breeds is extremelylimited, with the result that a mere enumeration of the known in-stances of parasitism means very little when compared with those ofa wide-ranging but less intensively imposed upon species. Further-more, since the parasite is a recent invader in the breeding range ofthis warbler, the latter has not been able to develop any effectivedefenses against its new enemy.Mayfield reported that, of 137 complete sets of Kirtland's warblereggs, 75 sets, or 55 percent, contained 1 or more cowbird eggs. Up
HOST RELATIONS OF PARASITIC COWBIRDS 109
to 4 cowbird eggs were found in individual nests; the average numberof cowbird eggs was 1.67?with 1.89 fewer warbler eggs in the para-sitized nests than in unmolested ones. Hence, it follows that 1.13warbler eggs were removed for each cowbird egg laid. "The loss ofwarbler eggs in parasitized nests was 41 percent of the eggs laid; theloss in all nests, 55 percent of them parasitized, was 25 percent ofwarbler eggs laid?these losses from egg removal alone."Mayfield's calculations showed that it is not only in the matter ofhost egg removal that the parasite exerts a heavy toll, but also in thefact that this continues at all stages of the breeding process. "Theprobability that eggs present at hatching time will hatch is 85 percentamong warbler eggs alone, but 75 percent with cowbird eggs present;the rate is lower in nests ^vith several cowbird eggs than in nests withonly one. The presence of young cowbirds in the nests reduces by
.55 the probability that warblers will be fledged. The presence oftwo or more cowbirds hatched ahead of the warblers is lethal to thewarbler nestlings." Mayfield's figures suggest that Kirtland's war-bler, as a total species, would produce annually about 60 percentmore fledglings of its own kind if there were no interference fromthe parasite.Mayfield summarized (p. 176) the losses suffered by Kirtland'swarbler through cowbird parasitism as follows: 41 percent of the totalwarbler eggs laid were removed by the cowbird; 10 percent of thewarbler eggs present at hatching time failed to hatch as a result ofthe cowbird eggs present (as estimated from the excess over hatchingfailures in nonparasitized nests), which, if calculated as percentageof warbler eggs laid, is 6 percent; 59 percent of the warblers hatchedare not fledged because of cowbird nesthngs present (again, as esti-mated from excess over nestling loss in nonparasitized nests), whichfigure is 31 percent of the original total warbler eggs laid. In otherwords, 41 percent+6 percent+31 percent, or 78 percent, of all warblereggs laid in nests which were parasitized by the cowbird failed toproduce fledghngs. Since 55 percent of all Ku'tland's warbler nestswere parasitized, the cowbird was responsible for the loss of about43 percent of all Ivirtland's warbler eggs in nests not abandoned ordestroyed. If this is added to the other perils which the warbler hasto face, such as accidents to one or both of the adult birds, flooding ofthe nests, nest predators, aU of which, according to Mayfield's data,cause the loss of two-thirds of Kirtland's warbler nests, one can seethat cowbird parasitism is an insupportable affliction.When we consider the limited population of Ku'tland's warbler inits entirety, estimated in 1951 as comprising only one thousand adultbirds, and its strict dependence on a specialized and decreasinglyavailable type of nesting habitat, the added impact of the brown-
110 U.S. NATIONAL MUSEUM BULLETIN 233headed cowbird upon it is such as to endanger its continued existence.No other species is so heavily parasitized with such disastrous resultsover its entire population. Unless something happens, or is done, toreduce, if not to eliminate, the cowbird menace, the future of Kirt-land's warbler is perilously insecure.Only a few years ago, however. Van Tyne (in Bent, 1953, p. 426)wrote that, while the cowbird was a most important enemy of Kirt-land's warbler, there was no reason to think that the parasite mightbring about its extinction, as Leopold had feared. Van Tyne thoughtthat it was more probable that the observed changes in the populationsize of the warbler were the result of changes in the amount of suitablehabitat for it in its breeding grounds in Michigan or in its winteringarea in the Bahamas. Nevertheless, the alarming interpretation ofcowbird parasitism presented by Mayfield certainly suggests that thelosses caused thereby have brought Kirtland's warbler to a situationperilous to its continuity. Here is a case wherein the parasite, as anew enemy in the environment of the warbler, has "gotten out ofhand," and should be controlled, if not ehminated locally.Van Tyne has added some further observations on the relationsbetween this host and the parasite. He saw a female cowbird spendhours apparently watching a female Kirtland building its nest. Whenthe warbler was not actually working on the nest, the structure wasleft unguarded, and, "as soon as the main structure was finished
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even before the Hning was added?a cowbu'd (presumably the onethat had been watching the nest-building) came early in the morningand laid in it. After watching many hours at recently completed, ornearly completed, Eartland nests, I would judge that cowbirds layingin a Ku'tland's nest during this early part of the cycle, which is theperiod most favorable for the cowbirds' chances of producing young,run very httle risk of detection and attack. But after the warbler hasbegun incubation, the nest is rarely left unguarded, and the femalewarbler will attack violently and diive away any cowbird she findsin the vicinity."Although the cowbird is a major calamity to Kirtland's warbler,the latter, in turn, must certainly be rated as a good or successfulhost from the standpoint of the parasite. Based on his large amountof data, Mayfield (p. 179) estimated that about 41 percent of allcowbird eggs laid in nests of this host would survive to produce fledg-lings. This is a very high rate, which in itself adds yet anotherelement to the danger facing Kirtland's warbler. While it can beargued that the parasite's success may be of temporary duration sinceit may decimate its host to the point of eliminating its own supplyof victimizable nests, such a result would involve the permanent
HOST RELATIONS OF PARASITIC COWBIRDS 111
disappearance of Kirtland's warbler, after which the cowbird probablywould turn to other hosts in the area.
Prairie WarblerDendroica discolor (Vieillot)The prairie warbler is a bird whose relations with the brown-headedcowbird cannot be appreciated from the published data. When Ifirst studied this warbler (1929, p. 246), I was led to consider it a veryuncommon victim of the eastern race of the brown-headed cowbird;however, correspondence and discussions with experienced and reliableegg collectors since then indicate that in some localities the prau'iewarbler is a very frequently imposed upon host. Approximately 35records have come to my notice, distributed from New York, Connecti-cut, New Jersey, Maryland, the District of Columbia, Virginia, NorthCarolina and Georgia to Tennessee, Arkansas, Missouri, Indiana,Michigan, and Ontario.The most important study of this warbler and its relations with thecowbird is that made in Michigan by Walkinshaw (1959). He found18 nests of the warbler, five of which contained cowbird eggs. Inthese 18 nests, 63 warbler eggs had been laid, from which hatched 31young (49.2 percent), 20 of which (31.74 percent) lived to leave thenest. The five parasitized nests contained 6 cowbird eggs, of whichonly 1 produced a young cowbird that survived to the fledglingstage. It would appear from these data that the prairie warbler isnot a host with which the cowbird is very successful, and also it wouldappear that the cowbu'd is not a great check on the increase of thewarbler. Nolan (1958, p. 272) in Indiana suggests, however, that thepresence of the young cowbu'd in a nest is serious, if not fatal, to theyoung warblers. He found the prairie warblers to be a frequent hostand stated that the cowbird eggs "invariably hatched before those ofthe host. I have seen male warblers feeding cowbird nestlings beforetheir own eggs had hatched, and this doubtless contributed to theusual quick starvation of the young warblers."At Cape May, New Jersey, Stone (1940, p. 877) noted two para-sitized nests found by Turner McMuUen. He considered the prairiewarbler one of the favorite hosts of the cowbird in that locality.According to Bailey (1925, p. 129), this warbler has been known tobuild a new nest floor or lining over a cowbird's egg and any of its ownthat may be present and then start a new clutch.All the records refer to the nominate race of warbler and cowbird.Palm WarblerDendroica palmarum (Gmelin)The palm warbler rarely is victimized by the brown-headed cowbuxl.Only seven instances have come to my attention. They involve two
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races of the warbler, palmarum and hypochrysea, and two of theparasite, ater and artemisiae. Knight (1906) recorded a nest found byMorrell near Pittsfield, Maine, with 2 eggs of the warbler and 2 of thecowbird. Strong (1919) found a nest with a similar combination ofeggs at Penobscot, Maine. Morrell collected a nest with 1 cowbirdegg and 2 warbler eggs at Pittsfield, Maine, on May 27, 1891, a setnow in the U.S. National Museum. Clayton (1914) found anothernest with 1 cowbird egg and 2 warbler eggs; unfortunately, thelocality for this record was not reported.The above instances relate to the so-called yellow palm warbler(hypochrysea) and the eastern form of the cowbird. Two parasitizednests of the western race of host (palmarum) and parasite (artemisiae)were found in Alberta by T. E. Randall, who kindly informed me ofthe records. In the collections of the Carnegie Museum there is aset of 2 eggs of the palm warbler and 1 of the cowbird, collected atFawcett, Alberta, on June 3, 1941.
OvenbirdSeiurus aurocapillus (Linnaeus)The ovenbird is a very frequent host of the brown-headed cowbird,and, in this respect, it is something of a puzzle. As a rule, the cow-bu'd seldom bothers forest birds but prefers open nests buUt in opencountry. The ovenbird is strictly a bird of the forest floor, buildinga covered nest, and yet it is victimized very commonly. Over 280records have been noted, distributed among provinces of Canada
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Alberta, Saskatchewan, Ontario, and Quebec?and the followingof the United States: Massachusetts, Connecticut, New York, NewJersey, Pennsylvania, Ohio, Indiana, Illinois, Michigan, Minnesota,and Iowa. All the records relate to the nominate race of the oven-bird; those from Alberta and Saskatchewan involve the western raceof the cowbird, artemisiae; all the others, the eastern race, ater.The extent to which the ovenbu'd is victimized in some parts of itsrange is shown in the data produced by Hann (1937, p. 213) in Michi-gan. Out of all the nests which received eggs, 52 percent wereparasitized by the cowbird. Of the total number of ovenbird eggslaid, 63.4 percent hatched and 43.5 percent fledged. The greatestloss was due to predators; but the next greatest loss, to cowbirds,estimated as being responsible for the loss of 18 percent of ovenbirdeggs and young. The chief loss was due to the removal of eggs bythe cowbird. Out of 40 cowbird eggs, however, only 22 hatched,10 fledged, and probably not more than 5 survived to leave the woodsin which they were born. In light of these data, the ovenbird doesnot appear to be a particularly favorable host for the parasite whencompared with the song sparrow, for instance, or the red-eyed vireo.
HOST RELATIONS OF PARASITIC COWBIRDS 113
In later studies of the ovenbird and the cowbird, Hann (1941, p.212) found a loss of 30 eggs of the host which was attributable to thefemales of the parasite and, in addition, the loss of 4 cowbird eggswhich were removed in error by the parasite itself. Some 40 cow-bird eggs were laid, which made the loss of the host's eggs to be 75percent of the "gain" in parasitic eggs and made the total loss to be85 percent of all the eggs laid. In only one parasitized nest was thefuU number of laid eggs retained. Hann found that the earliestovenbird nests of the season were parasitized more heavily than thelater ones.In Ohio, Hicks (1934) found 112 nests, of which 41, or 36 percent,were parasitized; in southern Quebec, only 6 out of 61 nests reportedby TerriU (1961, p. 8) had cowbird eggs in them. Many years ago,L}mds Jones (1888, p. 133) wrote that, in his experience in Ohio,
"never yet has a nest been found here but two or more cowbu'd'seggs completed or completely made up the set. In one nest I foundonly three cowbnd's eggs nearly hatched; in another three of the cow-bird with one of [the ovenbird] . . . another contained four of thecowbird with two of the parent bird, and another . . . just fivecowbird eggs." In the J. P. Norris collection there were no less than25 parasitized sets of eggs from Pennsylvania. Sage and Bishop(1913, p. 160) observed in Connecticut that 11 nests were para-sitized, out of 30 examined.In the local studies referred to above, we find the percentage ofparasitized nests to vary from 33 in Connecticut to 36 in Ohio and 52in Alichigan. If we add the six major studies, we find that, out of 209active nests, a total of 89, or about 42.5 percent, were parasitized.Ovenbu^ds have been known to successfully rear the young para-sites; they are usually very tolerant of cowbird eggs, provided thatthe number present is not excessive. As many as 8 cowbu'd eggshave been reported in a single nest of the ovenbu'd by Mikesell(1898) in Ohio. A nest with 7 cowbird eggs was reported by Hess(1910). Northern WaterthrushSeiurus noveboracensis (Gmelin)The northern waterthrush is generally an infrequently used host,but there is some local variation in this regard. Only 15 recordshave come to my notice, involving two races of the warbler, nove-boracensis and notahilis, and one of the cowbird, ater. The reportedinstances are from Quebec, Ontario, New York, Michigan, and Iowa.The only place from which a fairly high incidence of cowbird parasitismhas been reported is southern Ontario, where Allin and Harrington{in Griscom and Sprunt, 1957, p. 196) found that 8 out of 40 nests
114 U.S. NATIONAL MUSEUM BULLETIN 233
examined contained cowbird eggs. This is more than half of all thecases noted. The reasons for this local difference (if there is a realdifference in the facts and not in the intensiveness of the observa-tional field work) are not readily apparent.Mr. John B. Hurley informed me that Dr. F. A. Starr collected aparasitized set of eggs of this warbler at Stm'geon Lake, Ontario.Bendire was the first to list the northern waterthrush as a cowbirdvictim but he gave no specific records. However, since this wasearlier than any of the published instances, it seems to follow thathe must have known of one or more parasitized nests. Anderson(1907, p. 229) mentions this waterthrush as a victim in Iowa, wherethe breeding race is notabilis. Short (1896, p. 14) found that the racenoveboracensis was parasitized in New York. In southern Quebec,three instances of cowbird parasitism out of 18 occupied nests whichwere examuied were found by Terrill (1961, p. 8). Near Woodville,Ontario, Starr (1931, p. 154) discovered a nest with 3 eggs of thewaterthrush and 1 of the cowbird; in Wayne County, Michigan, anest with similar contents was foimd by Barrows (1897, p. 47).
Louisiana WaterthrushSeiurus motacilla (Vieillot)This species is parasitized rather frequently by the brown-headedcowbird, much more so than the northern waterthrush, but it cannotbe ranked as one of the most used victims of the parasite. About76 records, ranging from Ontario, New York, Connecticut, andPennsylvania to West Virginia, Tennessee, Indiana, and Michigan,have come to my attention. The degree to which this bird is affectedby the parasite appears to depend upon local conditions. In regionstraversed by narrow wooded ravines and gorges, with open andimforested country between, this waterthrush often is victimized,whereas, in more consistently and extensively sylvan areas, it is lesslikely to be imposed upon. Cowbirds do not penetrate far into forests,and, as a result, seldom have occasion to make contact with this speciesin such areas.At Ithaca, New York, I twice found fledgling cowbirds attendedby these warblers; I was told by A. A. Allen that the great majorityof all their nests which he had found in the past contained eggs oryoung of the cowbird. Similarly, Eaton (1914, p. 444), quotingClarence Stone, wrote that "this warbler is much imposed upon bythe cowbird whose visits annually cause disaster by its clumsiness infilHng the nest with loose shale or dirt while kicking two to threeof the . . . eggs out of the nest. In two instances I have noticedfive eggs of the Louisiana water-thrush with two of the cowbird.
HOST RELATIONS OF PARASITIC COWBIRDS 115
Several times nests were deserted where the cowbu'd had depositedher egg."More than most of the regular hosts, this species is afflicted withmultiple eggs of the cowbird. In my earlier summary (1929, p. 248),I noted that, of 55 parasitized nests, 25 held 1 cowbird egg each,20 held 2, 7 held 3, and 3 held 4 eggs of the parasite. The abilityof this waterthrush to rear a large brood of mixed offspring is revealedin a case listed by Wood (1951, p. 412): a nest found in Michigan byWalldnshaw contained three young warblers and two young cowbu'ds,
all about ready to fledge.
Kentucky WarblerOporornis formosus (Wilson)The Kentucky warbler is a locally common victim of the brown-headed cowbird (race ater). About 150 records have been noted,ranging from Delaware, Pennsylvania, Ohio, Indiana, Illinois, andMichigan to Iowa, Kansas, Oklahoma, and Kentucky. The greatestnumber of records are from Pennsylvania, a fact which may reflect alocal difference in the incidence of parasitism but which also may bedue to the presence in that state of two unusually successful anddevoted egg collectors: J. Warren Jacobs (1893, 1938) and J. ParkerNorris (1892a). Jacobs (1893) found cowbird eggs in no less than 47nests of this warbler in Greene County, Pennsylvania. Many yearsago Norris wrote me that he had in his collection 54 parasitized setsfrom Pennsylvania and Delaware. In Greene County, Jacobs (1893)estimated that about one-fifth of all the bkds' nests which werefound by him with cowbird eggs consisted of this species. He notedthat of the 47 parasitized Kentucky warbler nests, 39 held 1 cowbhdegg each, 7 held 2, and 1 held 3. These figures present a considerablydifferent picture from that which we described for the Louisianawaterthi'ush.In a later paper (1938), discussing his long span of observationsnear Waynesbm'g, Pennsylvania, J. W. Jacobs stated that he hadexamined several hundred nests of the Kentucky warbler over morethan half a century. He kept records of 133 of these and found that60 nests, or 45 percent, were parasitized by the brown-headed cow-bird. Of 42 nests containing 5 warbler eggs each, 8, or 19 percent,held cowbird eggs; of 56 nests containing 4 warbler eggs each, 26, or46 percent, held cowbird eggs; of 35 nests containmg 3 warbler eggseach, 26, or 74 percent, contained cowbird eggs as well. In the 73unparasitized nests, the preponderance of full clutches of 5 eggsbrought the average up to 4.3 eggs per nest. The 60 parasitizednests showed an average of 3.8 warbler eggs per nest. In comparisonto this, it should be noted that there were 0.25 cowbird eggs per nest;
116 U.S. NATIONAL MUSEUM BULLETIN 23 3
or, to put it in other words, one out of every four pairs of Kentucky-warblers seemed to have lost 1 egg from its normal clutch. In addi-tion, some of the warbler eggs left in the nests were rendered lossesbecause of shell punctures, which resembled claw or bill marks.Further, a fair number of nests were found deserted even before theywere finished; other deserted nests may have contained 1 or 2 eggs,and some of these nests may have contained cowbu'd eggs, whosepresence may have been related to their desertion. Jacobs concludedthat, while the Kentucky warbler suffered heavily, the second broodswere usually less heavily victimized by the cowbird than were theearlier ones. Mourning WarblerOporornis Philadelphia (Wilson)The mourning warbler is a fairly frequent victim of the brown-headed cowbird in a few places, but generally it must be rated anuncommonly utilized host. Two parasite races are involved: arte-misiae in an instance reported from Garland, Manitoba, by Godfrey(1953, p. 45); ater in 19 cases ranging from Quebec (Lloyd, 1949)and Ontario in Canada to New York, Michigan, Illinois (Pitelka,1939), Wisconsin, and Minnesota (Chambers, 1947; Cox, 1958, 1960;Hickey et al., 1955) in the United States.Near Montreal, Quebec, L. M. Terrill (1916, p. 8) reported that,of 25 nests of this warbler, 8, or 32 percent, contained eggs or youngof the brown-headed cowbird. These figiu-es indicate that, althoughthe mourning warbler may be relatively unimportant in the economyof the parasite, the latter, in that area at least, may be a fairly seriousfactor in the numerical status of the former.A record for the eastern race of the parasite by Black (1955, p. 23),who observed adult hosts feeding two of their own young and oneyoung cowbird in Macomb County, Michigan, on June 26, is ofinterest because it shows that the presence of the parasite did notprevent the birds from rearing their own young along with it.At Ithaca, New York, A. A. Allen found a recently fledged cow-bird attended by a mourning warbler. Robbins (1947) reported twoparasitized nests in Oconto County, Wisconsin, found in 1947 byCarl Richter.Devitt (1944, p. 83) reported a nest with 2 eggs of the warbler and1 of the cowbird at Minesing, Ontario, on June 9, 1929. Dr. PaulHarrington informed me that on that same date he found a parasitizednest near Wasaga Beach, South Georgian Bay, Ontario. Other casesare represented by parasitized sets of eggs in the R. M. Barnes col-lection, now in the Chicago Natural History Museum, and the J. H.Bowles collection, now dispersed.
HOST RELATIONS OF PARASITIC COWBIRDS 117
MacGillivray's WarblerOporornis tolmiei (Townsend)This warbler still is observed rather seldom; as a result, it is difficultto interpret the nine records of cowbird parasitism. Nine recordswould be very few for a well-known bird, but in the present speciessuch a number is more significant. It appears, therefore, that Mac-Gillivray's warbler should be looked upon as a regular, if not a veryfrequent, victim of the brown-headed cowbird.Both of the currently recognized races of this warbler are knownto be parasitized b}^ the western race of the brown-headed cowbhxl,M.a. artemisiae. The nominate race of the warbler has been recordedas a host by S. J. Darcus from Penticton, British Columbia (Fried-mann, 1934a, p. 104), and by Schultz (1958, p. 435) on the basis of anobservation by Da\ddson at Victoria, British Columbia. Stephens(1932, p. 2) found the race O.t. monticola to be parasitized in YosemiteValley, Cahfornia, and French (1907, p. 156) found it thus in Colorado.A few additional cases for this race follow. LaFave (1955, p. 25)saw a fledgling cowbird attended and fed by a male MacGillivray'swarbler near Wandermere, Washington, on Jidy 29, 1954. King(1954) found a parasitized nest in Whitman County, Washington;
still another Washington record is the basis for a statement by Jewett,Taylor, Shaw, and Aldrich (1953, p. 767). Kogers (1958, p. 430)made an observation similar to LaFave's at Baker, Oregon, on August6. In the files of the U.S. Fish and Wildhfe Service there is an ob-servation by Edwin WiUis of an adult MacGilhvray's warbler attend-ing a fledgling cowbird near Camp ConneU, Calaveras County,Cahfornia. YellowthroatGeothlypis trichas (Linnaeus)This wide-ranging species is one of the common victims of thebrown-headed cowbird. Over 270 records have been noted fromprovinces of Canada?British Columbia, Alberta, Saskatchewan, On-tario, Quebec, New Brunswick?and the following of the UnitedStates: Arizona, Arkansas, California, Colorado, Connecticut, Dela-ware, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland,Massachusetts, Minnesota, Missouri, Montana, Nebraska, New Jer-sey, New York, Ohio, Oklahoma, Oregon, Pennsylvania, RhodeIsland, Tennessee, Texas, Utah, Virginia, Washington, West Virginia,Wisconsin, and Wyoming. AH 3 races of the cowbird are involvedas are 10 races of the yellowthroat: brachydadylus, trichas, ignota,campicola, occidentalis, inseperata, chryseola, arizela, sinuosa, andscirpicola.For some of the western races of the yellowthroat, the records arefew in number, but this fact seems to be due more to a lack of observers
118 U.S. NATIONAL MUSEUM BULLETIN 23 3
in some areas than to a real differential in the incidence of cowbirdparasitism. In the case of the salt marsh race of San Francisco Bay,sinuosa, reported so far as a cowbird victim only by Grinnell andWyeth (1927, p. 104), it is probable that the nature of this bird'shabitat is not especially attractive to the cowbird; this is not the casewith other sparsely reported victims such as occidentalis, campicola,and chryseola.In my own field work at Ithaca, New York, I discovered fiveinstances, and I was told of many others which had been observedin earlier years. In southern Quebec, Terrill found 113 nests inabout 60 years of observations; of these, eight were parasitized?
a
much lower percentage of parasitism than occurs farther south. InOhio, Hicks (1934) found that 19 out of 41 occupied nests wereparasitized.In spite of the fact that the yellowthroat long has been known asa frequent victim of the brown-headed cowbird, little in the way ofan analysis of the host-parasite relationship has been available untilrecent studies by Stewart (1953) and especially Hofslund (1957),both conducted in Michigan. Stewart found that the averagenumber of yellowthroat fledglings which were produced from anonparasitized nest was 1.9, whereas in nests parasitized by thecowbird this average was only 0.1 (the average number of fledglingcowbirds produced per parasitized nest was 0.4). During a periodof four years, Hofslund found 52 nests, 20 of which were parasitized.In these 52 nests, 152 yellowthroat eggs were Imown to be laid;of these 152 eggs, 52 were lost for various reasons. The loss of 30of these 52 could be attributed to the cowbird: 10 eggs were removedby the parasite, 6 were punctured by it, 4 were lost because of nestdesertion induced by cowbird activity, and there were 10 abortiveeggs whose loss was due to lack of heat during incubation?thepresence of larger cowbird eggs prevented close contact betweenthe smaller eggs and the body of the incubating warbler. Thepercentage of egg loss attributed to the cowbird varied in the fouryears of the study from 16.6 to 88.8 percent of the total egg loss.The hatching success of the warbler was related to the number ofcowbird eggs in a nest: "No more than two Cowbird eggs, or oneCowbird egg and two Yellow-throat eggs hatched in any nest; andif more than one Cowbird egg was present, no Yellow-throat eggshatched."Hofslund has attempted a quantitative analysis of hatching successin the yellowthroat. He started with Hann's estimate (1947, p. 174)that the probable limit of egg volume which a related warbler species,the ovenbird, can successfully incubate and hatch was between 1.3and 1.8 times the volume of its normal clutch of 5 eggs and that
HOST RELATIONS OF PARASITIC COWBIRDS 119
this limit was nearer to the lower than the higher figure. ApplyingSchonwetter's formula (1924) to average measurements for the yellow-throat and cowbird eggs, Hofslund calculated the average volumeof a yellowthroat egg to be close to 1.7 cc. and that of a cowbirdegg to be almost 3.1 cc. The volume of a normal 4-egg clutch ofthe yellowthroat would come to about 6.8 cc, which is little morethan that of 2 cowbird eggs?6.2 cc. If 2 eggs of the yellowthroatwere replaced by 2 of the cowbird, the resulting set would total9.6 cc. or 1.4 times that of a normal 4-egg set of the host alone. Wliilethese figures are calculations and have not been tested in the field,Hofslund's observations indicate that 1.3 times the normal clutchvolume "closely represents the limit of egg-volume that a Yellow-throat \vill normally hatch, and ordinarily one can say that a nestwith more than one Cowbird egg in it is doomed to failure as faras the Yellow-throat eggs are concerned."A surprising feature emerged from Hofslund's observations. Three-quarters of the parasitized nests contamed more than a single cowbirdegg; the average number in 20 parasitized nests was 2. Hah* ofthese eggs failed to develop to the fledgling stage; some were lostbefore hatching by nest desertion, predation, etc.; and some nestlingswere lost to predation. The percent of cowbhd eggs hatched was42.5; of yellow-throat eggs, 65.8. Only 9 of the 20 parasitized nestsproduced cowbird fledglings?an average of 1.3 cowbirds per suc-cessful nest but only 0.6 cowbird per parasitized nest. It can beconcluded that the cowbird is successful only moderately with theyellowthroat as a host, nevertheless, the former is an unportantcheck on the increase of the latter, with most of the damage to thehost occurring during the egg stage.The incidence of cowbird parasitism in several studies?reportedin some detail?ranged from 7 percent to 46 percent of all the yellow-throat nests found. If we combine the totals of several surveysdone in Michigan (Hofslund, 1957, Stewart, 1953; Batts, 1953; andDetroit Audubon Society, 1953-56) we find that, of a total of 90observed nests, 35 nests, or 39 percent, were parasitized by thebrown-headed cowbird.Shaver (1918) studied the progress of a nest in which one youngcowbu"d and two young yellowthroats were hatched. A summaryof aU the feedings indicated that the young parasite received 55percent of the total amount of food. On the last day m the nest,the nestlings were visited by the adult warblers 348 times; the youngcowbird received all, or part, of the food brought on 190 of these
visits.OccasionaUy, the yellowthroat may bury the cowbhd eggs undera new nest lining. Weed and Dearborn (1903, pp. 162-163) record630590?63 9
120 U.S. NATIONAL MUSEUM BULLETIN 23 3
a three-storied nest; each of the lower two stories contained a cowbirdegg-Since some of the western races of the yellowthroat are recordedonly sparsely, it may be worthwhile to mention two instances thathave not been referred to in my earlier lists. The race campicolahas been recorded as a host of the western form of the brown-headedcowbird, artemisiae, in eastern Washington (Jewett, Taylor, Shaw,and Aldrich, 1953, p. 594). An additional record for the subspeciesoccidentalis comes to me from Mr. K. Kreuger, who has in his collec-tion a set of 2 eggs of this race of the yeUowthroat with 1 of thecowbu-d, collected at Canston, British Columbia, on June 6, 1948,by W. L. Maguu-e.The northeastern subspecies, G.t. hrachydactylus , is known tobe a fairly frequent victim of the eastern race of the brown-headedcowbird. Aside from earher records (when the host was listed asG.t. trichas), it should be noted that, in southern Quebec, 8 out of113 nests, or 7 percent, which were found by L. M. Terrill (1961,p. 8) between 1897 and 1956, were parasitized.Rio Grande Ground ChatChamaethlypis poliocephala (Baird)There is a single record for this species (nominate race) as a hostof the small race of the brown-headed cowbird. F. F. Nye, Jr.,collected a nest containing 2 eggs of the host and 2 of the parasite7 miles southeast of Brownsville, Texas, on June 19, 1944. Thisset later was sent to A. J. B. Ku-n for the collection of birds' eggs atSt. Mary's University in San Antonio, Texas.
Yellow-breasted Chat
Icteria virens (Linnaeus)The yellow-breasted chat is imposed upon frequently by the brown-headed cowbu-d, but the degree to which it is affected appears to varyvery much locally. In some areas it is said to be one of the chiefvictims; in others it is molested only occasionally. About 180 recordshave been noted, ranging from Canada?Ontario, Saskatchewan(Potter, 1935), British Columbia?and the United States?Arkansas,Arizona, Cahfornia, Connecticut, Delaware, Illinois, Indiana, Iowa,Kansas, Kentucky, Maryland, Massachusetts, Michigan, Minnesota,Missouri, Montana, Nebraska, Nevada, New Jersey, New York,North Carolina, Ohio, Oklahoma, Pennsylvania, South Dakota, Texas,Virginia, Washington, and Wisconsin?to northwestern Mexico in thestate of Sonora, near Granados (A. PhiJlips, in htt.). There arenumerous records for both races of the chat, virens and auricoUis, and
HOST RELATIONS OF PARASITIC COWBIRDS 121
for all three races of the cowbird. The nominate race of the chat isparasitized by ater and artemisiae; the race auricollis is victimized byartemisiae and ohscurus.The eggs of the chat are very similar in appearance to those of thecowbird; nevertheless, in many parts of its range, the chat is said todesert its nest if a parasitic egg is laid in it. This action is probablydue to the sh3mess and nervousness of the bird rather than to anyunusual acuit}^ in distinguishing strange eggs from its own. (Manyobservers, particularly bird photographers, agree that the chat is oneof the most tmiid of birds, and hence one of the most difficult tophotograph at its nest.) Notwithstanding, on a fair number ofoccasions, chats have hatched and reared cowbirds. Nehrling (1896,p. 245) found such a case in southwestern Missouri. Smith (1921,pp. 175-177) found a chat's nest in Birdcraft Sanctuary, New York,containing 1 egg of its own and 1 of the cowbird. The next morning,there was a 2i!d cowbird egg; the chat was flushed from the nest.Smith visited this nest every morning, but no more eggs were laid.After observing several day's incubation, he disturbed the nest andeggs in order to photograph them ; even this did not seem to upset thechat. All 3 eggs hatched and all three of the nestlings grew uptogether and successfully fledged.In Oldahoma, Nice (1931, p. 163) quoted Kirn to the effect thatthe chats there do not desert their nests when cowbird eggs aredeposited in them. At Copan, of 22 nests found between 1910 and1917, 13 contained from 1 to 3 cowbird eggs apiece, and 1 nestcontained 4 chat eggs and 6 of the cowbird?a very crowded nestindeed.In southern Michigan, Nickell (1955, pp. 89-90) found 11 nests, ofwhich all but 1 were parasitized by the brown-headed cowbird.Five of these nests had a single cowbird egg apiece; two nests had 2each; and the three remaining nests had 3, 4, and 5 of the parasiticeggs, respectively. Cowbirds hatched in five of these nests. Four ofthese five nests reared young to the fledging stage, as follows: firstnest, two cowbirds and no chats; second nest, one cowbird and twochats; third nest, one cowbii'd and three chats; fourth nest, one cow-bird and four chats. The fifth nest in which a cowbu-d hatched wasdestroyed by accident when the young parasite was five days old.Two of the other parasitized nests were not abandoned when firstmolested but failed to come through successfully. Only 3 nestsout of the 10 that were parasitized were abandoned before incubation.Another case in which the young parasite and the young chat grew uptogether to the fledging stage was reported in North Carolina byChamberlain (1959).
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Here we have a body of evidence clearly at odds with data fromelsewhere in the range of the host. No matter how satisfying it mightbe to have a mathematical evaluation of the host-parasite relation-ship, it is meaningless to consider adding these two bodies of evidenceto produce an "average" behavioral response. Such an average wouldhave no biological significance since it would reflect the picture in noone individual. The only justifiable approach is to admit that thereis a surprising variability of response on the part of the chat andthat, in terms of present data, this variability appears to be local.Whether this evidence should be taken to imply, or even to suggest,the existence of parasite-tolerant and parasite-intolerant "strains"within the species cannot be debated without more detailed data frommany parts of its range; such data should include the inheritance, ifany, of parasite-tolerance in the area where it is known to occur.In 1924 in the lower Kio Grande Valley of Texas, I found thewestern race of the chat to be a common host of the dwarf race ofthe cowbird. Of four nests which were found, all were parasitized.Hanna (1928, p. 161) recorded five parasitized nests in southern Cali-fornia. E. M. Tait informed me many years ago that he found threenests with cowbird eggs (artemisiae) at Trout Creek Point, BritishColumbia. Mr. Guy Love wrote to me of a similar nest which wasfound on June 22, 1908, in Decatur County, Kansas. The instanceinvolved the eastern race of the parasite and the western race of thehost?the first time this particular subspecific combination has beenfound. Hooded WarblerWilsonia citrina (Boddaert)Although the number of definite instances of parasitism has increasedin recent years, the hooded warbler may be described as a somewhatuncommonly recorded victim of the brown-headed cowbird. Thirty-two cases have been noted, distributed among the following states:Connecticut, New York, New Jersey, Pennsylvania, Maryland, Vir-ginia, Georgia, Alabama, Indiana, Illinois, and Michigan. Stewartand Robbins (1958, p. 329) mention five cases in Maryland. Five,possibly six, occm-rences have been reported from one locality. LakeOrion, in Michigan: Middleton (1952, p. 7) gave four records;Wallace and Black (1949, p. 15) found a hooded warbler feedingtwo of its own and one cowbird fledgling; and Wickstrom (1951,p. 114) noted a record of a parasitized nest which may be amongthe four listed by Middleton. On the basis of these and other recentrecords, it seems that increasing data may make it necessary to recon-sider the status of the hooded warbler with respect to the cowbird.The best that may be said at present is that, while this warbler is nota frequently imposed upon species, it cannot be called a very uncom-
HOST RELATIONS OF PARASITIC COWBIRDS 123
mon host. Several records from Georgia (Chamberlain and Denton,1949; Parkes, 1950; Chamberlain, 1958; Webb and Wetherbee, I960)reveal that in this southeastern area, which recently has been invadedby the parasite, the hooded warbler seems to be a rather frequentlychosen host. Wilson's WarblerWilsonia pusilla (Wilson)Wilson's warbler has been reported very seldom as a cowbird victim,but locally it is probably a fairly common host. Fourteen recordshave been noted, all but two from southern California (race chryseola)
:
one from eastern California and the other from Alberta {vsice pusilla)
.
Most of the California records involve the small race of the cowbird,M.a. obscurus; two from Mono County (Dixon, 1934, p. 36; Kowley,1939, p. 251) and the record from Alberta refer to Al.a. artemisiae.In southern California, Willet (1912, p. 70) recorded three parasit-ized nests in Ventura County; LaJeunesse (1923, pp. 31-32) foundfive nests in Alameda County, each of which contamed eggs of thecowbu'd. The last five nests were all found within one month in alimited area, a fact which indicates that there the cowbird was makingmuch use of the nests of this warbler. M. C. Badger wrote me thatthe bird is a very common victim in southern California. Ungiish(1931, p. 214) found a parasitized nest in San Benito County; Peyton(1931, p. 162) found another in Ventura County. Other records inprivate egg collections, transmitted to me without definite localities,are three in number. Talmadge (1948) recorded a cowbird egg fromthe nest of either Wilsonia pusilla or Vermivora celata at Fernbridge,Humboldt County, California. Although this record is uncertain, itprobably involves Wilsonia.The one Alberta record was found by T. E. Randall at Boyle,Alberta, on May 27, 1934?a nest with 4 eggs of the warbler and1 of the cowbird. Canada WarblerWilsonia canadensis (Linnaeus)The Canada warbler is a regular but infrequent host of the brown-headed cowbird. It has been loiown to be imposed upon by thenominate race of the parasite in Ontario, New Brunswick, New York,Indiana, Michigan, and Minnesota. Recently, it has been found byStreet (Houston and Street, 1959, p. 176) to be molested by thewestern race, artemisiae, at Nipawin, Saskatchewan. Instances ofthis warbler as a victim of the eastern brown-headed cowbird may benoted as follows. C. T. Black (1955, p. 23) listed three cases inLapeer and Macomb Counties, Michigan, and Nolan (1958, p. 417)added another one from Dunes Park, Indiana. Besides these, there
124 U.S. NATIONAL MUSEUM BULLETIN 233
are three cases from Ontario and one each from New York and Min-nesota. The Canada warbler has been known to hatch and rearcowbirds: Roberts (1932, p. 277) noted a nest with young of theparasite in Minnesota. RedstartSetophaga ruticilla (Linnaeus)The redstart is one of the commonest victims of the brown-headedcowbird, but, probably because it is parasitized so frequently, manyobservers have felt it mmecessary to record their data. The result isthat the total published material is much less than that which existsfor a number of species less often imposed upon by the parasite. Inmy own field work in central New York, I found cowbird eggs oryoung in 23 out of 34 nests exam.ined; I have not found a similarlyhigh incidence of cowbu'd parasitism reported from any other area.In Ohio, Hicks (1934) discovered 22 nests, of which 7 were parasi-tized; and in southern Quebec, TerriU (1961, p. 8) found 145 nests,of which 23 held cowbu'd eggs. All in all, about 200 records have beennoted, ranging from Saskatchewan, Ontario, Quebec, and NewBrunswick to Idaho, Minnesota, Iowa, Wisconsin, Michigan, Ohio,Maine, Massachusetts, Connecticut, New York, Pennsylvania, NewJersey, Delaware, Maryland, Virginia, Alabama, Ai'kansas, andOklahoma.The incidence of cowbird parasitism noted in several studies, whichhave been reported on in some detail, varied from less than 2 percentto 10, 33, 42, and even as much as 70 percent of all the redstart nestsfound.The records include both races of the redstart, ruticilla and tricolora,and two races of the cowbird, ater and artemisiae. Both of theseraces of the parasite molest tricolora, while only ater has been observedin relation to ruticilla; in fact, only recently have the following tworecords, involving the northwestern cowbu'd artemisiae, been reported.Street {in Houston and Street, 1959, p. 166) found a nest of tricoloraat Nipawin, Saskatchewan, containing only a nestling covv^bird.Burleigh (1952) observed a recently fledged cowbii'd being fed byredstarts at Missoula, Montana.Occasionally, the redstart may build a new lining or floor over acowbird egg, if, as sometimes happens, the cowbu-d deposits her eggbefore the host female deposits hers. The redstart is usually a verytolerant host, accepting the strange eggs and rearing the young. Attimes, however, although the redstarts assume charge of the cowbirdeggs, they may show an initial hostility toward the female cowbirdprior to actual ovulation. Strum (1915, pp. 202-203), noting thatboth adult redstarts reacted aggressively toward female cowbirds,concluded that this show of hostilitj^ saved them from excessive para-
HOST RELATIONS OF PARASITIC COWBIRDS 125
sitism. He implied that this form of behavior might explain thefact that, out of 18 nests found, only 1 was parasitized. Terrillnoted that the redstart seldom tolerates the cowbird's parasitism incases wherein the latter lays first. Nine such nests which were knownto him were deserted. House SparrowPasser domesticus (Linnaeus)This widespread, introduced species is molested very seldom by thebrown-headed cowbird. The fact that the sparrow is so much a townand city bird has something to do with the phenomenon, but this,itself, in is not enough to account for the relative immunity of P.domesticus to parasitism. The following are the only records whichhave been noted. In the Hudson highlands of New York, Mearns(1878, p. 23) found that a cowbird egg had been hatched by housesparrows in Highland Falls; moreover, the young cowbird flourishedand remained with the sparrows for some time. Davie (1889) listedthe house sparrow as a cowbird host?possibly on the basis of theabove statement. R. B. Rockwell (1909, p. 92) found a partiallyincubated cowbird egg in a house sparrow's nest at Barr, Colorado.Linsdale (1937, p. 177) noted, also at Barr, that a pair of house spar-rows took over a magpie's nest after the original owners had left andstarted to build their own nest in it; afterwards, he found a cowbird'segg in the nest. Burleigh (1923, pp. 90-91) found a cowbird's egg in ahouse sparrow's nest inside a bird nestingbox in Alleghany County,Pennsylvania. Williams (1950, p. 153) listed the house sparrow as acowbird victim in the Cleveland, Ohio, area. Ellis (1924, p. 208)noted it as fosterer in southern California. Imhoff (in litt.) saw ahouse sparrov/ feeding a fledged cowbird at Bethesda, Maryland, onJuly 19, 1960. Leathers (1956, p. 68) reported that near his home atNew Castle, Pennsylvania, there were in use every year a half dozenhouse sparrow nests which the cowbirds parasitized regularly. Stamm(1961) made a similar observation in eastern Kentucky.The Colorado data involve the race M.a. arfemisae of the cowbird
;
the Ohio, New York, Pennsylvania, Maryland, and Kentucky recordsrefer to typical M.a. afer; the southern California record refers toM.a. ohscurus. BobolinkDolichonyx oryzivorus (Linnaeus)The bobolink is an infrequently used host, but, in Iowa, Gabrielson(1914, p. 79) considered it to be one of the commonest victims of theparasite (although he actually recorded only a single instance of cow-bird parasitism on this species). Some 22 records have been notedin all, distributed among the following states : Connecticut, New York,Ohio, Michigan, Wisconsin, Iowa, Minnesota, and Montana. When
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we remember what a small percentage of bobolink nests are everfound?secreted as they are in grassy meadows and invisible fromabove because of their semi-domed structure?it may not seemsurprising that relatively few records are available. However, itdoes not follow that the observed incidence of parasitism would beaffected by this rather meager sampling.Silloway (1917, p. 45, p. 158) found a nest in Judith Basin County,Montana, with 3 eggs of the bobolink and 2 of the cowbird. In thiscase, the cowbird was the race artemisiae. All the other records knownto me involve the eastern race ater.In Ohio, Hicks (1934) found the surprising total of 184 nests of thebobolink; of these, 10, or a little over five percent, were parasitized.Roberts (1932, p. 288) lists only one Minnesota record?a nest with 3eggs of the host and 3 of the parasite.
Eastern MeadowlarkSturnella magna (Linnaeus)The eastern meadowlark is an uncommon host of the brown-headedcowbird. Bendire (1895, p. 460) noted that "this bird is occasionallyimposed upon . . . and an instance has been recorded where a secondnest was built over the one containing the parasitic egg." Gross(in Bent, 1958, p. 74) concluded that, in most sections of its range,the meadowlark seems to escape the attentions of the cowbird. Henoted that G. B. Saunders, who studied some 50 nests in New Yorkand Oldahoma, never found a cowbird's egg in any of them; neitherdid Bent with, his varied nest-hunting experience. In southernQuebec, Terrill (1961, p. 8) examined 52 nests, only 1 of which wasparasitized. Yet, in Illinois, Gross found four parasitized nests andEifrig (1915, p. 418; 1919, p. 520) repeatedly found similar instancesin the Chicago area "with one or more eggs of the cowbird, and oneor more or all the eggs of the rightful owner apparently rolled out.An example of this was found June 24, 1917, with two cowbird eggsinside and four meadowlark eggs outside . . . ." Apparently, themeadowlark is parasitized more frequently in northern Illinois thanin many other areas. In Nebraska, Hergenreder (1962) found 31nests, of which 5 had been parasitized. In Wisconsin Lanyon (1957,p. 43) reported that, of 38 nests observed, 6 (16%) contained cowbirdeggs. One of these nests was deserted when the parasite made a holein 1 out of the full clutch of 5 meadowlark eggs.The fact that the hosts' eggs so often are found outside the nest ispuzzling and deserves study. It is probable that the large egg of themeadowlark is too big for the parasite to carry off, and the egg there-fore may be left on the ground not far from the nest. No mentionwas made as to whether or not these expelled eggs were damaged;
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if they were removed by the cowbirds, one might expect them toshow bm or claw holes.All in all, some 32 records have been noted, distributed in Ontario,Quebec, Massachusetts, Connecticut, New York, New Jersey, Penn-sylvania, Ohio, Indiana, Illinois, Michigan, Wisconsin, Minnesota,Iowa, Nebraska, Kansas, Oklahoma, Ai'kansas, and Texas. Theserecords involve three races of the meadowlark: argutula in Arkansas,hoopesi in Cameron County, Texas, and magna in all the other records.The cowbh'd involved in the Texas record is the race obscurus; in allthe other records, it is the typical race, ater.I know of no instance wherein a meadowlark has hatched andreared a young cowbird. As far as the parasite is concerned, this isnot a successful host. Western MeadowlarkSturnella neglecta AudubonThis species appears to be very similar to the eastern meadowlarkin its relations with the brown-headed cowbird. Occm-ing as it doesin areas under less observation, the western meadowlark has beennoted as a cowbird host even less often than its eastern counterpart.Twenty-four records have come to my attention from British Colum-bia, Alberta, Saskatchewan, Idaho, Montana, Colorado, Kansas, Ne-braska, North Dakota, Minnesota, and Wisconsin. All the recordsinvolve the typical race of the western meadowlark, neglecta: theNebraska record, anonymously published without definite locality(1934, p. 69), involves the eastern race of the cowbird, ater, as dothe Wisconsin records, while the remainder are of the northwesternrace, artemisiae.Silloway (1917, p. 45) found a nest with no fewer than 5 eggs ofthe cowbird and 2 of the host in Judith Basin County, Montana. Hewrote that this was the fu'st time he had ever found the parasite'seggs in a nest of this bird but that later he discovered that the cow-bird "frequently imposes upon the meadowlark in the northwest."These imphed records from the northwest have not appeared in print.In the files of the U.S. Fish and Wildlife Service there is the record of aparasitized nest found in Dickey and the Thousand Springs Valley,Idaho, in June 1912, by L. D. Wyman. Mr. T. E. Randall foundanother such nest in Alberta, and there is a Saskatchewan record inthe Provincial Museum at Regina. Lanyon (1957, p. 43) found 41nests with complete clutches in the course of his work in Wisconsin.Of these, 9, or 22%, contained eggs of the cowbird.
Yellow-headed BlackbirdXanthocephalus xanthocephalus (Bonaparte)The 3"ellow-headed blackbird has been reported only occasionallyas a victim of the brown-headed cowbird. I have found 11 records,
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distributed from Illinois, Minnesota, Montana, and "northwesternCanada" to Wyoming, Colorado, and California. T. S. Roberts(1909) reported three parasitized nests in one breeding colony ofyellow-heads. Lincoln (1920, p. 69) wrote that, in the Clear Creekdistrict of Colorado, this blackbird was one of the most imposedupon local hosts. These observations suggest that the j^ellow-headed blackbird locally may be a not uncommon victim; but overthe extensive range of its sympatry with the cowbird it is not Imownto be affected to any degree.As many as 6 eggs of the parasite along with 4 of the owner havebeen reported in a single nest at Laramie, Wj^oming, by Henninger(1915, p. 232).All three races of the parasite are involved in the known records:ater in those from Ilhnois, Michigan, and Minnesota; artemisiae inthose from Montana, Wyoming, Colorado, and northwestern Canada;and obscurus in one case from Los Banos, California. H. R. Eschen-berg informed me that there he found a nest on May 6, 1936, containinga dwarf cowbu*d's egg in addition to 4 eggs of the blackbird.
Redwinged BlackbirdAgelaius phoeniceus (Linnaeus)The redwinged blackbu'd is a fairly common victim of the brown-headed cowbu'd in some areas, but it is almost unmolested by theparasite in other localities. In regions where the redwings are largelycolonial nesters in cattail swamps, they are rarely bothered by thecowbird; where their nests are more scattered and in bushes, theyoften are parasitized.In Michigan, Nickell (1955, p. 91) examined 1300 active nests ofthis blackbird over a period of 15 years and found the frequency ofknown parasitism to be about 1 in every 185 nests. All the para-sitized nests were either solitary or at the perimeters of colonies
?
a hundred feet or more from their nearest conspecific neighbors.He concluded that, because of the combined aggressiveness andvigilance of the blackbirds, few cowbird eggs are deposited in red-wing nests that are in definite colonies. NickeU also concludedthat any cowbird which was hatched in a nest with two or more red-wings would have slight survival chances because of the larger sizeand aggressiveness of the host's own nesthngs. NickeU's observa-tions are in agreement with those first made by Sutton (1928) in thePymatuning Swamp in western Pennsylvania; these data demon-strated the tendency of the redwings to drive away any intrudingcowbirds, thereby protecting not only their own nests, but alsothough not intentionally?those of vireos and warblers breeding closeby. Trautman's experience at Buckeye Lake, Ohio, as summarized
HOST RELATIONS OF PARASITIC COWBIRDS 129by Bent (1958, p. 144), establishes further corroboration. Out ofhundreds of redwing nests found by Trautman, only four were para-sitized and these were isolated nests, considerably removed from themain colony. Trautman rightly concluded that it was possible fora cowbird to lay in a solitary nest without discovery and inevitablepursuit, but not in a colony. In Minnesota, Roberts (1932, p. 303)noted that those redwing nests which were built in the marshesusually were not parasitized, whereas those in bushes on uplandsnear the marshes generally contained cowbird eggs. AlthoughRoberts does not say so specifically, it appears that the nests builtin upland bushes were scattered more widely than those in the cattailswamps. In Kent Island, Maryland, during two successive seasons(1958-59), Meanley (in htt.) examined 367 nests and found that fivewere parasitized. He later wrote me that in his experience, inMaryland and elsewhere, such parasitism invariably occurred in thevery earliest redwing nests. The red^vings begin nesting earlierthan most of the other passerine birds and the cowbirds begin to layabout the same time as the redwings, but the parasites do not seem tobother the latter when other potential hosts become available.At Ithaca, New York, a region where both the redwing and thecowbird are very common and where both species have been exhaus-tively studied (A. A. Allen, 1913b; Friedmann, 1929), many hundredsof nests of the redwing have been examined but none have beenfound to be parasitized. That some variation may occiu-, even insuch areas, is suggested by the observations of Goelitz (1916, p. 147)in lUinois, who writes that, "until this year I have never found eggsof this bird [cowbird] in redwing's nests, but in a little colony of sometwenty-five pairs of red-winged blackbirds I destroyed eleven cowbirdeggs on June 17, and six on June 27 of the present season."Smith (1943, p. 198) studied these blackbirds near Chicago andfound that cowbirds seldom molested redwings nesting in sizeablecolonies. In 1940 at Orlando, the incidence of parasitism was only0.6 percent (a single case, in which 2 cowbird eggs were laid in anempty redwing nest, resulting in its desertion.) In 1941, no cowbirdeggs were found among 563 eggs of redwings. Smith suggested that
"there may be an aggregate effect of numbers which retards or evenprohibits the deposition of cowbird eggs in redwing populations ofhigh density. In view of the restricted incidence of cowbird parasit-ism and its apparent negligible effect upon redwing mortality, itwould appear that this factor is of httle importance in a considerationof the success of redwing reproduction."In fm-ther studies in Arkansas as well as in Illinois, the same author(1949, p. 60) found that, out of 653 nests of the redwing, 14 wereparasitized, 13 with 1 cowbird egg in each, and 1 with 2 cowbird
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eggs. During the four years of his study, 1,981 redwing eggs werelaid in the 653 nests with these 15 cowbu"d eggs. These data showan expected distribution of 2.1 percent of nest parasitism and anincidence of parasitism of 0.8 percent per redwing egg. Of the cow-bird eggs, 14, or 93.3 percent, failed to hatch. Six of them weredoomed by the situation in which they were laid: 3 in abandonednests, 2 deposited at least six days after the incubation of the hosts'eggs had begun, and 1 laid on cattail stalks just below a nest. Thehmited distribution of parasitized nests and the very low survivalsuccess of the cowbud eggs indicate that the redwinged blackbird isnot a favorable host species.In Decatur County, Kansas, L. R. Wolfe (in litt.) found that theredwings very frequently were parasitized. He wrote me that "prob-ably 90 percent of the redwing nests contained one or more eggs ofthe cowbird, and I remember frequent extended searches to find anest without eggs of the parasite. During the years 1909 to 1914 Iprobably collected twenty or more sets of the thick-billed redwingwith cowbird eggs." The incidence of cowbird parasitism in DecaturCounty as summarized by Wolfe is much higher than has been reportedin any other area. From Nebraska have come more than 30 records,a fact which suggests a high incidence there as well. In Colorado,Lincoln (1920, p. 69) considered the redwing one of the species mostfrequently parasitized, but he gave no quantitative data. It appearsthat at Brenham, Texas, the Gulf Coast race of the redwing, littoralis,frequently is victimized by the dwarf race of the cowbird. Nye (1936,p. 87) refers to the eggs of this redwing as consisting of the "usualsets of three plus a dwarf cowbird egg or two."About 180 records have been noted, distributed among provinces ofCanada?Alberta, British Columbia, Manitoba, Ontario, Quebec,Saskatchewan?^and the following of the United States: Arizona,Arkansas, California, Colorado, Connecticut, Illinois, Indiana, Iowa,Kansas, Maryland, Michigan, Minnesota, Missouri, Montana, Ne-braska, New Jersey, North Dakota, Ohio, Oklahoma, Pennsylvania,Rhode Island, Texas, Utah, Washington, Wisconsin, and Wyoming.All three races of the cowbird are involved, and nine races of the red-wing: phoeniceus, littoralis, megapotamus, arctolegus, fortis, nevadensis,californicus , neutralis, and sonoriensis. The racial combinations so farrecorded are as follows: M.a. ater has been found to parasitize phoeni-ceus, littoralis, megapotamus, arctolegus, and Jortis; M.a. artemisiae isparasitic on arctolegus,fortis, nevadensis, and californicus ; M.a. obscurusvictimizes megapotamus, californicus, neutralis, littoralis and son-oriensis. If the proposed race utahensis should be accepted offi,cially,to it would have to be referred a record of cowbird parasitism publishedby Bee and Hutchings (1942, p. 82).
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There are at least two records of a redwing hatching and rearing acowbird : an instance told to me years ago by the late Waldron de WittMiller, occuring in New Jersey, and a case reported by Blocher (1924).In the latter instance, the nest contained three young redwings andone cowbird when first found, but only the parasite survived.In Nebraska, Wolcott (1899, p. 18) noted the two-storied nest of aredwing, in the lower part of which a cowbird's egg was buried. Hewrote that, in his experience, the redwings, when parasitized afterthey already have laid some eggs themselves, "apparently peck holesin all, including that of the intruder, and desert the nest." Such be-havior would be most interesting, but there is no way to rule out thepossibility that the holes were not the work of marsh wrens or othercreatures coming upon a deserted nest.
Orchard OrioleIcterus spurius (Linnaeus)The orchard oriole is a fairly frequent host of the brown-headed cow-bird, but the actual records noted are few in number?^only 18 in all.Supplementing the actual instances there are statements such as onemade by Bendire (1895, p. 481) to the effect that, in the northernparts of its range, the orchard oriole is "more or less imposed upon bythe cowbird . . ." and the statement made by R. W. Quillin (in litt.)that around San Antonio, Texas, this oriole very frequently is parasit-ized. The actual cases have come from Ontario (Essex and KentCounties), Rhode Island, Connecticut, New Jersey, Maryland, Ohio,Indiana, Alichigan, Iowa, Kansas, Missouri, Tennessee, Oldahoma,and Texas. Two races of the parasite, ater and obscurus, are involved.Although he does not mention any specific records of parasitism inNew Mexico, Ligon (1961, p. 262) wi-ites that the scarcity of theorchard oriole in that state may be due partly to the fact that itsuffers from the attentions of the cowbird.
Black-headed OrioleIcterus graduacauda LessonThere is a single record of this oriole, race audubonii, as a host ofthe southwestern race, obscurus, of the brown-headed cowbird. NearBrownsville, Texas, in May, 1924, I found a nest of this oriole con-taining 1 egg of the dwarf cowbird, 1 of the red-eyed cowbird, Tan-gavius aeneus, and none of the oriole. When found, the nest had beendeserted. Hooded OrioleIcterus cucullatus SwainsonThe hooded oriole has been recorded a few times as a victim of thedwarf race, obscurus, of the brown-headed cowbu'd in California,
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Arizona, and Texas, The records from Texas refer to the easternrace of the oriole, sennetti; the Arizona and Cahfornia instances relateto the race nelsoni.Scott (1885, p. 163) recorded a parasitized nest m Arizona; Beudh-e(1895, p. 475) wrote that the eastern race was imposed upon consider-ably by both the dwarf cowbird and the red-eyed cowbird and thatoccasionally one nest held eggs of both species of parasites. NearBrownsville, Texas, in May, 1924, I (1925, p. 550) found 16 nestsof the hooded oriole, one of which was parasitized by the dwarfrace of the cowbird. Two additional parasitized sets of eggs fromBrownsville, Texas, taken in 1928, are now in the collections of theCarnegie Museum. In the C. E. Doe collection m the Florida StateMuseum there is a parasitized set of eggs taken in Hidalgo County,Texas, on May 22, 1878.Abbott (1933, pp. 124-125) found a nest with 4 eggs of the orioleand 2 of the cowbird on June 8 in California (locality not given).Rowley (1930, pp. 130-131), in southern California, late in the after-noon of a day in May, saw a female hooded oriole leave her nest. A fewminutes later, a female brown-headed cowbkd flew to the nest andentered it. The cowbird remamed in the nest not more than two orthree minutes, during which time she laid her egg and either lackedout or removed with her bill one of the oriole's eggs. Rowley found theoriole egg on the ground where it had been dropped. A similar obser-vation was made by Allanson (in litt., to J. T. Zimmer).EUis (1924, p. 208) and Bennett (1943, p. 240) report that hoodedorioles were seen feeding recently fledged cowbirds in southern Cali-fornia?evidence that this host can and does rear the young parasitebeyond the nestling stage. Two nests of the hooded oriole, collectedin 1917 at Tucson, Arizona, and now in the collection of the SantaBarbara Museum of Natural History, each contained 1 egg of thedwarf race of the brown-headed cowbkd, 1 of the bronzed cowbird,and 2 of the oriole. Another parasitized set, collected at Tucson,by J. W. Lytle, on June 2, 1897, is now in the Museum of NaturalHistory at the University of Minnesota.
Baltimore OrioleIcterus galbula (Linnaeus)This oriole is parasitized very infrequently by the brown-headedcowbu'd; only 13 actual cases have been noted and no observer haswritten that this bird is a common victim anywhere in its range. Therecords involve two races of the parasite: artemisiae in Alberta andSaskatchewan; ater in New York, Pennsylvania, Indiana, Michigan,Minnesota, Wisconsin, and Iowa.Warren (1890, pp. 209-210), in Pennsylvania, on three occasions
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found broken cowbird egg shells directly beneath the pendant nestsof Baltimore orioles and asked whether orioles occasionally throwout the parasitic eggs. No one yet has produced any evidence onthis point. If it were found that these birds do eject the strangeeggs, this factor might play a role in the apparent paucity of recordsof cowbird parasitism.Gregg (1891, p. 26) found a nest in Chemung County, New York,containing a nearly fledged cowbird "big enough to fly" and twoorioles much less advanced in development. Nauman (1930) watchedthe development of a young cowbird which was reared in the nestof a Baltimore oriole in Iowa.The northwestern records involve M.a. artemisiae. T. E. Randallwrote me many years ago that he had found a parasitized nest inAlberta; Street (Houston and Street, 1959, p. 176) found another atNipawin, Saskatchewan.The Baltimore oriole may at times cover over a cowbird egg witha new nest floor. Parshall (1884) discovered a deserted nest con-taining 3 eggs of the oriole and 3 of the cowbird plus 3 more eggs ofthe parasite imbedded under a new nest lining.
Bullock's OrioleIcterus bullockii (Swainson)Bullock's oriole is a rarely parasitized bird. I have learned of veryfew records, all of which are mentioned here. This species was listedby Bendire (1895, pp. 442, 448) as a host of two races of the cowbird,ater and obscurus. He wrote that "Bullock's Oriole may occasionallyrid herself of the parasitic egg; at any rate I noticed the remains ofone lying under a nest of this species, Avith portions of one of her own.The nest contained only three eggs of the rightful owner and the bu'dwas sitting on these." He found it occasionally parasitized in Ai-izonabut he did not list specific instances. In Oklahoma, R. C. Tate founda nest of Bullock's oriole on July 12, 1911, with one young oriole andtwo young cowbirds; two dead young orioles were on the groundbeneath the nest (Nice, in litt.; also 1931, p. 169). A parasitized setof eggs was taken in Baylor County, Texas, May 14, 1952, by T. C.Meitzen (in litt.). Mr. Griffing Bancroft wrote me years ago thathe had collected a set of 5 eggs of this oriole with 1 of the dwarf cow-bird in Imperial County, California, on May 18, 1921. Anotherparasitized nest, also found in Imperial County, on May 18, 1919,is now in the collections of the Western Foundation of VertebrateZoology. Linsdale (1949, p. 251) found Bullock's oriole feeding arecently fledged cowbird at Robles del Rio, California. The Californiarecords involve the race parvus of the host; the Arizona, Texas, andOldahoma records, typical bullockii.
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Rusty BlackbirdEuphagus carolinus (MixUer)The rusty blackbird has been recorded as a host of the north-western race of the brown-headed cowbird, M.a. artemisiae, in Alberta.T. E. Randall informed me many years ago that he had found twoparasitized nests of this blackbird; A. D. Henderson also wrote me ofsimilar observations.In a commercial price list of November, 1947, the natm-al historydealer, C. H. Gowland of Wirral, England, listed two sets of eggs ofthe rusty blackbird, each with eggs of the cowbird. No locality ordate was given for either set, and correspondence failed to obtaineither the specimens or further data about them.The Alberta records refer to the typical race of the host. Becausethe parasite does not breed in the range of the Newfoundland racenigrans, the Gowland sets presumably also involve the nominate raceof the host. Brewer's BlackbirdEuphagus cyanocephalus (Wagler)Brewer's blackbird frequently is imposed upon by the brown-headedcowbii'd in Alberta and Montana, and it also has been noted as acowbird host in British Columbia, Saskatchewan, Colorado, Minne-sota, and California. In the Rowan collection at the University ofAlberta there are seven parasitized sets of eggs which were taken inAlberta. Other Alberta records have come to my attention fromT. E. Randall and A. D. Henderson.In Gallatin County, Montana, A. A. Saunders (1911, p. 40) foundcowbird eggs more often in nests of Brewer's blackbird than in nestsof any other species; he wi'ote that a large percentage of the blackbirdnests were parasitized. Cameron (1907, pp. 396-397) found the birdparasitized in Custer and Dawson Counties, Montana, and Rust (1917,p. 37) found a parasitized nest in Fremont County, Idaho. At St.Vincent, Minnesota, Peabody (1909b, pp. 15-20) concluded that fewnests of this blackbkd seemed to escape the visitation of the cowbird.More recent observers (Hayward, 1950; Mierow, 1949; Warner, 1951)also have reported this blackbird as a regular host of the cowbird inMinnesota. Belts (1912, p. 204) found it imposed upon in BoulderCounty, Colorado. Mrs. K. Baton has informed me of at least threeparasitized nests at Oxbow, Saskatchewan.As many as 3 cowbird eggs have been found in one nest of this black-bird; in fact, 4 eggs of the parasite have been found in a single nesttogether with 7 of the owner?a crowded nest indeed.All the records, with the exception of one from California, refer tothe northwestern race of the cowbird, M.a. artemisiae. The south-western race, obscurus, is involved in the record of a parasitized nest
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found at Gustine, California, on June 6, 1932, by H. R. Eschenberg(Friedmann, 1943, p. 355). Common GrackleQuiscalus quiscula (Linnaeus)This species is a rarely victimized bird ; only six instances have cometo my attention. Because the grackle is much larger than the cowbirdand also very aggressive?well able to drive off an intruder?it is notsurprising that the bird rarely is molested. All the records refer tothe race versicolor of the grackle. One record, from North Dakota,refers to the race artemisiae of the parasite; the others, to typical ater.The North Dakota instance was found by Alfred Eastgate, who wroteto me about it without giving an exact locality or date. There is onerecord from Texas, where Strecker (1927, p. 47) found a parasitizednest in McLennan County. In Illinois, Strumberg (1879, p. 79)reported a nest at Galesburg, mth 5 eggs of the grackle and 1 of thecowbird. Barnes (1918, p. 109) found a nest with 4 eggs of the victimand 2 of the parasite; he wrote to me that he had in his collectiontwo parasitized sets of grackle eggs, both collected "May 10, 1896, alittle over one mile from this place (Lacon, Illinois) in the overflowbottoms of the Illinois River, both nests in willow trees, one onlyeighteen inches above the water and the other four feet up. Each ofthe nests contained one Cowbird [egg] and all of the eggs were fresh,the nests were less than a hundred feet apart; never before or sincehave I found Cowbird's eggs in the nest of this species." In thecollections of the California Academy of Sciences there is a cowbirdegg taken from a grackle's nest near Winchester, Illinois, on April 26,1889, by W. C. Hutchinson.It should be pointed out that Bent (1958, p. 415) referred to arecord of cowbird parasitism on the grackle in Iowa. This may bebased on Keyes and Williams (1888, pp. 24-25), who made a statementwhich suggests, without actually giving explicit data, that the commongraclde is parasitized in Iowa. What they wrote is that, early in theseason before the smaller species of birds have begun to nest, thecowbird is forced to lay in the nests of larger species?among whichthey list the bronzed graclde.Western TanagerPiranga ludoviciana (Wilson)The western tanager has been reported as a victim of the brown-headed cowbird only three times to my knowledge. E. M. Tait wroteme that he found two parasitized nests at Trout Creek Point, BritishColumbia. One contained young of both the victim and the parasite;the other held eggs of both species. A. D. Henderson informed me630590?63 10
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that he had found this tanager to be victimized in Alberta; andrecently, Rogers (1956, p. 399) has reported it as a victim at MelitaIsland, Montana. In all these cases the cowbird involved is the raceartemisiae. Scarlet TanagerPiranga olivacea (Gmelin)The scarlet tanager is the most commonly parasitized species ofits family, but it is not among the chief hosts of the brown-headedcowbird. About 50 records have been noted, distributed amongthe following states : Connecticut, Illinois, Indiana, Iowa, Maryland,Massachusetts, Michigan, Minnesota, Missouri, Nebraska, New York,New Jersey, Ohio, Pennsylvania, West Virginia, and Wisconsin;and Ontario, in Canada (3 records).J. P. Norris (1892b, pp. 21-22) stated that, of 22 sets of eggs ofthis tanager in his collection, 7 contained 1 or more cowbirdeggs. All seven of the parasitized sets were collected at Nazareth,Pennsylvania, during two successive summers, 1887 and 1888. Sincea fair percentage of the nests were parasitized, it would appear thatin this locality the scarlet tanager was a frequent host. In Iowa, Keyesand Williams (1888, p. 34) found the scarlet tanager to be parasitizedso heavily that they wrote that the nests of this species "almostinvariably" contained from 1 to 3 eggs of the parasite. Mulliken(1899, p. 18) noted a nest containing the surprising total of 9 eggs,5 of which were cowbird, and, judging from the variation in colorand pattern, these 5 seemed to have been laid by five different indi-viduals. Hess (1910, p. 26) reported a scarlet tanager incubating4 cowbird eggs with 1 of its own. At Ithaca, New York, I saw arecently fledged cowbird being fed by a female scarlet tanager.Statements to the effect that this tanager may occasionally desertits nest if a cowbird lays in it have been made loosely without sup-porting evidence.All the records refer to the eastern race of the cowbird, ater.Summer TanagerPiranga rubra (Linnaeus)The summer tanager is an uncommon victim of the brown-headedcowbird. Eighteen records have come to notice, distributed fromMaryland, the District of Columbia, and Virginia to Ohio, Illinois,Kentucky, Tennessee, Alabama, Oklahoma, and southern Texas.These records involve two races of the summer tanager, rubra andcooperi, and two of the cowbird, ater and obscurus.Because of the small number of known cases of cowbird parasitism,it is somewhat unexpected to find that Stewart and Robbins (1958,p. 329) noted seven instances in Maryland. These seven probably
HOST RELATIONS OF PARASITIC COWBIRDS 137
include the five Dorchester cases taken from the late F. C. Kirkwood'smanuscript notes. Despite this, it begins to appear that in easternMaryland the summer tanager must be a regular fosterer; however,even there it is not one of the most frequently chosen hosts.In Oldahoma, Nice (1931, p. 173) has reported three records.In Nelson County, Kentucky, Beckham (1883, p. 141) called thebird an occasional victim. In Texas, it appears to be more thanoccasionally imposed upon; it has been recorded as a cowbird fostererin several parts of the state. R. W. Quillin informed me many yearsago that the summer tanager was a common host of the cowbird inthe environs of San Antonio and he added that, in his extensiveobservations, he rarely found unparasitized nests of this bird.Simmons (1925, p. 172) similarly found it to be imposed upon inthe Austin region, and Sutton (1938, p. 198) noted it in the samecapacity in Tarrant County; it has been reported to be parasitizedalso in Brewster County by Van Tyne and Sutton (1937, p. 94).Sutton wrote me that on May 15, 1935, he and J. B. Semple sawa pair of summer tanagers (cooperi) feeding a recently fledged cowbirdnear Hot Springs along the Rio Grande. This is the only actualrecord of this host rearing a young cowbird, but there is no reasonto think the instance unusual.
CardinalRichmondena cardinalis (Linnaeus)The status of the cardinal as a cowbhd fosterer varies more indifferent parts of its range than is the case with most birds. In myoriginal summary (1929, pp. 228-229) I observed that, while in someplaces the cardinal appears to be one of the commonest host species,in other areas it is very much the contrary. Recently, Berger (1951a,p. 29) reported that 10 out of 22 nests (45.4 percent) which werefound by him in Michigan were parasitized?a notably high percent-age. He noted that 7 of these 10 nests on which he had sufficientdata to allow for analj^sis?containing at least 11 cardinal eggs and13 cowbu-d eggs-?produced no fledged cardinals and only two fledgedcowbirds. He attributed this fact to the tendency of the cardinal todesert its nest when a cowbird lays in it. In the same general area,Sutton (1959, p. 81) noted that a cardinal deserted its nest and 4eggs when a cowbird added its own to the clutch. Out of 21 cardinalnests observed by him, only 2 were victimized by the cowbird.In the area about Nashville, Tennessee, Monk (1936, p. 33) reportedthat 'local students have examined thousands of Cardinal nests withonly one Cowbhd record, indicating how very rarely this species isparasitized." Even allowing for loose writing and substituting
"scores" for "thousands," the tendency seems clear. Laskey (1944a,
138 U.S. NATIONAL MUSEUM BULLETIN 233
p. 33; 1944b, pp. 17-18), however, kiiew of at least nine cases ofcowbird parasitism on the cardinal in Tennessee.In the 35 years since I first summarized the status of this bird as acowbird host, many dozens of additional records have come to notice;however, in most areas from which there is sufficient information thecardinal appears to be a relatively uncommon victim. Nevertheless,the total mass of instances allows no general evaluation other than tocall this bird a regular and fairly common fosterer of the brown-headedcowbird.All in all, about 75 records have been noted, distributed among thefollowing states: Ai'izona, Arkansas, Delaware, Florida (Newman andWarter 1959), Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana,Marjdand, Michigan, Minnesota, Mississippi, Missouri, New Jersey,Ohio, Oklahoma, Pennsylvania, Tennessee, Texas, Virginia, and WestVirginia; and Ontario (Essex and York Counties) in Canada. Theserecords involve four races of the cardinal
?
cardinalis, canicauda,swperha, magnirostris?and two races of the cowbird
?
ater and obscu-rus. The cardinal is parasitized chiefly in the central portions of itsrange.A curious item is recorded by Alexander Wilson (1810, p. 40), whoplaced a nestling cowbird in a cage with a cardinal and found thatthe latter fed and reared the young bird "with great tenderness."
PyrrhuloxiaPyrrhuloxia sinuata (Bonaparte)The pyrrhuloxia has been reported only six times to my knowledgeas a victim of the brown-headed cowbird. According to informationreceived from C. G. Abbott, a parasitized nest was found near Tucson,Arizona, by N. K. Carpenter. Another case was observed at Guay-mas, Sonora, on June 25, 1928, by Griffing Bancroft. Both of theserecords refer to the r&ce fulvescens of the host (not sinuata as I noted,1934, p. 107) and the race ohscurus of the parasite. Nye (in litt.)discovered a nest five miles north of Raymondville, Willacy County,Texas, on April 22, 1952, with 3 eggs of the pyrruloxia and 1 of thedwarf brown-headed cowbird. In the files of the U.S. Fish and Wild-fife Service, there are three additional Texas records: two parasitizednests found at Somerset by A. J. lurn; and one, near San Antonio,reported by R. W. Quillin. These Texas records refer to the nominaterace of the host. Rose-breasted GrosbeakPheucticus ludovicianus (Linnaeus)This is a fairly frequent victim of the brown-headed cowbird.Forty-three records have been noted, distributed from Saskatchewan,Ontario, and Quebec, in Canada, to the following of the United States:
HOST RELATIONS OF PARASITIC COWBIRDS 139New York, New Jersey, Ohio, Indiana, Illinois, Michigan, Wisconsin,Minnesota, Iowa, and North Dakota. The northwestern race of theparasite, M.a. artemisiae, is involved in the Saskatchewan and NorthDakota records ; the eastern race, M.a. ater, in all the others. Althoughmost of the records merely refer to eggs in nests, the rose-breastedgrosbeak has been known to rear young cowbirds to the fledgling stage.At Ithaca, New York, on July 6, 1922, I observed a pair of grosbeaksfeeding an almost fully grown young cowbird. In southern Quebec,Terrill (1961, p. 9) noted three instances of parasitism in 42 nestsexamined. Black-headed GrosbeakPheucticus melanocephalus (Swainson)The black-headed grosbeak has been reported as a cowbird victimin only a few places in Kansas, Nebraska, Colorado, Utah, and Mon-tana. In Lincoln County, Nebraska, Tout (1947) recorded the factwithout giving any detailed cases. Sclater (1912, p. 401) wrotethat this grosbeak is imposed upon not infrequently bj^ the cowbirdin Colorado, but he also gave no specific instances. Silloway (1917,p. 159) and A. A. Saunders (1914, p. 136, p. 143) reported parasitizednests from Montana, while Bee and Hutchings (1942, p. 82) foundan instance at Utah Lake, Utah, on June 5. Mr. Guy Loveinformed me years ago that he found two parasitized nests in DecaturCounty, Kansas?one on June 11, 1909, and the other on May 25,1912. The Kansas records refer to the eastern race of the cowbird,M.a. ater, whereas the others relate to the northwestern race, Al.a.artemisiae. All involve the nominate race of the host.Recent studies of hybridization between the rose-breasted and theblack-headed grosbeaks suggest that the two are related very closely.Although outside the interest of the present study, it should bementioned that there is no apparent difference between the twobirds in their relation to cowbu'd parasitism. As far as our presentknowledge goes, the cowbird treats them alike.
Blue GrosbeakGuiraca caerulea (Linnaeus)The blue grosbeak is a fairly frequent victim of the brown-headedcowbird, but, at times and in certain localities, it may be imposedupon very much. Whereas in most areas it has been recorded as a hoston the basis of one or a very few instances, the opposite is the casein some areas, as seen in the experience of Bleitz (1956) in southernCalifornia. In a single season, within the limits of a very restrictedlocality, he found seven nests of the blue grosbeak, every one of whichhad been parasitized. If this were a typical or even fairly usualcondition, it could be expected that many more instances would have
140 U.S. NATIONAL MUSEUM BULLETIN 233found their way into print, but they have not. The report serves tocaution against generahzations too easily derived from negative orinsufficient data as to the status of this species as a cowbird host.Similarly, in Decatur, Arkansas, Plank (1919, p. 18) wrote that theblue grosbeak "is one of the worst preyed-on birds. In a nest near apasture a few years ago I found thi'ee Cowbird's eggs in various stagesof incubation and one Grosbeak's egg nearly ready to hatch. Anothernest contained two Cowbird's eggs and two Grosbeak's. One rarelyfinds a nest of this species that has not been visited by a Cowbird."In Woods County, Oklahoma, Mr. Guy Love collected no fewer thanfive parasitized sets of eggs, which suggests a high incidence of cow-bird parasitism there. All in all, I have noted about 30 cases ofparasitism on the blue grosbeak.The cases are distributed among the following states: Arkansas,California, Kansas, Maryland, Mississippi, New Mexico, Oldahoma,Texas, and Virginia. The total number of records involves thi*eeraces of the grosbeak: salicaria in southern California; interfusain Texas, Oldahoma, and New Mexico; and caerulea in the otherareas that were listed. Two cowbhd races are involved in theserecords: ohscurus with salicaria and interfusa; ater with caeruleaand interfusa.Previously unpublished and?as far as I know?the only recordfrom New Mexico is a set of eggs with 1 of the cowbird, taken inEddy County on June 18, 1923, by E. E. Pilquist and now in theCruttenden collection at Qumcy, Illinois.Evidence of the ability of this grosbeak to rear young of the para-
site is afforded by the record of a young cowbird and a young grosbeakreared together at Norman, Oklahoma (Nice, 1931, pp. 174-175).
Indigo BuntingPasserina cyanea (Linnaeus)The indigo bunting is a very frequent host of the brown-headedcowbkd. About 200 records have been noted, distributed in Ontarioand Quebec, in Canada, and the following of the United States:Alabama, Ai-kansas, California, Connecticut, Delaware, Illinois,Indiana, Iowa, Kansas, Kentucky, Maryland, Massachusetts,Michigan, Minnesota, Missouri, New Jersey, New York, Ohio,Oklahoma, Pennsylvania, Rhode Island, Virginia, West Virginia,and Wisconsin. These records aU involve the eastern race of thecowbird, M.a. ater, with the exception of one record from SoledadCanyon, California, where Bleitz (1958) found that the indigo buntingwas victimized by the southwestern race of the parasite, M.a. ohscurus.In some areas, a fairly high percentage of the nests contain eggs ofthe cowbu'd. In Ohio, Hicks (1934) found 43 nests, of which 17,
HOST RELATIONS OF PARASITIC COWBIRDS 141
or nearly 40 percent, were parasitized; also in Ohio, Phillips (1951)found 14 nests, of which 6, or 42.8 percent, were parasitized. Thelatter observer reported that, in the total 14 nests, 41 bunting eggsand 7 cowbu'd eggs were laid; these produced 18 fledged buntings(43.9 percent) and one fledged cowbird (14.3 percent).In his study of this bunting, Twomey (1945, pp. 193-195) foundthat 12 out of 33 nests, observed during two successive years, wereparasitized. In most of these cases, fatahties to some of the hostyoung occurred: about 30 percent of those that hatched failed toreach the fledging stage. Twomey studied the growth of the nestlingsof both host and parasite and found that the presence of a youngcowbird decreased the growth rate of the 3'Oung buntings which wereits nest-mates and that the presence of two young cowbirds in a nestproved fatal to the young of the fosterer. Using Twomey's data,Lack (1947, p. 323) attempted to equate one yoimg cowbird with twoyoung buntings in the factor of feeding by the host adults.In the Edwm S. George Keserve of southeastern Michigan, Sutton(1959, pp. 95-99) found 26 nests of the indigo bunting, of which 4were parasitized. In these 26 nests, 53 bunting and 6 cowbird eggshad been laid. Of these, 44 bunting and 3 cowbird eggs hatched;of the 44 bunting chicks, 23 fledged successfuUy. None of the para-sitized nests produced fledglings of either parasite or host.In southern Quebec, Terrill (1961, p. 9) found 30 nests, of which6, or 20 percent, were parasitized. In most places where it is para-sitized, the indigo bunting appears to be a frequently chosen fosterer.Orduiarily, it does not attempt to rid itseK of the strange eggs sofrequently foisted upon it, but one instance has come to my noticeof an indigo bunting burying under a new nest lining a cowbird eggwhich had been deposited before the host had laid any of its own.On other occasions, as indicated above, the indigo bunting hasbeen known to rear young cowbirds to the fledging stage. I sawtwo such cases at Ithaca, New York, in 1921 and 1922, and one of theearliest and one of the most complete accounts of this finch as acowbird fosterer?published by Ord in 1836 (pp. 68-69)?gives a detailedrecord of the development of two young cowbu-ds in an indigo bun-ting's nest. As many as 5 eggs of the cowbird have been reported ina single next of this host (Pius, 1949) and as many as two young cow-birds have been known to be reared in one nest (Ord, loc. cit. ; Bradley,1948). Lazuli BuntingPasserina amoena (Say)The lazuU bunting is known as a victim of the brown-headedcowbird in California, Colorado, Idaho, Montana, and Washington.Two races of the parasite are involved
?
obscurus in southern Califor-
142 U.S. NATIONAL MUSEUM BULLETIN 233
nia, where Hanna (1928, p. 161) and Stoner (1937) recorded fourparasitized nests, and artemisiae in the following instances: inColorado, where Sclater (1912, p. 405) noted one nest with an egg ofthe parasite and where Acken and Warren (1941, p. 575) recordedanother near Bear Creek on July 19, 1898; in Idaho, where Bendirecollected a parasitized set of eggs on June 21, 1871; in Montana,where B. Bailey (1914, p. 143) collected a similar clutch of mixedeggs; and in Washington where Decker found the lazuli bunting tobe a cowbird victim (Jewett, Taylor, Shaw, and Aldrich, 1953,p. 594) and where King (1954, pp. 150-154) found two parasitizednests in Whitmore County,
Varied BuntingPasserina versicolor (Bonaparte)The varied bunting is a very slightly laiown bu"d ; it is included as avictim of the southwestern race of the brown-headed cowbird, M.a.obscurus, on the basis of only two records. R. D. Camp collected aset of 2 eggs of this bunting with 1 of the cowbird in Cameron County,Texas, on June 4, 1927; the set later became part of the J. HooperBowles collection, A second record, the date and localit}'^ of whichare unknown to me, is based upon a parasitized set of eggs in thecollection of J, C, Braly of Portland, Oregon. These records refer tothe typical race of the varied bunting.
Painted BuntingPasserina ciris (Linnaeus)The painted bunting is a fairly frequent victim of the brown-headed cowbird and, in some areas, it appears to be a very commonhost. About 50 records have been noted from Oldahoma, Texas, andMississippi. In southern Texas, the parasite is the small race of thecowbird, M.a. obscurus; in Oldahoma and Mississippi, it is the easternrace, M.a. ater. Two races of the painted bunting are involved:P.c. pallidior in southern Texas; P.c. ciris in Oklahoma, northern andcentral Texas, and Mississippi.Mr. R. W. Quillin wrote to me many years ago that this bird is oneof the commonest victims of the cowbud around San Antonio, Texas.According to him, the bunting does not tolerate the imposition of theparasite as well as some other birds do and, in about eight cases outof ten, the buntings desert their nests when a cowbird lays in them.When the bunting has completed or nearly completed its set of eggsis the time that it will usually tolerate the addition of the strange egg.Parmalee (1959), pp. 1-18) has added greatly to our knowledge ofthe situation, particularly in southern Oldahoma. Out of 45 nestsfound in 1957, 13 were parasitized and all but 4 of these were de-
HOST RELATIONS OF PARASITIC COWBIRDS 143
serted by the buntings during the egg-hiying period. He suggeststhat nest desertion occurs if the nest is parasitized early in egg-layingbefore the third or fourth egg of the host is laid. No nest had morethan 2 cowbird eggs and, in at least two nests, young of both parasiteand host matured to the fledgling, nest-departing stage.More records of cowbird parasitism on this bunting are from Texasthan elsewhere. Besides Quillin's statement, mention should bemade, among others, of Nye (1939, p. 87), Simmons (1925, p. 172),and Savary (1936, p. 62).
DickcisselSpiza americana (Gmelin)The dickcissel is a not uncommon victim of the brown-headed cow-bird. About 55 instances have been reported from Arkansas, Illinois,Indiana, Iowa, Kansas, Michigan, Nebraska, Oldahoma, and Texas.In southern Texas, it is parasitized by the small race of the cowbird,obscurus; elsewhere, by the eastern race, ater. R. W. Quillin in-formed me many years ago that around San Antonio, Texas, hehad examined hundreds of dickcissel nests and had found cowbirdeggs in only four cases. Philo Smith, Jr. (1882, p. 182), reportedas many as 4 cowbird eggs with 3 of the owner in one dickcisselnest. This species is not bothered by the cowbirds to the samedegree that some other ground-nesting birds are. Judging by thepublished records, it appears to be imposed upon more often inTexas, Oklahoma, Nebraska, and Kansas than elsewhere. In additionto Quillin's San Antonio records, there are others from Texas?theAustin area (Simmons, 1925, p. 172) and Brenham (Nye, 1929,p. 87). In 1907 at Lawrence, Kansas, Hanna collected three para-sitized sets which are now in the collections of the California Academyof Sciences. According to information received from R. F. Johnston(in litt.), 6 out of 23 nests found in one area in Kansas were para-sitized?^an incidence of 25 percent. Overmire (1962, pp. 115-116)recorded a higher frequency of parasitism in Oklahoma, where hefound that 19 out of 61 dickcissel nests (31 percent) contained eggsof the cowbird?not one of which survived to the hatching point.The highest frequency of cowbird parasitism which I have yetfound is 53 percent: reported in Nebraska by Hergenrader (1962,pp. 85-88). Evening GrosbeakHesperiphona vespertina (Cooper)This species is included in the present list on the basis of a singleobservation, which was made at Saranac Lake, New York, in July,1949. The case already has been described in detail by Schaub(1949) and by Nichols (1949). It involves a fledgling cowbird
144 U.S. NATIONAL MUSEUM BULLETIN 233
which came to a feeding shelf with an adult male grosbeak ; the fledglingwas fed repeatedly by the latter. As yet, no nest of the evening grosbeakhas been found with eggs or j^oung of the parasite; for this reasonit cannot be said with certainty that the cowbird in question actuallywas reared by the apparent fosterer, but the indication that it wasis very strong. The record refers to the nominate race of bothvictim and parasite. Purple FinchCarpodacus purpureus (Gmelin)The purple finch is a very uncommon victim of the brown-headedcowbird. Eighteen records have been noted, distributed among thefollowing areas: Alberta, Saskatchewan, and Quebec in Canada;California, Washington, Michigan, Connecticut, New York, andRhode Island in the United States. In California, Washington,Alberta, and Saskatchewan the parasite is the race artemisiae; else-where, ii is the eastern race ater. In all cases the nominate race ofthe victim is involved.Sage and Bishop (1913, p. 110) record two nests in Connecticut,each with a cowbird's egg. In addition to this there is another Con-necticut record, a nest with 3 cowbird eggs and 4 of the host, listedby Hoffman (1881, p. 53). Still another parasitized nest from thesame state was taken near New London on May 26, 1887, by C. L.Rawson and later was incorporated into the J. P. Norris collection.Nearby, in Rhode Island, two more cases were found, one at Warwickon June 13, 1882, and one at Cranston on May 30, 1902; both sets ofeggs are now in the C. E. Doe collection in the Florida State Museum.Several cases have been noted in New York, of which two may bementioned: at Ithaca, Alberger (1890, p. 46) recorded a parasitizednest; at Mayville, Kibbe (1892, pp. 133-134) found another onJune 8, 1892.Mr. T. E. Randall informed me that he had found three instancesof cowbird parasitism on the purple finch in Alberta. Street (Houstonand Street, 1959, p. 176) reported this finch as a cowbird host in Sas-katchewan. The lone Washington record (from the files of the BritishColumbia Nest Records Scheme, Univ. of B.C.) is a nest containing3 eggs of the finch and 1 of the cowbird, found two miles south ofOrrondo, Douglas County, on June 25, 1959. This record was sentto me with a note that the observer (name not given) was not entirelycertain as to the identity of the host but considered it to be a purplefinch. In southern Quebec, a single case was reported by Terrill(1961, p. 9); an earher one had been recorded by Lloyd (1944, p. 172)from Hull on May 28, 1899. The National Museum of Canada hasa parasitized set, taken at Hull, by A. R. Legge on May 28, 1897.This may be the same one mentioned by Llo3^d. In the collections of
HOST RELATIONS OF PARASITIC COWBIRDS 145
the Santa Barbara Museum of Natural History there is a parasitizedset of eggs of the purple finch, taken at Smith's Camp, Bishop,California, May 7, 1922. House FinchCarpodacus mexicanus (MuUer)The house finch appears to be imposed upon only occasionally bythe brown-headed cowbird. Ten instances have come to my notice:one record from New Mexico, where Jensen (1925, p. 461) found thisfinch was parasitized in northern Santa Fe County; three records fromsouthern California?Buena Park (Robertson, 1931a, p. 138; 1931b,205), the San Bernardino Valley (Hanna, 1933, p. 205) Bloomington,San Bernardino County (a set in the San Bernardino Count}^ Museum)
;
two from Arizona, where Hensley (1954, p. 204) noted a house finchdeserting its parasitized nest and where he later (1959, p. 91) reporteda parasitized nest in the Organ Pipe Cactus National Monument;one record from Texas, where Nye (in litt.) informed me that he hadfound the nest of a house finch with 3 eggs of the host and 1 of thedwarf cowbird at Kerrville, Kerr County, on May 14, 1938; a recentrecord from Oregon, where Alderson (1960, p. 22) recorded twoparasitized nests at North Portland, on May 22, 1960; and one fromCahfornia, where Mr. E. Z. Rett, informed me that, in the files of theSanta Barbara Museum of Natural History, there is a card for a setof 5 eggs of the house finch and 1 of the cowbird, collected at Smith'sCamp, Bishop, California, in May, 1922, but the eggs themselvescould not be found at the time of his writing.The parasite in the last instance and in the Oregon cases was of therace artemisiae; in the New Mexico record it was of the eastern raceater; in the Arizona and southern California records, the dwarf raceobscurus. In all the records the race of the house finch was Cm.frontalis. White-coUared SeedeaterSporophila torqueola (Bonaparte)This bird is a little known victim of the brown-headed cowbu-d.It was established previously as a molothrine host only on the basisof its inclusion in the Hst of hosts in Bendu-e's pioneer study (1895).The following definite records may now be added to this otherwiseunsupported statement. In the Cruttenden collection, Quincy,Illinois, there is a set of eggs of this seedeater with a single egg of thedwarf race of the bro\vn-headed cowbird, collected "in Mexico" onJune 5, 1947. Meitzen (in litt.) found a parasitized nest near Browns-
ville, Texas. Fred F. Nye, Jr., also wrote me that in Cameron County,Texas, and in the adjacent portions of Tamaulipas he found severaldozen nests of this seedeater, of which three were parasitized. Twoof these each held 2 eggs of the host and 1 of the parasite.
146 U.S. NATIONAL MUSEUM BULLETIN 233The third case was more involved as indicated in the following de-scription. On July 15, 1947, when first examined, the nest contained 2eggs of the seedeater; the next morning there was a cowbird egg in itas well; foui- days later a 2nd cowbird egg was laid in it, apparentlyby a different female as far as could be judged from the dissimilarityof the eggs; two days later Nye removed the last laid egg and a fewminutes later the female host was back on the nest, incubating. Afterfour days, the first cowbird egg hatched ; that same day Nye removedthe young parasite. The next day one of the host's eggs was missingand a new, 3rd, cowbird egg was in the nest. Three days later thenest was empty and deserted; a snake in the same tree was thoughtto have been the predator.All the records refer to the race sharpei of the host and the raceohscwus of the parasite. Common RedpollAcanthis flammea (Linnaeus)Since most of the breeding range of this boreal finch is north ofthat of the brown-headed cowbird, the redpoll generally is unavailableas a host. A single instance of its being parasitized has been broughtto my attention from the files of the British Columbia Nest RecordsScheme. A nest of the common redpoll (AJ. flammea) containing 1egg of its own and 1 of the cowbird {M.a. artemisiae) was found atCastor, Alberta, on June 25, 1959. The nest was deserted whenfound and both eggs were in addled condition.
Pine SiskinSpinus pinus (Wilson)Generally, the pine siskin is ecologically allopatric with the brown-headed cowbird, a fact which effectively protects it from the attentionsof the parasite. However, there are places where the two speciesoverlap and here the siskin occasionally is imposed upon. Elevensuch instances have come to my notice, distributed among the followingstates: Iowa, Kansas, Nebraska, South Dakota; and in Canada:Ontario and British Columbia.Klugh (1906, pp. 17-18) recorded three parasitized nests in Welling-ton County, Ontario. These were the first cases to be known. Dalesand Bennett (1929, pp. 74-77) recorded a nest in Iowa containing 3eggs of the siskin and 1 of the cowbird. The latter egg hatched andthe chick grew to the fledging stage as the sole survivor of the brood.Swenk (1929, pp. 79, 82) noted two parasitized nests in Nebraska:one at Child's Point, south of Omaha, on May 13, with 3 eggs of thesiskin and 1 of the cowbu'd; another at Lincoln, on May 16, with oneyoung siskin in the nest and a young cowbird on the ground beneath
HOST RELATIONS OF PARASITIC COWBIRDS 147
it. The two adult sisldns were observed feeding both of the youngbirds.At Haj^s, Kansas, on April 28, 1961, Dr. Charles Ely found a cow-bird egg and an egg of the host in a pine siskin's nest. On May 5only the cowbhd egg remained; on May 8 a 2nd cowbird egg hadbeen laid in the nest. Krause (1954, p. 42) found six nests of thepine siskin at Sioux Falls, South Dakota, one nest of which contained acowbird 's egg. Dr. Ian McTaggert Cowan informed me that aparasitized nest was found at Enderby, British Columbia. This andKrause's South Dakota record are the only instances I have noted inwhich the northwestern race of the parasite, M.a. artemisiae, wasinvolved; all the other cases refer to M.a. ater. The race of the hostin all these instances is the typical one S.v. pinus.
American GoldfinchSpinus tristis (Linnaeus)In some parts of its range the goldfinch breeds so late in the summer(from July to mid-September in many northern portions) that itobviously becomes unavailable as a host for the brown-headed cow-bird; but the overlap elsewhere is sufficient to enable the latter toparasitize this bird rather frequently. This fact is due to variationsnot only in the date of inception of breeding by the goldfinch but alsoin the date of termination of egg-laying by the cowbird. Jensen(1918, p. 347), writing of the birds of Wahpeton, North Dakota,reported a nest of the goldfinch with 4 newly-laid eggs of its ownand 1 of the cowbird on August 6?over a month later than mylatest date for a cowbird's egg in central New York.Some 53 records have been noted: from British Columbia, Alberta,Saskatchewan, Ontario, and Quebec in Canada; from California,Connecticut, Illinois, Indiana, Iowa, Massachusetts, Michigan,Minnesota, Missouri, New York, North Dakota, Ohio, Oklahoma,Pennsylvania, and Wisconsin in the United States. In most areasthe goldfinch is a rare victim; in southern Quebec, Terrill (1961,p. 9) found 313 nests during nearly 60 yeare of observing, and of theseonly 7 contained eggs of the cowbird. Similarly, at Ithaca,New York, an area where both the goldfinch and the cowbird arecommon and where many nests of the former had been found priorto the end of my work there in 1923, no instances of cowbird para-sitism on this bird were on record. In his extensive study of thegoldfinch in southern Michigan, Nickell (1951) noted 264 nests buthe mentioned cowbirds in connection with only a single instance
?
a nest which had b? abandoned with three young cowbirds in it.The presence of the pa asites was not linked directly or inferentiallywith the abandonment of the nest. In the same region, Walkinshaw
148 U.S. NATIONAL MUSEUM BULLETIN 233
(1938, pp. 3-11) observed 111 nests, not one of which had been para-sitized. Berger (1960, p. 118) in the same general area found 796nests, of which 11 were parasitized. Three of these cases were two-storied nests and two were reported in an earher paper (Berger,1948, pp. 52-53).Conversely, Eaton (1914, p. 227) lists the goldfinch as one of thecommon victims of the cowbird in New York, and so it seems thatconsiderable local variation must occur. In southern California thegoldfinch apparently is a frequent fosterer. Hanna (1928, p. 161)recorded eight parasitized nests in a limited area and a limited time,and M. C. Badger wi'ote me that, in his experience, the goldfinchwas a very common victim in southern California.In the absence of recent records of a cowbird being fledged from agoldfinch's nest, Berger (1961, p. 271) considered it unlikely that theyoung parasite could survive on a diet of regurgitated seeds such asthe goldfinch habitually gives its nestlings. Nevertheless, this phe-nomenon has occurred. The earliest recorded instance, observednear Baltimore, Maryland, and described by Dr. Nathaniel Potter,is given in full in Alexander Wilson's pioneering work on Americanbirds (1810, p. 158).The records relate to three races of the goldfinch
?
tristis, pallidus,salicamans?and to the three races of the cowbird: obscurus inCalifornia; artemisiae in British Columbia, Alberta, Saskatchewan,and North Dakota; and ater elsewhere.
Lesser GoldfinchSpinus psaltria (Say)The lesser goldfinch has been reported on a few occasions as avictim of the brown-headed cowbird in California and Texas. Thelate J. Hooper Bowles informed me many years ago that he had inhis collection a set of 4 eggs of this goldfinch with 1 of the cowbird,taken at Santa Paula, California, by M. C. Badger. The collectorwrote me that he had found this bird to be an occasional victim butthat it was not as frequently imposed upon as its congener, S. tristis.Woods (1930, p. 126) recorded another parasitized nest at Azusa.A. M. Ingersoll and GriflSng Bancroft have both found similar casesin San Diego County; there are three sets taken by them in the collec-tion of the Western Foundation of Vertebrate Zoology and one inthe San Diego Museum of Natural History. In the collection of theSan Bernardino County Museum there is a parasitized nest of eggstaken in the San Gabriel Mountains. All these Cahfornia recordsrelate to the race hesperophilus of the host and the race obscurus ofthe parasite.
HOST RELATIONS OF PARASITIC COWBIRDS 149The data from Texas is incomplete. Tlie late G. F. Simmons wroteme that, shortly after the publication of his book on the bu-ds of theAustin region (1925), he was informed of a local instance of cowbirdparasitism on this goldfinch. The race of this bu'd breeding in theAustin area is the nominate one, S.p. psaltria.
Lawrence's GoldfinchSpinus lawrencei (Cassin)This goldfinch is known as a victim of the brown-headed cowbirdon the basis of two records, both from southern California. H. R.Eschenberg informed me that he had found a nest with 4 eggs of thegoldfuich and 1 of the dwarf race of the cowbird at Gih'oy, on June 20,1934. In the collections of the Museum of Vertebrate Zoology atBerkeley, there is a set of 1 egg of this host and 2 of the dwarf cow-bird, collected at Candalanga, Ventura County, by Ashworth.Red CrossbillLoxia curvirostra (Linnaeus)On the whole, the red crossbill is ecologically allopatric with thebrown-headed cowbird, and thus it is generally unavailable as a hostfor the latter. There is only a single case of cowbird parasitism onrecord. Saunders and Dale (1933, p. 240) collected a nest with 3eggs of the crossbill and 1 of the cowbu'd on April 29, 1909, two mileseast of London, Ontario. This instance refers to the race minor ofthe crossbill, as now understood; previously I (1938, p. 49) hadlisted this record as L.c. pusilla, a name now restricted to the popu-lation breeding in Newfoundland. The cowbird involved is the typicaleastern race, M.a. ater.
Olive SparrowArremonops rufivirgata (Lawrence)The nominate race of this sparrow is known as a victim of the smallrace of the brown-headed cowbird, M.a. obscurus, on the basis of onlya few records. Merrill (1878, p. 130) hsted it as a cowbkd victim atBrownsville, Texas; Sennett (1879, p. 396) also listed it. Probablyon the bases of one or both of these statements, Bendu-e (1895, p. 442)included this sparrow as a victim of the dwarf cowbird. In the filesof the U.S. Fish and Wildlife Service there are two records, both fromsouthern Texas. Mr. Jolm B. Hurley informed me that he has inhis collection a parasitized set of eggs of this bird collected in CameronCounty, Texas, on July 12, 1927, by R. D. Camp. F. F. Nye, Jr.(in litt.), found two more parasitized nests near Brownsville, CameronCounty, Texas.
150 U.S. NATIONAL MUSEUM BULLETIN 233
Green-tailed TowheeChlorura chlorura (Audubon)The green-tailed towhee has been reported a few times as a host ofthe brown-headed cowbird in Colorado, New Mexico, and California.Henshaw (1875, p. 308) recorded finding a cowbird egg in a nest ofthis bird at Fort Garland, southern Colorado, (originally reportedby Yarrow, 1874, p. 82); Rockwell (1908, p. 173) listed this towheeas one of the favorite hosts of the parasite in Mesa County, Colorado.In the collections of the Western Foundation of Vertebrate Zoologythere is a parasitized set of eggs from Beaver Creek, Colorado, takenon June 6, 1897, and another from Santa Fe, New Mexico, collectedon June 12, 1923. Mitchell (1898, p. 309) considered this towheeone of the most frequently imposed upon victims in San MiguelCounty, New Mexico. Mr. N. K. Carpenter informed me manyyears ago that he had found a parasitized nest in Mono County,California. The Colorado and New Mexico observations refer tothe eastern race of the cowbird, Al.a. ater; the California one, to therace Al.a. artemisiae. Rufous-sided TowheePipilo erythrophthalmus (Linnaeus)The rufous-sided towhee is a very frequent victim of the brown-headed cowbird. Nearly 300 records have been noted, distributedas follows- Alberta, British Columbia, Manitoba, Ontario, Quebec,and Saskatchewan in Canada; Arkansas, California, Colorado,Connecticut, Delaware, District of Columbia, Illinois, Indiana,Iowa, Kansas, Louisiana, Maryland, Massachusetts, Michigan,Minnesota, Missouri, Montana, Nebraska, New Jersey, New York,North Dakota, Ohio, Pennsylvania, Rhode Island, South Dakota,Tennessee, Virginia, West Virginia, and Wyoming in the UnitedStates. These records involve eight races of the towhee
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erythroph-thalmus, canaster, ardicus, montanus, curtatus, oregonus, Jalcifer, andmegalonyx?and aU three races of the cowbird: ater, artemisiae, andohscurus.Not only is this towhee victimized over a vast, transcontinentalarea, but also, in many parts of its range, it is one of the chief main-stays of the cowbird. It has been called one of the commonest hostsin New York by Eaton (1919), in Connecticut by Sage and Bishop(1913), in Ohio by Jones (1903), in Indiana by Evermann (1889),in Iowa by Anderson (1907), etc. In Ohio, Hicks (1934) found 103,nests in the course of many years of local observation, and 22 of these,or more than 20 percent, had been parasitized by the cowbird.In California, on the contrary, Baumann (1959, pp. 191-193)knew of only two instances of parasitism (Harmon, 1928, p. 161;Rowley, 1930, p. 131). He noted that the presence of an adult
HOST RELATIONS OF PARASITIC COWBIRDS 151
cowbird seemed to disturb the towhees greatly but he observed noparasitism. Davis (1960, p. 455) also commented on the scarcity ofinstances in California but he predicted that the spread and increaseof the brown-headed cowbird in coastal California would result inmore frequent usage of towhees' nests by the parasite. A parasitizedset of eggs, taken near Riverside, is now in the San BernardinoCounty Museum.The towhee is one of the larger of the regular victims of the cow-bird. With none of its fosterers is the parasite more successful. Ihave learned of no case of a towhee covering over, or in any waytrying to get rid of, the strange eggs. Moreover, no host has beensaddled so often with large numbers of parasitic eggs; the highest totalfound in a single nest was 8 cowbird eggs together with 5 of the tow-hee, a set taken in northern Iowa. Sanborn and Goelitz (1915,p. 444) found a nest in Lake County, Ilhnois, also with 8 cowbndeggs, but with only a single egg of the towhee. There are otherrecords of nests with 8, 6, 5, and 4 cowbird eggs, but, unfortunately,none of these were watched to see what the outcome would be. Mostof them were collected as specimens for egg collections?after themanner of the time in which they were found.In other nests, with smaller numbers of eggs, the rufous-sidedtowhee has been found to rear the young cowbirds to the fledgingstage. There is, however, a dearth of information as to the fre-quency with which any of the rightful brood survive with the para-site. This is a case wherein observers have failed to place data onrecord, probably because of their feehng that the occurrence was toocommon to be worth reporting.
Brown TowheePipilo fuscus SwainsonThe brown towhee has been reported as a victim of the brown-headed cowbird a few times in north-central New Mexico, Ai'izona,and California. GrifRng Bancroft informed me many years ago(Friedmann, 1934, pp. 109-110) that he had in his collection twoparasitized sets of eggs of this bird; of the race mesoleucus, they hadbeen collected in Santa Fe County, New Mexico, on June 4 and 12 ofthat year. A third and similar set was mthout precise data ; taken atSanta Fe, New Mexico, on June 12, 1925, it is now in the collection ofthe Western Foundation for Vertebrate Zoology. Another parasitizedset of eggs, taken near Tucson, Arizona, on May 18, 1936, is now inthe collections of the Carnegie Museum. J. T. Marshall, Jr. (inlitt.) wrote to me that, in the few nests of the brown towhee which hefound in the mesquite covered areas near Tucson, Arizona, there wereno cowbird eggs but that, in nearby desert locaHties, R. S. Crossin630590?63 11
152 U.S. NATIONAL MUSEUM BULLETIN 233had found parasitized nests of tliis species. In the collections of theHancock Foundation at the University of Southern California thereis an egg of the brown-headed cowbird, from a nest of a brown towheecollected at Alhambra, California, on June 13, 1944. The host inthat area is the race PJ. senicula. The Arizona and California recordsinvolve the southwestern race of the parasite, M.a. obscurus; theNew Mexico ones refer to the nominate race, M.a. ater.
Abert's TowheePipilo aberti BairdAbert's towhee is a rather poorly known and little studied species*but it has been found to be parasitized by the small race of the brown-headed cowbird, M.a. obscurus, at least nine times in southern Arizonaand at least once in California (Westmoreland, Imperial County).The latter set is now in the San Bernardino County Museum. Brown(1903, p. 47) merely reported it as a molotlu^ine victim in Ai'izonawithout giving any actual instances. G. F. Breninger, however,collected a parasitized set of eggs at Phoenix, on May 2, 1896, a setnow in the collections of the California Academy of Sciences. Asrecorded in my first account (1929, p. 228), A. B. Howell found aparasitized nest about four miles southwest of Gadsden, on May 20,1918. The late J. Hooper Bowles wrote me that he had in his col-lections two more records, one collected at Mesa on May 14, 1919,and one from the same place on June 19, 1921. One nest contained2 eggs of the host and 2 of the parasite and the other held 3 eggs ofeach.J. T. Marshall, Jr. (in litt.) informed me that, in the mesquite woodsof the San Xavier Keservation, ten miles south of Tucson, Aiizona,he noted four parasitized nests of Abert's towhee. He wrote methat this bird usually started to nest before the cowbirds arrived inthe spring and that the early broods have a chance of coming to suc-cessful fruition without interference by the parasite. Another recordfrom Tucson is a parasitized set of eggs, taken in 1917 and now inthe Santa Barbara Museum of Natural History.The various records given above involve both races of the host,aberti and dumeticolus.
Rusty-crowned Ground SparrowMelozone kieneri (Bonaparte)J. Stuart Rowley (mss.) found that this sparrow frequently wasparasitized by the bronzed cowbird in Morelos, Mexico; but in onenest he also found an egg of the brown-headed cowbird, M.a. abscurus.The local race of the host is M.k. ruhricatum.
HOST RELATIONS OF PARASITIC COWBIRDS 153
Lark BuntingCalamospiza melanocorys (Stejneger)The lark bunting apparently is a fairly common local victim ofthe northwestern race of the brown-headed cowbird, M.a. artemisiae,but if the species is considered in a general, comparative way, it is arather infrequent victim. J. A. Allen (1874, pp. 58-59) observed thebird in the Dakotas and Montana and found that, "in a series of eight-een nests, five, or nearly one-third, contained eggs of the Cowbird,two even containing two each, and one had three; while out of twenty-nine nests of other ground-nesting prau'ie birds, collected at the sametime and over the same area, not one contained an egg of the Cow-bird . . . ." He concluded that the cowbird formed "no inconsider-able check upon the increase of this bird." Coues (1874, p. 164, and1878b, p. 597) \vi"ote that eggs of the cowbird frequently were foundin nests of the lark bunting, and Hoffman (1875, p. 172) noted a para-sitized nest in North Dakota.All of the foregoing information was included in ni}^ fu-st account(1929, p. 232). It is strange that, in the succeeding years, only oneadditional record has come to my attention: a parasitized set of eggstaken in McHenry County, North Dakota, on June 9, 1933, and nowin the Brandt Collection of the Carnegie Museum. When we considerthat the most recent of the earlier cases was prior to 1878, it is all themore surprising that supplementary information has not been forth-coming. This phenomenon cannot be blamed completely on thedropping off of interest in egg collecting, but, at the same time, there isno reason for thinking that the lark bunting has become immune tocowbird parasitism. Savannah SparrowPasserculus sandwichensis (Gmelin)The savannah sparrow is a very infrequent victim of the brown-headed cowbird. Although the geographic spread of the recorded in-stances of cowbird parasitism is extensive, there are no more than a fewrecords in any area, and in most there are only single or scattered re-ports. Twenty-eight records have been noted, distributed as follows:Alberta, Manitoba, New Brunswick, Ontario, Quebec, and Saskatche-wan in Canada; Colorado, Maine, Michigan, Montana, New York,North Dakota, Ohio, Oregon, and Utah in the United States. Therecords involve four races of the sparrow: labradorius in New Bruns-wick; ohlitus in Manitoba, Montana, North Dakota, and Wisconsin;nevadensis in Alberta, Saskatchewan, Colorado, Oregon, and Utah;savanna in Ontario, Quebec, Maine, Michigan, New York, and Ohio.Two races of the cowbird, ater and artemisiae, are involved.
154 U.S. NATIONAL MUSEUM BULLETIN 233The one record found for labradorius is a nest with 4 eggs of thesparrow and 1 of the cowbird, collected at Grand Menan, New Bruns-wick, on July 2, 1883, by G. M. Cheney; from him it passed into theJ. P. Norris collection.Of the race oblitus the following instances may be mentioned. F. S.Hersey collected a parasitized set of eggs at Lake Winnepegosis,Manitoba, on June 2, 1913; this set is now in the Bent collection inthe U.S. National Museum. Other cases were recorded by Coues(1878, p. 588) in Montana and North Dakota and by Barger (1940,pp. 91-94) in Wisconsin.Of the race nevadensis, mention should be made of two parasitizednests found in Alberta by T. E. Randall in addition to another nestfrom that area, all recorded by Horsbrugh (1915, p. 688); a number ofsimilar instances in Oregon was given by Jewett (1936, p. 46) and byGabrielson and Jewett (1940, p. 530) ; in Saskatchewan, by Bent (1908,p. 28) and by Ferry (1910, pp. 199-200). In Utah, Clarence Cottamfound a parasitized nest near Utah Lake, four miles west of Provo, onMay 17, 1928, and in Colorado a similar instance was found by E. R.Warren (1910, p. 36).A notable addition to the available data for the race savanna comesfrom southern Quebec, where Terrill (1961, p. 10) found 5 para-sitized nests out of a total of 140 occupied nests of this sparrow whichhe had examined over a period of nearly 60 years of field study. Mid-dleton (in Detroit Audubon Society, 1956, p. 92) found one such caseat Mt, Clemens, Alichigan, on June 2, 1954. Older records whichshould be mentioned here are Snyder and Logier (1930, pp. 194-195)in Ontario, Friedmann (1929, p. 218) in New York, and Vasicek (1935)in Ohio. The eastern race savanna has been known to rear the youngcowbird to the fledging stage.Even though we now have 28 records and undoubtedly others willbe found, it appears safe to say that the savannah sparrow is molestedinfrequently, that it is not of great importance in the economy of thebrown-headed cowbird, and that the parasite is not a serious factor inthe welfare of the sparrow.
Grasshopper SparrowAmmodramus savannarum (Gmelin)This secretive denizen of grassy fields is difficult to observe, and,as a result, its nests very seldom are discovered. Three races
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pratensis, perpallidus, ammolegus?however, have been found tobe parasitized by the brown-headed cowbu'd. The number of recordsis small, 11 in all, distributed from Manitoba in Canada to the "north-eastern United States," and Maryland, Ohio, Indiana, Michigan,Kansas, Nebraska, Texas, and Arizona. The race perpallidus is
HOST RELATIONS OF PARASITIC COWBIRDS 155
parasitized by two subspecies of the cowbird, artemisiae and ater;pratensis is molested by ater; and ammolegus, by ohscurus (one record,a parasitized nest from Ai'izona, now in the collections of the CarnegieMuseum).Considering the difficulty of finding the nests of this bird, Price'sexperience (1934, pp. 107-108) is exceptional. He examined about 100nests in Paulding County, Ohio, and found cowbird eggs in 2 ofthem. This is the only even slightly quantitative data available asto the frequency of parasitism on this host.A review of the actual records, all previously listed in my earliersummaries (1929, p. 219; 1931, p. 62; 1934, p. 110; 1938, p. 49),reveals that no one has ever attempted to study a parasitized grass-hopper sparrow: all that the cases show is that eggs of the parasitewere seen in nests of this bird. No one has jQi recorded this host asrearing a young cowbu'd, but there is no reason to assume that it cannot and does not do so. It seems probable, however, that the grass-hopper sparrow and the cowbird are of little importance to each otheras host and parasite. Baird's SparrowAmmodramus hairdii (Audubon)So little is known of the life history of this sparrow that it is notpossible to estimate the extent to which the bird is affected by theparasitism of the cowbird. There are only six records?from Mani-toba and North Dakota?and one without definite locality. Raine(1894, p. 71) reported a nest of Bau-d's sparrow with 2 eggs of its ownand 3 of the cowbird. No locality was given, but it was either inMontana or in some adjacent area of Canada. Alfred Eastgate wTOteme many years ago that he had found a parasitized nest in NorthDakota. L. B. Bishop collected two parasitized sets of eggs nearDevil's Lake, North Dakota. B. W. Cartwright wi-ote me that T. S.Roberts found a nest with 4 eggs of the sparrow and 2 of the parasitein northern Sargent County, North Dakota, on June 18, 1883. Cart-wright's co-worker, R. D. Harris, found eight nests of Bau'd's sparrowin Manitoba in 1931, one nest of which contained a cowbird egg inaddition to 3 of the sparrows. On July 14, Harris, watching anothernest from a blind, saw a female cowbird approach the nest at 4 : 50p.m. It inspected the blind but came within only two feet of the nest,which held young of the sparrow. The female Bau'd's sparrow re-turned and fed its young; then it saw and drove away the cowbird,after which it returned and began to brood the chicks.
LeConte's SparrowPasserherbulus caudacutus (Latham)LeConte's sparrow is known to be parasitized by the brown-headedcowbird in Alberta, Saskatchewan, and Minnesota. Although the
156 U.S. NATIONAL MUSEUM BULLETIN 23 3
actual records are still few in number, the fact appears that in suitablelocalities this bird may be a fairly common victim. In the Red Rivervalley, Kittam County, Minnesota, P. B. Peabody (1901, pp. 131-132)found 14 nests, of which 4 were parasitized; 3 of them containeda single cowbird egg apiece in addition to eggs of the host, and 1held a half-grown cowbird and 2 addled eggs of the sparrow. Inthe National Museum of Canada there is a parasitized set of eggs ofthis sparrow taken at Crane Lake, Saskatchewan, in 1895 by Wm.Spreadborough. Many jesirs later Ferry (1910, pp. 199-200) alsofound that LeConte's sparrow was parasitized in Saskatchewan, andA. D. Henderson informed me that he has noted this in Alberta aswell. Two races of the parasite are involved in these records, ater inMinnesota, and artemisiae in Saskatchewan and Alberta.
Henslow's SparrowPasserherbulus henslowii (Audubon)Henslow's sparrow is a bird of which relatively little is known as faras its relations with the brown-headed cowbird are concerned. Only afew records have come to my attention. Hathaway (1913, p. 555)found a parasitized nest in Rhode Island on May 28, 1911. E. J.Court informed me that, out of 7 nests found in southern Mary-land in 1932, 2 contained eggs of the cowbird, and that, out of about15 nests found in previous years, several had been victimized. Heconsidered Henslow's sparrow a locally common host. The late J. P.Norris wi'ote me that he had a set with a cowbird's egg, collected byCourt in Maryland on May 28, 1917. This probably is one of the
"several" referred to by Court. Stewart and Robbins (1958, p. 329)mentioned that they had learned of five cases of cowbird parasitism onthis sparrow in Maryland. These five are probably also among thosefound by Mr. Court. Hicks (1934, pp. 385-386) noted a parasitizednest in Franklin County, Ohio. In Michigan, Olsen (1931, p. 482)reported a parasitized nest found by Walkinshaw near Battle Creek.Neither Hyde (1939) nor Sutton (1959, p. 150) found any evidence ofcowbird parasitism on Henslow's sparrow m their studies in Michigan,which suggests that there this bird is only an occasional victim of thecowbird. At Hegewisch, lUinois, on June 19, 1932, G. J. Suthardcollected a parasitized set of this sparrow's eggs.The Michigan, Illinois, and Ohio records refer to the western, typicalrace of the sparrow, while the Rhode Island and Maryland instancesare of the eastern race, susurrans. The cowbird in all cases is typicalater.In spite of Court's experience in AIaryland,it is not possible, exceptlocally, to consider Henslow's sparrow as a frequent host of the parasite.Because of the relative scarcity and rather "spotty" local distribution
HOST RELATIONS OF PARASITIC COWBIRDS 157
of the sparrow and the general abundance of the cowbird, it appearsthat the former is less important in the economy of the parasitethan the latter is in that of the host.
Sharp-tailed SparrowAmmospiza caudacuta (Gmelin)The race nelsoni of this sparrow is included in the present survey onthe folloAving basis. Many years ago the late P. B. Peabody v/rote methat he remembered very clearly that one of his associates once found acowbird egg in a nest of Nelson's sharp-tailed sparrow. Peabody hadno wa}" of getting the exact data on this occurrence. No one else smcehas reported a case of cowbird parasitism on this species. It wouldseem, from the fact that the sharp-tail is a marsh bh'd, that probably itis usually unmolested by the parasite.
Seaside SparrowAmmospiza maritima (Wilson)The seaside sparrow is an unusual and rarel}^ imposed upon victimof the brown-headed cowbird. The latter ordinarily does not inhabitbracldsh or salt water marshes, where this sparrow lives, and, asa result, it rarely would have a chance to parasitize the bird. There isonly a single record for this sparrow (nominate race). Bagg andEliot (1937, p. 634, ftn.) stated that the seaside sparrow was recordedas a fosterer of the cowbird at Martha's Vinej'ard by ]\Irs. SethWakeman. In response to my inquiry, Mrs. Wakeman informed methat the record referred to a fledged cowbird being fed and attendedby a seaside sparrow. No young sparrows were observed with them.
Vesper SparrowPooecetes gramineus (Gmelin)The vesper sparrow is a fairly frequent victim of the brown-headedcowbird. About 70 records have been noted, involving two races ofthe sparrow, gramineus and confinis, and all three races of the cowbird.These records come frojn the following areas: Alberta, British Col-umbia, Quebec, and Saskatchewan in Canada; Colorado, the Districtof Columbia, Idaho, Illinois, Indiana, Iowa, Kentucky, ^Maryland,Michigan, Minnesota, Montana, Nebraska, New York, Ohio, Texas,Washington, and Wyoming in the United States. The race gramineusis parasitized by ater; confinis, by artemisiae and obscurus. In nolocale is the vesper sparrow one of the commonest fosterers althoughEaton (1914, p. 227) has listed it as such in New York. In Ohio,Hicks (1934) found 112 nests, of which 9 were parasitized; in southernQuebec, Terrill (1961, p. 10) found 74 nests, of which 3 had cowbirdeggs. There is no need to repeat here the various records of geo-
158 U.S. NATIONAL MUSEUM BULLETIN 233
graphic interest since they are given in my previous accounts (1929,pp. 217-218; 19-34, p. 111).The vesper sparrow has been known to rear the young of the para-site to the fledging stage. Lark SparrowChondestes grammacus (Say)The lark sparrow is a relatively uncommon host of the brown-headed cowbird. Thirty records have been noted, involving all threeraces of the cowbird and two of the sparrow, grammacus and strigatus.The typical race, grammacus, is known to be parasitized by ater andartemisiae; the race strigatus is molested by ater, artemisiae, andobscurus. The records are distributed among the following states:California, Iowa, Kansas, Louisiana, Minnesota, Montana, Nebraska,North Dakota, Oklahoma, South Dakota, and Texas.In his study of the lark sparrow in the upper Ohio valley, Brooks(1938b, p. 197) noted that the comparatively open nests of this speciesseemed well suited for the cowbird's requirements; he concluded that,in some areas, there must be a severe loss in numbers of the sparrowbecause of the activities of the cowbird. I have failed to detectevidence for a marked effect anywhere, and Brooks did not supply itfor the region he studied. In Kansas, R. F. Johnston (in litt.) in-formed me of 6 parasitized nests out of a total of 22 found?an inci-dence of parasitism of about 25 percent.
Rufous-winged SparrowAimophila carpalis (Coues)The rufous-winged sparrow is a poorly known bu"d and the factthat little is on record concerning its relations with the brown-headedcowbird is not surprising. So little information exists that it all maybe repeated here. Henshaw (1875, p. 292) wrote that "its nest appearsto be the one most favored by the Dwarf Cow Bunting ... as therecipient of its eggs." Bendire (1895, p. 292) made a similar state-ment, possibly based on the earlier one by Henshaw. In the U.S.National Museum were two sets of Aimophila carpalis eggs, each witha cowbird egg, reported to have been collected by Bendire, butthey no longer can be located. They may have been the actual basisfor Bendire's statement. A third set in the U.S. National Museum,also with a cowbird egg, was collected by H. P. Attwater at San An-tonio, Texas, on June 5, 1899.Davie (1889, p. 119), commenting on Bendire's experiences with thissparrow, wrote that "about one half of the nests found contained oneor more eggs of the Dwarf Cowbird." Unfortunately, no indicationis given as to the total number of nests found. J. T. Marshall, Jr.(in litt.), informed me that, in the mesquite woods of the San Xavier
HOST RELATIONS OF PARASITIC COWBIRDS 159
Reservation, ten miles south of Tucson, Ai'izona, he found two para-sitized nests, and that, in the University of Arizona collection, there is
still a third such case, collected in the same area by P. J. Gould.
Bachman's SparrowAimo-phila aestivalis (Lichtenstein)This is an uncommonly victimized sparrow; only the followingfew records have been noted.E. S. Woodruff (1907, p. 349) found a nest in southern Missouri onMay 27, 1907, containing 2 sparrow and 3 cowbird eggs. This recordrelates to the race A.a. illinoensis of the sparrow.Near Bardstown, Kentucky, Blincoe (1921, p. 100) on May 2 founda nest which at the time contained 1 sparrow egg. The next day thenest held 1 cowbird and 2 sparrow eggs ; two days later all the eggs haddisappeared, apparently having been removed by some predator. Ina later paper the same author (1925, p. 412), discussing the cowbird atBardstown, states that its eggs were found in nests of Bachman'ssparrow and the indigo bunting. It is not clear whether or notBlincoe had seen additional instances of cowbird parasitism on Bach-man's sparrow in the four years between the two reports.Brooks (1938a, p. 100) reported a nest with 3 eggs of the sparrow and1 of the cowbird at French Creek, West Virginia.The Kentucky and West Virginia records refer to the race A.a.baclimani of the host. In all the above cases the nominate race ofthe parasite is involved. Cassin's SparrowAimophila cassinii (Woodhouse)Cassin's sparrow appeal's to be an infrequent victim of the brown-headed cowbird. The known records are few enough to be listed here.R. W. Quillen wrote me that at San Antonio, Texas, Cassin's spar-row rarely was bothered by the parasite, probably because the formerconcealed its nests so well. This, however, might explain why thenests were not found more often by human eyes than by the cowbird.Quillen found only three parasitized nests. The late J. H. Bowleswrote me that he had in his collection a similar set from San Antonio;the U.S. National Museum has two more sets from the same place,collected by H. P. Attwater. Finally, E. J. Court informed me thathe also found this sparrow to be victimized near San Antonio. Nye(in litt.) informed me that he collected a parasitized set of eggs nearLoma Alta Lake, nine miles north of Brownsville, Texas, on June 21,1943. In the files of the U.S. Fish and Wildlife Service there is therecord of a parasitized nest found 30 miles south of Vernon, Texas,on May 2, 1930, by R. L. More. All of these records refer to the small
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race of the cowbird, M.a. ohscurus. In McLennon County, Texas,Strecker (1927, p. 47) found this sparrow to be a host of the easterncowbird, M.a. ater. Black-throated SparrowAmphispiza hilineata (Cassin)The black-throated sparrow has been recorded only a few times as avictim of the brown-headed cowbird. Quillin and Holleman (1918,p. 42) found it parasitized in Bexar County, Texas, where they con-sidered the bird to be a common victim. Merrill (1878, p. 130) notedit as a cowbird host at Brownsville, Texas. Many years later, I (1925,p. 551) also found it to be imposed upon there by the parasite. Inthe same area I was told by the late R. D. Camp that this sparrow wasthe commonest victim of the cowbird early in the season before manyother birds began to nest. Another record from Brownsville, a set of4 eggs of the sparrow and 2 of the dwarf cowbird, taken on June 16,1913, is now in the collections of the Western Foundation of VertebrateZoology. In the U.S. National Museum there is a parasitized set ofeggs taken at Eagle Pass, Texas, on June 3, 1902, by Nelson andGoldman. F. C. Nye, Jr., (in litt.) found another parasitized nesteast of Laredo, Texas, on June 11, 1942, and still another near the newdam on North Concho River, Tom Greene County, Texas, on June 11,1953. All but the last of the Texas observations refer to the nominaterace of the sparrow, A.h. hilineata; the latter report involves the raceA.h. opuntia. At Tucson, Arizona, Scott (1887, p. 22) found eggs ofthe cowbird in nests of the western race, A.b. deserticola, and Bendire(1895, p. 443) also reported a parasitized nest in the same place.
Sage SparrowAmphispiza belli (Cassin)The sage sparrow is a very uncommon victim of the brown-headedcowbird. Only a single record has come to my notice. In FremontCounty, Idaho, Rust (1917, pp. 38-39) found a nest of this sparrow,race A.b. nevadensis, with 1 egg of the sparrow and 2 of the cowbird,race Al.a. artemisiae. White-winged JuncoJunco aikeni RidgwayThe white-winged junco was found to be a victim of the brown-headed cowbird, race Al.a. artemisiae, in southeastern Montana.A. H. Miller (1948, p. 92) discovered two parasitized nests in theopen pine woods of Powder River Count}^, near Otter, in late June,1947. One of the nests contained 1 egg and one young each of thehost and the parasite; the other held 2 junco eggs and two youngcowbirds. No other instances of cowbird parasitism on this birdhave been noted.
HOST RELATIONS OF PARASITIC COWBIRDS 161
Slate-colored JuncoJunco hyemalis (Linnaeus)The slate-colored junco is an infrequently reported host; probablyit is molested very slightly b}^ the brown-headed cowbird. Eighteeninstances have come to my attention. Three races have been re-corded as victims: cismontanus in British Columbia; carolinends inVirginia and West Virginia; hyemalis in Alberta, Saskatchewan, On-tario, Quebec, Nova Scotia, New York, Pennsylvania, and Ohio.These records involve two races of the parasite : artemisiae from Sas-katchewan to British Columbia and ater in all the other areas. Bothcismontanus and hyemalis have been known to rear young cowbirds.In the Peace River District of British Columbia, Cowan (1939, p.59) found that no fewer than four out of five junco nests which wereobserved were parasitized?evidence which suggests that in thisregion the bird is a commoner host than it has been found to be else-where. The Nova Scotia record is of interest as a far northeasternreport. Mills (1957, pp. 25-27) noted that E. C. Allen found afledgling cowbird attended and fed by juncos near Halifax, NovaScotia, on July 17, 1933.Terrill (1961, p. 10) made one observation which may imply agreater frequency of parasitism than the actual records have indicated.He found the junco to be a "very close sitter . . . not readilyflushed from its well-concealed nest, so that few nests are found. . . ."
Oregon JuncoJunco oreganus (Townsend)This junco has been recorded as a cowbird victim onl}?- a few times tomy knowledge. In British Columbia, Cowan (1939, p. 59) found aparasitized nest in the Peace River district, and Schultz (1958, p.435) reports that Davidson saw a young cowbird of the northwesternrace, M.a. artemisiae, attended by Oregon juncos at Victoria, BritishColumbia. Still another report from that province, sent to me fromthe files of the British Columbia Nest Records Scheme at the Univer-sity of British Columbia, concerns a nest with 4 eggs of the junco and1 of the cowbu'd, found 35 miles south of Vernon, Okanagan Lake,June 17, 1959. The junco breeding in British Columbia is of therace J.o. montanus. At Berkeley, California, Johnston (1960, p. 137)observed a fledgling cowbird being attended and fed repeatedly by afemale Oregon junco (race pinosus).
Chipping SparrowSpizella passerina (Bechstein)The chipping sparrow is one of the commonest victims of thebrown-headed cowbird. Over 600 records have been noted from
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Alberta, British Columbia, New Brunswick, Ontario, Quebec, andSaskatchewan in Canada to the following of the United States: Ark-ansas, California, Colorado, Connecticut, Delaware, the District ofColumbia, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland,Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska,New Jersey, New Mexico, New York, North Dakota, Ohio, Oklahoma,Oregon, Pennsylvania, Rhode Island, South Dakota, Tennessee,Texas, Virginia, Washington, West Virginia, and Wisconsin.Three races of the sparrow are involved
?
passerina, arizonae,boreophila?plus all three races of the cowbird. Typical ater is knownto parasitize passerina and arizonae; artemisiae is a parasite onboreophila; obscurus molests arizonae. Strangely, this last combina-tion has been recorded but once, to my knowledge; a parasitized nestwas found by Talmadge (1948, p. 273) at Hooper, Humboldt County,California, in June, 1948. To the recently described and officiallyrecognized race boreophila should be referred the records formerlyassigned to arizonae from Alberta, British Columbia, Saskatchewan,and the recent records published by King (1954, pp. 150-154) fromWashington,Not only is the chipping sparrow a very frequent victim?in thetotal number of loiown instances of cowbird parasitism?but it seemsto be one of the main fosterers in almost every locality. In Ohio,Hicks (1934) found 115 nests of this bird, of which 60, or more thanhalf, were parasitized. In Maryland, Stewart and Robbins (1958,p. 329) listed 18 records. In southern Quebec, Terrill (1961, p. 10)reported cowbird eggs in 16 out of 138 nests.In my own field studies in central New York, over a dozen caseswere observed. The percentage of parasitized nests of this speciesin that region was not as high as it was for some other bu'ds, such asthe phoebe, the red-eyed vireo, and the redstart; judging solely frommy own local records, the percentage was about 15. This agreesroughly with Terrill's experience in Quebec but falls far short of Hicks'sOhio data. A surprisingly low incidence of parasitism was reportedin Michigan by Walkinshaw (1949, pp. 193-205), who found thatonly 3 nests had been molested out of a total of 66 observed nests
?
less than five percent. An even lower degree of parasitism wasreported in an adjacent area by Sutton (1960, p. 50). In the EdwinS. George Reserve of southeastern Michigan, he found only a singleparasitized nest out of 38 observed. Sutton suggested that, sincemost chipping sparrow nests in that area were well hidden in thedense foliage of red cedars, such a phenomenon might be a factor inreducing the incidence of parasitism.Not only is this sparrow a frequent victim, but it seems to beuniformly tolerant of the parasitic eggs; it has been known, on many
HOST RELATIONS OF PARASITIC COWBIRDS 163
occasions, to rear the alien young. Nuttall (1840, p. 105) recordedwatching a chipping sparrow remove its dead young from a nestwhich contained a healthy young cowbird. I know of no case of achipping sparrow attempting to bury a cowbird egg under a newnest-lining, and I am not aware of any instances of nest desertionwhich could be ascribed to the presence of cowbird eggs. No oneyet has made a statistical survey of nesting success in the chippingsparrow, a survey against which to appraise the effect of cowbirdparasitism, as Hofslund has done with the yellowthroat or Nice withthe song sparrow. Clay-colored SparrowSpizella pallida (Swainson)The clay-colored sparrow is a frequent victim of the brown-headedcowbird in Alberta. The late William Rowan told me that he hadcollected a series of nearly 20 parasitized sets of eggs near Edmonton,Rowan and T. E. Randall considered the clay-colored sparrow thecommonest victim in Alberta.Apart from this one area, the sparrow also has been found to beimposed upon by the parasite in British Columbia (two records, nowin the collections of the Carnegie Museum), Saskatchewan, Montana,North Dakota, Minnesota, and Wisconsin. The North Dakotarecord, previously unpublished, consists of a set of 4 eggs of thesparrow with 1 of the cowbird, taken at Stump Lake on June 1, 1901,by A. C. Bent and now in the U.S. National Museum,Near Endersley, Saskatchewan, Fox (1961, p. 223) studied ninenests of this sparrow in one season. Of these, eight were parasitizedby the brown-headed cowbu-d. In six of the eight, the parasitic eggswere laid before the host had begun to incubate, but in one nest thecowbird egg was deposited after the four young sparrows had hatched.Three of the nests were deserted after they had been parasitized. Innone of the eight nests did any of the cowbird eggs hatch. No clay-colored sparrows hatched in any of the nests which had been par-asitized by the cowbird before the host eggs hatched.The claj^-colored sparrow has been known to rear the young parasite(Raine, 1894, p. 120; Sparkes, 1952).All in all, some 50 records of parasitism have been noted. Theyinvolve two races of the brown-headed cowbird; typical ater inWisconsin and Minnesota; artemisiae westward from North Dakotaand Saskatchewan. Brewer's SparrowSpizella breweri CassinBrewer's sparrow is a poorly knowm victim of the bro%vn-headedcowbird. It has been recorded in this capacity only in Wyoming
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and New Mexico. No new information has been acquired since myfirst (1929, p. 223) account, which may be summarized as follows.Jensen (1923, p. 4G1) wrote that he had found cowbird eggs innests of this sparrow in northern Santa Fe County, New Mexico,but he gave no details. What may be one of Jensen's records is aparasitized clutch of eggs, taken on June 7, 1919, and now in thecollections of the Western Foundation of Vertebrate Zoology. Inthe files of the U.S. Fish and Wildlife Service there is a field note byMerritt Gary from the Upper Green River Valley of W^yoming; thenote reports a recently fledged cowbird attended and fed by Brewer'ssparrow at Gora, Wyoming, on August 8. Another field note, byH. E. Anthony from the same area and with the same date, probably isbased on the identical case.The records refer to the typical race of the sparrow, to the north-western race, artemisiae, of the cowbird in Wyoming, and to thenominate race, ater, in New Mexico.
Field SparrowSpizella pusilla (Wilson)The field sparrow is a frequent victim of the brown-headed cowbu'd.Over 125 records have been noted, distributed from Quebec in Ganadato the following of the United States: Gonnecticut, Illinois, Indiana,Iowa, Kansas, Maryland, Massachusetts, Michigan, Missouri, NewJersey, New York, Ohio, Oklahoma, Pennsylvania, Rhode Island,South Dakota, Tennessee, Virginia, and Wisconsin.Almost all of the records refer to the typical, eastern race of thefield sparrow. The lack of additional data for the western race,arenacea, probably reflects a lack of human observation rather thanan actual difference in the lives of the sparrow and the cowbird inthat area from western Oklahoma to the Dakotas and Montana.In Ohio, Hicks (1934) found 159 nests of this sparrow, of which 51contained eggs or young of the cowbird?a notably high percentageof parasitism. In Iowa, Anderson (1907, pp. 297-300) considered thefield sparrow one of the two most parasitized birds; a similar con-clusion was made in Ohio by Dawson (1903, p. 15).A recent study by Walkinshaw (1949) in Galhoun Gounty, Michi-gan, has given new insight into the host-parasite relations of the fieldsparrow and the brown-headed cowbird. Eggs of the latter (appar-ently from one individual!) were laid in 20 field sparrow nests, ofwhich 15 were deserted when the parasite laid its own and removeda host egg. At least 17 field sparrow eggs and four young disappearedfrom 16 nests, presumably removed by the cowbird. It follows fromthis that, at times and in places such as Galhoun Gounty, the cowbirdmay be a very serious factor in the welfare of the field sparrow. How-
HOST RELATIONS OF PARASITIC COWBIRDS 165
ever, the frequency with which this sparrow is molested must varyfrom time to time ; m an earher study, the same observer (Walkinshaw,1936) noted that, out of 70 nests of the field sparrow, only four con-tained eggs of the cowbird, whereas, in only 12 nests found in 1935,four were parasitized. All but one of the parasitized nests weredeserted by the sparrows.In the nearby Edwin S. George Reserve, Sutton (1960, pp. 57-58)found 59 nests of the field sparrow, of which 11 were parasitized.However, he noted that he had never seen a fledgling cowbird attendedby field sparrows, and he concluded that, although parasitism appar-ently cuts down sharply the percentage of nest-success for the host,it does so without producing any parasitic young. In Marylandand the District of Columbia, Stewart and Robbins (1958, pp. 329,363) listed 11 cases of parasitism but they recorded data on some 265field sparrow nests.As many as 5 cowbird eggs have been reported from a single nesttogether wdth 2 of the field sparrow.The field sparrow quite often is tolerant of the cowbird eggs andhas been known on several occasions to rear the young parasites tothe fledgling stage. Walkinshaw's data, noted above, seems to haveinvolved an unusually intolerant group of bhds.Two records from South Dakota refer to the western race, arenacea,of the sparrow and to the race artemisiae of the cowbhd. All theother records involve the nominate race of each bird.
Black-chinned SparrowSpizella atrogularis (Cabanis)This little known bird has been recorded only twice as far as IIniow as a victim of the dwarf race of the bro'WTi-headed cowbird.In the files of the U.S. Fish and Wildlife Service there is a record byStokely Ligon reporting a parasitized nest which was found 18 milesabove Santa Rosa, New Mexico, on July 6, 1913. The sparrow thereis the race evura. Bent (1958, p. 454) noted that Hanna collected twoparasitized nests in San Bernardino County, California. The localrace of the sparrow is cana.White-crowned SparrowZonotrichia leucophrys (Forster)The white-crowned sparrow is imposed upon infrequently b}^ thebrown-headed cowbird. There are only a few records, which areoutlined below. Rust (1917, pp. 37-39) found a nest with 4 eggs ofthe sparrow and 1 of the cowbird in Fremont County, Idaho. Twoparasitized nests were found at Okotoks, southern Alberta, one byLings (Friedmann, 1949, p. 161) on June 11, 1930, the other by
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Beaurre on June 8, 1907. The latter set is now in the Koyal OntarioMuseum of Zoology at Toronto.At Potsdam in northern New York, Keclney (1869, p. 550) foundon May 15, 1868, the two-storied nest of a white-crowned sparrowcontaining the single egg of a cowbird under the second nest floorplus 2 more cowbird eggs and 3 sparrow eggs in the new nest above.These were being incubated by the sparrow when found ; on blowing,they proved to be well advanced in incubation.Barnes (1918, p. 109) recorded a set of white-crowned sparroweggs with 1 of the cowbird, but, unfortunately, he gave neither datenor locality.The Idaho and Alberta records relate to the race oriantha of thesparrow and artemisiae of the cowbird; the New York instance, totypical leucophrys and to typical aier.
White-throated SparrowZonotrichia albicollis (Gmelin)The white-throated sparrow is generally an infrequent host ofthe brown-headed cowbird, but in southern Quebec it appears to bea regular and not uncommon victim. In the course of nearly 60years of field observation, TerriU (1961, p. 10) found the astonishingnumber of 507 nests of this sparrow within a limited area of southernQuebec; of these, 20, or 4 percent, had been parasitized by the cow-bird. While the percentage of parasitism was relatively small, thetotal number of observed cases of parasitism is slightly more thanaU the other reported instances I have been able to gather. (Duringthe same long period of years, Terrill found 481 nests of the songsparrow, of which 62, or 12.7 percent, contained eggs of the cowbird.)Of the 20 most frequently victimized host species in that area, onlythe goldfinch was less often victimized (7 nests, out of 318 examined,or 2.2 percent).All in all, some 36 records have come to my notice. Apart fromsouthern Quebec, the white-throated sparrow has been found to bevictimized in Itaska County, Minnesota, in Michigan, by A. R.Cahn (1920, p. 116; 1918, p. 497), and in Wisconsin, by Robbins(1949). Rowan (1922, p. 229) found this sparrow rearing a youngcowbird at Indian Bay, Manitoba. Snyder and Logier (1930, pp.194-195) found a parasitized nest in York County, Ontario. Har-rington and Beaupre collected other parasitized nests in Ontario,which are now in the Royal Ontario Museum. J. D. Carter (1906,p. 32) reported a nest in Monroe County, Pennsylvania. Hooperand Hooper (1954) noted a fledgling cowbird being fed by a white-throated sparrow in the Somme district, Saskatchewan. T. E. Ran-
HOST RELATIONS OF PARASITIC COWBIRDS 167
dall and A. D. Henderson wrote me of at least seven parasitized nestsin Alberta.The records from Alberta, Saskatchewan, and Manitoba refer tothe race artemisiae of the cowbird; the others, to ater.
Fox SparrowPasserella iliaca (Merrem)The fox sparrow is an infrequent victim of the brown-headed cow-bird. Only in one place has anj^one considered it a common host;Saunders (1911, p. 40) wrote that in Gallatin County, Montana,
"Mr. Thomas found the eggs and young quite commonly in the nestsof the Slate-colored Sparrow." Ridgway (1887, p. 501) recorded aparasitized nest at Parley's Park, Wasatch Mountains, Utah, onJune 23, 1869. The late J. H. Bowles wrote me years ago that afriend of his collected several sets of fox sparrow eggs with cowbirdeggs near Spokane, Washington. Bendire (1889, p. 113) noted acowbird's egg in a fox sparrow's nest at Palouse Falls, southeasternWashington, on June 18, 1878. Street (Houston and Street, 1959,p. 176) found another parasitized nest at Nipawin, Saskatchewan.J. B. Hurley (in litt.) found a nest with 2 eggs of the sparrow and 1of the cowbird, five miles southeast of Sesters, Deschutes County,Oregon, on May 16, 1960. In the collections of the Santa BarbaraMuseum of Natural History there is a parasitized set of eggs collectedon June 9, 1922, at Mammoth Lakes, Mono County, California.These few records are all that I have noted. They refer to thenorthwestern race of the cowbird, M.a. artemisiae, and to the followingraces of the fox sparrow: zaboria in Saskatchewan; olivacea in Wash-ington; schistacea in Gallatin County, Montana; swarthi in theWasatch Mountains, Vtah;fulva in Oregon; and monoensis in MonoCounty, California. Lincoln's SparrowMelospiza lincolnii (Audubon)This sparrow has been recorded as a cowbird victim only a smallnumber of times. S. S. Stansell, A. D. Henderson, and T. E. Randallinformed me independently of parasitized nests, six in number, whichthey had found in Alberta. Dr. Ian McTaggert Cowan wrote me ofa parasitized nest found at Elk Island Park, Alberta, the notes onwhich are in the files of the University of British Columbia. Thelate J. H. Bowles wrote me that he had in his collection a parasitizedset of eggs taken at Kalevala, Manitoba, on June 6, 1920. G. Ban-croft informed me of set found in Monroe County in northern NewYork on June 1, 1903. Street (Houston and Street, 1959, p. 195)found a nest at Nipawin, Saskatchewan, on June 3, containing only630590?63 12
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1 egg of the sparrow; two days later it held 2 sparrow eggs and 2 cow-bird eggs; and two days later, again, it held 3 cowbird eggs, no sparroweggs, and the shell of another cowbird egg outside but near the nest.The New York record refers to the eastern race of the cowbird, M.a.ater; the others, to M.a. artemisiae. All refer to the typical race ofthe sparrow. Swamp SparrowMelospiza georgiana (Latham)The swamp sparrow is generally an uncommon victim of the brown-headed cowbird. A number of authors have mentioned it as a hostwithout giving any details. Bendire, Davie, and others of the old
"egg collectors" have made such statements, but the actual recordswhich have been found are relatively few. Although the cowbirdfrequents marshes during migration, it tends to leave marsh nestsalone. At Ithaca, New York, where both the swamp sparrow and thecowbird are common, there were no records of parasitism on thespecies.This sparrow has been found by Ferry (1910, pp. 199-200) to be amolothrine fosterer in Saskatchewan; in Alberta, by Stansell (in litt.);in Ontario, by several observers (eggs in museums of Toronto andOttawa); in Minnesota, by Currier (1904, p. 37); in Wisconsin, byGunderson (1948); and in Michigan, by Cook (1893, p. 88) and Berger(1951). There are other records, mostly of parasitized sets, the dataof which are not available to me since they were in collections whichhave been dispersed. In Michigan, Berger (1951, p. 28) reported anunusual degree of parasitism on the swamp sparrow: he observed fivenests, four of which had been victimized by the cowbird.Although the swamp sparrow appears to be a rather uncommonvictim of the brown-headed cowbird in most areas where the two existtogether, it has been found to be a frequent and submissive host insouthern Quebec. Here, L. M. Terrill (1961, p. 10), between 1897and 1956, found 322 nests of the swamp sparrow, of which 34, orroughly 10 percent, contained eggs of the cowbird. He wrote thatthe swamp sparrows in his area nested chiefly in sedgy tussocks amongsmall willows in shallow water. Apparently this environment wasmore acceptable to the cowbirds than are the usual marshy areas.The Alberta and Saskatchewan records refer to the race ericrypta ofthe sparrow and artemisiae of the cowbird; the Quebec, Minnesota,and Michigan records involve the nominate race of both host andparasite. Song SparrowMelospiza melodia (Wilson)The song sparrow is one of the most frequent, if not the mostfrequent, victim of the brown-headed cowbird. Since the former is
HOST RELATIONS OF PARASITIC COWBIRDS 169
sympatric with the latter throughout the entire breeding range of theparasite, it is parasitized probably more often and over a greater areathan any other bird. The total number of records is very great.After accumulating over 900, I stopped noting them except for recordsof special interest. The data came from every province of Canadaand every state of the United States included in the breeding rangesof both birds, illl three races of the parasite are involved, and no lessthan 17 races of the song sparrow: melodia, atlantica, euphonia, juddi,montana, inexpectata, merrilli, Jisherella, morphna, cleonensis, gouldii,samuelis, pusillula, heermanni, cooperi, fallax, and saltonis. So far,none of the purely Mexican races have been reported as fosterers ofthe cowbird, but this fact is probably due more to a lack of humanobservation than to any actual immunity of the bird to cowbirdparasitism.There is no need to detail actual instances for the various races ofthe song sparrow since such cases already have been given in my earliersummaries (1929, pp. 225-226; 1934, pp. 113-114; 1938, p. 50; 1943,p. 356; 1949, pp. 161-162). However, a few additional records ofinfrequently reported races of the host species should be mentioned.Talmadge (1948, p. 273) found a nest of the subspecies cleonensis witli3 eggs of the sparrow and 1 of the dwarf cowbird at Mad River Bar,Humboldt Co., Cahfornia, in June, 1947. M.m. fallax was reportedas a cowbird host in Wyoming by McCreary (1957, p. 94). M.m.morphna was seen feeding a fledgling cowbird at Comox, BritishColumbia, by W. R. Goodge and Z. M. Schultz (1956, p. 404). M.m.saltonis is represented by five parasitized sets of eggs, all from Yuma,Arizona, and now in the collections of the University of Arizona(J. T. Marshall, Jr., in Utt.). For M.m. samuelis, two instances ofcowbird parasitism (Johnston, 1956, p. 29; 1960, p. 138) are of interestas evidence of the cowbird's laying in nests within salt marsh vegeta-tion. Johnston noted that, in the San Francisco Bay marshes, thesong sparrows built their nests within lumps of pickleweed (Salicorniaambigua), cordgrass {Spartina foliosa) , or gumplant (Grindelia cunei-folia) . The two nests that had been parasitized were found in gumplantshi'ubs, which, of the three plants, is the most similar to the nonswampvegetation of the cowbird's more usual habitat. For M.m.inexpectata, two additional instances of cowbird parasitism in theVanderhoof region, British Columbia, were recorded by Munro (1949,p. 113).In recent years, not only many hundreds of additional cases,but also much more quantitative data on the host-parasite relationshave become available. Hicks (1934) found that 135 out of 398 nests(34 percent) of this sparrow were parasitized in Ohio. Nice (1937a,pp. 196-201; 1937b, p. 159), also in Ohio, reported that 98 out of
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223 nests (43.9 percent) contained eggs or young of the cowbird(the annual percentage varied from 24.6 to 77.7 percent). Sixty-sixunparasitized nests raised an average of 3.4 song sparrows whereas28 successful but parasitized broods averaged only 2.4 song sparrows,indicating that each cowbird was reared at the expense of one songsparrow. In one instance Nice (1930) found that a pair of songsparrows raised a young cowbird together with five of then* ownyoung. Apparently here no loss of sparrows was involved. Inanother paper, Nice (1936) noted that, in all the song sparrow nestswhich she had watched during a period of five years, adult cowbirdsremoved 5.7 percent of the song sparrow eggs and nestling cowbirdscrushed or starved 3.5 percent of the young sparrows. The cowbirdeggs did not succeed as well as those of the host; only 30.7 percent ofthe former, but 35.8 percent of the latter, reached the fledging stage.In 1930-31 there was one female cowbird to about 11.5 pairs of suitablehosts, but in 1934-35 there was one to 8.6 pairs of suitable victims.Of all song sparrow nests parasitized, Nice reported that 70 percentheld a single cowbird egg each, 27 percent held 2 each, and 3 per-cent held 3 each. In the area of study?-near Columbus, Ohio^?^thesong sparrow was the most important host of the paeasite. Norris(1947, p. 90) noted that 11 out of 27 nests (40.7 percent) in Pennsyl-vania were parasitized, and Berger (1951a, p. 30) recorded 37 outof 59 nests found in Michigan (62.7 percent). In the Detroit area,as reported by the Detroit Audubon Society (1956, p. 90), the averagefrequency of parasitism of the song sparrow was 40.1 percent of allthe nests found: in 1950, 41 nests were found, of which 20, or 49percent, were parasitized; in 1951, 18 nests were located, of which8, or 44 percent, were parasitized; in 1954, 39 nests were found,of which 14, or 35.9 percent, contained eggs or young of the brown-headed cowbird. These figures are considerably below Berger'sfigures, which included the Ann Arbor section.One is drawn toward attempting an over-all estimate of the fre-quency with which the song sparrow is victimized, but to do sowith any feehng of accuracy is difficult because the incidence ofparasitism appears to vary geographically (or, at least, the frequencywith which it is reported varies). From this it follows that theover-all percentage depends on how many geographically differentareal data are used in the estimation. For example, if we puttogether, as a geographical unit, a group of studies made in Penn-sylvania (Norris, 1947), Ohio (Hicks, 1934; Nice, 1937), and Michigan(Berger, 1951; plus Detroit Audubon Survey Kecords), we come upwith a total of 323 parasitized nests out of 804 nests observed, ora httle over 40 percent. On the other hand, in southern Quebec(TerriH, 1961, p. 11), out of 486 nests observed, only 62, or 12.7
HOST RELATIONS OF PARASITIC COWBIRDS 171
percent, were parasitized. If we put all these studies together,we get a total of 382 out of 1,285 nests victimized, or 29 percent.This figure becomes yet smaller when we attempt to include datafrom other parts of the continent.An interesting case, reported by Berger (1951b), involves 10consecutive nests of a single color-banded song sparrow over a periodof three seasons, from 1948 through 1950. In seven of these nests,18 cowbird eggs were laid, plus at least 27 sparrow eggs. One cowbirdand six sparrows were fledged from all 10 nests. In the summerof 1949, the sparrow had no fewer than five consecutive nests; andin 1950, four. It would seem that, if none of these nests had beeninterfered with, there would not have been sufficient time for fouror five in one season. This, therefore, must be kept in mind whenattempting to evaluate the damage to the host which is done bythe cowbird. It appears that one of the effects of parasitism maybe to increase the "nesting potential" of the host. (See also thediscussion of Walkinshaw's field sparrow data, p. 164.)As many as 7 cowbird eggs have been found in a single nest ofthis sparrow; there are numerous records of 3, 4, and 5 parasiticeggs to a nest. Occasionally, but not often, song sparrows maypartly bury cowbird eggs by building a new nest lining over them
?
if the ahen egg is laid before any eggs of the host.Salmon (1933, p. 100) has reported seeing a song sparrow feedingthree fledghng cowbirds; no young sparrows were mentioned. Lees(1939, p. 121) recorded that near Wetaskiwin, Alberta, he watched asong sparrow feeding no less than five young cowbirds. This mustbe a record of fledgling success for any host species.
McCown's LongspurRhynchophanes mccownii (Lawrence)McCown's longspur is not well known as a host of the brown-headed cowbird since relatively few observers have studied it. Raine(1894, p. 120) listed it as a cowbird victim (race M.a. artemisiae) asdid Bendu-e also, the following year, possibly on the basis of Raine'sstatement. Many years later, about 1921, Alfred Eastgate informedme that he had found this longspur to be a victim in North Dakota.Later still, the late L. B. Bishop \vrote me that, out of three nestsof this species found near Cando, North Dakota, two contained eggsof the cowbird m addition to those of the longspur. S. J. Darcussent me data on one record from Saskatchewan?a parasitized nesthe found at Cypress Hill on June 7, 1920. No other records havecome to my attention. In his study of McCown's longspur, Mickey(1943) found no evidence of cowbird parasitism near Laramie, Wyo-ming, nor did DuBois^(1935, 1937) in Montana.
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Chestnut-collared LongspurCalcarius ornatus (Townsend)This longspur is probably a not uncommon local victim of the north-western race of the brown-headed cowbird. The paucity of recordsseems to be due to a scarcity of observers in the breeding range of thehost. In the country around Grand Forks, North Dakota, R. P.Currie (1892, p. 243) observed that the nests of the chestnut-collaredlongspur frequently were victimized; 1, 2, or 3 cowbird eggs werediscovered in various nests. Raine (1894, p. 120) wrote that he foundthis species to be victimized, and Alfred Eastgate informed me thathe had also found this to be the case in North Dakota. There arethree parasitized sets of eggs collected by Elmer T. Judd from TownesCounty, North Dakota, in the U.S. National Museum. In thecollections of the Western Foundation of Vertebrate Zoology there isanother set from Townes County, taken on May 27, 1894.I am informed by Professor R. E. Ware that, among other speci-mens in the Harllee collection at Clemson College, there is a para-sitized set of eggs of this longspui", taken on June 19, 1933, at Deering,North Dakota, by George C. Wliithey. This is one of the very fewrecent records of the bird as a cowbird fosterer, but, as noted above,the chestnut-collared longspur had been reported as a frequent hostat Grand Forks, North Dakota in the 1890's. North Dakota is theonly area where this longspur has been observed repeatedly as acowbu'd victim.Mr. S. J. Darcus wi"ote to me that he had found a parasitized nestat Cypress Hills, Saskatchewan, on June 1, 1920.
Bronzed CowbirdTangavius aeneus (Wagler)DiscussionThe following catalog of the known hosts of the bronzed cowbirdincludes 52 species, or, with subspecies, 64 forms of birds. Theycomprise 12 families, one of which, the pigeons, can only be looked uponas accidental, as these bu'ds are quite unsuited for the role of potentialfosterers. One other family, the cotingas, is known as a host froma single instance; the thrushes are represented by a single species,with two records of parasitism; the jays are known from three instancesinvolving a single species; the warblers, with three instances involving2 species; and the vireos are represented by 2 species, one with a singlerecord of parasitism and the other with five such records. Theremaining 6 families are represented as follows : flycatchers?4 specieswith 7 records; wi-ens?5 species with 1 record apiece; thrashers
?
4 species with 7+ records; tanagers?3 species with 5 records; oriolesand blackbii'ds?11 species with 84 records; finches?16 species with51 records.Since the bulk of all the cases recorded are in the last two families,it becomes increasingl}^ clear that these two groups comprise theprimary hosts of the bronzed cowbh-d. This parasite is, thus, moreselective, or more restricted, in its choice of fosterers than are thebrown-headed and the shiny cowbirds. The infrequent use of vu'eosand wood warblers and the relative scarcity of records of tyrantflycatchers are striking and significant differences from the situationrevealed in a survey of the frequent hosts of the brown-headedcowbird.As I described in my first account (1929, pp. 328-334) of thebronzed cowbird's fosterers, its relatively restricted range of hostchoice becomes meaningful when we remember that its nearest relative(and possible ancestral stock) is the screaming cowbu-d, Molothrusrujo-axillaris. T'hat species is parasitic entirely on its very closeancestral relative, the bay-winged cowbird, M. hadius. From M.rvfo-axUlaris, or the stock of which it is the extant representative,two lines have diverged, one leading to a wide host-tolerant groupof parasites, AI. bonariensis and M. ater, and one that retained moreof the restricted host relationships of its ancestor, the present speciesT. aeneus. Not having any self-breeding immediate relatives toparasitize, as does M. rujo-axillaris, the bronzed cowbird apparently173
174 U.S. NATIONAL MUSEUM BULLETIN 233
centered its attentions on the nests of an allied group, the hangnestsof the genus Icterus. It has gradually widened its scope of parasitismto include many other birds, but even today a large percentage of itsrecorded eggs and young are to be found in the nests or in the care ofspecies of Icterus and related birds. The process has gone far enoughto make some of the finches equally acceptable in this respect, as isevidenced by Dickerman's observations on the degree of parasitisminflicted on the song sparrow in Chapultepec Park, Mexico City, andRowley's report on the frequency with which the rusty-crownedsparrow is victimized in Morelos?as high a local frequency as hasbeen noted for any species of host.The data in my 1929 report (p. 328) referred to 76 victimized nests,of which no fewer than 51 belonged to 4 species of Icterus. Thepresent material is more than twice as great?186 individual recordsplus an indefinite number that can only be inferred from the use ofadjectives such as "common" or "frequent" inserted before the word
"host" by the describers. Of the 186, 84 refer to the genus Icterus,9 species of which are now included. In addition, it may be notedthat all the hosts described loosely in print or in correspondence as
"common" or "frequent" were species of Icterus. The percentageof the total that concerns species of Icterus is less now than in the 1929material, about 45 percent instead of two-thirds. This drop is inpart a contrived result, due to the fact that many recent observationson Icterme hosts have not been published because of their repetitivenature while every additional instance of a less frequent host ismore apt to be put on record.In the present catalog the hosts are discussed as species. How-ever, to make the data as readily usable as possible, I have firsttabulated them by subspecies both of the hosts and of the parasite.In this table no column has been left for the Colombian race of thebronzed cowbird, T.a. armenti, for the reason that nothing is knownof its hosts. In fact, it is only an assumption, although a likelyone, that it is parasitic in its breeding. It will be obvious at a glancethat very little is known of the breeding habits of the small southwestMexican race T.a. assimilis. The fact that none of its 4 knownhosts is a species of Icterus should not be assumed to be meaningful;this is probably a matter of insufficient field observation in its range.The greater number of hosts recorded for T.a. aeneus than for T.a.milleri is, again, merely a reflection of differential amounts of studyand collecting in their respective habitats.Approximately one-third of all the victims have been found to rearthe young bronzed cowbirds (at least as far as the fau-ly well-featherednestling stage). For many of the others, the absence of such records
HOST RELATIONS OF PARASITIC COWBIRDS 175
means only that the observers had no opportunity of revisiting thenests later or else that they collected the eggs and thereby put to anend their chances of success. Aside from the two species of doves, allthe hosts seem potentially able to incubate, hatch, feed, and giveproper care to the young of the parasite.
Hosts of the Bronzed CowbirdSummary
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White-winged DoveZenaida asiatica (Linnaeus)In an earlier paper (1933, p. 189) I noted a single record of thisdove as a cowbird victim. Since then no other has come to myattention. The unique instance was observed by J. T. Wright atGuirocoba, Sonora, during late May, 1931. The dove involved was ofthe race Z.a. mearnsi; the parasite, T.a. milleri.Ground DoveColumbigallina passerina (Linnaeus)The ground dove is a purely accidental victim. There is but asingle record, which I have seen in the sale catalog of an egg collec-tion; the latter was offered in 1929 to the late Senator F. C. Walcott,who showed the record to me. As the eggs were said to have beentaken in southern Arizona, the parasite must have been of the raceT.a. milleri; the host, of the race C.p. pallescens.
Rose-throated BecardPlatypsaris aglaiae (Lafresnaye)A single instance of the rose-throated becard as a victim of thebronzed cowbird has come to my notice. In his price list of eggs for
sale, Schliiter (1899) mentioned a set of eggs of this bird (under thename Hadrostomus alhiventris) which included an egg of Tangavius a.aeneus (probably now to be interpreted as T.a. milleri).
Tropical KingbirdTyrannus melancholicus VieillotThis kingbird was found to have been parasitized by the bronzedcowbird four times to my knowledge, a fair degree of frequency for abird as seldom studied as this. It happens that these records involvethree different races of the host. A parasitized set taken at Browns-
ville, Texas, May 24, 1902, by F. B. Armstrong (the eggs are now inthe A. E. Price collection. Grant Park, Illinois) is of the race couchii;at Refugio, Texas, T. C. Meitzen (in litt.) obtained another parasitizedset of this same subspecies; a third set, found at Mazatlan, Sinaloa,June 14, 1882, by A. Forrer (the eggs are now in the collection of theFlorida State Museum, Gainesville), is of the race occidentalis; and afourth set, taken near San Antonio, Orange Walk, British Honduras,May 2, 1926, by G. D. Smooker (the eggs are now in the R. Kjeugercollection, Helsinki, Finland), is of the subspecies chloronotus. TheSinaloa record involves the race milleri of the parasite, the otherthree refer to nominate aeneus.
HOST RELATIONS OF PARASITIC COWBIRDS 177
Scissor-tailed FlycatcherMuscivora forficata (Gmelin)As far as I have been able to learn the scissor-tailed flycatcher hasbeen recorded only twice as a host of the bronzed cowbird. Merrill(1877) wrote that a soldier at Fort Brown brought him a bronzedcowbird egg which the soldier said he had found in a scissor-tail's nest.A parasitized set taken in Lee County, Texas, May 20, 1887, now inthe Chicago Natural History Museum, is the only other record. Bothrecords refer to the nominate race of the cowbird.
Vermillion-crowned FlycatcherMyiozetetes similis (Spix)A set of 4 eggs of this flycatcher with 1 of the bronzed cowbird(race milleri), taken at Presidio, Sinaloa, Mexico, May 15, 1881, byA. Forrer (the set is now in the A. M. Ingersoll collection), is the onlyrecord for this bird as a host. The host subspecies here involved isM.S. primulus. Kiskadee FlycatcherPitangus sulphuratus (Linnaeus)Owen (1861, pp. 61-62) wrote that at San Geronimo, Guatemala,eggs of the bronzed cowbird (race T.a. aeneus) were found occasionallyin the nests of this flycatcher. Salvin and Godman (1886, p. 452) listthe kiskadee as a host, probably on the basis of Owen's statement.An indication of how little has been observed of this host-parasitesituation may be seen in the fact that no further data have beenplaced on record in the century since Owen's observation. TheGuatemalan race of the kisadee is P.s. derbianus.
Green JayCyanocorax yncas (Boddaert)Dr. Travis C. Meitzen (m litt.) collected two parasitized nests ofthe green jay, at Mante, Tamaulipas, one on May 28, 1948, andanother on May 21, 1952. The first one contained 3 eggs of thehost and 1 of the bronzed cowbird; the second one held 3 eggs ofthe jay and no less than 6 of the bronzed cowbird. It is veryunusual to find so many eggs of the parasite in any one nest, but therecord appears to be reliable.Bent (1958, p. 462) notes that Skutch found a nest of the green jaynear Matias Romero, in the Isthmus of Tehuan tepee, Oaxaca, on July8, 1934; the nest contained a young bronzed cowbird, almost ready tofledge, together with two young jays.The Tamaulipas records refer to the race vivida of the jay andaeneus of the cowbird; the Oaxaca one involves the race luxuosa ofthe jay and assimilis of the parasite.
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Plain WrenThryothorus modestus CabanisThere is but a single record of this wren as a host of the bronzedcowbird. Stone (1932, p. 336) mentioned a fledged cowbird being fedand attended by a plain wren at Cantarranas, Honduras, August 5.The wi'en at that locality is of the race T.m. pullus; the parasite isnominate aeneus. Sinaloa WrenThryothorus sinaloa (Baird)Stager (1954, p. 30) found a nest of this wren (subspecies cinereus)near Naranjo, southwestern Chihuahua, on May 29, containing 2eggs of the wren and 1 of the bronzed cowbird (subspecies milleri).This is the only instance to be recorded as yet.
Banded WrenThryothorus pleurostictus SclaterAt Canon de Lobos, Morelos, on July 19, 1960, J. Stuart Rowley(mss.) found a nest of this wren containing 2 eggs of the bronzedcowbird (nominate race) and none of the wren (T.p. nisorius). Thisis the only record known to me for this host.Happy WrenThryothorus felix SclaterA single record, without detailed data, is all I have seen of thiswren as a host of the bronzed cowbird. A set of eggs of the raceT.f. pallidus containing an egg of the parasite (race T.a. milleri)was listed in the catalog of an egg collection offered in 1929 to thelate Senator F. C. Walcott, who showed the record to me.
Bewick's WrenThryomanes hewickii (Audubon)There is still but the one record of this wren as a victim of thebronzed cowbird, a record which was included in my first list (1929,p. 334). On May 6, 1924, near Brownsville, Texas, the late A. H.Cordier found a nest of this wren (race T.h. cryptus) containing 3eggs of the bronzed cowbird (race T.a. aeneus) and 1 of the wren.The female wren was sitting on the eggs at the time of observation.The next day all the eggs hatched, but two days later all were de-stroyed by a predator, probably a skunk.
Northern MockingbirdMimus polyglottos LinnaeusThis is a rarely victimized species. At Brownsville, Texas, Iwas told of a nest of this mocldngbird with a very light, bluish-white,
HOST RELATIONS OF PARASITIC COWBIRDS 179
unspotted egg in it, as well as 3 of the ordinary mockingbird eggs.When my informant was shown several assorted eggs, he picked outa bronzed cowbird's egg and said it was like the one he saw in themocldngbird's nest. Since then, no additional records have come tomy attention. The mockingbird at Brownsville is of the race M.p.leucopterus; the cowbird is nominate aeneus.
Southern MockingbirdMimus gilvus (Vieillot)On the basis of Owen's observations (1861, pp. 60-62) at SanGeronimo, Guatemala, this bird is known as a host of the bronzedcowbird. Owens considered it to be a frequent victim and, in onenest, he noted as many as 5 eggs of the parasite together with 2 ofthe host. Salvin and Godman (1886, p. 452), on the basis of Owen'snotes, merely listed this mockingbird as a cowbird host; they gaveno additional data, and, indeed, since then no one else has done so.The race of the mockingbird at San Geronimo is M.g. gracilis;that of the cowbird is T.a. aeneus.
Long-billed ThrasherToxostoma longirostre (Lafresnaye)There are only a very few records of this thrasher as a host of thebronzed cowbird. In my fu-st account (1929, p. 334), I listed twoparasitized nests in Cameron County, Texas, both found by the lateR. D. Camp. Since then, one additional case has been reported:Webster (1956, p. 396) saw a pair of long-billed thrashers feedingtwo newly fledged bronzed cowbirds at Ohnito, Texas, on July 28.This is the first observation showing that this host may rear the para-sitic young; the earlier records were only of observed eggs. The localrace of the thrasher is T.l. sennetti; of the cowbird, T.a. aeneus.
LeConte's ThrasherToxostoma lecontei LawrenceIn the collections of the Hancock Foundation at the Universityof Southern California there is an egg of the bronzed cowbird whichis reported to have been found in a nest of Le Conte's tkrasher. Un-fortunately, no locaUty nor date is given on the label. Since theranges of this thrasher and of the bronzed cowbird overlap chiefly inArizona, it seems likely that the record came from somewhere in thatarea; if so, the report would involve the nominate race of the hostand the northwestern race, T.a. milleri, of the parasite.This is the only record that has come to my attention. Since LeConte's thrasher is a denizen of exceedingly barren and hot desertplains and valleys, the bird probably is largely ecologically allopatric
180 U.S. NATIONAL MUSEUM BULLETIN 233
with the bronzed cowbird; accordingly, the two seldom would havecontact with each other.
Orange-billed Nightingale-thrushCatharus aiirantiirostris (Hartlaub)This thrush has been noted as a cowbird host only two times,Cherrie (1891, p. 273) saw a thrush (race C.a. costaricensis) feedinga fledgling bronzed cowbird (race T.a. aeneus) near San Jose, CostaRica. In Morclos, 5 miles east of Cuernavaca, on June 10, 1959,J, Stuart Rowley (mss.) found a parasitized nest with 3 eggs of thehost (race C.a. clarus) and 2 of the parasite (nominate race).
Solitary VireoVireo solitarius (Wilson)Brandt (1951, p. 406) recorded a nest of this vireo (subspeciesV.s. plumbeus), with 3 eggs of its own and 1 of the western race ofthe bronzed cowbird, which was found late in May, 1944, at RamsayCanyon, Arizona. Not only is this an addition to the known victimsof the parasite, the race of which in this case is T.a. milleri, but alsoit is an instance of competition for hosts between the red-eyed and thebrown-headed cowbirds. The latter is prone to lay its eggs in nestsof vireos; the former appears seldom to use the vireo.
Yellow-green VireoVireo flavoviridis (Cassin)I know of five instances of parasitism by the bronzed cowbirdon this vireo. Mr. E. J. Coiu-t told me many years ago that hehad at one time in his collection a set of eggs, collected in Costa Rica,of the yellow-green vireo containing 1 Qgg of the bronzed cowbird.A second record of this vireo as a host of the bronzed cowbird hasbeen mentioned by Skutch (1960, p. 26) and by Bent (1958, p. 462,ex Skutch). The latter was shown a nest containing three nestlings ofthe host and one of the parasite on July 25, 1935, in the Pacific slopearea of Guatemala. In Morelos, J. Stuart Rowley (mss.) found threeparasitized nests. In all these cases the nominate races of the hostand of the parasite were involved.
Yellow-breasted ChatIcteria virens (Linnaeus)The yellow-breasted chat was recorded as a victim of the bronzedcowbird near Brownsville, Texas, by Merrill (1877, pp. 85-87). Heexamined many nests of the chat and, finding only one to be para-sitized, he concluded that the bird was rarely imposed upon. His con-clusion is upheld by the fact that just one other observer has reported
HOST RELATIONS OF PARASITIC COWBIRDS 181
a similar occurrence since then. Dr. T. C. Meitzen (in litt.) informedme that he found a parasitized nest at Refugio, Texas. The chat inthe lower Rio Grande Valley is of the race I.v. auricollis; the parasite,T.a. aeneus. Rufous-capped WarblerBasileuterus rufifrons (Swainson)This warbler has recently been added to the list of hosts by J.Stuart Rowley (mss.), who found a parasitized nest at Canon deLobos, Morelos, July 15, 1960. The local race of the warbler is B.r.dugesi; the cowbird is of the nominate race T.a. aeneus.
Mexican CaciqueCassiculus melanicterus (Bonaparte)At Tehuantepec, Oaxaca, Mexico, on June 11, 1955, Dr. Travis C.Meitzen (in litt.) collected a nest of this cacique containing 4 eggsof the owner and 1 of a bronzed cowbird. R. W. Dickerman (1960,p. 473) found a parasitized nest five miles southwest of Naudreete,Nayarit, on July 13, 1956. Two races of the bronzed cowbird areinvolved in these records, T.a. assimilis in Oaxaca, and T.a. milleriin Nayarit. Redwinged BlackbirdAgelaius phoeniceus (Linnaeus)I have learned of only four instances of parasitism by the bronzedcowbird on the redwinged blackbird. Two records are based on setsof eggs in the J. P. Norris collection. One was taken at Camargo,Tamaulipas, June 29, 1890, by T. H. Jackson; the other, in HidalgoCounty, Texas, May 18, 1889, by J. A. Single. Dr. T. C. Meitzen hastwo parasitized sets of eggs from Refugio, Texas, in his collection. Allfour of these records refer to the race A.p. megapotamus of the host andto the nominate race of the parasite. There is some evidence that theredwinged blackbird is usually unmolested; at least, considerablenumbers of its nests, examined around Brow^nsville, Texas, failed toreveal any eggs of the bronzed cowbird although that bird was locallyfairly numerous. Orchard OrioleIcterus spurius (Linnaeus)The orchard oriole was designated by Merrill (1877) to be a frequenthost of the bronzed cowbird in the lower Rio Grande Valley, Texas.R. W. Quillen found it to be parasitized at San Antonio and in KlebergCounty, Texas; Meitzen (in litt.) had the same experience at Refugio,Texas. In the J. P. Norris collection there was a parasitized set ofeggs collected at Camargo, Tamauhpas. The records involve thenominate race of the parasite.
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Fuertes' OrioleIcterus fuertesi (Chapman)Graber and Graber (1954, p. 277) have added this oriole to theknown hosts of the eastern race of the bronzed cowbu-d. BetweenTampico and Loma del Real, Tamaulipas, they found a nest con-taining one young each of the host and the parasite. From thelocality, it is apparent that we are dealing here with the eastern,nominate race of the bronzed cowbird. The orchard oriole, /.spurius, a close relative of the present species, has long been knownas a not uncommon victim of this parasite.
Scott's OrioleIcterus parisorum (Bonaparte)A single record of this oriole as a victim of the bronzed cowbirdhas come to my attention. Bent (1958, p. 242) stated that in southernAi'izona he found it to be imposed upon by the northwestern race ofthe parasite, T,a. milleri.
Black-headed OrioleIcterus graduacauda (Lesson)Bendu'e (1895, p. 601) considered this species the most frequentvictim of the bronzed cowbird; he added that, out of 9 sets of eggsin the U.S. National Museum, 7 contained from 1 to 3 of the parasiticeggs, together with 1 or 2 of their own, and that in most cases someof the latter were punctured. Near Brownsville, Texas, in 1924, Ifound two nests, both of which had been parasitized. In the samearea, Goldman and Watson (1953, p. 320) reported seeing a pair ofthese orioles feeding three practically grown bronzed cowbirds. Kin-ball (1935, p. 59) saw a fledghng bronzed cowbird with a black-headedoriole in attendance at Los Fresnos, Texas, F. F. Nye, Jr. (in litt.),wrote me that he has two parasitized sets of eggs from southern Texasin his collection. All the Texas records refer to the nominate race ofthe parasite ; Bendire's observations, made in Arizona, concern the raceT.a. milleri] all the instances have to do with the race I.g. auduhoniiof the host. Spotted-breasted OrioleIcterus pectoralis (Wagler)This oriole was recorded as a host of the bronzed cowbird m thelowlands of El Salvador by van Rossem (Dickey and van Rossem,1938, p. 540). He was told by some of the local people that the birdwas one of the most commonly imposed upon victims of the parasitein that area, but he did not list any specific instances. The localform of the oriole is the nominate subspecies; that of the parasiteis also the nominate form.
HOST RELATIONS OF PARASITIC COWBIRDS 183
Lichtenstein's OrioleIcterus gularis (Wagler)Two races of this oriole have been found to be victims of thebronzed cowbii'd. In El Salvador, van Rossem (Dickey and vanRossem, 1938, p. 540) was informed by the natives that this oriole isone of the most frequent victims of the parasite in the lowlands ofthat country. Since van Rossem cited no specific instances, it seemsthat he personally did not observe any but merely reported whathe had been told. The nominate race of the oriole is the form breedingin El Salvador; the cowbird there is the race T.a. aeneus. At Monte,Tamaulipas, the race I.g. iamaulipensis was found to be victimized;on May 28, 1949, a nest containing 3 eggs of the oriole and 1 of thebronzed cowbird (typical aeneus) was discovered by Dr. Travis C.Meitzen (in litt.). Dr. Meitzen wrote me that this oriole is seldomparasitized; he had examined at least 150 nests and found eggs of thebronzed cowbird in only 2 of them.
Hooded OrioleIcterus cucullatus (Swainson)The hooded oriole is one of the chief fosterers of the bronzed cow-bird; it has been reported as a victim in Texas (at Refugio, at Browns-
ville, in the Nueces River Flats), in Arizona (at Tucson, at Tomb-stone, near Oracle, at Sacaton, and in the Sabino Canyon), andDickerman (in litt.) recorded it in San Luis Potosi (El Salto), Mexico.Meitzen (in litt.) wrote me that at Refugio, Texas, he had foundabout a dozen parasitized nests of the hooded oriole. In his compila-tion, Bent (1958, p. 456) noted that as many as 6 eggs of the bronzedcowbird were found in a single nest of this oriole (by Brandt, in theSabino Canyon). The hooded oriole has been found to rear the para-
sitic young (Friedmann, 1929, p. 331; Visher, 1910, p. 210). TheTexas and the San Luis Potosi records refer to the race I.e. sennettiof the host and to the nominate race of the parasite; the Arizona in-stances relate to I.e. nelsoni and T.a. milleri.
Scarlet-headed OrioleIcterus pustulatus (Wagler)The scarlet-headed oriole has been found to be a victim of thebronzed cowbird at San Geronimo, Guatemala, by Owen (18G1, pp.61-63); in the lowlands of El Salvador, where it was one of the mostfrequently chosen hosts, according to van Rossem (Dickey andvan Rossem, 1938, p. 540); at San Bias, Nayarit, by Bailey (1906,p. 390); at Mazatlan, Sinaloa (Schliiter, 1899); at Guaymas, Sonora,by Bancroft (Friedmann, 1933, p. 190); and near Cuernavaca, Morelos(J. Stuart Rowley, mss.). The Guatemala and El Salvador records630590?63 13
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refer to the host race I.y. alticola and to the parasite race T.a. aeneus;the Nayarit, Sinaloa, and Sonora ones, to I.p. microstictus and toT,a. milleri; the Morelos one, to I.p. pustulatus and T. a. aeneus.
Bullock's OrioleIcterus bullockii (Swainson)Bullock's oriole is a frequent victim of the bronzed cowbird, but sofew observations have been made in recent years that my 1929 (p. 331)account needs little change to bring it up to date.Merrill (1877, pp. 85-87) intimated that Bullock's oriole occasionallytried to get rid of the parasitic eggs; twice he found broken shells ofbronzed cowbird eggs on the ground below occupied nests. Also heonce found a female cowbird hanging, mth a stout fiber around itsneck, from a Bullock's oriole nest. The nest contained one young ofthe parasite, which caused Merrill to deduce that "its parent afterdepositing the egg was entangled in the thread on hurriedly leavingthe nest, and there died. It had been dead about two weeks." Att-water (1892, p. 237) found a parasitized nest near San Antonio.F. F. Nye, Jr. (in litt.), found another near Pharr, Texas. The raceof the oriole involved in all these records is the nominate; the parasiteis also represented by its nominate form.One uncertain record of this bird as a victim of the bronzed cowbirdhas been noted. In the Nueces Kiver Flats, Texas, W. B. Savary(1936, p. 62) examined a nest of the "Baltimore oriole" containing anegg of the bronzed cowbird. The record, however, is open to questionas the locality is south of the aclmowledged breeding range of thatoriole. Although Savary definitely states that the bird breeds there,it seems likely that his record involved Bullock's oriole, not the oneto which he attributed it. Hepatic TanagerPiranga flava (Vieillot)A record, recently published by Bent (1958, p. 495), adds thistanager to the list of victims of the bronzed cowbird. Bent writesthat Frank C. Willard informed him that he once found an egg of thewestern race of the parasite in a nest of P./. hepatica. Although noexact locahty is given, the race of the parasite must be milleri. Stillmore recently, J. Stuart Rowley (mss.) found this tanager to be para-sitized near Cuernavaca, Morelos; a nest with 3 eggs of the tanagerand 2 of the parasite was found June 15, 1958. In this case theparasite was of the nominate race.Summer TanagerPiranga rubra (Linnaeus)There are two records of this tanager as a victim of the bronzedcowbird, both records involving the western race, P.r. cooperi, of the
HOST RELATIONS OF PARASITIC COWBIRDS 185
victim and T.a. milleri of the parasite. J. T. Wright saw one of thesetanagers feeding and attending a fledgling of the cowbu'd at Saric,Sonora, August 28, 1929 (Friedmann, 1933, p. 190). Amadon (1940,p. 257) reported a parasitized set of eggs which came from LomitaRanch, near Tucson, Arizona, and is now in the collection of theAmerican Museum of Natural History. Apart from these records, itshould be mentioned that A. R. Phillips wrote me that this tanagerseemed to be a fairly regular victim in northern Sonora.
Red-headed TanagerPiranga erythrocephala (Swainson)The one record I pubhshed in 1938 (p. 50) is still the only one Ihave found of the red-headed tanager as a host of the bronzed cow-bird: at Rosario, Sinaloa, J. T. Wright found a nest of this bird(subspecies P.e. Candida) containing a nestling cowbird (T.a.milleri)as its sole occupant. CardinalRichmondena cardinalis (Linnaeus)The cardinal has been found to serve as a host for the bronzed cow-bird in eastern and southeastern Texas. Merrill and Camp (Fried-mann, 1929, p. 333) each noted instances at Brownsville many yearsapart; Merritt (1940, pp. 141-142) recorded another case, in NuecesCounty; Webster (1958, p. 427) reported one at Rockport Cottages ineastern Texas; Dr. T. C. Meitzen (in litt.) found a parasitized nest atRefugio, Texas; and F. F. Nye, Jr., took a similar set near Pharr,Texas. The parasite in all these cases is the nominate race T.a.aeneus; the cardinal in eastern Texas is R.c. magnirostris ; in south-eastern Texas, R.c. canicauda.
Black-headed GrosbeakPheucticus melanocephalus (Swainson)This bird may be added to the known hosts of the bronzed cowbirdon the basis of a statement by Brandt (1951, p. 695), who found acowbird's egg (subspecies milleri) in a nest of this grosbeak (nominaterace) in Arizona. Unfortunately, no further details were given.
Blue GrosbeakGuiraca caerulea (Linnaeus)The blue grosbeak was first recorded by Sennett (1879, p. 396) asa host of the bronzed cowbird in the lower Rio Grande Valley. Asfar as I have been able to learn, no one else has added any furtherobservations until recently, when I was informed by Mr. R. Kreuger(in litt.) of a set of eggs in his collection in Helsinki, Finland, contain-ing 1 egg of the parasite as well as 4 of the host. This set was col-
186 U-S. NATIONAL MUSEUM BULLETIN 233
lected at Oaxaca, Oaxaca, Mexico, June 3, 1936, by G. D. Smooker;it consists of the race Gx. eurhyncha of the grosbeak and T.a. assimilisof the cowbird. Sennett's instance from Texas concerns the nominatesubspecies of both the host and the parasite.
Painted BuntingPasserina ciris (Linnaeus)The painted bimting, a frequent victim of the brown-headed cow-bu'd, appears to be imposed upon much less often by the bronzedspecies. I loiow of only one such case; an egg of the latter bird wastaken from a painted bunting's nest near San Antonio, Texas, April1895, by H. P. Attwater, from whom it passed into the A. C. BentCollection, now in the U.S. National Museum. The record refers tothe nominate race of the parasite and to the race P.c. pallidior of thehost. Blue SeedeaterAmaurospiza concolor (Cabanis)This poorly known species recently has been added by J. StuartRowley (mss.) to the list of victims of the nominate race of the bronzedcowbird. At Canon de Lobos, Morelos, on July 8, 1960, he found anest of this bird (apparently of the subspecies A.c.relicta) containing2 eggs of the seedeater and 1 of the bronzed cowbird.
Yellow-throated AtlapetesAtlapetes gutturalis (Lafresnaye)This tropical finch is known as a frequent victim of the bronzedcowbird in Costa Rica. At San Jose, Cherrie (1892, pp. 25-26) foundfive nests, four of which contained from 1 to 3 eggs each of the bronzedcowbird. Alfaro (1904, p. 180) also has recorded this host in CostaRica. The parasite in that area is the nominate subspecies, T.a.aeneus; the host is of the race A.g. parvirostris.
Olive SparrowArremonops rufivirgata (Lawrence)Two records of bronzed cowbird parasitism on the olive sparrowhave come to my notice, both reports from southern Texas. Amadon(1940, p. 257) recorded a parasitized set of eggs from Lomita Ranch,near Hidalgo; the eggs are now in the collection of the AmericanMuseum of Natural History. F. F. Nye, Jr. (in litt.), informed methat he has a similar set taken by himself in southern Texas. Therecords involve the nominate races of both the host and the parasite.Green-backed SparrowArremonops conirostris (Bonaparte)As reported in an earlier paper (Friedmann, 1933, p. 191), thereare three parasitized sets of eggs of this sparrow (race A.c. richmondi).
HOST RELATIONS OF PARASITIC COWBIRDS 187
They were collected in Costa Rica; at present they are in Germancollections, one in the Schonwetter and two in the Domeier Collection.The bronzed cowbird of Costa Rica is of the nominate subspecies.
Rufous-sided TowheePipilo erythrophthalmus (Linnaeus)Bent (1958, p. 462) quoted a commmiication from Skutch to theeffect that on June 14, 1933, Skutch saw a recently fledged bronzedcowbird attended by a pair of Guatemalan spotted towhees (P.e.repetens) ; this took place in the Guatemalan highlands, at an elevationof about 8,500 feet. The cowbird is of the nominate race, but it shouldbe mentioned that, in his account of the birds of Guatemala, Griscom(1935, p. 387) stated that the bronzed cowbird has been noted onlyin clearings in the eastern lowlands. The present record would seemto extend its range well up into the highlands. This is the onlyinstance I know of the rufous-sided towhee as a host of the bronzedcowbird. Brown TowheePipilo fuscus SwainsonThe brown towhee has been recorded as a victim of the bronzedcowbird a few times?in Arizona and in the Distrito Federal, Mexico.R. S. Crossin (in litt.) found the nest of a brown towhee (race PJ.mesoleucus) containing one towhee egg about to hatch, one newlyhatched towhee, and one bronzed cowbird egg of about five days incu-bation; the observation was on May 16, 1959, near Sabino Dam,Sabino Canyon, Pima County, Arizona. Visher (1910, p. 210) foundthis host victimized nearTucson, where he noted 2 young of the parasitebeing raised by a pair of brown towhees. R. W. Dickerman (1960,p. 473) found a nest of this species in Chapultepec Park, Mexico City,containing 5 eggs of the bronzed cowbird and none of the towhee.The brown towhee at that locality is P.f. fuscus; in Ai-izona it is therace P.f. mesoleucus. The parasite is of the nominate race in MexicoCity and T.a. milleri in Arizona.
Sclater's TowheePipilo albicollis SclaterFour records of this towhee as a victim of the bronzed cowbird havecome to my notice: one parasitized set of eggs from Etla, Oaxaca,May 20, 1912, now in the J. P. Norris collection; two similar sets alsofrom Oaxaca, now in the Chicago Natural History Museum. Mr.J. Stuart Rowley has informed me that he recently found anothercase in Oaxaca. The host involved is of the nominate race; theparasite, of the race T.a. assimilis.
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Rusty-crowned Ground SparrowMelozone kieneri (Bonaparte)In Morelos, J. Stuart Rowley (mss.) found 11 nests of this sparrow,no less than 9 of which contained from 1 to 5 eggs of the bronzed cow-bird. The local race of the host is M.k. rubricatum; the parasite isthe nominate race, T.a. aeneus. One of the parasitized nests alsocontained an egg of the brown-headed cowbird.
Black-chested SparrowAimophila humeralis (Cabanis)This little known black-chested sparrow recently has been found tobe a host of the nominate race of the bronzed cowbird in Morelos;J. Stuart Rowley (mss.) discovered a parasitized nest near Acatlipaon June 25, 1960. Russet-tailed SparrowAimophila ruficauda (Bonaparte)J. Stuart Rowley (mss.) recently has added this sparrow (race A.r.acuminata) to the known hosts of the nominate race of the bronzedcowbird in Morelos. Near Acatlipa on July 25, 1960, he found threenests, one of which contained 1 egg of the parasite in addition to 3 ofthe sparrow. Rusty SparrowAimophila rufescens (Swainson)The rusty sparrow has been recorded as a host of the bronzed cow-bird in Veracruz by Sumichrast (1869, p. 551; 1870, p. 309) and byHerrera (1911, p. 124). Herrera's statement seems to be based onSumichrast rather than on any additional data. The rusty sparrowfound in Veracruz is of the race A.r. pyrgitoides the parasite is of thenominate race, T.a. aeneus. In Morelos, J. Stuart Rowley (mss.)found eight nests of this sparrow about five miles east of Cuernavaca;one of these contained an egg of the bronzed cowbird. The host inMorelos is the nominate race, A.r. rufescens.
Song SparrowMelospiza melodia WilsonIn Chapultepec Park, Mexico City, Dickerman (1960, p. 472)found 13 nests of the song sparrow, of which 6 proved to contain eggsor young of the bronzed cowbird. The number of parasitic eggsvaried from 1 to 3 in these nests. The 13 nests contained a total of14 eggs and six young of the sparrow plus 13 eggs and two young ofthe cowbu'd. Dickerman reported that some of the parasitized nestshad been deserted, but it is not clear if they had already been aban-doned when the parasite laid in them or if the desertion was due to its
visits. The local race of the song sparrow is M.m. mexicana; thecowbird, T.a. aeneus.
Shiny CowbirdMolothrus bonariensis (Gmelin)DiscussionAs stated in the introductory pages of this report, there is no pressingneed for a complete, new, annotated catalog of the victims of thiswide-ranging cowbird of South America: there has not been such ademand as has been expressed in the case of the brown-headed andthe bronzed species of North America. The original host list givenin my 1929 book, the various supplements to it, and the new materialnow presented, are here brought together and summarized in tabularform, but written accounts are given only for the additional hostsand for those in which significant new information alters or extendsour earlier estimates of them as cowbird victims. In the table, thenomenclature of all the earlier publications has been brought intoagreement with current usage.In the decades since my 1929 book, disappointingly little has beenadded to many aspects of our knowledge of the breeding habits of theshiny cowbird and of the main features of its host relationships.There seems, therefore, to be little need to elaborate upon many ofthe statements made in my earlier publication, and only topics thathave been developed since or that were not adequately treated thenwill be discussed here. The newer record data are given chiefly inconnection with the individual host species involved. In addition tothe following discussion the reader interested in reviewing the over-allpicture should consult pages 81-91 of my 1929 description of the sub-ject, and pages 91-121 for the accounts of the hosts known at thattime. Imperfections in Host RelationsApart from some important differences in its choice of hosts, asalready discussed in the present report (pp. 9-10), the shiny cowbirdis essentially similar in its brood parasitism to the better knownbrown-headed species, but it does exhibit one imperfection in itsbreedmg habits that has not been found in its more advanced northernrelative. Since this affects its host relations, it merits discussion here.The fecundity of the shiny cowbird is less closely and less accuratelygeared to the availability of potential hosts than is that of its NorthAmerican counterpart. In his pioneer work in Argentina in the1860's, Hudson noted that the shiny cowbird wasted numbers of itseggs by laying them on the ground and simply leaving them or, not189
190 U.S. NATIONAL MUSEUM BULLETIN 23 3
infrequently, by utilizing deserted nests. In Salta, northwestern Ar-gentina, Hoy (in litt.) also has noted eggs on the ground or in desertednests. As discussed more fully below (pp. 193-194), it may be notedthat late in the southern summer the year-old bu"ds tend to remainin flocks and that individuals therein lay large numbers of eggs in size-able nests which either have been aheady deserted or are quicklyabandoned as a result of the parasites' mass visitations.Careful reading of Hudson's statements conveys the impressionthat finding scattered eggs on the ground was frequent in his experienceand that it was not restricted to the late summer months. In Hoy'sexperience in Salta such evidence of wasted eggs chiefly was foundearly in the breeding season. In other words, it was not restricted toyear-old, inexperienced birds. It is still somewhat puzzling to me, asduring six months that I spent in the field in Argentina, paying atten-tion particularly to the cowbirds in areas where they were very numer-ous, I never came across such a deserted egg. I do not doubt thatHudson found many, but I can only wonder if this might have beena local condition brought about by undue destruction of available nestsby weather or predators or by an undue numerical abundance of cow-birds there. Furthermore, it is conceivable that Hudson may haveunwittingly multiplied his experiences in his memory, when writingabout them, by attaching too much inferential significance to a rela-tively few such instances. At that time it was thought not improbablethat the cowbu'ds laid their eggs on the ground and then carried themin their bills to the nests in which they were finally placed. This wasthe current, although fallacious, assumption concerning the Europeancuckoo, at that time the best known parasitic bird. There is no longerany reason to assume that either cowbirds or cuckoos do this.Actually, the only way in which it ever became known to Hudson thatthe shiny cowbird did sometimes lay on the ground was the fact thatthe eggs were left there and were not carried to a nest and that theywere found subsequently by him and his co-observers.We still know too little about the actual or the potential fecmidityof the shiny cowbird to be able to estimate with any accuracy the per-centage of its eggs that are wasted by depositing them either on theground or in abandoned nests. However, the waste is real, and it isan element largely absent in the case of the brown-headed cowbird.Still another thought must be expressed in this connection. Ordi-narily, cowbirds and, for that matter, parasitic birds in general, findthe nests they subsequently parasitize by watching the hosts buildthem. There is even some reason to discern in this watching a stim-ulus to ovulation. Therefore, depositing eggs on the ground or in old,abandoned nests implies that this important directing and connectingcircumstance somehow is lacldng in these cases. This, in turn,
HOST RELATIONS OF PARASITIC COWBIRDS 191
suggests a less close and accurate coordination between the ovulationof the parasite and the nestmg activity of the prospective hosts.The point is an important one, and to emphasize it, by contrast,we may cite one of Hann's conclusions (1941, p. 220) from his carefuland protracted study of the brown-headed cowbird in relation to theovenbird, Seiurus aurocapillus, in Michigan. He foimd that thefemale cowbh^d made regular inspection trips to nests dming theabsence of the o^\^lers, between the time of first discovery of the nestand the time of her o^^^l egg-laying, and that she seemed to know inadvance where she was going to lay. This is certainly a contrast tothe condition of misplaced ovulation we have just described in theshiny cowbird.A further consideration emerges from these data. There is somereason to think that in a parasitic bu'd with well-marked individualhost specificity, such as the Em'opean cuckoo, the individual hens laytheir eggs in nests of the same species of host as those by which theythemselves were reared. A cuckoo raised by a meadow pipit latertends to lay its eggs m meadow pipits' nests, while another individualthat has been reared by a hedge sparrow uses nests of that speciesfor its own eggs. There is no evidence of a comparable degree of obli-gate host restriction in the shiny cowbu'd although there is whatappears to be a high degree of it in the ancestral screammg cowbu'dstock. The habit of chopping eggs indiscriminately on the gromid,not even in a nest at all, or of using old deserted nests clearly suggeststhe absence of any trace of a tendency toward host specificity. Theinference here is clearer and more du^ect than in the more usual in-stances of nest parasitism by this cowbu'd, as in the bulk of thosecases we have no evidence to suggest or to dismiss the possible effect,or even existence, of ontogenetic host preference.One other relative imperfection?like the preceding, also a sourceof loss to the parasite and not to its hosts?is the lack of "understand-ing" or the lack of proper attunement in conniiunication betweenthe alarm calls of the hosts and the response of the parasite durmgits nestling and early fledgling stages. When danger in the form ofa hawk or other predator threatens, the young cowbird appears tobe unaffected by the seemingly obvious distress calls of its foster-parents. Instead of crouching quietly, it clamors noisily for food asif no peril were imminent. This often results in its being capturedand eaten by the instigator of the alarm it failed to comprehend.Many years ago Hudson commented on this in central eastern Argen-tina, and I had essentially the same experience in the same and otherparts of that country. Hudson noticed that in his area a large pro-portion of the nests of the cachila pipit, (Anthus correndera were para-sitized, but that it was a rare thing to find a young fledgling cowbird,
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since the chimango hawk, Milvago chimango, was common there andpicked off the noisy fledglings to feed its young.Hudson's comments (1920, pp. 82-86) are worth repeating. "Theyoung of Synallaxis spixi, though in a deep domed nest, will throwitself to the ground, attempting thus to make its escape. The youngMimus patagonicus sits close and motionless, with closed eyes, mim-icking death. The young of our common Zenaida, even before it isfledged, will swell itself up and strike angrily at the intruder withbeak and wings; and by making so brave a show of its inefficientweapons it probably often saves itself from destruction. But any-thing approaching the young Molothrus is welcomed with flutteringwings and clamorous cries, as if all creatures were expected to ministerto its necessities.
"I found a young Molothrus in the nest of a Screaming Finch,Sporophila caerulescens ; he cried for food on seeing my hand approachthe nest; I took him out and dropped him down; when finding him-self on the ground he immediately made off half flying. I succeededin recapturing him, and began to twirl him about, making him screamso as to inform his foster-parents of his situation, for they were notby at the moment. I then put him back in the nest, and pluckedhalf a dozen large measure worms from an adjacent twig. The cater-pillars were handed to the bird . . . and with great greediness hedevoured them all notwithstanding the ill treatment he had justreceived and utterly disregarding the wild excited cries of his foster-parents, just arrived and hovering within three or four feet of thenest . . . ."Some lack of attunement between the reaction of the parasiticnestling or fledghng and those of its foster-parents exists in thebrown-headed cowbird as well as in the shiny one, but it appearsto be more noticeable and more disastrous to the species in the shinycowbird than in its North American relative.
Frequency of Host SelectionAlthough it is entirely parasitic in its breeding, the shiny cowbirdgenerally evinces more interest in nests than does the brown-headedcowbird. This interest is shown by males as well as females beforeand after, as well as dui-ing, their breeding season. In Argentina Ioften noticed both males and females of this species examining nestsof ovenbirds, Furnarius, and of woodhewers, Anumhius, Synallaxis,etc., without actually entering them. My observations were antici-pated by many years by Hudson, who wrote (1874, pp. 171-172) thatthis interest did not seem like idle cm-iosity but "precisely like that ofbirds that habituaUy make choice of such breeding places. . . .Whenever I set boxes up in my trees the female Cowbirds were the
HOST RELATIONS OF PARASITIC COWBIRDS 193
first to visit them, . . . It is amusing to see how pertinaciously theyhang about the ovens of the Ovenbirds, apparently determined to takepossession of them, flying back after a hundred repulses, and yet notentering them when they have the opportunity. Sometimes one isseen following a wren to its nest beneath the eaves, and then clingingto the wall beneath the hole into which it disappeared. I could fillmany pages with instances of this habit of M. bonariensis, which use-less though it be, is as strong an aft'ection as the bird possesses. Thatit is a recurrence to a long disused habit I can scarcely doubt ... itseems to me that if M. bonariensis when once a nest builder, hadacquired the semiparasitical habit of breeding in doomed nests of otherbirds, such a habit might conduce to the formation of the instinctwhich it now possesses . . . . "If we recall that the bay-winged cowbird still prefers the old nestsof ovenbirds and woodhewers for its breeding and that the species willbuild its own nest mainly if no others are available, the interest shownby the shiny cowbird seems to be a relict habit from the self-breedingmode of life of its remote ancestral stock. This is borne out by thefact that the male shows this interest as well as the female; in thebay-wing, both sexes may struggle with the builders for the possessionof their nest or share in the construction of a new one. Related tothis is the observation of Young (1930, pp. 256-257) to the effect that,in his experience in British Guiana, the male shiny cowbird seemed todo most of the work of prospecting for nests.Other suggestive evidence pertinent to the above is the tendency ofyear-old shiny cowbu-ds breeding in flocks late in the season to layvery large numbers of eggs in some of these domed nests, especiallythe mud nests of the ovenbird. Individual nests of this bird havebeen found which contained 15, 17, 20, 25, 26, and even, in one case,37 eggs of the shiny cowbird. In all such cases the nests were de-serted, often before most of the parasitic eggs were deposited. AU ofthese instances were noted late in the breeding season?in January(the season extends from September to February). No such multipledepositions of eggs in single nests have been recorded early in theseason although, as in the North American brown-headed cowbii'd,cases of 8 eggs in a nest occasionally have been noted. In Salta, innorthwestern Argentina, Leo Miller (1917, pp. 584) noted that, inmany of these instances of excessive parasitism, flocks of shiny cow-birds were seen in the same tree as the overburdened nest. In myoriginal appraisal of this situation (1929, p. 97) I pointed out that
"in migration and in the establishment of breeding areas the adultCowbirds come first and the year-old birds follow a good deal later.
. . . most of the adults would be through breeding before the year-oldbirds and from this it follows that the latest eggs of the season would
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probably be those of the younger birds. Then too, by the time theyear-old birds were ready to begin laying, all the district would havebeen already staked out into territories by the adults. From this itfollows that there would be a tendency for the yearling birds to con-gregate in whatever places were left. Also most small birds would bethrough breeding and their nests either destroyed by the elements orhard to find as the Cowbirds usually find such nests by watching thebirds coming and going. ... if the year old Cowbirds found largenests it would not be surprising if many of them would lay in each oneand not only once at that. It should be remembered that of 217Ovenbirds' nests found early in the season (September through De-cember), only 20 contained Cowbirds' eggs, so that these are not [sogreatly] favored by the Molothrus when they can avail themselves ofnests of smaller birds, as Brachyspiza, Muscivora, etc. I think thatthe large clutches of 25 and 37 eggs are the product of year-old birdswithout territories . . . ." It may be added that Miller estimated,from the appearance of the eggs in a nest containing 25 of them, thatat least 12 hen cowbirds were responsible. It may also be mentionedthat a fair number of these late-breeding males still showed some of theJuvenal remiges; thus they were clearly year-old birds. The plumageof the females unfortunately is of a kind as to give no opportunity forsuch revealing criteria of age.The pertinence of the above is, as already stated, merely suggestive.The younger buds show an active interest in these domed nests andless so in open ones. Since atavistic traits and tendencies seem tocrop up more often in younger than in older birds, these factors maybe operative here. It must be admitted that these late breeding, year-old birds also may occasionally use open nests for their wastefulmultiple ovulation. Nests of the yellow-breasted marsh bird, Pseudo-leistes virescens, have been reported with from 10 to 17 cowbird eggsin them. One nest of a mockingbu-d, Mimus saturninus modulator,with 14 cowbird eggs, the product of at least seven hens, was foundvery late in the season (February 12). Ottow (in litt.) studied 14cowbird eggs, found on January 10 in another nest of this mockingbird,and attributed them to 14 different hen cowbirds. Nests of Leistesmilitaris supercUiaris also have been reported with as many as 19cowbird eggs in them.That the interest in domed nests is more atavistic than currentlyuseful is indicated by the frequency with which the various kinds ofhosts actually are chosen. The data in our present host cataloginvolve between 825 and 900 parasitized nests; of these, 165 were nestsof Zonotrichia capensis, no less than 10 races of which species are knownto be parasitized. The second most frequent, although geographicallyrestricted, host is Diuca diuca, with 80 records; the third, Muscivora
HOST RELATIONS OF PARASITIC COWBIRDS 195
tyrannus, with 57; the fourth is one of the domed-nest builders,Furnarius rufus, with 38 instances; the fifth, Mimus triurus, with 28;then Agelaius ruficapillus and Troglodytes musculus, with 15 recordseach. The chingolo, Zonotrichia capensis, is, as far as present dataindicate, the primary host, with a very wide geographic range overwhich it has been found to serve as a fosterer?Argentina, Chile,Bohvia, and Brazil as far as Peru and Venezuela. In Chile, wherethe shiny cowbird appears to be a fairly recent addition to the fauna,the main host is the diuca finch, Diuca diuca. Goodall, Johnson, andPhilhppi (1946, p. 130) wrote that, of 100 nests found in Chile withcowbird eggs in them, 72 were of the diuca finch. The domed-nestbuilders other than Furnarius?-Anumbius, Synallaxis, Cranioleuca,Phacellodomus , etc.?have only one or two kno\vn records of parasitismapiece. In the case of the rufous ovenbird, Furnarius rufus, the onespecies of domed-nest builder that is frequently parasitized, it ma^^be noted that, of 217 of its nests examined by me in Argentina, only20 contained eggs or young of the shiny cowbird. In other words,current use of domed nests as repositories for eggs of the shiny cow-bird indicate that the nests are used less by the parasite than itsinterest in such structures would suggest.In some areas, observers have credited other species as the mostfrequently imposed upon hosts even though actual instances in suffi-cient quantit}^ are not yet recorded. In British Guiana coastlands,Young (1929) called the white-headed marsh tyrant, Arundinicolaleucocej)hala, the commonest victim of the shiny cowbird, whila othershave so characterized the wren, Troglodytes musculus. The lastnamed bird is stated by Haverschmidt (1955, p. 127) to be the princi-pal host in Surinam. In response to an inquiry, Mr. Haverschmidthas told me of at least 11 such records in 15 years in his own experiencein Surinam (and only a single record of another host species!). Asimilar great use of this wren was reported also from Trinidad byHerklots (1961, p. 222), who found as many as 3 eggs of the parasitein individual nests of the small fosterer. This is certainly differentfrom the situation in Argentina.On the other hand, as Sick (1957, pp. 16-17) has noted, theintroduced and now wide-spread European house sparrow, Passerdomesticus, has not been "accepted" by the cowbirds as a host althoughSick has found, near Rio de Janeiro, mixed groups of the two speciessleeping together in small roosts. The fact that there is one instanceon record of the shiny cowbird's parasitizing the house sparrow doesnot alter the general validity of Sick's comments.While no one has stated in so many words that the shiny cowbirdexhibits any tendency toward individual specificity in its choice ofhosts, the observations of Sick and Ottow (1958) in the vicinity of
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Rio de Janeiro constitute strong evidence that a number of the femalecowbirds they studied were restricted to one host species, the chingolosparrow, Zonotrichia capensis, even though other potential victimsnesting in the area were seasonally and ecologically available. It ispossible that something of this sort may be involved in the case of thewren Troglodytes musculus in Surinam. There, however, the evidenceis as yet less explicit and less impressive.
Destruction of Host Eggs by ParasiteAs in the case with many parasitic birds, the shiny cowbird destroysmany eggs of its hosts before, after, or at the time of the laying of itsown eggs in their nests. In the species, however, there is some evi-dence that the habit of deliberately puncturing eggs with its biU hasbecome established beyond any immediate or even approximatecorrelation with its own ovulation. In Salta, northwestern Argen-tina, Hoy (mss., 1961) found that this cowbird continued to destroyeggs of other birds long after its own breeding season. Not onlywas the habit unduly protracted, but also it was continued withundiminished frequency. Egg destruction was not limited to fe-male cowbu'ds but was indulged in by males as well. On Janu-ary 26 Hoy was watching the nest of a tanager, Thraupis bonariensis,which nest contained no cowbird eggs and 3 tanager eggs. Whenthe incubating bird left the nest for a moment, a male shiny cowbirdsuddenly appeared, went directly to the nest and immediately de-stroyed aU 3 eggs by pecking holes in them.It is weU established that egg-pecking is far from universal; manyparasitized nests show no such activities. The situation is thussimilar to that of the brown-headed cowbird, with the importantdifference that, in the latter case, egg-pecking is restricted to nestsalready parasitized or about to be parasitized?and only to suchnests. In other words, there is a close correlation between egg-layingand egg-pecking in the bro^vn-headed species but not in the shinycowbird.
Hosts Known To Have Reared Young of the ParasiteThe present host catalog is heavily weighted with records of eggswhich were seen and collected instead of being allowed to hatch andthus afford an opportunity to watch the young develop. Thisnecessarily increases the number of cases wherein we have no definiteinformation that the host could and would rear the parasitic young,but the absence of such data cannot be taken as meaningful. Of the146 species in our present list, the 26 listed below have been reported as
HOST RELATIONS OF PARASITIC COWBIRDS 197having reared young shiny cowbirds. This number will undoubtedlyincrease with further field study.It is worth noting that one of the most frequently imposed uponvictims, the fork-taHed flycatcher, Muscivora tyrannus, for whichsome 57 records of parasitism are available, has not yet been reportedas having reared the parasitic young. In this species the earherobservations, especially those of Hudson (1874, pp. 153-154), indi-cated that the much harassed flycatcher frequently deserted its nestbecause of excessive parasitism; in some instances its own eggs wereoutnumbered 3 to 1 by those of the parasite.
rufous ovenbird, Furnarius rufusfirewood gatherer, Anumbius anumbiwhite-naped ant shrike, Sakesphorusbernardiwhite-headed marsh tyrant, Arundi-nicola leucocephalashort-tailed ground tyrant, Musci-gralla brevicaudabellicose tyrant, Tyrannus vielan-cholicusreed tyrant, Pseudocolopierix flavi-ventrisSouth American house wren. Troglo-dytes muscidusPatagonian mockingbird, Mimus pata-gonicuslong-tailed mockingbird, Mimuslongicaudatuscalandria, Mimus saturninuswhite-banded mockingbird, Mimustriurus
dusky thrush, Turdus amaurochaUnnsred-bellied thrush, Turdus rufiventrisbrush gnatcatcher, Polioptila dumicolabicolored ateleodacnis, Ateleodacnisbicolorgolden warbler, Dendroica petechiaSwainson's grackle, HoloquiscaluslugubrisGrace's oriole, Icterus grace-annaeblue and yellow tanager, Thraupisbonariensisgrayish saltator, Saltator coerulescensorange-billed saltator, Saltator auran-tiirostrisscreaming seedeater, Sporophila caeru-lescensDiuca finch, Diuca diucaChingolo sparrow, Zonotrichia capensisblack and chestnut warbling finch,Poospiza nigro-rufa
New information on the life histories of Neotropical birds accumu-lates very slowly compared with the rate of progress in our knowledgeof the systematics and distribution of these creatures. In view ofthe paucity of observers in South America, it is all the more pleasantto be able to note and extract interesting data from two importantand recently published studies from opposite sides of that continent.Marchant (1958, 1960) has brought to the attention of ornithologiststhe first information available on the brood-hosts of the Ecuadorianrace of the shiny cowbird (M.6. aequatorialis), and Sick and Ottow(1958) have made a significant study of this parasite and the chingolosparrow, its chief victim, in southeastern Brazil. In addition tothese, Ottow and Hoy (mss., 1961) have made interesting studies in
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northeastern Argentina, and they have generously sent me data fromtheir unpubUshed work.When one considers the vast geographic range of the shiny cow-bird?from Patagonia to the Colombian-Panamanian border andto some of the islands of the West Indies?and when one also considersthe very large number of available host species in all of that diversifiedarea, it is obvious that the known instances of host choice by theshiny cowbird are still little more than a sampling of what one mayexpect to be reported in time. A slight inlding of this may be gatheredfrom Mrs. Mitchell's experience in Brazil (1957, pp. 204-205), whereshe recorded seeing a female shiny cowbird attempting unsuccess-fully to enter the nest of a becard, Platypsaris rufus, and of a fly-catcher, Satrapa icterophrys, both of which probably will be foundeventually to be victimized there; as yet this fact has not been re-corded. And these are the relatively casual observations of oneobserver in a limited area! It is true that in some parts of SouthAmerica, such as most of Argentina (except the extreme north),Uruguay, and southeastern Brazil, we probably now know the vic-tims most frequently imposed upon by the parasite. On the otherhand, there are many species of birds that seem to be utilized ratherseldom but only because, so far, merely a few records have been notedby occasional observers. South American birds have yet to be ade-quately studied by sufficient numbers of observers.The earlier reports in this series have become exceedinglydifficult for readers to use and compare because of numerous changesin nomenclature and systematic treatment of the various species andsubspecies involved. In a few cases, what had been recorded asseparate forms now have been united; others have been divided inways that are different from earlier usage. To give a composite pic-ture of the present state of knowledge, I am including in tabular form alist of all the known hosts, divided into races both of the host and of theparasite. In this table no columns have been made for two racesof the shmy cowbird, nigricans and riparius, for the reason thatso far no host records are available for them. A perusal of thistable shows that the host list for Molothrus honariensis now includes193 species and subspecies (148 species) of birds, as compared with98 forms (82 species) in my 1929 list.
HOST RELATIONS OF PARASITIC COWBIRDS 199
Hosts of the Shiny CowbirdSummary
200 U.S. NATIONAL MUSEUM BULLETIN 233Summary?Continued
HOST RELATIONS OF PARASITIC COWBIRDSSummary?Continued 201
202 U.S. NATIONAL MUSEUM BULLETIN 233Summary?Continued
HOST RELATIONS OF PARASITIC COWBIRDS 203
Since the last addendum to the known fosterers (Friedmann, 1949,pp. 154-157), 24 additional species and subspecies of birds have beenfound to be parasitized by this cowbird, bringing the corrected totalup to 193 forms. The new hosts are listed below.pyrrhophia pyrrhophiaCranioleuca(Vieillot)Aslhenes baeri baeri (Berlepsch)Sakesphorus bernardi bernardi (Lesson)Xolmis cinerea (Vieillot)Muscigralla brevicauda Lafresnaye andd'OrbignyPitangus sidphuratus maximiliani (Ca-banis and Heine)Thryothoriis superciliaris superciliarisLawrenceTroglodytes viusctdus tobagensis Law-renceMimus longicaudatus albogrisevs Les-sonTurdus falklandii magellanicus KingVireo flavoviridis griseobarbatus (Ber-lepsch and Taczanowski)
Dacnis cayana cayana (Linnaeus)Dendroica petechia riificapilla (Gnielin)Macroagelaius subalaris imthurmi(Sclater)Icterus bonana (Linnaeus)Icterus chrysocephalus (Linnaeus)Icterus grace-annae CassinIcterus chrysater giraudii CassinIcterus jamacaii croconotus (Wagler)Pezites militaris belUcosa (Filippi)Pheucticus chrysopeplus chrysogaster(Lesson)Oryzoborus angolensis angolensis (Linn-aeus)Aimophila strigiceps dabbenei (Hell-mayr)Zonotrichia capensis subtorquata Swain-sonIn addition to the above, some other birds previously known asfosterers of one race of the parasite, have now been found to serve inthis manner for other races as well. To simplify matters, we maylist the new hosts by subspecies of the cowbird before considermg themindividually.The following are additions to the recorded victims of the nominateform of the cowbird, M.h. bonariensis, bringing its list of known hostsup to 122 forms.Cranioleuca pyrrhophia pyrrhophia(Vieillot)Asthenes baeri baeri (Berlepsch)Xolmis cinerea (Vieillot)Pitangus sulphuratus maximiliani (Ca-banis and Heine)Turdus falklandii magellanicus KingThe Ecuadorian race of the shiny cowbird, Al.b. aeqnaforialis,none of whose hosts previously have been recorded by me, has recentlybeen found to parasitize the following eight birds.
Oryzoborus angolensis angolensis (Linn-aeus)Aimophila strigiceps dabbenei (Hell-mayr)Zonotrichia capensis subtorquata Swain-son
Sakesphorus bernardi bernardi (Lesson)Muscigralla brevicauda Lafresnaye andd'OrbignyThryothorus superciliaris superciliarisLawrenceMimus longicaudatus albogriseus Les-son
Vireo flavoridis griseobarbatus Berlepschand TaczanowskiIcterus grace-annae CassinPezites militarus bellicosa (FilipiM)Pheucticus chrysopeplus chrysogaster(Lesson)
204 U.S. NATIONAL MUSEUM BULLETIN 233To the previously listed fosterers of the small, northern race of thecowbird, M.h. minimus, the following are added, bringing the total upto 34 forms. This race is extending its range in the West Indian area,an expansion which brings it into contact with new potential hosts.
Troglodytes musculus tobagensis Law- Icterus bonana (Linnaeus)rence Icterus chrysocephalus (Linnaeus)Dacnis cayana cayana (Linnaeus) Icterus jamacaii croconotus (Wagler)Dendroica petachia ruficapilla (Gmelin)Macroagelaius stibalaris imthurmi(Sclater)Two additions to the hosts of the Venezuelan race of the shinycowbird, M.b. venezuelenis, are here recorded, bringing its knownfosterers to a total of 10.Holoquiscalus lugubris (Swainson) Icterus nigrogularis nigrogularis (Hahn)Single records of two additional hosts of the large Colombian raceof the parasite, M.h. cabanisii have come to my attention, bringing itsknown hosts up to 8 forms.
Icterus chrysater giraudii Cassin Tachyphonus rufus (Boddaert)In the following catalog the pertinent data are given for theseadditional hosts and also new data on previously listed hosts in caseswhere the information appreciably alters our understanding and ourearlier summation.
Stripe-crowned SpinetailCranioleuca pyrrhophia (Vieillot)This spinetail recently has been added to the known hosts of theshiny cowbird in the Province of Salta, northwestern Argentina,by Gunnar Hoy, to whom I am indebted for the information. Thenominate races of both host and parasite are involved in this record.
Baer's SpinetailAsthenes baeri (Berlepsch)The first records of this spinetail as a host of the shiny cowbirdonly recently have come to my attention?all of them from parasitizednests found near Salta, northwestern Ai^gentina, by Gunnar Hoy,according to Dr. Johann Ottow (in htt., 1961). The nominate raceof host and of parasite are involved here. Further details, receiveddirectly from Hoy, indicate that this bird is rather frequently vic-timized and that as many as 3 cowbird eggs have been found inone nest. Hoy found that the host usually accepted and incubatedthe parasitic eggs. "As usual, the Asthenes would not forsake thenest for an egg or two of the cowbird. In some cases it would incubateeven three, but I never saw it incubate four."
HOST RELATIONS OF PARASITIC COWBIRDS 205Hoy noted a peculiar situation for which, with present information,no explanation can be advanced. Asthenes baeri and another spine-tail, Phacellodomus rufifrons sincipitalis, are both common locally;both build similar types of nests in similar places, the nests of thelatter differing from those of the former only in their somewhat larger
size. Despite the similarity, the shiny cowbird parasitizes the formerof these two and apparently does not show any interest in the latter.Yet the nonparasitic bay-winged cowbird, Molothrus badius, uses withequal frequency old nests of both of these spinetails for its ownbreeding site. Firewood-gathererAnumbius anumbi (Vieillot)To the single earlier record Usted by me (1938, p. 43), may beadded one more. G. Harrison (1950, p. 6) mentions an egg of theshiny cowbird taken with a set of eggs of the firewood-gatherer.Apparently it was collected in Argentina, which was the locality in theearlier case. The large stick nests of this and other woodhewers arenot particularly favored by the shiny cowbird.
White-naped Ant ShrikeSakesphorus bernardi (Lesson)The white-naped ant shrike is a recent addition to the recordedhosts of the shiny cowbird, which was reported in this capacity fromthe Santa Elena peninsula of southwestern Ecuador by Marchant(1958, p. 384; 1960, p. 369, 584). The typical race of the host and therace A/.6. aequatorialis of the parasite are involved here. Marchantobserved four parasitized nests, of which only one produced a youngcowbird; two were total losses, with their included eggs, and in a thirdthe cowbird egg disappeared before the host young was well along inits development. Gray PepoazaXolmis cinerea (Vieillot)This flycatcher has been found to be parasitized in the state ofMinas Geraes, Brazil, by the local race of the shiny cowbird {M.b.bonariensis) . The report was made by Chagas (in litt.). There areno previous records of this bird as a cowbird victim.Widow PepoazaXolmis irupero (Vieillot)Recently Hoy (mss., 1961) near Salta, northwestern Argentina,found that this flycatcher, which breeds in old nests of the ovenbird,Furnarius rujus, is parasitized regularly by the shiny cowbird. Judg-ing from his experience of finding broken cowbird egg shells onthe ground beneath such nests, he concluded that Xolmis showed a
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tendency to throw out the parasitic eggs. Prior to Hoy's observations,this flycatcher had been noted as a cowbird victim a few times in theprovince of Tucuman, not very far to the south of Salta. The nom-inate race of host and of parasite are involved in both cases.
Short-tailed Ground-tyrantMuscigralla brevicauda Lafresnaye and D'OrbignyThis bird was not known to be imposed upon by the shiny cowbirduntil very recently, when Marchant (1958, p. 384; 1960, pp. 372, 584)listed it as a host of the Ecuadorian race of the parasite M.b. aequator-ialis in the Santa Elena peninsula of southwestern Ecuador. Out of36 nests observed, only a single case of parasitism was noted. Inthis nest there were three young cowbirds.
Fork-tailed FlycatcherMuscivora tyrannus (Linnaeus)Known as a frequently used fosterer of the nominate form of theshiny cowbird in Argentina, the fork-tailed flycatcher has now beennoted in a similar capacity in eastern Brazil, where Chagas (in litt.)found it to be parasitized in the state of Minas Geraes. All therecords have to do with the nominate race of the fork-tailed flycatcher.In a study of Venezuelan birds, Friedmann and Smith (1955, p. 507)pointed out how surprisingly little has been published on the nestingof this wide-ranging flycatcher other than in the Argentine habitat ofits nominate race. Such a situation probably accounts for the ab-sence of records of cowbird parasitism in the more northern parts ofits range; it is very unlikely that the fork-tailed flycatcher is leftunmolested by the shiny cowbird in these regions.
Kiskadee FlycatcherPitangus sulphuratus (Linnaeus)To the few previously noted records from Argentina may be addedthe report by Harrison (1950, p. 6) that he found a "substantial"nmnber of victimized nests in Uruguay. On geographic grounds,these Uruguayan records refer to the subspecies bolivianus of the host.Recently, in the state of Minas Geras, Brazil, Chagas (in litt.)has found that the subspecies maximiliani is also victimized by theshiny cowbird. The nominate race, M.b. bonariensis, is involved in
all of these cases. Superciliated WrenThryothorus superciliaris (Lawrence)In the Santa Elena peninsula of southwestern Ecuador, Marchant(1960, pp. 377, 585) found that the superciUated wren was victimizedfrequently by the shiny cowbird (subspecies M.b. aequatorialis) . Of
HOST RELATIONS OF PARASITIC COWBIRDS 207
five nests found in 1958, all were parasitized; of three found in thesame area in 1957, one or two were similarly affected. The highincidence of parasitism on this species, taken in consideration withthe number of other, unmolested, but apparently suitable, potentialhosts in the unmediate area, suggests pronounced preference on thepart of the parasites for this wren. The record refers to the nominaterace of the host. South American House WrenTroglodytes musculus NaumannOne additional subspecies of the wren, T.m. tobagensis, has beenfound to be parasitized by the shiny cowbird (subspecies M.b. mini-mus). In Tobago, at Caledonia, on October 29, Mees (Junge andMees, 1958, p. 127) twice saw a fledgling cowbird being fed by adidtsof this species. A second record for the Chilean race of the Avren{T.m. chilensis) recently has been reported?a nest with 4 eggs of thewren and 3 of the cowbird (subspecies M.b. bonariensis) found atVucro de Linares in November, 1948, by R. Barros Valenzuela(1956, p. 91). The eggs of the wren had been punctured, apparentlyby the coM'-bird.In Peru, the subspecies T.m. audax was known as a host of theshiny cowbird (subspecies M.6. occidentalis) only on the basis ofTaczanowsld's statement (1884, pp. 422-424) that it had been re-ported as such by Stolzmann and Jelski. Recently, Dr. MariaKoepcke has informed me that near Lima she has seen a recentlyfledged cowbird attended by a pair of house wrens. Howe andSingh (1960, pp. 94, 95) considered this wren (subspecies clarus) asthe favorite and, indeed, the only recorded host in British Guiana, asdid Harper (1907, p. 66) years earlier. Similarly Haverschmidt(1955, p. 127) concluded that this bird was the principal host inSurinam; he informed me (in litt.) of 11 instances that had comeunder his own observation there. In Trinidad, Herklots (1961, p.222) reported frequent impositions on this wren; he wrote that severalnests had been found each with from 1 to 3 eggs of the shiny cowbird.The frequent choice of this host by the parasite in northeasternSouth America is noteworthy in view of the fact that in Ai-gentina,Paraguay, and Uruguay Troglodytes musculus is victimized much lesscommonly. Even in these more temperate southern latitudes, how-ever, this wren is parasitized more frequently than its counterpart.Troglodytes aedon, is parasitized anywhere in North America by thebrown-headed cowbird. Long-tailed MockingbirdMirnus longicaudatus TschudiThe subspecies albogriseus of this species of mockingbird has beenadded to the Hst of victims of the shiny cowbird (subspecies Al.b.
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aequatorialis) . In the Santa Elena peninsula of southwestern EcuadorMarchant (1958, p. 384; 1960, p. 380) found two parasitized nests.He also saw, on one occasion, a fledged young cowbird being attendedby one of these mockingbirds (1960, p. 584). The nominate race ofthe long-tailed mockingbird was previously known as a host of theshiny cowbird (subspecies M.h. occidentalis) in Peru (Friedmann,1943, p. 351). White-banded MockingbirdMimus triurus (Vieillot)Already known as a common victim of the shiny cowbird in Men-doza and San Luis provinces, the white-banded mocldngbird wasnoted as the most frequently imposed upon fosterer in Pampa provinceas well, according to Pereyra (1937, p. 289). The frequency withwhich the shiny cowbird parasitizes mockingbirds in Argentina is apuzzhng contrast to the tendency of the brown-headed cowbird toleave the North American mockingbird unmolested in the southernUnited States. Chilean RobinTurdus falklandii Quoy and GaimardR. Barros Valenzuela (1956, p. 92) has recorded the Chilean sub-species of this thrush, T.f. magellanicus, as a victmi of the shiny cow-bird in Chile. This is an addition to the known hosts. In view ofthe recent spread of the shiny cowbird in various parts of centralChile, it may be anticipated that additional hosts will be reportedfrom that coimtry. Spix's ThrushTurdus leucomelas (Vieillot)To the few earlier records of the northern race of this thrush {T.l.albivenier) as a host of the Venezuelan subspecies of the shiny cow-bird {M.b. venezuelensis) may be added another?a nest with 2 eggsof the host and 2 of the parasite. This was found at Casa Blanca,Venezuela, on April 17, and was recorded by GiUiard (1959, p. 26),who wrote that this thrush is frequently imposed upon in that area.
Brush GnatcatcherPoUoptila dumicola (Vieillot)In my original study (1929, p. 110), I noted that, while Hudson hadlisted this gnatcatcher as a victim of the shiny cowbird in Argentina,he gave no specific records or details. Harrison (1950, p. 6) now haspublished a definite record, which removes the earlier uncertaintyattached to this bird as a molothrine host. The nominate race ofboth the host and the parasite are involved here.
HOST RELATIONS OF PARASITIC COWBIRDS 209
Yellow-green VireoVireo flavoviridis (Cassin)Marchant (1958, p. 384; 1960, p. 382, 584) has reported that theEcuadorean race of the shiny cowbu'd, M.h. aequatorialis, parasitizesthe local race {VJ. griseoharhatus) of this vireo in the Santa Elenapeninsula, southwestern Ecuador. He noted that 7 nests of this vireosucceeded and 6 failed, and of these failures, 3 were due ostensiblyto parasitism by the cowbird.Ochre-fronted VireoHylophilus aurantiifrons LawrenceOne subspecies of this vireo, H.a. saturatus, was previously recorded,on the the basis of two records (Friedmann, 1938, p. 44), as a victimof the shiny cowbird in Trinidad. Recently, Mr. R. Kreuger hasinformed me that he possesses five parasitized sets of eggs of thisbird, all from Trinidad and all collected by Smooker, who had collectedthe two earlier records. It seems probable that the first two areincluded in the five cases. With such an increase in Imown instancesof parasitism, it now would appear that this vireo is locally a regularhost of the shiny cowbird. Cayenne DacnisDacnis cayana (Linnaeus)At Caroni Swamp, Trinidad, on July 18, 1932, G. D. Smookerfound a nest of this bird containing 2 eggs of the shiny cowbird and1 of its own. The set is now in the collection of R. Kreuger ofHelsinki, to whom I am indebted for this record. The species wasnot previously known as a cowbird host. The nominate race of thehost and the race M.b. minimus of the parasite are involved.
Bicolored AteleodacnisAieleodacnis bicolor (Vieillot)Previously known, on the basis of a single record (Friedmann, 1938,p. 44), as a host of the shiny cowbird in Trinidad, this little-knownspecies of honey-creeper now has been found to be parasitized alsoin Surinam. Haverschmidt (in litt.) informs me that on February28, 1953, in the vicinity of the Corentyne River near Nickeries, heobserved a recently fledged shiny cowbhd being attended and fed byone of these honey-creepers. This observation adds it to the list ofhosts known to have reared the parasite; the former record was oneof eggs only. It should be pointed out that the Trinidad record maynot be wholly satisfactory when one considers the uncertain aspectsof our knowledge of the nesting habits of this honey-creeper. (SeeBelcher and Smooker 1937, p. 520.) Both records here refer to thenominate race of the host and to the small, northeastern race of theparasite, M.b. minimus.
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Golden WarblerDendroica petechia (Linnaeus)Mrs. F. C. K. Anderson wrote me the following: she had been toldby a friend who was interested in birds that on two occasions he hadseen young fledgling shiny cowbirds being fed by a pair of thesewarblers near Bridgetown, Barbados. Pinchon and Bon Saint-Come(1951, p. 273) also have noted this warbler as a cowbird fosterer, and,on the strength of their comments, Bond (1951), p. 20) in turn hasmentioned it. These records refer to the race ruficapilla of the warblerand to the race minimus of the cowbird.
Imthurm's GrackleMacroagelaius suhalaris (Boissonneau)On the basis of a parasitized set of eggs in the C. J. MarinkelleCollection, The Hague, Netherlands, this graclde (race M. s. imthurmi)may be added now to the list of victims of the shiny cowbrid (raceM.h. miniinus). The set is said to have been collected in the Guianas,but exact data are not available to me.
Swainson's GrackleHoloquiscalus lugubris (Swainson)Previously known as a victim of the shiny cowbird in TrinidadM.b. (minimus), this grackle has been found to be the commonestvictim of the Venezuelan subspecies of the parasite {M.b. venezuelen-
sis.) Foster D, Smith (Friedmann and Smith, 1955, p. 514) dis-covered that in northeastern Venezuela the shiny cowbird parasitizedthe nominate race of this grackle not just frequently but apparentlyexclusively. Smith noted that about a quarter of the young whichaccompainied the gi-ackles to his feeding station were cowbirds. Later,while still in juvenal plumage, the cowbirds left the grackle flocksand joined flocks of adults of their own species. This is one of therelatively rare cases of a frequently imposed upon host which isconsiderably larger in size than the parasite.
Martinique OrioleIcterus bonana (Linnaeus)This Oriole is an addition to the known victims of the West Indianrace of the shiny cowbird {M.b. minimus). Pinchon and Bon Saint-Come (1951, p. 273) record it as being parasitized in Martinique.
Moriche OrioleIcterus chrysocephalus (Linnaeus)A single record, from Surinam, of this hitherto unrecorded host isin the collection of Dr. C. J. Marinkelle, to whom I am indebted for
HOST RELATIONS OF PARASITIC COWBIRDS 211
the information. The cowbird involved is the small northern raceM.b. minimus. Grace's OrioleIcterus grace-annae CassiiiMarchant (1960, p. 586) recently has added this oriole to the listof hosts of the shiny cowbird in southwestern Ecuador. He found anest in March, 1958, containing five young birds, "three of whichlater observations showed were cowbirds: one young oriole died inthe nest when more than seven days old and well-feathered, but I wasuncertain of the fate of the other. It would have been most excep-tional if it had survived in such a heavily parasitized nest. Bothadult orioles were feeding the young. When empty, I found a paleblue, very faintly spotted, unhatched egg m the nest, presumablyanother cowbird egg, since those of the genus Icterus are bluish white,more or less heavily marked with chocolate and brown." The raceof shiny cowbird involved is M.b. aequatorialis
.
Lesson's OrioleIcterus chrysater (Lesson)Dr. F. C. Lehman V. (in litt.) recently informed me that a nest ofthis oriole containing a shiny cowbird 's egg was found at El Tambo,Cauca, Colombia, m 1938. The cowbird there is of the race Al.b.cabanisi; the oriole, I.e. giraudii. There are no previous records ofthis oriole as a cowbird host.
Black-throated OrioleIcterus nigrogularis (Hahn)This oriole was previously known as a victim of the Colombian raceof the shiny cowbird, M.b. cabanisii, and of the race Al.b. minimus inTrinidad and in Dutch Guiana. It has since been reported in Vene-zuela by Gines, Avelado, et al (1951, p. 303) as a host of the localrace M.b. venezuelensis. The Trinidad and Guiana records refer tothe local race of the oriole (I.n. trinitatis), the others to the nominatesubspecies. Orange-backed OrioleIcterus jamacaii croconotus (Wagler)Dr. C. J. Mariukelle informed me (m litt.) that he has hi his col-lection a set of eggs of the orange-backed oriole with a shiny cowbirdegg which was collected in British Guiana. The cowbird is of the sub-species M.b. minimus. I know of no other record for this host.
Red-breasted BlackbirdLeistes militaris (Linnaeus)The southern race L.m. superciliaris , previously (Friedmann, 1938,p. 45) known from only two records, is apparently a frequent host of
212 U.S. NATIONAL MUSEUM BULLETIN 233
the shiny cowbird in the province of Pampa, Argentina, where Pereyra(1937, p. 297) noted that it was unusual to find an unparasitizednest of this bird.To the northern, nominate race of the red-breasted blackbirdshould be referred a record of cowbird parasitism in Surinam, firstcited by me (1929, p. 120) on the basis of the Penards (1910), asLampropsar tanagrinus guianensis. I am indebted to Dr. FrancoisHaverschmidt for correcting this old, erroneous identification.
Red-breasted StarlingPezites militaris (Linnaeus)A single instance of this bird as a victim of the shiny cowbird insouthwestern Ecuador was recently reported by Marchant (1960,p. 584). The local race of the parasite is M.h. aeguatorialis; the hostis P.m. hellicosa. Palm TanagerThraupis palmarum (Wied)To the previous single record known to me (Friedmann, 1934b,p. 345) may be added the data that Chagas (in litt.) found this tanagerto be a victim of the shiny cowbird in Minas Geraes, Brazil. Bothrecords have to do with the typical race of the parasite and of thetanager. Brazilian TanagerRamphocelus bresilius (Linnaeus)In Rio de Janeiro province, Brazil, Sick and Ottow (1958, p. 45)found two parasitized nests of this tanager (subspecies dorsalis)?onewith 3 eggs of the host plus 1 of the shiny cowbird, on November 22
;
the other with 2 eggs of the tanager plus 1 of the parasite, onDecember 7. These additions to the very few previous records makeit appear that this tanager may be a fairly regular victim.
Greater White-shouldered TanagerTachyphonus rufus (Boddaert)A second record of this tanager as a host of the Venezuelan race ofthe shiny cowbird recently has been published. Near Caracas onAprU 24 GHHard (1959, p. 29) found a nest with 1 egg of the hostand 1 of the cowbird. According to information kindly sent meby F. C. Lehmann V, a hitherto unpublished case of this bird as ahost of the Colombian race of the parasite was found in 1961 on afarm near Bitaco, west of Call, by Alfred Kyburz.
Golden-bellied GrosbeakPheucticus chrysopeplus (Vigors)Marchant (1960, p. 584, 587) found eggs of the shiny cowbirdsubspecies M.b. aeguatorialis) in two nests of this grosbeak (sub-
HOST RELATIONS OF PARASITIC COWBIRDS 213
species P.c. chrysogaster) in southwestern Ecuador. No previousinstances of cowbird parasitism on this bird are known.
Antillean BullfinchLoxigilla noctis (Linnaeus)According to information sent me by Mrs. F. C. K. Anderson ofthe Barbados Museum and Historical Society, 1 egg of the shinycowbu'd (Al.b. minimus) was found in a nest of this finch nearBridgetown, Barbados. This is the second record for this host(race L.n. harhadensis)
.
Chestnut-bellied Rice GrosbeakOryzoborus angolensis (Linnaeus)According to Chagas (in litt.), this finch is victimized by the shinycowbird in Minas Geraes, Brazil. No previous records for the speciesare known. The nominate race of the finch as well as of the parasiteis involved here. Yellow FinchSicalis flaveola (Linnaeus)The subspecies S. f. pelzelni has been recorded as a host of theshiny cowbird on only a few occasions (see Friedmann, 1929, p. 113;1934, p. 345). It is worth noting that Pereyra (1937, p. 302) smcehas found it to be parasitized in Pampa province, Argentina, as hasHoy (ms., 1961) in Salta province. The latter observer found thatthis fijich was prone to desert its nest somewhat readily when it wasparasitized. Misto Yellow FinchSicalis luteola (Sparrman)On the basis of reports by Gibson and by Devincenzi, I originallylisted this finch (race luteiventris) as a victim of the shiny cowbu'din Argentma and Uruguay, but I had no fmother data. Harrison(1950, pp. 6-7) has since recorded an egg of the parasite from a nestof this fosterer in Argentina. Inasmuch as neither the finch nor thecowbird are local or rare, and inasmuch as the nest of the formerseems in every way suitable, it is difficult to see why the misto finchis not parasitized more frequently. The nominate races of both thefinch and the cowbird are involved here. The authors mentionedabove refer to this finch under the name Sicalis arvensis.
Red-crested FinchCoryphospingus cucullatus (P. L. S. Miiller)Near Salta, northwestern Argentina, Hoy (ms., 1961) found thatthis bird (subspecies ruhescens) was parasitized rather frequently andthat it deserted its nest in a number of such instances. It has
214 U.S. NATIONAL MUSEUM BULLETIN 233been recorded a few times previously as a host in Tucunian provinceand in southeastern Brazil.
Striped-headed SparrowAimophila strigiceps (Gould)I am informed by Dr. Johann Ottow that at Salta, Argentina, onDecember 16, 1960, Gunnar Hoy collected a set of eggs of thissparrow containing 1 egg of the shiny cowbird, thereby adding thisspecies to the roster of laiown hosts of the parasite. The recordinvolves the race A.s. dahhenei of the sparrow and the nominate raceof the shiny cowbird. Chingolo SparrowZonotrichia capensis (P. L. S. Miiller)The recent study by Sick and Ottow (1958) has added greatly toom' knowledge of the relations between the shiny cowbird and thissparrow, the parasite's commonest host in southeastern Brazil andArgentina. Worldng in the province of Rio de Janeiro, Sick andOttow found 93 nests of the sparrow, of which 57, or 61 percent, wereparasitized. This may be compared with Moojen's data (1938, p.17) at Vicosa, Minas Geraes, where 75 percent of the nests wereaffected. In the latter province, Chagas (in litt.) has found hundredsof nests, and "almost all" contained 2, 3, or 4 eggs of the shinycowbird, and, in one instance, as many as 14 eggs of the parasite.Allowing even for loose writing, "almost all" must signify a majority.Sick and Ottow never found more than a single egg from any onecowbird in any nest. In the course of 80 days of observations ina carefully watched "control" area about .2 kilometers square, 41female cowbirds deposited 64 eggs. The identity, and hence, thenumber, of the laying birds was arrived at by a study of the coloration,size, and shell thiclaiess of the eggs. The predilection of the shinycowbird for the chingolo as a host is indicated further by the factthat, in the same area and during the same period of observation, onl}^2 nests of a tanager, Ramphocelus bresilius, were parasitized, andnone of 31 nests of 9 other potential host species were affected.The success of the cowbird in nests of this sparrow may be judgedfrom that fact that 44 percent of the parasitic eggs hatched and26 percent lived to the fledging stage, while 41 percent of the hosteggs hatched and 24 percent survived to the fledging stage.The data from Minas Geraes refer to the subspecies Zx. subtorquatawhile the coastal data have to do with another race of the host,Z.c. matutina.Dr. Maria Keopcke has recently informed me that, on 15 ormore difi'erent occasions, she has seen fledglings of the shiny cowbird(race Ad.h. occidentalis) being cared for by chingolos (race Z.c.
HOST RELATIONS OF PARASITIC COWBIRDS 215
peruviensis), near Lima, Peru. While there are earlier records fromPeru, the number of Dr. Koepcke's instances make it clear that inthat country, as in Argentina and Brazil, this sparrow is a veryfrequent, if not the most frequent, host.
White and Gray Warbling FinchPoospiza melanoleuca (Lafresnaye and d'Orbigny)Commonly parasitized by the shiny cowbird in the province ofTucuman, this finch also has been noted as a cowbird host in Salta,by Hoy (ms., 1961), who listed it as one of those fosterers which oftenare motivated to desert their nests by the intrusions of the parasite.Many-colored Ground SparrowSaltatricula multicolor (Burmeister)This finch, previously known as a cowbird victim from a singlerecord in Tucuman province, Argentina, has been found recent!}^ byHoy (ms., 1961) to be parasitized not infrequently farther nortli inthe province of Salta. Hoy considered this bird as one of those hostswhich are prone to desert their nests when they are parasitized, buthe gave no actual estimates of the number of cases he observed.
La Plata Ground FinchEmbernagra platensis (Gmelin)Hoy (ms., 1961) found that this bird was victimized not infrequentlynear Salta, northwestern Argentina. It was recorded previousl}^ as ahost species in Paraguay and in Buenos Aires province. According toHoy, it was caused readily to desert its nest because of the attentionsof the parasite. The Salta and Paraguayan records involve the raceolivascens and the Buenos Aires record, the nominate. All the casesinvolve the nominate race of the parasite.
630590?63 15
Screaming Cowbird
Molothrus rufo-axillaris CassinThe host-parasite relations of this, the most primitive of the para-
sitic cowbirds, are quite simple. The species is parasitic only on itsancestral and very closely related non-parasitic congener, the bay-winged cowbird, M. badius. This relationship was first discovered byHudson (1874, pp. 161-166) and was further elucidated and describedin greater detail in my 1929 book (pp. 46-53). Unfortunately, exceptfor a still unpublished study by Hoy and Ottow, almost nothing ofimportance has been added to our knowledge since then and there isno need to repeat here the details available in my earlier publication.Suffice it to say that the eggs and the nestlings of the parasite and ofthe host are very similar and evince no signs of interspecific competi-tion in any way different from what would normally transpire betweeneggs or young of the host alone. The young of the two species growup together in apparent amity.Only one recent observation should be mentioned here. In theprovince of Salta, northwestern Ai'gentina, Hoy (mss., 1961) foundevidence that a certain amount of mutual egg destruction may takeplace between this species and its host. However, in view of myfeeling of uncertainty as to the identification of the eggs in each ofthe cases he noted, it is still not clear to me which species did the eggpecking and to which species the pecked eggs belonged. Hoy hasfound a situation that differed from what I found in Tucuman andEntre Rios provinces, where no such frequent egg destruction wasnoted. It is only fair to add that Hoy and Ottow have far less of afeeling of uncertainty about this than I do. Eventual publication oftheir data should be of much interest and may be expected to clarifythe situation.There have been reports to the effect that the screaming cowbirdwas parasitic on other birds at least occasionally, but none of thesecases has been authenticated, and their status is highly doubtful.Grant (1911, p. 104) wrote that he had found eggs of the screamingcowbird in nests of the yellow-breasted marsh bird, Pseudoleistesvirescens. However, the bay-winged cowbird has been known tobreed in old nests of this species, and Grant admitted that he hadfound Pseudoleistes nests with nothing but cowbird eggs in them.Since the eggs of the bay-wing and of the screaming cowbird aredistinguishable only with difficulty, the identification of these eggs asthe latter species is not certain. In this connection, it may be recalled216
HOST RELATIONS OF PARASITIC COWBIRDS 217
that, many years earlier, Hudson (Sclater and Hudson, 1888, vol. 1,p. 97) once saw two young "bay-winged cowbirds" following and beingfed by a yellow-breasted marsh bu'd. This originally caused Hudsonto assume that the bay-wing was occasionally parasitic, but later, ashe learned of the parasitic breeding of the screaming cowbird, hefelt that this observation must have been of two fledglings of thatspecies. This is the most nearly "evidential" observation on recordfor M. rufo-axiUaris parasitizing any bu'ds other than AI. badius.By itself it is not too good, as young cowbirds are apt to beg for foodfrom adults that did not rear them and very frequently succeed ingetting fed by them.On the basis of eggs collected by Pablo Girard in western Argentina,Pereyra (1938, p. 260) listed half a dozen other species of birds ashosts of M. rufo-axillaris?an ovenbird, Furnarius rufus; an ant shrike,Taraba major; a flycatcher, Pitangus sulphuratus; a mocking bird.Animus saturninus; a thi'ush, Turdus rufiventris; and a finch, Sicalispelzelni; but these seem almost certainly to be misidentified recordsofM. bonariensis, a species which is known to parasitize all of these bu'ds.
Giant CowbirdPsomocolax oryzivorus (Gmelin)The giant cowbird is related to the bronzed cowbird stock, fromwhich it differs chiefly by its much greater size and by the moredeveloped "cape" feathers. Apart from one recent observation(Lehman, 1960), it is known to be parasitic only on other icterinebirds of the oropendola and cacique group, and, while the situationneeds further investigation, enough is known to make it apparentthat the range of host choice is usually restricted to these birds.All of these fosterers have in common the habit of colonial nesting:many of their long, woven, pouch-like nests are suspended from thebranches of a single tree. In its restricted range of hosts the giantcowbird is more like the screaming cowbird, M. rufo-axillaris, thanit is like the bronzed cowbird. The latter, as stated earlier, is pre-dominantly parasitic on icterine species, chiefly orioles, but hasextended its parasitism to include many other birds as well (seepp. 173-188).We may recall that the bronzed cowbird, Tangavius, is consideredan evolutionary offshoot of the stock represented by the screamingcowbird, which is parasitic entirely on one species, the closely relatedbay-winged cowbird. I have long considered it probable that thephjdetic arrangement between these three cowbirds would rank themthus: M. rufo-axillaris as the most primitive, then Tangavius, and thenPsomocolax. However, the fact that there is greater similarity inrestricted host dependence between the large Psomocolax and thesmaller M. rufo-axillaris than there is between either of them andTangavius raises the possibility that the giant cowbu"d may be a verylarge derivative from the screaming cowbird line, and that it, in turn,gave rise to the more "normal" sized bronzed cowbird stock. Thepresent geographical distribution of the three would support such apossible interpretation. The screaming cowbird occurs from centralArgentina north to extreme southern Brazil and to Paraguaj^;the giant cowbird ranges from northeastern Argentina, Paraguay,eastern Bolivia, and southern Brazil to Mexico; while the bronzedcowbird is found in Colombia, and again from western Panama,north through Costa Rica, Nicaragua, El Salvador, Guatemala,and Mexico to Texas and Arizona. The chief difficulty in this con-ception of relationships is that we have to accept a giant formbetween two smaller ones. The evidence, if it may be dignified bysuch a term, is not at all conclusive, but merely suggestive. If one218
HOST RELATIONS OF PARASITIC COWBIRDS 219
merely examines specimens of the three, the giant species wouldcertainly be looked upon as a climax development and not as anintermediate one. Ethologically and geographically, the data aremore readily arranged with the giant form in the middle.In keeping with its large size, the giant cowbird parasitizes largehosts. Although it occurs over a vast range and is not a rare bird inmany areas, Psomocolax remains a very inadequately studied species.Indeed, since my 1929 account, little really new or significant informa-tion has been added to our knowledge of its breeding habits. However,Belcher and Smooker (1937, pp. 525-526), Skutch (1954, pp. 316-320),Tashian (1957, pp. 87-97), Schafer (1957, pp. 135-138), and Lehmann(1960, pp. 272-273) have added welcome supplementary observationson its habits in Trinidad, in Central America, in Venezuela, and inC'Olombia.Seven species have been recorded as hosts of the giant cowbird,four of which are listed in my earlier account.green jay, Cyanocorax yncas green oropendola, Xanthornus viridis(Boddaert) (P. L. S. Muller)Wagler's oropendola, Zarhynchus yellow-rumped cacique, Cacicus celaloagleri (Gray and Mitchell) (Linnaeus) *Montezuma oropendola, Gymnostinops red-rumped cacique, Cacicusmontezuma (Lesson) haemorrhous (Linnaeus),crested oropendola, Xanthornusdecunianus Pallas
? Cacicus persicus, previously listed as a host, Is now considered to be a synonym of C. cela.The recent addition of so unexpected a bird as the green jay to theknown hosts by Lehmann (1960, p. 273) can only be looked upon,in light of cm-rent knowledge, as an unusual host choice. The greenjay makes an open, saucer-shaped nest of twigs and rootlets, oftenplaced in the denser portions of the foliage of the trees in which theyare built, a very different type of nest from the long, conspicuous,pendant nests of the oropendolas.Lehmann watched a pair of these jays attending and feeding a re-cently fledged giant cowbird in August 1957, at Cajibio, Cauca,Colombia. He observed these three birds together repeatedly onseveral mornings as they came to feed in his garden. No young jayswere seen with them. The fact that the observation was of someduration indicates that it was a real foster parent-young relationship.(If it had been a single casual observation, the possibility would haveremained that the young parasite might not actually have been rearedby the jays but that it had begged for food from them and had suc-ceeded in obtaining their temporary response and attention. Suchoccurrences are known to happen not infrequently with the smallercowbirds and even with fledglings of non-parastitic species.)
220 U.S. NATIONAL MUSEUM BULLETIN 233Chapman (1928, pp. 152-154) and Skutch (1954, pp. 298, 318-319)have described something of the host relationship of the giant cow-bird with two of its usual victims. Here we have a situation far moretense and militant than in the smaller cowbirds. Writing of theMontezuma oropendola, Skutch summarized his notes as follows:
"The Giant Cowbird who lays in an oropendola's nest meets far moreopposition than the parasitic birds of other species which lay their eggsin the nests of small birds which breed in isolated pairs. The GiantCowbird that fuially succeeds in laying in an oropendola's nest mustnot only dodge the watchful oropendolas of both sexes, but sometimesshe must also outwit jealous rivals of her own species, each eager todrop her own eggs into the newly finished nest and ready to driveaway another cowbird who attempts to get ahead of her. It costs thecowbirds so much effort to foist their eggs on the oropendolas that Isuspect that it would involve very little more labor for them to buildsome simple nest and rear their own young.
"Had the oropendolas made a concerted attack upon these unbiddenguests, they might have driven them permanently from the nest tree;but they are mild mannered birds and seemed to be content merely toprevent entry of the cowbirds into then- nests . . . ."Skutch once saw a giant cowbird enter the nest of a Montezumaoropendola. A few minutes later he saw an oropendola emerge, carry-ing a giant cowbird egg in her bill. She dropped the egg, whichlanded on the ground, unbroken by a fall of some 80 feet, Skutchwas able to measure it and found it agreed with published dimensionsof eggs of this parasite.All oropendolas are not as discerning or as hostile as this one, andthe species does at times accept the strange egg and rears the youngparasite.Studying Wagler's oropendola, Chapman concluded that thesebirds appear to recognize the giant cowbird as an enemy "notonly when she seeks to enter a nest, but when, early in the nesting-season, she enters the nest tree. Not alone the bird whose nest isthreatened but other birds in the same group, and also from othergroups, join in attacking her; while Legatus assails at times with morezeal than Zahrynchus." It may be added here that Legatus is a smallflycatcher that usurps the nests of the much larger oropendolas, andthen breeds in them. This is the case of a nest robber driving awaya nest parasite even while the nest is still in the possession of itsoriginal builder and owner.The above observations on the hostility toward the giant cowbirdshown by these colonial nesting icterids reminds one of the comparablesituation that occurs between the brown-headed cowbird and theredwinged blackbirds, which nest in rather closely integrated groups
HOST RELATIONS OF PARASITIC COWBIRDS 221
in cattail swamps. In the latter host-parasite relationship, theparasite is successful only, or chiefly, with those redwings which nestat wider intervals in bushes or at the periphery of a colony.The pugnacity and persistence often displayed by the giant cowbirdwhen attempting to gain entry mto the nests of its intended victimsis of some interest. This parasite is related to the bronzed cowbirdand, more remotely, to the screaming cowbird, a species which is alsoquite pugnacious and resolute when about to enter a nest. Theshiny and the brown-headed cowbirds are more timid and are moreapt to sneak in while the owners are absent.The number of eggs laid by a giant cowbird in any one nest seemsto be usually 1 or 2. Schultz, as reported by Kuschel (1896, p.585), recorded as many as 6 eggs of the giant cowbird in a singlenest of the yellow-rumped cacique near Para, Brazil, but some doubtmay be attached to this statement, as Kuschel's description of theeggs, which are supposed to be those of giant cowbirds, do not agreevery closely with others subsequently collected.Many years ago in Brazil, Goeldi (1894, 1897) found that the younggiant cowbird did not starve out or otherwise elimmate a nest-mateof the host's species (at least in the case of Xanthornus decumanus),but that the two grew up together. Crandall (1914, p. 338, 342)found a parasitized nest of each of the two chief host species in CostaRica, Zarhynchus wagleri and Gymnostinops montezuma, each ofwhich contained a nestling giant cowbird together with one of thehost young. In both instances the disparity in appearance of theparasite and its nest-mate was very striking, but in both cases theadult fosterers attended them equally. In British Guiana, Young(1929, p. 256) also noted that the nestling of the giant cowbird andthat of its host developed together without obvious hostility. Skutchnoted that he never found fledgling giant cowbirds in flocks of oropen-dolas but only with an individual foster parent. He was led to ask,
".
. . can it be that the other oropendolas will not tolerate the pres-ence of these intruders and that the foster mother prefers to lead alonely life along with her foster young rather than desert it?"In British Guiana, Young (1929, pp. 251-253) concluded that thegiant cowbirds seemed to lay 2 eggs in nests of the crested oropen-dola, Xanthornus decumanus, and in nests of the yellow-rumpedcacique, Cacicus cela, but he did not make it clear whether his evidencepointed to the same hen laying 2 eggs in each nest or to two individ-uals depositing 1 each. He found the yellow-rumped cacique to beimposed upon frequently and he noted that the young parasites grewup together with, not at the expense of, theu* rightful nestmates.Unlike Skutch's experience in Central America, Young saw flocks ofyellow-rumped caciques accompanied by both theu' own young and
222 U.S. NATIONAL MUSEUM BULLETIN 233
that of giant cowbirds. He also noted that there was no evidence toeven suggest that the adult Psomocolax attempted to destroy or toremove eggs of its victims. He found Cacicus cela was parasitized toa greater extent than Xanthornus decumanus, but, unfortunately, hegave no actual figures for either.In Venezuela, Schafer (1957, pp. 135-138) found that Xanthornusdecumanus was parasitized by the giant cowbird, but he found noevidence that another local oropendola, X. angiistifrons , was soaffected, even in mixed colonies. This may reflect a selectivity onthe part of the parasite, or a greater degree of nest protection on thepart of X. angustifrons, or it may be merel}^ that the total observationaldata is incomplete.Although the giant cowbird is intermediate in size between thesetwo frequent victims, it lays an egg considerably smaller than eitherof them. Psomocolax eggs average 28.6 x 19.2 mm.; those of Cacicus
cela, 32.5 x 24.5 mm. ; and those of Xanthornus decumanus, 33.8 x 24.1mm. In this respect, Psomocolax is unusual since, in the smallercowbirds, Molothrus and Tangavius, the parasites' eggs are ordinarilylarger than, or at least as large as, those with which they are placed.The problem of small egg size in proportion to body size becomesacute in the case of the European cuckoo, Cuculus canorus. In thisspecies the egg weight is one-thirtieth of the body weight, whereas in164 species of birds, as tabulated by Romanoff and Romanoff (1949,p, 63), the egg weight averages one-ninth of that of the body. It hasbeen suggested by many wi'iters that the small egg size here is a directadaptation to parasitism on small fosterers, but it seems safer to saythat the small egg size made it possible for the cuckoo to use manysmall hosts. There is no reason why Cuculus, had its egg been corre-spondingly large, could not have been parasitic on larger birds, as arethe species of Clamator.
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Paessler, Richard1925. Ueber einige Brutschmarotzer und die Anpassung ihrer Eier an dieihrer Pflegeeltern. Beitr. Fortpfl.-Biol. Vogel, vol. 1, pp. 29-32.1933. Molothrus purpurascens (Hahn u. Kiister) eine Subspecies von Mol.bonariensis, jetzt M. occidentalis (Berlepsch u. Stolzmann)? Beitr.Fortpfl-Biol. Vogel, vol. 9, pp. 136-137.Palmer, Ralph S.1949. Maine birds. Mus. Comp. Zool. Bull. 102, pp. 656.Parks, Richard A.1950a. Cowbird breeding in Atlanta. Oriole, vol. 15, pp. 8-9.1950b. Cowbird breeding at Atlanta again. Oriole, vol. 15, p. 32.1958. Brown-headed cowbird breeding at Atlanta. Oriole, vol. 23, pp.48-49.Parmelee, David F.1959. The breeding behavior of the painted bunting in southern Oklahoma.Bird Banding, vol. 30, pp. 1-18.1960. The icteridae of Dickinson and Iron Counties, Michigan. Jack-Pine Warbler, vol. 39, pp. 145-147.Parshall, S. E.1884. The cowbird nuisance. Ornithologist and Oologist, vol. 9, p. 138.Peabody, p. B.1899. The prairie horned lark. Osprey, vol. 3, pp. 118-119.1901. Nesting habits of Leconte's sparrow. Auk, vol. 18, pp. 129-134.1909a. Chat the pantaloon. Warbler, vol. 5, pp. 10-14.1909b. Cyanocephalus the obscure. Warbler, vol. 5, pp. 15-20.Penard, Frederik Paul, and Penard, Arthur Philip1910. De Vogels van Guyana. Vol. 2, pp. 587.Pereyra, Jose A.1937. Contribucion al estudio y observaciones ornitologicas de la zonanorte de la Gobernacion de la Pampa. Mem. Jardin Zool., LaPlata, vol. 7, pp. 198-326.1938. Aves de la zona riberena nordeste de la Provincia de Buenos Aires.Mem. Jardin Zool., La Plata, vol. 9, pp. 304, pis. 26.Peyton, Sydney1931. 1931 breeding records Ventura County, California. Oologist, vol.48, pp. 161-163.Phillips, Richard S.1951. Nest location, cowbird parasitism, and nesting success of the indigobunting. Wilson Bull., vol. 63, pp. 206-207.Pickwell, Gayle B.1931. The prairie horned lark. Trans. St. Louis Acad. Sci., vol. 27, pp.153, figs. 18, pis. 34.PiNCHON, R., and Bon Sainte-Come, M.1951. Notes et observations sur les oiseaux de Antilles Fran^aise.L'Oiseaux, new ser., vol. 21, pp. 229-277.PiTELKA, Frank A.1939. Mourning warbler in the Chicago region. Auk, vol. 56, p. 481.1940. Breeding behavior of the black-throated green warbler. WilsonBull., vol. 52, pp. 1-18.PiTELKA, Frank A., and Koestner, E. J.1942. Breeding behavior of Bell's vireos in Illinois. Wilson Bull., vol.54, pp. 97-106.
HOST RELATIONS OF PARASITIC COWBIRDS 243
Pius, Brother1949. Indigo bunting nest with five cowbird eggs. Flicker, vol. 21, p. 121.Plank, William1919. Cowbird impositions. Oologist, vol. 36, p. 18.Poling, Otho C.1890. Further notes on the cowbird, with remarks on the nesting of theprothonotary warbler at Quincy, Illinois. Ornithologist andOologist, vol. 15, p. 92.Poole, Earl L.1930. The bird life of Berks County, Pennsylvania. Reading PublicMus. and Art Gallery, Bull. 12, pp. 70.PossoN, Neil F.1890. More cowbird eggs. Ornithologist and Oologist, vol. 15, p. 31.Potter, Julian K., and Murray. J. J.1950. Middle Atlantic coast region. Audubon Field Notes, vol. 5, pp.268-270.Potter, Lawrence B.1935. Nesting of the j'ellow-breasted chat in Saskatchewan. Condor,vol. 37, p. 287.1939. Shrikes, red-wings, and the cowbird. Condor, vol. 41, pp. 219-220.Pray, R. H.1952. Middle Pacific coast region. Audubon Field Notes, vol. 6, p. 298.Prechtl, H. F. R.1953. Sur Physiologie der angeborenen auslosenden Mechanismen. Be-haviour, vol. 5, pp. 32-50.Prescott, Kenneth W.1947. Unusual behavior of a cowbird and scarlet tanager at a red-eyedvireo nest. Wilson Bull., vol. 59, p. 210.Preston, Frank W.1961. [Letter on Wiest's observation.] Butler (Pa.) Eagle, December 11,1961, p. 11.Preston, Junius Wallace1889. The Blackburnian warbler at home. Ornithologist and Oologist,vol. 14, p. 35.Price, Homer F.1934. A few cowbird notes. Oologist, vol. 51, pp. 107-108.Pulich, Warren M.1961. Birds of Tarrant County. Pp. 107.QuiLLiN, Roy W., and Holleman, Ridley1918. The breeding birds of Bexar County, Texas. Condor, vol. 20, pp.37-44.Raine, Walter1894. Bird nesting in northwest Canada. Nidiologist, vol. 1, pji. 119-120.Reiff, Isaac S.1893. A few days among the blue-winged warblers. Ornithologist andOologist, vol. 18, pp. 6-8.Reinecke, Ottomar1912. Personal observations and notes on breeding, migrant, or visitingbirds on the Niagara frontier. Bull. Buffalo Soc. Nat. Sci., vol.10, pp. 513-546.Renard, a.1933. Observaciones sobre el parasitismo del Tordo {Molothriis bonariensis)
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El Hornero, vol. 5, pp. 219-220.
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Reynolds, Ariel1942. A hermit warbler family. Gull, vol. 24, p. 28.RiDGWAY, Robert1887. Report of the geological exploration of the 40th parallel, vol. 4, pt. 3.Ornith., pp. 303-670.RoBBiNs, Samuel D.1947. The 1947 nesting season. Passenger Pigeon, vol. 9, pp. 133-137.1949. The 1948 nesting season. Passenger Pigeon, vol. 11, pp. 21-28.Roberts, Theodore S.1909. Study of a breeding colony of yellow-headed blackbirds. Auk, vol.26, pp. 371-389.1932. The birds of Minnesota. Vol. 2, pp. 821, pis. 90.Robertson, John Mc B.1931a. Birds and eucalyptus trees. Condor, vol. 33, pp. 137-139.1931b. Some changes in the bird life of western Orange County, California.Condor, vol. 33, pp. 204-205.Rockwell, R. B.1908. An annotated list of the birds of Mesa County, Colorado. Condor,vol. 10, pp. 152-180.Rogers, Thomas1955. Palouse-northern Rocky Mountain region. Audubon Field Notes,vol. 9, p. 392.1956. Palouse-northern Rocky Mountain region. Audubon Field Notes,vol. 10, p. 399.1958. Palouse-northern Rocky Mountain region. Audubon Field Notes,vol. 12, p. 430.1959. Northern Rocky Mountain-inter mountain region. Audubon FieldNotes, vol. 13, pp. 443-446.Romanoff, Alexis L., and Romanoff, A. J.1949. The avian egg. Pp. 918.Root, Oscar M.1942. Myrtle warbler feeding young cowbird. Wilson Bull., vol. 54, p. 253.Rowan, William1922. Some bird notes from Indian Bay, Manitoba. Auk, vol. 39, pp.224-232.Rowley, J. Stuart1930. Observations on the dwarf cowbird. Condor, vol. 32, pp. 130-131.1939. Breeding birds of Mono County, California. Condor, vol. 41, pp.247-254.Rowley, J. Stuart, and Orr, Robert T.1960. The nest and eggs of the slaty vireo. Condor, vol. 62, pp. 88-90.Rust, Henry J.1917. An annotated list of the birds of Fremont County, Idaho, as observedduring the summer of 1916. Condor, vol. 19, pp. 29-43.Sage, John H., and Bishop, Louis B.1913. The birds of Connecticut. Connecticut State Geol. and Nat. Hist.Surv. Bull. 20, pp. 370.Salmon, W. L.1933. Song sparrow and cowbirds. Bird Lore, vol. 35, p. 100.Salvin, Osbert, and Godman, Frederick duCane1886. Biologia Centrali-Americana: Vol. 1, Aves. Pp. 512.
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Sanborn, C. C, and Goelitz, W. A.1915. A two year nesting record in Lake County, Illinois. Wilson Bull.,vol. 27, pp. 445-448.Saunders, Aretas A.1911. A preliminary list of the birds of Gallatin County, Montana. Auk,vol. 28, pp. 26-49.1923. Summer birds of the Allegany State Park. Roosevelt Wild LifeBull., vol. 1, no. 3, pp. 239-354.Saunders, William E.1900. Nesting habits of the cerulean warbler. Auk, vol. 17, pp. 358-362.Saussure, M. M.1870. Fauna indigena: Los tordos. La Naturaleza, vol. 1, pp. 352-358.Savage, David L.1894. Notes on the birds of Iowa. Iowa Ornithologist, vol. 1, pp. 1-17.1895. Notes on the birds of Iowa. Iowa Ornithologist, vol. 1, pp. 29-45.1897. Observations on the cowbirds. Iowa Ornithologist, vol. 3, pp. 4-7.Savary, Walter B.1936. Nests found on a portion of the Nueces River Flats, Texas. Oologist,vol. 53, pp. 62-66, 77.Schafer, Ernst1957. Les Corotes. Etude comparative de Psarocolius angustifrons etPsarocolius decumanus. Bonner Zool. Beit., Sonderheft, pp. 147.SCHAUB, B. M.1951. Young evening grosbeaks, Hesperiphona vespertina, at Saranac Lake,New York, 1949. Auk, vol. 68, pp. 517-519.ScHLtJTER, WiLHELM1899. Price list of birds' eggs.Schonwetter, M.1924. Relatives Schalengewicht inbesondere bei Spar- und Doppeleiern.Beitr. Fortpfl.-Biol. Vogel, vol. 1, pp. 49-52.1928. Anmerkungen zum Nehrkorn-Katalog. Beitr. Fortpfl.-Biol. Vogel,vol. 4, pp. 129-136, 200-201.1932. Vier Vogelarten und nur ein Nest. Beitr. Fortpfl.-Biol. Vogel, vol.8, pp. 58-59.Schorger, a. W.1931. The birds of Dane County, Wisconsin, Part II. Trans. WisconsinAcad. Sci., Arts and Letters, vol. 26, pp. 60.Schrantz, F. G.1943. Nest Ufe of the eastern yellow warbler. Auk, vol. 60, pp. 367-387.SCHULTZ, ZeLLA M.1958. Northern Pacific coast region. Audubon Field Notes, vol. 12, p. 435.ScLATER, William Lutley1912. A history of the birds of Colorado. Pp. 576, pis. 16.Scott, W. E. D.1887. On the avifauna of Pinal County, with remarks on some birds ofPuna and Gila Counties, Arizona. Auk, vol. 4, pp. 16-24.Selander, Robert K., and La Rue, Charles J., Jr.1961. Interspecific preening invitation display of parasitic cowbirds. Auk,vol. 78, pp. 473-504.Sennent, George B.1879. Further notes on the ornithology of the lower Rio Grande of Texas,from observations made during the spring of 1878. Bull. U.S.Geol. and Surv. Terr., vol. 5, no. 3, pp. 371-440.
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Stoner, Emerson A.?Continued1938. A black phoebe's nest with eggs of three species. Condor, vol. 40,p. 42.Street, Maurice G.1943. A list of the birds of Nipawin, Saskatchewan. Yorkton Nat. Hist.Soc, contr. no. 2, pp. 8.Strong, W. A.1919. Curious eggs. Oologist, vol. 36, pp. 180-181.Strumberg, C. W.1879. [Note.] Oologist (Utica), vol. 4, p. 79.Strum, Louis1945. A study of the nesting activities of the American redstart. Auk, vol.62, pp. 189-206.SuMiCHRAST, Francisco1870. Memoria sobre la distribucion geograjBca de las aves del Estado deVeracruz. La Naturaleza, vol. 1, pp. 298-312.Sutton, George Micksch1928. The birds of Pymatuning Swamp and Conneaut Lake, CrawfordCounty, Pennsylvania. Annals Carnegie Mus., vol. 18, pp. 19-239,pis. 2-10.1938. The breeding birds of Tarrant County, Texas. Annals CarnegieMus., vol. 27, pp. 171-206.1949. Studies of the nesting birds of the Edwin S. George Reserve, pt. 1:The vireos. Misc. Publ. Mus. Zool. Univ. Michigan, no. 74, pp.37, 5 pis.1959-60. The nesting Fringillids of the Edwin S. George Reserve, south-eastern Michigan, pt. III. Jack-Pine Warbler, vol. 37, pp. 77-101. Pt. IV: pp. 127-151; pt. VI: vol. 38, pp. 46-65.Swain, .1. Merton1899a. The black-throated green warbler. Journ. Maine Ornith. Soc, vol.1, pp. 32-34.1899b. Unusual nesting sites. Forest and Stream, vol. 52, p. 325.Swales, Bradshaw H.1892. Michigan bird notes, 1891. Oologist, p. 45.1893. Detroit, Mich., 1891 notes. Ornithologist and Oologist, vol. 18, pp.100-101.Swenk, Myron H.1929. The pine siskin in Nebraska: Its seasonal abundance and nesting.Wilson Bull., vol. 41, pp. 77-92.Taczanowski, Ladislas1884. Ornithologie du P6rou. Vol. 2, pp. 566.Talmadge, Robert R.1948. The cowbird moves northward in California. Condor, vol. 50, pp.273-274.Tashian, R. E.1957. Nesting behavior of the crested oropendola (Psarocolius decumanus)in northern Trinidad. B.W.I. Zoologica, vol. 2, pp. 87-97.Terrill, Lewis McIver1961. Cowbird hosts in southern Quebec. Canadian Field Nat., vol. 75,pp. 2-11.Thomas, Ruth Harris1946. A study of eastern bluebirds in Arkansas. Wilson Bull., vol. 58, pp.143-183.
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Thorpe, William H.1956. Learning and instinct in animals. Pp. 493.TiNBERGEN, N,1951. The study of instinct. Oxford Univ. Press, pp. 228, figs. 130.1954. The origin and evohition of courtship and threat display. In Evolu-tion as a process, edit. Huxley, Hardy, and Ford, pp. 233-250.Todd, Henry O.1936. The cowbird in summer near Murfreesboro. Migrant, vol. 7, p. 72.Todd, Walter Edmund Clyde1940. Birds of western Pennsylvania. Pp. 710, pis. 23.Tout, Wilson1947. Lincoln County birds. Pp. 191.Trautman, Milton B.1940. The birds of Buckeye Lake, Ohio. Misc. Publ. Mus. Zool. Univ.Michigan, no. 44, pp. 466, pis. 15.Trippe, T. M.1868. The warblers. Amer. Naturalist, vol. 2, pp. 171-172.TuRCOTTE, William1933. Hinds County, Mississippi, nesting dates, 1932-1933. Oologist,vol. 50, pp. 120-121.TwoMEY, Arthur C.1942. The birds of the Uinta Basin, Utah. Annals Carnegie Mus., vol. 28,pp. 341-490.1945. The bird population of an elm-maple forest: With special referenceto aspection, territorialism, and coactions. Ecol. Monogr., vol. 15,pp. 173-205, 193-155.Unglish, W. E.1931. The dwarf cowbird in San Benito County, California. Condor, vol.33, p. 214.Vaiden, Merritt G.1952. Some birds of the Yazoo- Mississippi delta. Migrant, vol. 23, pp. 1-4.Van Winkle, Edward1890. [Letter.] Ornithologist and Oologist, vol. 15, p. 48.Vasicek, John M.1935. A savannah sparrow as a cowbird victim. Wilson Bull., vol. 47,p. 294.ViSHER, S. S.1910. A correction: A new bird for the United States. Auk, vol. 27, p. 210.Vogel, Howard H., Jr.1945. Cowbird parasitizes wood thrush and indigo bunting. Auk, vol. 62,p. 633.Walkinshaw, Lawrence H.1936. Notes on the field sparrow in Michigan. Wilson Bull., vol. 48,pp. 94-101.1938. Life history studies of the eastern goldfinch. Jack-Pine Warbler,vol. 16, pp. 3-11.1944. The eastern chipping sparrow in Michigan. Wilson Bull., vol. 56,pp. 193-205.1949. Twenty-five eggs apparently laid by a cowbird. Wilson Bull., vol.61, pp. 82-85.1952. Observations on the pine warbler in Michigan. Jack-Pine Warbler,vol. 30, pp. 94-99.
250 U.S. NATIONAL MUSEUM BULLETIN 23 3
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Williams, Arthur B. (ed.)1950. Birds of the Cleveland Region. Sci. Publ. Cleveland Mus. Nat.Hist., vol. 10, bull. 2, pp. 215.Williams, C. S., and Trowbridge A. H.1939. Wilson's phalarope host of Nevada cowbird. Auk, vol. 56, pp. 77.Williams, Laidlaw1957. Middle Pacific coast region. Audubon Field Notes, vol. 11, pp.426-428.Wilson, Alexander1810. American ornithology. Vol. 2, pp. 167.WiNTLE, E. D.1896. Birds of Montreal. Pp 281.WoLcoTT, Robert H.1899. Red-winged blackbird and cowbird. Bull. Michigan Ornith. Club,vol. 3, p. 18.Wood, Norman A.; Smith, Frank; and Gates, Frank C.1916. The summer birds of the Douglas Lake region, Cheboygan Co.,Michigan. Occas. Papers Mus. Zool. Univ. Michigan, no. 27, pp.21.Wood, Norman A.1951. The birds of Micliigan. Misc. Publ. Mus. Zool. Univ. Michigan,no. 75, pp. 559.Woods, Robert S.1930. Two more victims of the cowbird. Condor, vol. 32, p. 126.Yarrow, H. C.1874. Report upon ornithological specimens collected in the years 1871,1872, and 1873. In U.S. Army, Engineer Dept., Geogr. and Geol.Expl. and Surveys West of the One Hundredth Meridian, pp. 148.Young, Charles G.1929. A contribution to the ornithology of the coastland of British Guiana,pt. III. Ibis, ser. 12, vol. 5, pp. 221-261.

IndexPage numbers of principal accounts in italics
aberti, Pipilo, 152Pipilo aberti, 152Abert's towhee, 15&Acadian flycatcher, 7, 3G, 39, 53Acanthis flammea, I46flammea flammea, 146achrusterus, Turdus migratorius, 72acuminata, Aimophila ruficauda, ISSaedon, Troglodytes, 66, 207aeneus, Tangavius, vii, 2, 173-188Tangavius aeneus, 174, 176, 177,178, 179, 180, 181, 182, 183, 184,185, 186, 187, 188aequatorialis, Molothrus bonariensis,197, 203, 205, 206, 208, 209, 211,212Muscigralla brevicauda, 206aestiva, Dendroica petechia, 97aestivalis, Aimophila, 159Aimophila aestivalis, 159African glossy cuckoo, 33Agelaius icterocephalus icterocephalus,201phoeniceus, 128, 181phoeniceus arctolegus, 130phoeniceus californicus, 130phoeniceus fortis, 130phoeniceus littoralis, 130phoeniceus megapotamus, 130, 181phoeniceus neutralis, 130phoeniceus nevadensis, 130phoeniceus phoeniceus, 130phoeniceus sonoriensis, 130phoeniceus utahensis, 130ruficapillus, 195ruficapillus ruficapillus, 201thilius petersi, 201thilius thilius, 201aglaiae, Platypsaris, 176aikeni, Junco, 160Aimophila aestivalis, 159aestivalis aestivalis, 159aestivalis bachmani, 159aestivalis illinoensis, 159carpalis, 158
Aimophila ?Continuedcassinii, 159humeralis, 188rufescens, 188rufescens pyrgitoides, 188rufescens rufescens, 188ruficauda, 188ruficauda acuminata, 188strigiceps, 214strigiceps dabbeuei, 203, 214albicillius, Heleodytes minor, 200albicoUis, Pipilo, 187Zonotrichia, 166albigularis, Furnarius rufus, 199albilora, Dendroica dominica, 106albinucha, Xenopsaris, 199albirostris, Archiplanus, 201albiventer, Fluvicola pica, 199Turdus leucomelas, 208albiventris, Hadrostomus, 176albogriseus, Mimus longicaudatus, 203,207alopecias, Cranioleuca vulpina, 199alpestris, Eremophila, 58alticola, Icterus pustulatus, 184Vireo solitarius, 86altus, Tliryomanes bewickii, 67amaurochalinus, Turdus, 197, 200Amaurospiza concolor, 186concolor relicta, 186ambigua, Salicornia, 169Amblyramphus holocericeus, 201American goldfinch, 7, 8, 36, 40, 147redstart, 7, 36, 40americana, Certhia familiaris, 65Parula, 97Spiza, 143americanus, Coccyzus, 48Ammodramus bairdii, 155savannarum, 164savannarum ammolegus, 154, 155savannarum perpallidus, 154savannarum pratensis, 154, 155ammolegus, Ammodramus savannarum,154, 155 253
254 U.S. NATIONAL MUSEUM BULLETIN 233
Ammospiza caudacuta, 157caudacuta nelsoni, 157maritima, 167amnicola, Dendroica petechia, 97amoena, Passerina, 1^1amoenissima, Polioptila caerulea, 77Amphispiza belli, 160belli nevadensis, 160bilineata, 160bilineata bilineata, 160bilineata deserticola, 160bilineata opuntia, 160Anas discors, 4J^andina, Lichenops perspicillata, 199angolensis, Oryzoborus, 213Oryzoborus angolensis, 203, 213angustifrons, Xanthornus, 222annexus, Auriparus flaviceps, 64anthracinus, Turdus chiguanco, 200ant shrike, 217white-naped, 197, 205ant-tlu-ushes, 10Anthus correndera, 191correndera chilensis, 200correndera correndera, 200lutescens lutescens, 200lutescens peruvianus, 200spragueii, 80Antillean bullfinch, 218anumbi, Anumbius, 197, 205Anumbius, 192, 195anumbi, 197, 205Archilochus colubris, 4^Archiplanus albirostris, 201
arcticus, Pipilo erythrophthalmus, 150arctolegus, Agelaius phoeniceus, 130arenacea, Spizella pusilla, 165argentina, Cyanocompsa cyanea, 202Zonotrichia capeusis, 202argutula, Sturnella magna, 127
arizela, Geothlypis trichas, 117arizonae, Spizella passerina, 162Vireo bellii, 84armenti, Tangavius aeneus, 174Arremonops conirostris, 186conirostris richmondi, 186rufivirgata, 1^9, 186rufivirgata rufivirgata, 186artemisiae, Molothrus ater, 6, 45, 46,49, 50, 51, 53, 55, 57, 58, 65, 66,68, 70, 71, 72, 74, 75, 77, 80, 81,
artemisiae, Molothrus ater,?Continued86, 87, 89, 90, 91, 94, 95, 96, 100,102, 103, 106, 112, 116, 120, 121,122, 123, 124, 125, 126, 127, 130,132, 133, 134, 135, 136, 139, 142,144, 145, 146, 147, 148, 150, 153,155, 156, 157, 158, 160, 161, 162,163, 164, 165, 166, 167, 168, 171Arundinicola leucocephala, 195, 197, 199arvensis, Sicalis, 213asiatica, Zenaida, 176assimilis, Pipilo albicoUis, 187Tangavius aeneus, 174, 177, 181,186Asthenes baeri, 20^baeri baeri, 203hudsoni, 199ateleodacnis, bicolored, 197, 209Ateleadacnis bicolor, 197, 209ater, Molothrus, vii, 2, 5-172, 173Molothrus ater, 6, 48, 49, 51, 54, 55,58, 59, 60, 61, 62, 63, 65, 66, 70,71, 72, 74, 75, 77, 80, 81, 82, 83,84, 86, 90, 91, 94, 97, 106, 107,112, 113, 115, 116, 121, 124, 125,126, 127, 130, 131, 132, 133, 135,136, 138, 139, 140, 142, 143, 144,145, 147, 148, 149, 150, 152, 153,155, 156, 157, 158, 160, 161, 162,163, 164, 166, 167, 168atlantica, Melospiza melodia, 169atlapetes, yellow-throated, 186Atlapetes citrinellus, 202gutturalis, 186gutturalis parvirostris, 186atricapilla, Vireo, 81
atricapillus, Parus, 62atricristatus, Parus, 63atrogularis, Spizella, 165audax. Troglodytes musculus, 207auduboni, Dendroica, 102Dendroica auduboni, 102Hylocichla guttata, 74, 75audubonii, Icterus graduacauda, 131,182Audubon's warbler, 102aurantiifrons, Hylophilus, 209aurantiirostris, Catharus, 180Saltator, 197Saltator aurantiirostris, 201aurantio-atrocristatus, Empidonomusaurantio-atrocristatus, 199
INDEX 255
aureo-ventris, Pheucticus aureo-ventris,202auricollis, Icteria virens, 120, 121, 181Auriparus flaviceps, 64flaviceps annexus, 64auriventris, Sicalis, 202aurocapillus, Seiurus, 112, 191australis, SynaUaxis albescens, 199
bachmani, Aimophila aestivalis, 159Bachman's sparrow, 159badius, Molothrus, 2, 26, 173, 205, 216,217Molothrus badius, 201baeri, Asthenes, W4Asthenes baeri, 203Baer's spinetail, 204bairdi, Sialia bairdi, 77bairdii, Ammodramus, 155Baird's sparrow, 155baldwini, Troglodytes aedon, 66Baltimore oriole, 15, 36, 37, 40, 132, 184banded wren, 178bank swallow, 69barbadensis, Loxigilla noctis, 213barbatus, Spinus, 202barn swallow, 15, 59Bartramia longicauda, 4^BasUeuterus rufifrons, 181rufifrons dugesi, 181bay-breasted warbler, 107bay-wing cowbird, vii, 2, 23, 26, 173,193, 205, 216, 218becard, 198rose-throated, 176belli, Amphispiza, 160bellicosa, Pezites militaris, 203, 212bellicose tyrant, 197bellii, Vireo, 84Vireo bellii, 84Bell's vireo, 7, 14, 19, 35, 36, 37, 40, 84,86bendirei, Toxostoma, 71Bendire's thrasher, 71bernardi, Sakesphorus, 197, 205Sakesphorus bernardi, 203bewickii, Thryomanes, 67, 178Thryomanes bewickii, 67Bewick's wren, 35, 67, 178bicolor, Ateleodacnis, 197, 209Iridoprocne, 59Parus, 63bicolored ateleodacnis, 197, 209
bilineata, Amphispiza, 160Amphispiza bilineata, 160black and chestnut warbling finch, 197black phoebe, 52black-and-white warbler, 7, 13, 14, 40,91black-billed cuckoo, 48black-capped chickadee, 16, 39, 62vireo, 40, 81black-chested sparrow, 188black-chinned sparrow, 165black-crested titmouse, 63black-headed grosbeak, 139, 185black-headed oriole, 131, 182black-tailed gnatcatcher, 40, 78black-throated blue warbler, 40, 100black-throated gi-ay warbler, 40, 102black-throated green warbler, 40, 103black-throated oriole, 211black-throated sparrow, 160black-whiskered vireo, 9blackbird, 8, 9, 10Brewer's, 134red-breasted, 211redwinged, 7, 8, 9, 11, 30, 33, 35,36,40,98,^^5, 181,220rusty, 134yellow-headed, 13, 127Blackburnian warbler, 40, 105blue and yellow tanager, 197blue grosbeak, 7, 11, 40, 139, 185blue jay, 61blue seedeater, 186blue-gray gnatcatcher, 7, 36, 40, 77blue-winged teal, 44blue-winged warbler, 7, 40, 94bluebird, 16, 67eastern, 7, 35, 76mountain, 77western, 77bobolink, 40, 125Bohemian waxwing, 80bolivianus, Pitangus sulphuratus, 206Bombycilla cedrorum, 80garrula, 80garrula pallidiceps, 80bonana, Icterus, 203, 204, 210bonariae, Troglodytes musculus, 200bonariensis, Molothrus, vii, 2, 9, 10,20, 26, 50, 52, 66, 189^215, 217Molothrus bonariensis, 204, 205,206, 207, 208, 213, 214, 215Thraupis, 196, 197
256 U.S. NATIONAL MUSEUM BULLETIN 233
bonariensis?ContinuedThraupis bonariensis, 201borealis, Nuttallornis, 57boreophila, Spizella passerina, 162boreus, Myiarchus crinitus, 51brachydactylus, Geothlypis trichas, 117,120brachyrhynchos, Corvus, 61Brachyspiza, 194Brazilian tanager, 212bresilius, Ramphocelus, 212, 214brevlcauda, Muscigralla, 197, 203, 206brevipennis, Neochloe, 90breweri, Spizella, 16SBrewer's blackbird, IS If.Brewer's sparrow, 41, 163brewsteri, Empidonax, 54bronzed cowbird, vii, 2, 29, 173-188,218, 221brown creeper, 38, 39, 65brown thrasher, 7, 9, 16, 39, 71brown thrush, 9brown towhee, 151, 187brown-headed cowbird, vii, viii, 2, 3, 4,5-173, 189, 192, 196, 207, 208,220, 221brush gnatcatcher, 197, 207, 208bullfinch, 33Antillean, 213bullockii, Icterus, 133, 184Icterus bullockii, 133Bullock's oriole, 37, 40, 153, 184bunting, 22indigo, 7, 13, 36, 40, I40, 159lark, 153lazuli, 14ipainted, 7, 35, 40, I42, 186varied, I42bush-tit, 36, 64Buteo regalis, 45
cabanisi, Knipolegus, 199Poospiza lateralis, 202cabanisii, Molothrus bonariensis, 204,211Cachila pipit, 191Cacicus cela, 219, 221, 222haemorrhous, 219persicus, 219cacique, Mexican, 181red-rumped, 219yellow-rumped, 219, 221caerulea, Guiraca, 139, 185
caerulea?ContinuedGuiraca caerulea, 140Polioptila, 77, 79PolioptUa caerulea, 77caerulescens, Dendroica, 100Sporophila, 192, 197Sporophila caerulescens, 202Calamospiza melanocorys, 153calandria, 197Calcarius ornatus, 172calendula, Regulus, 80Regulus calendula, 80California gull, 46californica, Polioptila melanura, 79californicus, Agelaius phoeniceus, 130Larus, 46Psaltriparus minimus, 64campicola, Geotlilypis trichas, 117, 118.120cana, Spizella atrogularis, 165Thraupis virens, 201Canada warbler, 40, 123canadensis, Sitta, 65Wilsonia, 123canaster, Pipilo erythrophthalmus, 1 50Candida, Piranga erythrocephala, 185canorus, Cuculus, 20, 23, 222canicauda, Richmondena cardinalis, 138,185Cape May warbler, 100capensis, Zonotrichia, 11, 194, 195, 196,197, 214Zonotrichia capensis, 202capitata, Paroaria, 202cardinal, 3, 7, 15, 34, 35, 36, 40, 137, 185cardinalis, Richmondena, 137, 185Richmondena cardinalis, 138Carolina chickadee, 63Carolina wren, 39, 68carolinensis, Dumetella, 69Dumetella carolinensis, 70Junco hyemalis, 161Parus, 63Sitta, 64caroHnus, Euphagus, 134Euphagus carolinus, 134carpalis, Aimophila, 158Carpodacus mexicanus, 145mexicanus frontalis, 145purpureus, 144Cassiculus melanicterus, 181cassinii, Aimophila, 159Vireo solitarius, 86, 87
INDEX 257
Cassin's kingbird, 50Cassin's sparrow, 159castanea, Dendroica, 107catbird, 7, 9, 15, 36, 37, 39, 60Catharus aurantiirostris, 180aurantiirostris clarus, 180aurantiirostris costaricensis, 180caudacuta, Ammospiza, 167caudacutus, Passerherbulus, 155cayana, Dacnis, 209Dacnis cayana, 203, 204Cayenne dacnis, 209cedar waxwing, 16, 40, 80cedrorum, Bombycilla, 80cela, Cacicus, 219, 221, 222celata, Vermivora, 95, 123Certhia familiaris, 65familiaris americana, 65Certhiaxis cinnamomea cinnamomea,199cerulea, Dendroica, 104Cerulean warbler, 104Chamaea fasciata, 65fasciata henshawi, 65fasciata rufula, 66Chamaethlypis poliocephala, 120Charadrius vociferus, 46chat, Rio Grande ground, 120yellow-breasted, 3, 7, 8, 13, 35, 40,120chestnut-bellied rice grosbeak, 213chestnut-collared longspur, 172chestnut-sided warbler, 7, 14, 36, 40, 106chickadee, black-capped, 16, 39, 62Carolina, 63chilensis, Troglodytes musculus, 207Zonotrichia capensis, 202Anthus correndera, 200Elaenia albiceps, 200Cliilean robin, 208chimango, Milvago, 192chimango hawk, 192chimney swift, 16chingolo, 11chingolo sparrow, 196, 197, 214chipping sparrow, 4, 7, 8, 16, 28, 36, 41,69, 73, 161chivi, Vireo flavovuidis, 200chloronotus, Tyrannus melancholicus,176chlorura, Chlorura, 150Chlorura chlorura, 150
Chondestes grammacus, 158grammacus grammacus, 158grammacus strigatus, 158chopi, Gnorimopsar chopi, 201choraules, Zonotrichia capensis, 202clirysater, Icterus, 211chryseola, Geotlilypis trichas, 117, 118Wilsonia pusilla, 123chrysocephalus. Icterus, 203, 204, 210chrysogaster, Phoucticus chrysopeplus,203, 213chrysoparia, Dendroica, 103chrysopeplus, Pheucticus, 212chrysoptera, Vermivora, 9Scinerea, Piezorhina, 202Xolmis, 203, 206cineraceus, Regulus calendula, 80cinereus, Thryothorus sinaloa, 178cinnamomea, Certhiaxis cinnamomea,199
ciris, Passerina, 142, 186Passedna ciris, 142cismontanus, Junco hyemalis, 161citrea, Protonotaria, 91citrina, Wilsonia, 122citrinellus, Atlapetes, 202Clamator, 222clarus, Catharus aurantiirostris, 180Troglodytes mtisculus. 207clay-colored sparrow, 7, 36, 41, 163cleonensis, Melospiza melodia, 169
cliff swallow, 60Coccyzus americanus, 4Serythrophthalmus, 48coerulescens, Saltator, 197Saltator coerulescens, 201colubris, Archilochus, 48Columbigallina passerina, 47, 176passerina pallescens, 48, 176commersoni, Furnarius rufus, 199common crow, 61common grackle, 30, 135common redpoll, 146concolor, Amaurospiza, 186confinis, Pooecetes gramineus, 157conirostris, Arremonops, 186Contopus sordidulus, 57sordidulus veliae, 57virens, 56cooperi, Melospiza melodia, 169Piranga rubra, 136, 137, 184coronata, Dendroica, 101Paroaria, 201
258 U.S. NATIONAL MUSEUM BULLETIN 2 33
correndera, Anthus, 191Anthus correndera, 200Corvus brachyrhynchos, 61Coryphospingus cucuUatus, 213cucuUatus rubescens, 213pileatus pileatiis, 202costaricensis, Catharus aurantiirostris,180Cotingas, 10couchii, Tyrannus melancholicus, 176cowbird, bay-wing, vii, 2, 23, 26, 173193, 205, 216, 218bronzed, vii, 2, 29, 173-188, 218,221brown-headed, vii, viii, 2, 3, 4, 5-178, 189, 192, 196, 207, 208, 220,221dwarf, 132giant, vii, 2, 31, 218-222red-eyed, 27, 132, 180screaming, vii, viii, 2, 20, 22, 26,27, 191, 216-217, 218, 221shiny, vii, 2, 3, 4, 10, 11, 20, 22,34, 50, 52, 66, 69, 189-215, 221Cranioleuca, 195pyrrhophia, 204.pyrrhophia pyrrhophia, 203, 204vulpina alopecias, 199crassirostris, Oryzobonis, 202creeper, brown, 38, 39, 65crested flycatcher, 16crested oropendola, 219, 221crinitus, Myiarchus, 50cristata, Cyanocitta, 61Gubernatrix, 201cristatus, Furnarius, 199croconotus. Icterus jamacaii, 203, 204,211crossbill, red, H9crow, common, 61cryptus, Thryomanes bewickii, 67, 178cuckoo, 4, 14, 20, 190, 191African glossy, 33black-billed, 48European, 20, 23, 24, 33, 67, 190,191, 222yellow-billed, 45cucuUatus, Coryphospingus, 213Icterus, 131, 183Cuculus, 4, 222canorus, 20, 23, 222cuneifolia, Grindelia, 169currucoides, Sialia, 77
curtatus, Pipilo erythrophthalmus, 150curve-billed thrasher, 72curvirostra, Loxia, 149curvirostre, Toxostoma, 72cyanea, Passerina, I40cyanirostris, Knipolegus, 199cyanocephalus, Euphagus, IS4Cyanocitta cristata, 61Cyanocompsa cyanea argentina, 202cyanea minor, 202Cyanocorax yncas, 177, 219yncas luxuosa, 177yncas vivida, 177Cyclarhis gujanensis viridis, 200
dabbenei, Aimophila strigiceps, 203, 214dacnis, Cayenne, 209Dacnis cayana, 209cayana cayana, 203, 204decumanus, Xanthornus, 219, 221, 222defilipii, Pezites, 201Dendroica auduboni, 102auduboni auduboni, 102auduboni memorabilis, 102castanea, 107cerulea, IO4chrysoparia, 103discolor. 111dominica, 106dominica albilora, 106fusca, 105kirtlandii, 108nigrescens, 102caerulescens, 100coronata, 101graciae, 106magnolia, 100occidentalis, I04palmarum. 111palmarum hypochrj'sea, 112palmarum palmarum, 112pensylvanica, 106petechia, 97, 197, 210petechia aestiva, 97petechia amnicola, 97petechia morcomi, 97petechia petechia, 200petechia rubiginosa, 97petechia ruficapilla, 203, 204, 210petechia sonorana, 97pinus, 107tigrina, 100virens, 103
INDEX 259
derbianus, Pitangus sulphuratus, 177deserticola, Amphispiza bilineata, 160dickcissel, 7, IJfSdifficilis, Erapidonax, 55discolor, Dendroica, 111discors, Anas, 4.4diuca, Diuca, 11, 194, 195, 197Diuca diuca, 202Diuca diuca, 11, 194, 195, 197diuca diuca, 202diuca minor, 202diuca finch, 11, 195, 197Dives dives warszewiczi, 201Dolichonyx oryzivorus, 125domesticus. Passer, 125, 195, 200dominica, Dendroica, 106dorsalis, Ramphocelus bresilius, J212dove, ground, 47, 176Inca, 30mourning, 10, 30, 39, J,6, 70white-winged, 176dugesi, Basileuterus rufifrons, 181dugandi, Ziphorhynchus picus, 199Dumetella carolinensis, 69-70carolinensis carolinensis, 70carolinensis meridianus, 70carolinensis rufricrissa, 70dumeticolus, PipUo aberti, 152dumicola, Polioptila, 197, 20Sdusky thi-ush, 197dwarf cowbird, 132dwarf vireo, 83
eastern bluebird, 7, 35, 76eastern hermit thrush, 75eastern kingbird, 36, 37, 39, 49eastern meadowlark, 36, 126, 127eastern phoebe, 4, 7, 8, 36, 39, 51eastern wood pewee, 7, 39, 56Elaenia albiceps chilensis, 200flavogaster flavogaster, 200Emberizoides herbicola herbicola, 202Embernagra platensis, 215platensis olivascens, 215platensis platensis, 215Empidonax, 4brewsteri, 54difficilis, 55flaviventris, 53minimus, 54, 55traUlii, 54vlrescens, 63, 54
Empidonomus aurantio-atrocristatusaurantio-atrocristatus, 199varius varius, 199enthymia, Eremophila alpestris, 58Eremophila alpestris, 58alpestris enthymia, 58alpestris leucolaema, 58alpestris praticola, 58erycripta, Melospiza georgiana, 1 68erytlii-ocephala, Pii-anga, 185erythrocephalus, Melanerpes, 49erythrogaster, Hirundo rustica, 60erythrophthalmus, Coccyzus, 48Pipilo, 150, 187Pipilo erythrophthalmus, 150Eudynamis honorata, 20Euphagus carolinus, 134carolinus carolinus, 134carolinus nigrans, 134cyanocephalus, 134euphonia, Melospiza melodia, 169eurhyncha, Guiraca caerulea, 186European cuckoo, 20, 23, 24, 33, 67, 190,191, 222European house sparrow, 195European wren, 67evening grosbeak, 40, 143evura, Spizella atrogularis, 165extimus, Parus carolinensis, 63
falcifer, Pipilo erythrophthalmus, 150falklaudii, Turdus, 208fallax, Melospiza melodia, 169familiaris, Certhia, 65fasciata, Chamaea, 65fasciatus, Myiophobus fasciatus, 199faxoni, Hylocichla guttata, 74, 75feUx, Thryothorus, 178ferruginous hawk, 45field sparrow, 7, 14, 16, 19, 21, 23, 24,35, 41, 164finch, 8, 9, 10, 217black and chestnut warbling, 197Diuca, 11, 195, 197house, 145misto yellow, 213purple, 144red-crested, 213screaming, 192white and gray warbling, 215yellow, 213firewood-gatherer, 197, 205
260 U.S. NATIONAL MUSEUM BULLETIN 233
fisherella, Melospiza melodia, 109flammea, Acauthis, lJf6Acanthis flammea, 146flammeus, Pyrocephalus rubinus, 57flammiceps, Myiophobus fasciatus, 199flava, Piranga, 184Piranga flava, 201flaveola, Sicalis, 213Sicalis flaveola, 202flaviceps, Auriparus, 64flavifrons, Vireo, 85flaviveutris, Empidonax, 53Pseudocolopterix, 197, 199rtavogaster, Elaenia flavogaster, 200flavoviridis, Vireo, 87, 180, 209flavus, Xanthopsar, 201flicker, 15Fluvicola pica albiventer, 199pica pica, 199flycatcher, ;8, 9, 11,^22, 197,"l98, 217, 220Acadian, 7, 36, 39, 53 'crested, 16fork-tailed, 50, 197, 206great-crested, 60Kiskadee, 177, 206least, 55olive-sided, 57scissor-tailed, 39, 50, 177Traill's, 7, 8, 15, 19, 39, 54tyrant, 8, 10, 36Vermillion, 57vermillion-crowned, 177western, 39, 52, 55yellow-belUed, 53foliosa, Spartina, 169fortirostris, Holoquiscalus fortirostris,201forficata, Muscivora, 50, 177fork-tailed flycatcher, 50, 197, 206formosus, Opororuis, 115fortis, Agelaius phoeniceus, 130fox sparrow, 41, 167frater, Mimus saturninus, 200frontaUs, Carpodacus mexicanus, 145fuertesi. Icterus, 182Fuertes' oriole, 182fuUginosa, Hylocichla fuscescens, 76fuliginosus, Pitylus, 201fulva, Passerella iliaca, 167fulvescens, Pyrrhuloxia sinuata, 138Furnarius, 192, 195cristatus, 199rufus, 52, 195, 197, 205, 217
Furnarius?Continuedrufus albigularis, 199rufus commersoni, 199rufus Paraguayae, 199rufus rufus, 199fusca, Dendroica, 105Phaeoprogne tapera, 200fuscescens, Hylocichla, 76Hylocichla fuscescens, 76fuscus, Pipilo, 151, 187Pipilo fuscus, 187
galbula, Icterus, 132garrula, Bombycilla, 80georgiana, Melospiza, 168Geothlypis aequinoctialis velata, 200trichas, 117trichas arizela, 117trichas brachydactylus, 117, 120trichas campicola, 117, 118, 120trichas chryseola, 117, 118trichas ignota, 117trichas insperata, 117trichas occidentalis, 117, 118, 120trichas scirpicola, 117trichas sinuosa, 117trichas trichas, 117, 120giant cowbird, vii, 2, 31, 218-222gilvus, Mimus, 179Vireo, 90Vireo gilvus, 90giraudii. Icterus chrysater, 203, 204, 211gnatcatcher, black-tailed, 40, 78blue-gray, 7, 36, 40, 77brush, 197, 207, 208Gnorimopsar chopi chopi, 201golden warbler, 197, 210golden-bellied grosbeak, 212golden-cheeked warbler, 8, 40, 103golden-wuiged warbler, 40, 93goldfinch, 7, 8, 16, 36, 40, 147lesser, 148gouldii, Melospiza melodia, 169Grace's oriole, 197, 211Grace's warbler, 40, 106grace-annae. Icterus, 197, 203, 211graciae, Dendroica, 106gracilis, Mimus gilvus, 179grackle, common, 135great-tailed, 30Imthurm's, 210Swainson's, 197, 210graduacauda, Icterua, 131, 182
INDEX 261grammacus, Chondestes, 158Chondestes grammacus, 158gramineus, Pooecetes, 157Pooecetes gramineus, 157grasshopper sparrow, 154gray pepoaza, 205gray vireo, 85grayish saltator, 197great-crested flycatcher, 50great-tailed grackle, 30greater white-shouldered tanager, 212green jay, 177, 219green oropendola, 219green-backed sparrow, 186green-tailed towhee, 150Grindeha cuneifoUa, 169griseobarbatus, Vireo flavoviridis, 203,209griseus, Vireo, 82grosbeak, 27black-headed, 139, 185blue, 7, 11, 40, 139, 185chestnut-belhed rice, 213evening, 40, 1^3golden-belUed, 212rose-breasted, 7, 27, 40, 138ground dove, 47, 176Gubernatrix cristata, 201guianensis, Lampropsar tanagrinus, 212Guiraca caerulea, 139, 185caerulea caerulea, 140caerulea eurhyncha, 186caerulea interfusa, 140caerulea saUcaria, 140guirahuro, Pseudoleistes, 201gukris, Icterus, 183Paroaria gularis, 202gull, California, 46guttata, Hylocichla, 74Hylocichla guttata, 74gutturaUs, Atlapetes, 186Gymnomystax mexicanus, 201Gymnostinops montezuma, 219, 221Hadrostomus albiventris, 176haemorrhous, Cacicus, 219happy wren, 178hawk, chimango, 192ferruginous, 45hedge sparrow, 191heermanni, Melospiza melodia, 169Heleodytes fasciatus pallescens, 200minor albicilUus, 200unicolor, 200
Helmitheros vermivorus, 92henshawi, Chamaea fasciata, 65henslo^^^i, Passerherbulus, 156Passerherbulus henslowii, 156Henslow's sparrow, 156hepatic tanager, 184hepatica, Piranga flava, 184herbicola, Emberizoides herbicola, 202hermit thrush, 7, 39, 74hermit warbler, 40, 104Hesperiphona vespertiua, 143hesperophilus, Spinus psaltria, 148hiemalis. Troglodytes, 67Hirundo rustica, 69rustica er\'throgaster, 60Holoquiscalus fortirostris fortirostris,201lugubris, 197, 204, 210holosericeus, Amplyramphus, 201holti, SicaUs flaveola, 202honey-creepers, 10, 209honey-guides, 33honorata, Eudynamis, 20hooded oriole, 40, 131, 183hooded warbler, 40, 122hoopesi, Sturnella magna, 127horned lark, 58house finch, 145house sparrow, 16, 30, 40, 69, 73, 125, 195house wren, 15, 39, ^6'hudsoni, Asthenes, 199humeralis, Aimophila, 188Myospiza humerahs, 202hummingbird, ruby-throated, 48huttoni, Vireo, 83Hutton's vireo, 40, 83hyemalis, Junco, 161Junco hyemalis, 161Hylociclila, 9fuscescens, 76fuscescens fuliginosa, 76fuscescens fuscescens, 76fuscescens salicicola, 76guttata, 74guttata auduboni, 74, 75guttata faxoni, 74, 75guttata guttata, 74guttata polionota, 74, 75mustelina, 73ustulata, 75ustulata swainsoui, 75ustulata ustulata, 75
262 U.S. NATIONAL MUSEUM BULLETIN 23 3
Hylophilus aurantiifrons, 209aurantiifrous saturatus, 209hypochrysea, Dendroica palmarum, 112hypoleuca, Zonotrichia capensis, 202
Icteria, 22virens, 130, 180virens auricollis, 120, 121, 181virens virens, 120ictericus, Spinus magellanicus, 202Icterldae, 2icterocephalus, Agelalus icterocephalus,201icterophrys, Satrapa, 198, 199Icterus, 2, 174, 211bonana, 203, 204, 310bullockii, 133, 184bullockii bullockii, 133bullockii parvus, 133cayanensis pyrrhopterus, 201chrysater, 211chrysater giraudii, 203, 204, 211chrysocephalus, 203, 204, 210cucullatus, 131, 183cucullatus nelsoni, 132, 183cucullatus sennetti, 132, 183fuertesi, 182galbula, 132grace-annae, 197, 203, 211graduacauda, 131, 182graduacauda audubonii, 131, 182gularis, 183gularis tamaulipensis, 183jamacaii croconotus, 203, 204, 211nigrogularis, 211nigrogularis nigrogularis, 204, 211nigrogularis trinitatis, 211parisorum, 182pectoralis, 182pustulatus, 183pustulatus alticola, 184pustulatus microstictus, 184pustulatus pustulatus, 184spurius, 131, 181, 182ignota, Geothlypis trichas, 117iliaca, Passerella, 167illinoensis, Aimophila aestivalis, 159imthurmi, Macroagelaius subalaris, 203,204, 210Imthurm's grackle, 210Inca doves, 30Indian koel, 20indigo bunting, 7, 13, 36, 40, 140, 159
inexpectata, Melospiza melodia, 169insperata, Geothlypis trichas, 117interfusa, Guiraca caerulea, 140Iridoprocne bicolor, 69leucorrhoa, 200irupero, Xolmis, 205
Jay, 2blue, 61green, i 77, 219juddi, Melospiza melodia, 169junco, 34Oregon, 41, 161slate-colored, 41, 161white-winged, 41, 160Junco aikeni, 160hyemalis, 161hyemalis carolinensis, 161hyemalis cismontanus, 161hyemalis hyemalis, 161oreganus, 161oreganus montanus, 161oreganus pinosus, 161Kentucky warbler, 7, 36, 40, 115kieneri, Melozone, 152, 188killdeer, 45kingbird, Cassin's, 50eastern, 36, 37, 39, 49tropical, 176western, 49kinglet, ruby-crowned, 40, 80kirtlandii, Dendroica, 108Kirtland's warbler, 7, 8, 11, 15, 19, 21,25, 40, 108Kiskadee flycatcher, 177, 206Knipolegus cabanisi, 199cyanirostris, 199koel, Indian, 20La Plata ground finch, 216labradorius, Passerculus sandwichensis,153, 154Lampropsar tanagrinus guianensis, 212lanceolata, Rhinocrypta lanceolata, 199Lanius ludovicianus, 38lark, horned, 58lark bunting, 153lark sparrow, 7, 8, 41, 168Larus californicus, 46lawrencei, Spinus, 149LawTcnce's goldfinch, 149Lazuli bunting, 141least flycatcher, 66
INDEX 263
lecontei, Toxostoma, 179LeConte's sparrow, 40, 156LeConte's thrasher, 179Legatus, 220Leistes militaris, 211militaris militaris, 212militaris superciliaris, 194, 211lepida, Phainopepla nitens, 81Leptastheuura aegithaloides pallida, 199lesser goldfinch, 1^8Lesson's oriole, 211leucocephala, Arundinicola, 195, 197, 199leucolaema, Eremophila alpestris, 58leucomelas, Turdus, 208leucophrys, Zonotrichia, 175Zonotrichia leucophrys, 160leucopolius, Vu'eo gilvus, 90leiicopterus, Mimus polyglottos, 69, 179leucorrhoa, Iridoprocne, 200leucotis, Thrj^othorus leucotis, 200Lichenops perspicillata andina, 199perspicillata perspicillata, 199Lichtenstein's oriole, 183Limnothlypis swainsonii, 92lincolnii, Melospiza, 167Lincoln's sparrow, 167littoralis, Agelaius phoeniceus, 130long-billed thrasher, 71,179long-tailed mockingbird, 197 207longicauda, Bartramia, 45Toxostoma rufum, 71longicaudatus, Mimus, 197, 203, 207longirostre, Toxostoma, 71, 179longspur, chestnut-collared, 172longspur, McCown's, 171Louisiana waterthrush, 7, 12, 40, 11/^Loxia curvirostra, 149curvirostra minor, 149curvirostra pusilla, 149Loxigilla noctis, 213noctis barbadensis, 213luciae, Vermivora, 96lucida, Polioptila melanura, 79Lucy's warbler, 40, 96ludoviciana, Piranga, 135ludovicianus, Lanius, 38Pheucticus, 138Thryothorus, 68lugubris, Holoquiscalus, 197, 204, 210luteiventris, Sicalis luteola, 213luteola, Sicalis, 213lutescens, Anthus lutescens, 200Vermivora celata, 95630950?63 18
luxuosa, Cyanocorax yncas, 177
MacGillivray's warbler, 40, 117Machetornis rixosa rixosa, 199Macroagelaius subalaris, 210subalaris imthurmi, 203, 204, 210macroura, Zenaidura, 46magellanicus, Turdus falklandii, 203,208magna, Sturnella, 126Sturnella magna, 127magnirostris, Ramphocelus carbo, 201Richmondena cardinalis, 138, 185magnolia, Dendroica, 100magnolia warbler, 40, 100major, Taraba, 217Taraba major, 199many-colored ground sparrow, 215margaritae, Polioptila melanura, 79marginella, Zenaidura macroura, 46maritima, Ammospiza, 157marsh bird, yellow-breasted, 194, 216,217marsh wrens, 131martin, purple, 15, 37, 60Martinique oriole, 210Maryland yellowthroat, 35, 36raatutina, Zonotrichia capensis, 214mccownii, Rhynchophanes, 171maximiliani, Pitangus sulphuratus, 203,206McCown's longspur, 171meadow pipit, 191meadowlark, 30eastern, 36, 126, 127western, 127mearnsi, Zenaida asiatica, 176medius, Vireo bellii, 84megalonyx, Pipilo erythrophthalmus,150megapotamus, Agelaius phoeniceus, 130,181melancholicus, Tyrannus, 176, 197Tyrannus melancholicus, 199Melanerpes erythrocephalus 49melanicterus, Cassiculus, 181melanocephalus, Pheucticus, 139, 185melanocorys, Calamospiza, 153melanoleuca, Poosi^iza, 215melanoptera, Metropelia melanoptera,199melanopterus, Miraus gilvus, 200
264 U.S. NATIONAL MUSEUM BULLETIN 233
melanura, Polioptila, 78Melodia melodia mexicana, 188raelodia, Melospiza, 168, 188Melospiza melodia, 169Melospiza georgiana, 168georgiana ericrypta, 168lincolnii, 167melodia, 168, 188raelodia atlantica, 169melodia cleonensis, 169melodia cooperi, 169melodia euphonia, 169melodia fallax, 169melodia fisherella, 169melodia heermanni, 169melodia inexpectata, 169melodia gouldii, 169melodia juddi, 169melodia melodia, 169melodia merrilli, 169melodia montana, 169melodia morphna, 169melodia pusillula, 169melodia samuelis, 169melodia saltonis, 169Melozone kieneri, 152, 188kieneri rubricatum, 152, 188memorabilis, Dendroica auduboni, 102meridianus, Dumatella carolinensis, 70merrilli, Melospiza melodia, 169mesoleucus, Pipilo fusciis, 151, 187Metropelia melanoptera melanoptera,199Mexican cacique, 181mexicana, Melodia melodia, 188Sialia, 77mexicanus, Carpodacus, 145Gymnomystax, 201Pyrocephalus rubinus, 57microstictus, Icterus pustulatus, 184micrus, Vireo griseus, 82migratorius, Turdus, 72Turdus migratorius, 72militaris, Leistes, 211Pezites, 212Pezites militaris, 201Leistes militaris, 212milleri, Tangavius aeneus, 174, 176, 177,178, 179, 180, 181, 182, 183, 184,185, 187Milvago chimango, 192Mimus, 4gilvus, 179
Mimus?Continuedgilvus gracilis, 179gilvus melanopterus, 200gilvus tobagensis, 200longicaudatus, 197, 203, 207longicaudatus albogriseus, 203, 207patagonicus, 192, 197, 200polyglottos, 69, 178polyglottos leucopterus, 69, 179saturninus, 197, 217saturninus frater, 200saturninus modulator, 194, 200thenca, 200triurus, 195, 197, 208minimus, Empidonax, 54, 55Molothrus bonariensis, 204, 207,209, 210, 211, 213Psaltriparus, 64minor, Cyanocompsa cyanea, 202Diuca diuca, 202Loxia curvirostra, 149minuta, Sporophila minuta, 202misto yellow finch, 213Mniotilta varia, 91mockingbird, 10, II, 69, 194, 217long-tailed, 197, 207northern, 178Patagonian, 197southern, 179white-banded, 197, 208modestus, Thryothorus, 178modulator, Mimis saturninus, 194, 200Molothrus, 222ater, vii, 2, 5-172, 173ater artemisiae, 6, 45, 46, 49, 50,51, 53, 55, 57, 58, 65, 66,68,70,71, 72, 74, 75, 77, 80, 81, 86,87, 89, 90, 91, 94, 95, 96, 100,102, 103, 106, 112, 116, 120, 121,122, 123, 124, 125, 126, 127, 130,132, 133, 134, 135, 138, 139, 142,144, 145, 146, 147, 148, 150, 153,155, 156, 157, 158, 160, 161, 162,163, 164, 165, 166, 167, 168, 171.ater ater, 6, 48, 49, 51, 54, 55, 58, 59,60, 61, 62, 63, 65, 66, 70, 71, 72,74, 75, 77, 80, 81, 82, 83, 84, 86,87, 90, 91, 94, 97, 106, 107, 112,113, 115, 116, 121, 124, 125, 126,127, 130, 131, 132, 133, 135, 136,138, 139, 140, 142, 143, 144, 145,147, 148, 149, 150, 152, 153, 155,156, 157, 158, 160, 161, 162, 163,
INDEX 265
Molothrus?Continued164, 166, 167, 168ater obscurus, 6, 47, 56, 57, 67, 68,73, 75, 76, 77, 82, 84, 86, 87, 90,96, 97, 102, 103, 104, 121, 123,125, 127, 130, 131, 133, 134, 136,138, 140, 141, 142, 143, 145, 146,148, 149, 150, 152, 165, 157, 158,160, 162badius, 2, 26, 173, 205, 216, 217badius badius, 201bonariensis, vii, 2, 9, 10, 20, 26, 50,52, 66, 189-215, 217bonariensis aequatorialis, 197, 203,205, 206, 208, 209, 211, 212bonariensis bonariensis, 204, 205,206, 207, 208, 213, 214, 215bonariensis cabanisii, 204, 211bonariensis minimus, 204, 207, 209,210, 211, 213bonariensis nigricans, 198bonariensis occidentalis, 207, 208,214bonariensis riparius, 198bonariensis venezuelensis, 204, 208,210, 211, 212rufo-axillaris, vii, 2, 26, 173, 216-217, 218monoensis, Passerella iliaca, 167montana, Melospiza melodia, 169montanus, Junco oreganus, 161Oreoscoptes, 72Pipilo erythrophthalmus, 150montezuma, Gymnostinops, 219, 221Montezuma oropendola, 219, 220monticola, Oporornis tolmiei, 117morcomi, Dendroica petechia, 97Moriche oriole, 210morphna, Melospiza melodia, 169motacilla, Seiurus, 114mountain bluebird, 77mourning dove, 16, 30, 39, 46, 70mourning warbler, 40, 116multicolor, Saltatricula, 215Muscigralla brevicauda, 197, 203, 206brevicauda aequatorialis, 206Muscivora, 194forficata, 50, 177tyrannus, 50, 195, 197, 206musculus. Troglodytes, 11, 66, 195, 196,197, 207Troglodytes musculus, 200mustelina, Hylocichla, 73
Myiarchus crinitus, 50crinitus boreus, 51Myiodynastes solitarius, 199Myiophobus, 4fasciatus fasciatus, 199fasciatus flammiceps, 199Myiozetetes similis, 177similis primulus, 177Myospiza humeralis humeralis, 202humeralis xanthornus, 202myrtle warbler, 7, 35, 36, 40, 101
nanus, Vireo, S3Nashville warbler, 40, 95neglecta, Sturnella, 127nelsoni, Ammospiza caudacuta, 157Icterus cucullatus, 132 183Nelson's sharp-tailed sparrow, 157nesophila, Thraupis virens, 201Xeochloe brevipennis, 90neutralis, Agelaius phoeniceus, 130nevadensis, Agelaius phoeniceus, 130Amphispiza belH, 160Passerculus sandwichensis, 153, 154nightingale-thrush, orange-billed, ISOnigrans, Euphagus carolinus, 134nigrescens, Dendroica, 102nigricans, Molothrus bonariensis, 198Serpophaga, 199SayornLs, 52nigriceps, Turdus, 200nigro-genis, Paroaria gularis, 202nigro-rufa, Poospiza, 197Poospiza nigro-rufa, 202nigrogularis. Icterus, 211Iceterus nigrogularis, 204, 211nisorius, Thryothorus pleurostictus, 178nitens, Phainopepla, 81noctis, Loxigilla, 213North American winter wren, 67northern mockingbird, 178northern waterthrush, 113notabilis, Seiurus noveboracensis, 113,114noveboracensis, Seiurus, 113Seiurus noveboracensis, 113, 114Vireo griseus, 83nuthatch, red-breasted, 65white-breasted, 64Nuttallornis borealis, 57
oberholseri, Toxostoma curvirostre, 72oblitus, Passerculus sandwichensis, 153, 154
266 U.S. NATIONAL MUSEUM BULLETIN 233
obscura, Polioptila caerulea, 77obscurus, Molothrus ater, 0, 47, 56, 57,67, 68, 73, 75, 76, 77, 82, 84, 86,87, 90, 96, 97, 102, 103, 104, 121,123, 125, 127, 130, 131, 133, 134,136, 138, 140, 141, 142, 143, 145,146, 148, 149, 150, 152, 155, 157,158, 160, 162obsoletus, Salpinctes, 6Soccidentalis, Dendroica, 10J^Geothlypis trichas, 117, 118, 120Molothrus bonariensis, 207, 208,214Tyrannus melancholicus, 176ochre-fronted vireo, 209olivacea, Piranga, 136Passerella iliaca, 167olivaceus, Vireo, 87oUvascens, Embernagra platensis, 215oUve sparrow, 1^9, 186olive-sided flycatcher, 57Oporornis formosus, 115Philadelphia, 116tolmiei, 117tolmiei monticola, 117opuntia, Amphispiza bilineata, 160orange-backed oriole, 211orange-billed nightingale-thrush, 180orange-billed saltator, 197orange-crowned warbler, 95orchard oriole, 40, ^ Si, i 5/, 182oreganus, Junco, 161Oregon junco, 41, 161oregonus, Pipilo erythrophthalmus, 150Oreoscoptes montanus, 72oriantha, Zonotrichia leucophrys, 166oriole, 8, 9, 10Baltimore, 15, 36, 37, 40, 132, 184black-headed 131, 182black-throated, 211Bullock's, 37, 40 133, 184Fuertes', 182Grace's, 197, 211hooded, 40, 131, 183Lesson's, 211Lichtenstein's, 183Martinique, 210Moriche, 210orange-backed, 211orchard, 40, 131, 181, 1S2scarlet-headed, 183Scott's, 182spotted-breasted, 182
ornata, Thraupis, 201ornatus, Calcarius, 172oropendola, 219, 220crested, 219, 221green, 219Montezuma, 219, 220Wagler's, 31, 219, 220oryzivorus, Dolichonyx, 125Psommocolax, vii, 2, 31, 218-222Oryzoborus angolensis, 213angolensis angolensis, 203, 213crassirostris, 202ovenbird, 7, 13, 16, 19, 21, 22, 25, 33,36, 40, 112, 118, 191, 192, 193,194, 205, 217rufous, 52, 195, 197oyster-catcher, 13
Pachyramphus polychopterus spixii, 199painted bunting, 7, 35, 40, 142, 186pallescens, Columbigallina passerina, 48,176Heleodytes fasciatus, 200jiaUida, Leptasthenura aegithaloides,199Spizella, 163pallidiceps, Bombycilla garrula, 80pallidior, Passerina cLris, 142, 186pallidus, Spinus tristis, 148Thryothorus felix, 178palm warbler. 111palm tanager, 212palmarum, Dendroica, 111Dendroica palmarum, 112Thraupis, 212paraguayae, Furnarius rufus, 199parakeets, shell, 30parisorum Icterus, 182parkmanii. Troglodytes aedon, 66Paroaria capitata, 202coronata, 201gularis gularis 202gularis nigro-genis, 202Parula americana, 97parula warbler, 97Parus atricapillus, 62Parus atricristatus, 63atricristatus sennetti, 63bicolor, 63carolinensis, 63carolinensis extimus, 63parvirostris, Atlapetes gutturalis, 186parvus, Icterus buUockii, 133
INDEX 267
Passer domesticus, 126, 195, 200Passerculus sandwichensis, 153sandwichensis labradorius, 153, 154sandwichensis nevadensis, 153, 154sandwichensis obHtus, 153, 154sandwichensis savanna, 153, 154Passerella iliaca, 167ihaca fulva, 167iliaca monoensis, 167iliaca olivacea, 167iliaca schistacea, 167iliaca swarthi, 167iliaca zaboria, 167Passerherbulus caudacutus, 166henslowii, 166henslowii henslowii, 156henslowii susurrans, 156passerina, Columbigallina, 4'^', 176Spizella, 161Spizella passerina, 162Passerina amoena, 1^1
ciris, 142, 186
ciris ciris, 142
ciris pallidior, 142, 1S6cyanea, I40versicolor, I42passerines, 13, 15, 16, 22, 33, 38Patagonian mockingbird, 197patagonicus, Mimus, 192, 197, 200Phrygilus, 202pectoralis, Icterus, 182pewee, eastern wood, 7, 39, 66pelzelni, Sicalis, 217Sicalis flaveola, 213pensylvanica, Dendroica, 106pepoaza, gray, 206widow, 206peregrina, Vermivora, 94perpallidus, Ammodramus savannaruiii,154persicus, Cacicus, 219perspicillata, Lichenops pcrspicillata,199peruvianus, Anthus lutescens, 200peruviensis, Zonotrichia capensis, 215petechia, Dendroica, 97, 197, 210Dendroica petechia, 200petersi, Agelaius thilius, 201Petrochelidon pyrrhonota, 60Pezites defilipii, 201militaris, 212militaris bellicosa, 203, 212militaris militaris, 201
Phacellodomus, 195ruber, 199rufifrons sincipitalis, 205striaticolhs striaticollis, 199Phaeoprogne tapera fusca, 200phainopepla, 40, 81Phainopepla nitens, SInitens lepida, 81phalarope, Wilson's, 45Pheucticus aureo-ventris aureo-ventris,202chrysopeplus, 212chrysopeplus chrysogaster, 203, 213ludovicianus, 138melanocephalus, 139, 186Philadelphia, Oporornis, 116Philadelphia vireo, 40, 89philadelphicus, Vireo, 89phoebe, Sayornis, 61phoebe, 15, 36black, 62eastern, 4, 7, 8, 36, 39, 61Say's, 63phoeniceus, Agelaius, 128, 181Agelaius phoeniceus, 130Phrygilus patagonicus, 202unicolor unicolor, 202pica, Fluvicola pica, 199Piezorhina cinerea, 202pileatus, Coryphospingus i^ileatus, 202pine siskin, 40, 146pine warbler, 40, 107pinosus, Junco oreganus, 101pinus, Dendroica, 107Spinus, 146Spinus pinus, 147Vermivora, 94Pipilo aberti, 162aberti aberti, 152aberti dumeticolus, 152albicollis, 187albicoUis assimilis, 187erythrophthalmus, 160, 187orytlirophthalmus arcticus, 150erythrophthalmus canaster, 150erythrophthalmus curtatus, 150erythrophthalmus erythrophthal-mus, 150erythrophthalmus falcifer, 150erythrophthalmus megalonyx, 150erythrophthalmus montanus, 150erythrophthalmus oregonus, 150erj4hrophthalmus repetens, 187
268 U.S. NATIONAL MUSEUM BULLETIN 233
Pipilo?Continuedfuscus, , 161 187fuscus fuscus, 187fuscus mesoleucus, 161, 187fuscus senicula, 152pipit, cachila, 191meadow, 191Sprague's, 80Piranga erythrocephala, 185erythrocephala Candida, 185flava, 184flava flava, 201flava hepatica, 184flava saira, 201ludoviciana, 1S5olivacea, 136rubra, 136, 184rubra cooperi, 136, 137, 184rubra rubra, 136Pitangus sulphuratus, 177, 206, 217sulphuratus bolivianus, 206sulphuratus derbianus, 177sulphuratus maximiliaui, 203, 200Pitylus fuliginosus, 201plain wren, 178platensis, Embernagra, 215Embernagra platensis, 215Platypsaris aglaiae, 176rufus, 198pleurostictus, Tliryothorus, 178plumbeus, Saltator coerulescens, 201Vireo solitarius, 86, 180plover, upland, 45poliocephala, Chamaethlypis, 120polionota, Hylocichla guttata, 74, 75Polioptila, 4caerulea, 77, 79caerulea amoenissima, 77caerulea caerulea, 77caerulea obscura, 77dumicola, 197, 208melanura, 78melanura californica, 79melanura lucida, 79melanura margaritae, 79polyglottos, Mimus, 69, 178Pooecetes gramineus, 157gramineus confinis, 157gramineus gramineus, 157Poospiza lateralis cabanisi, 202melanoleuca, 215nigro-rufa, 197nigro-rufa nigro-rufa, 202
Poospiza?Continuednigro-rufa whitii, 202prairie warbler, 7, 14, 36, 40, ///pratensis, Ammodramus savannum, 154,155praticola, Eremophila alpestris, 58primulus, Myiozetetes similis, 177Progne subis, 60propinquus, Turdus migratorius, 72prothonotary warbler, 7, 11, 14, 36, 76,91Protonotaria citrea, 91psaltria, Spinus, 148psaltria, Spinus psaltria, 149Psaltriparus minimus, 64minimus californicus, 64Pseudocolopterix flaviventris, 197, 199guirahuro, 201virescens, 194, 201, 216Psomocolax, vii, 218, 219, 222oryzivorus, vii, 2, 31, 218-222pulcayensis, Zonotrichia capensis, 202pullus, Thryothorus modestus, 178purple finch, 144martin, 15, 37, 60purpureus, Carpodacus, 144pusilla, Loxia curvirostra, 149Spizella, 164Wilsonia, 123Wilsonia pusilla, 123pusillula, Melospiza melodia, 169pusillus, Vireo bellii, 84pustulatus. Icterus, 183Icterus pustulatus, 184pyrgitoides, Aimophila rufescens, 188Pyrocephalus rubinus, 57rubinus flammeus, 57rubinus mexicanus, 57rubinus rubinus, 199pyrope, Xolmis, 199pyrrhonota, Petrochelidon, 60pyrrhophia, Cranioleuca, 204Cranioleuca pyrrhophia, 203, 204pyrrhopterus, Icterus cayanensis, 201Pyrrhuloxia, 138sinuata, 138sinuata fulvescens, 138sinuata sinuata, 138
quiscula, Quiscalus, 135Quiscalus quiscula, 135quiscula versicolor, 135
INDEX 269
Ramphocelus bresilius, 21^, 214bresilius dorsalis, 212carbo magnirostris, 201red crossbill, 149red-bellied thrush, 197red-breasted blackbird, 211red-breasted nuthatch, 65red-breasted starling, 213red-crested finch, 213red-eyed cowbird, 27, 132, 180red-eyed vireo, 4, 7, 8, 13, 14, 16, 19,20, 35, 36, 40, 86, 87red-headed tanager, 185red-headed woodpecker, 4!Jred-rumped cacique, 219redpoll, 9, 11common, 146redstart, 14, 124American, 7, 36, 40redwinged blackbird, 7, 8, 9, 11, 30, 33,35, 36, 40, 98, 128-131, 181, 220reed tyrant, 197Regulus calendula, 80calendula cinereus, 80calendula calendula, 80relicta, Amaurospiza concolor, 186regalis, Buteo, 45repetens, Pipilo erythrophthalmus, 187Rhynchophanes mccownii, 171Rhinocrypta lanceolata lanceolata, 199Richmondena cardinalis, 137-138, 185cardinalis canicauda, 138, 185cardinalis cardinalis, 138cardinalis magnirostris, 138, 185cardinalis superba, 138richmondi, Arremonops conirostris, 186Rio Grande ground chat, 120riparia, Riparia, 59Riparia riparia, 59riparius, Molothrus bonariensis, li)8rixosa, Machetornis rixosa, 199robin, 37, 70, 72Chilean, 208rock wren, 68rose-breasted grosbeak, 7, 27, 40, ISSrose-throated becard, 176ruber, Phacellodomus, 199rubescens, Coryphospingus cucullatus,213rubiginosa, Dendroica petechia, 97rubinus, Pyrocephalus, 57Pyrocephalus rubinus, 199rubra, Piranga, 136, 184
rubra, Piranga rubra, 136rubricatum, Melozone kieneri, 152, 188ruby-crowned kinglet, 40, 80ruby-throated hummingbird, 48rufous ovenbird, 52, 195, 197rufous-capped warbler, 181rufous-sided towhee, 7, 8, 13, 22, 36, 40,150, 187rufescens, Aimophila, 188Aimophila rufescens, 188ruficapilla, Dendroica petechia, 203, 204,210Vermivora, 95ruficapillus, Agelaius, 195Agelaius ruficapillus, 201Thamnophilus ruficapillus, 199ruficauda, Aimophila, 188rufifrons, Basileuterus, 181rufiventrus, Turdus, 197, 217Turdus rufiventris, 200rufivirgata, Arremonops, 149, 186Arremonops rufivirgata, 186rufo-axillaris, Molothrus, vii, 2, 26, 173,216-217, 218rufous-winged sparrow, 158rufricrissa, Dumatella carolinensis, 70rufula, Chamaea fasciata, 66rufum, Toxostoma, 71Toxostoma rufum, 71rufus, Furnarius, 52, 195, 197, 205, 217Furnarius rufus, 199Platypsaris, 198Tachyphonus, 204, 212russet-tailed sparrow, 188rustica, Hirundo, 69rusty blackbird, 134rusty sparrow, 188rusty-crowned ground sparrow, 152, 188rusty-crowned song sparrow, 174
ruticilla, Setophaga ruticilla, 124Setophaga, 124rutilus, Thryothorus rutilus, 200
sage sparrow, 160sage thrasher, 72saira, Piranga flava, 201Sakesphorus bernardi, 197, 205bernardi bernardi, 203salicamans, Spinus tristis, 148salicaria, Guiraca caerulea, 140salicicola, Hylocichla fuscescens, 76Salicornia ambigua, 169Salpinctes obsoletus, 68
270 U.S. NATIONAL MUSEUM BULLETIN 2 33
saltator, grayish, 197orange-billed, 197Saltator aurantiirostris, 197aurantiirostris aurantiirostris, 201coerulescens, 197coerulescens coerulescens, 201coerulescens plumbeus, 201similis similis, 201Saltatricula multicolor, 216saltonis, Melospiza melodia, 169samuelis, Melospiza melodia, 169sandwichensis, Passerculus, 163Satrapa icterophrys, 198, 199saturatus, Hylophilus aurantiifrons, 209saturninus, Mimus, 197, 217savanna, Passerculus sandwichensis, 153,154Savannah sparrow, 7, 40, 163savannarum, Ammodramus, 164saya, Sayornis, 53sayaca, Thraupis sayaca, 201Sayornis nigricans, 62phoebe, 61saya, 63Say's phoebe, 63scarlet tanager, 7, 13, 14, 35, 40, 136scarlet-headed oriole, 183schistacea, Passerella iliaca, 167scirpicola, Geothlypis trichas, 117scissor-tailed flycatcher, 39, 60, 177Sclater's towhee, 187Scott's oriole, 182screaming cowbird, vii, viii, 2, 20, 22,26, 27, 191, 216-217, 218, 221screaming finch, 192screaming seedeater, 197seaside sparrow, 41, 167seedeater, blue, 186screaming, 197white-collared, 146Seiurus, 22aurocapillus, 112, 191motacilla, 114noveboracensis, 113noveboracensis notabilis, 113, 114noveboracensis noveboracensis, 113,114senicula, Pipilo fuscus, 152sennetti, Icterus cucullatus, 132, 183Parus atricristatus, 63Toxostoma longirostre, 71, 179Serpophaga nigricans, 199
Setophaga ruticilla, 124ruticilla ruticilla, 124ruticilla tricolora, 124sharpei, Sporophila torqueola, 146sharp-tailed sparrow, 167shell parakeets, 30shiny cowbird, vii, 2, 3, 4, 10, 11, 20, 22,34, 50, 52, 66, 69, 189-216, 221short-tailed ground tyrant, 197, 206shrike, 38ant, 217white-rumped, 38Sialia currucoides, 77mexicana, 77mexicana bairdi, 77
sialis, 76
sialis, Sialia, 76Sicalis auriventris, 202arvensis, 213flaveola, 213flaveola flaveola, 202flaveola holti, 202flaveola pelzelni, 213luteola, 213luteola luteiventris, 213pelzelni, 217similis, Myiozetetes, 177Saltator similis, 201sinaloa, Thryothorus, 178sinaloa wren, 178sincipitalis, Phacellodomus rufifrons,205sinuata, Pyrrhuloxia, 138Pyrrhuloxia sinuata, 138sinuosa, Geothlypis trichas, 117siskin, pine, 40, 146Sitta canadensis, 66carolinensis, 64slate-colored junco, 41, 161slaty vireo, 90
solitarius, Myiodynastes, 199solitary vireo, 36, 40, 86, 180song sparrow, 7, 8, 13, 15, 16, 19, 20,24, 34, 36, 39, 41, 168, 174, 188sonorana, Dendroica petechia, 97sonoriensis, Agelaius phoeniceus, 130sordida, Thlypopsis sordida, 201sordidulus, Contopus, 57
solitarius, Vireo, 86, 180Vireo solitarius, 86South American house wren, 197, 207southern mockingbird, 179
INDEX 271
sparrow, 11, 73Bachman's, 159Baird's, 155black-chested, 188black-chinned, 165black-tliroated, 160Brewer's, 41, 163Cassin's, 159chingolo, 196, 197, 214chipping, 4, 7, 8, 16, 28, 36, 41, 69,73, 161clay-colored, 7, 36, 41, 163European house, 195field, 7, 14, 16, 19, 21, 23, 24, 35, 41,17Afox, 41, 167grasshopper, 154green-backed, 186hedge, 191Henslow's, 156house, 16, 30, 40, 69, 73, im, 195lark, 7, 8, 41, 158LeConte's, 40, 155Lincoln's, 167many-colored ground, 215Nelson's sharp-tailed, 157olive, 149, 186rufous-winged, 158russet-tailed, 188rusty, 188rusty-crowned ground, 152^ 188rusty-crowned song, 174Savannah, 7, 40, 153seaside, 41, 157sharp-tailed, 157song, 7, 8, 13, 15, 16, 19, 20, 24, 34,36, 39, 41, 168, 174, 188striped-headed, 214swamp, 7, 41, 168vesper, 7, 41, 157white-crowned, 36, 165white-throated, 7, 41, 166Spartina foliosa, 169spinetail, 10, 205Bear's, 204stripe-crowmed, 204Spinus barbatus, 202lawrencei, 149magellanicus ictericus, 202pinus, 146pinus pinus, 147psaltria, 148psaltria hesperophilus, 148
Spinus barbatus?Continuedpsaltria psaltria, 149tristis, 147, 148tristis palhdus, 148tristis sahcamans, 148tristis tristis, 148spixi, Synallaxis, 192, 199spixii, Pachyramphus polychopterus,199Spix's thrush, 208Spiza americana, 143Spizella atrogularis, 165atrogularis cana, 165ati'ogularis evura, 165breweri, 163pallida, 163passerina, 161passerina arizonae, 162passerina boreophila, 162passerina passerina, 162pusilla, 164pusilla arenacea, 165Sporophila, 4caerulescens, 192, 197caerulescens caerulescens, 202minuta minuta, 202torqueola, 145torqueola sharpei, 146spotted-breasted oriole, 182spragueii, Anthus, 80Sprague's pipit, 80spurius. Icterus, 131, 181, 182starling, 15, 81red-breasted, 212Steganopus tricolor, 45stephensi, Vireo huttoni, 83striaticoUis, Phacellodomus striaticoUis,199strigatus, Chondestes grammacus, 158strigiceps, Aimophila, 214stripe-crowned spinetail, 204striped-headed sparrow, 214Sturnella magna, 126magna argutula, 127magna hoopesi, 127magna magna, 127neglecta, 127Sturnus vulgaris, 81subalaris, Macroagelaius, 210subis, Progne, 60subtorquata, Zonotrichia capensis, 203,214
suiriri, Suiriri, 200
272 U.S. NATIONAL MUSEUM BULLETIN 233
Suiriri suiriri, 200sulphuratus, Pitangus, 177, 206, 217summer tanager, 14, 40, 136, 184superba, Richmondena cardinalis, 138superciliaris, Leistes militaris, 194, 211Thryothorus, 206Thryothorus superciliaris, 203superciliated wren, 206susurrans, Passerherbulus henslowii, 156swainsoni, Hylocichia ustulata, 75Limnothlypis, 92Vireo gilvus, 90Swainson's grackle, 197, 210Swainson's thrush, 76Swainson's warbler, 92swallow, bank, 69barn, 15, 69
cliff, 60tree, 39, 69swamp sparrow, 7, 41, 168swarthi, Passerella iliaca, 167
swift, chimney, 16Synallaxis, 192, 195albescens australis, 199spixi, 192, 199
Tachyphonus rufus, 204, 212tamauhpensis. Icterus gularis, 183tanager, 8, 9, 10, 13, 196, 214blue and yellow, 197Brazilian, 212greater white-shouldered, 212hepatic, 184palm, 212red-headed, 186scarlet, 7, 13, 14, 35, 40, 136summer, 14, 40, 136, 184western, 40, 136Tangavius, 218, 222aeneus, vii, 2, 173-188aeneus aeneus, 174, 176, 177, 178,179, 180, 181, 182, 183, 184, 185,186, 187, 188aeneus armenti, 174aeneus assimilis, 174, 177, 181, 186aeneus milleri, 174, 176, 177, 178,179, 180, 181, 182, 183, 184, 185,187Taraba major, 217major major, 199Tennessee warbler, 40, 94teal, blue-winged, 44
Thamnophilus ruficapillus ruficapillus,199thenca, Mimus, 200thilius, Agelaius thilius, 201Thlypopsis sordida sordida, 201thrasher, 8Bendire's, 71brown, 7, 9, 16, 39, 71curve-billed, 72LeConte's, 179long-billed, 71, 179sage, 72Thraupis bonariensis, 196, 197bonarieusis bonariensis, 201ornata, 201palmarum, 212sayaca sayaca, 201virens cana, 201virens nesophila, 201thrush, 8, 9, 217brown, 9dusky, 197eastern hermit, 75hermit, 7, 39, 74red-belhed, 197Spix's, 208Swainson's, 75wood, 7, 12, 13, 16, 36, 37, 39, 73Thryomanes bewickii, 67, 178bewickii altus, 67bewickii bewickii, 67bewickii cryptus, 67, 178Thryothorus feUx, 178feUx palhdus, 178leucotis leucotis, 200ludovicianus, 68modestus, 178modestus pullus, 178pleurostictus, 178pleurostictus nisorius, 178rutilus rutilus, 200sinaloa, 178sinaloa cinereus, 178superciliaris, 206superciliaris superciHaris, 203tigrina, Dendroica, 100titmouse, black-crested, 63tufted, 63, 67tobagensis, Mimus gilvus, 200Troglodytes musculus, 203, 204,207tolmiei, Oporornis, 117torqueola, Sporophila, 145
INDEX 273
towhee, Abert's, 152brown, 161, 187green-tailed, 150rufous-sided, 7, 8, 13, 22, 36, 40,150, 187Sclater's, 187Toxostoma, 4bendirei, 71curvirostre, 72curvirostre oberholseri, 72lecontei, 179longirostre, 71, 179longirostre sennetti, 71, 179rufum, 71rufum longicauda, 71rufum rufum, 71traillii, Empidonax, 54Traill's flycatcher, 7, 8, 15, 19, 39, 54tree swallow, 39, 59trichas, Geothlypis, 117Geothlypis trichas, 117, 120tricolor, Steganopus, 45tricolora, Setophaga ruticilla, 124trinitatis, Icterus nigrogularis, 211tristis, Spinus, 147, 148Spinus tristis, 148triurus, Mimus, 195, 197, 208troglodytes, Troglodytes, 67Troglodytes aedon, 66, 207aedon baldwini, 66aedon parkmanii, 66hiemalis, 67musculus, 11, 66, 195, 196, 197, 207musculus audax, 207musculus bonariae, 200musculus chilensis, 207musculus clarus, 207musculus musculus, 200musculus tobagensis 203, 204, 207troglodytes, 67tropical kingbird, 176tufted titmouse, 63, 67Turdus amaurochalinus, 197, 200chiguanco anthraciuus, 200falklandii, 208falklandii magellanicus, 203, 208leucomelas, 208leucomelas albiventer, 208migratorius, 72migratorius achrusterus, 72migratorius migratorius, 72migratorius propinquus, 72nigriceps, 200
Turdus?Continuedrufiventris, 197, 217rufiventris rufiventris, 200tyrannus, Muscivora, 50, 195, 197, 206Tyrannus, 49Tyrannus melancholicus, 176, 197melancholicus chloronotus, 178melancholicus couchii, 176melancholicus melancholicus, 199melancholicus occidentalis, 176tyrannus, 49verticalis, 49vociferans, 50tyrant, bellicose 197reed, 197short-tailed ground, 197, 206white-headed marsh, 195, 197tyrant flycatchers, 8, 10, 36
unicolor, Heleodytes, 200Phrygilus unicolor, 202upland plover, 4^ustulata, Hylocichla, 76Hylocichla ustulata, 75utahensis, Agelaius phoeniceus, 130
varia, Mniotilta, 91varied bunting, 142varius, Empidonomus varius, 199veery, 7, 13, 14, 36, 40, 75velata, Geothlypis aequinoctialis, 200veliae, Contopus sordidulus, 57venezuelae, Zonotrichia capensis, 202venezuelensis, Molothrus bonariensis,204, 208, 210, 211, 212verdin, 35, 64Vermillion flycatcher, 67vermillion-crowned flycatcher, 177Vermivora celata, 96, 123celata lutescens, 95chrysoptera, 93luciae, 96peregrina, 94pinus, 94ruficapilla, 95
virginiae, 96vermivorus, Helmitheros, 92
versicolor. Passerina, 142Quiscalus quiscula, 135
verticalis, Tyrannus, 49vespertina, Hesperiphona, 14^
274 U.S. NATIONAL MUSEUM BULLETIN 233
vesper sparrow, 7, 41, 157vicinior, Vireo, 85virens, Contopus, 56Dendroica, lOSIcteria, 120, 180Icteria virens, 120vireo, 8, 9, 10, 22Bell's, 7, 14, 19, 35, 36, 37, 40, 84, 86black-capped, 40, 81black-whiskered, 9dwarf, 83gray, 85Button's, 40, 83ochre-fronted, 209Philadelphia, 40, 89red-eyed, 4, 7, 8, 13, 14, 16, 19, 20,35, 36, 40, 86, 87slaty, 90solitary, 36, 40, 86, 180warbling, 7, 8, 36, 40, 90white-eyed, 7, 14, 40, 82, 86yellow-green, 87, 180, 209yellow-throated, 7, 8, 36, 40, 85, 86Vireo atricapilla, 81bellii, 84bellii arizonae, 84beUii bellii, 84bellii medius, 84bellii pusillus, 84flavifrons, 85flavoviridis, 87, 180, 209flavoviridis chivi, 200flavoviridis griseobarbatus, 203, 209flavoviridis vividior, 200gilvus, 90gilvus gilvus, 90gilvus leucopolius, 90gilvus swainsonii, 90griseus, 82griseus micrus, 82griseus noveboracensis, 83huttoni, 83huttoni stephensi, 83nanus, 83ohvaceus, 87philadelphicus, 89sohtarius, 86, 180solitarius alticola, 86solitarius cassinii, 86, 87solitarius plumbeus, 86, 180solitarius solitarius, 86vicinior, 85virescens, Empidonax, 53, 54
Pseudoleistes, 194, 201, 216Virginia warbler, 40, 96virginiae, Vermivora, 96
viridis, Cyclarhis gujanensis, 200Xanthornus, 219vivida, Cyanocorax yncas, 177vividior, Vireo flavoviridis, 200vociferans, Tyrannus, 50vociferus, Charadrius, 45vulgaris, Sturnus, 81
wagleri, Zarhynchus, 31, 219, 221Wagler's oropendola, 31, 219, 220warbler, 9, 22, 25Audubon's, 102bay-breasted, 107black-and-white, 7, 13, 14, 40, 91black-throated blue, 40, 100black-throated gray, 40, 102black-throated green, 40, 103Blackburnian, 40, 105blue-winged, 7, 40, 94Canada, 40, 123Cape May, 100cerulean, 104chestnut-sided, 7, 14, 36, 40, 106golden, 197, 210golden-cheeked, 8, 40, 103golden-winged, 40, 93Grace's, 40, 106hermit, 40, 104hooded, 40, 122Kentucky, 7, 36, 40, 115Kirtland's, 7, 8, 11, 15, 19, 21, 25,40, 108Lucy's, 40, 96Macgillivray's, 40, 117magnolia, 40, 100mourning, 40, 116myrtle, 7, 35, 36, 40, 101Nashville, 40, 95orange-crowned, 95palm. 111parula, 97pine, 40, 107prahie, 7, 14, 36, ^0, 111prothonotary, 7, 11, 14, 36, 76, 91rufous-capped, 181Swainson's, 92Tennessee, 40, 94Virginia, 40, 96Wilson's, 95, 123wood, 8, 9, 10, 22
INDEX 275
warbler?Continuedworm-eating, 7, 40, 92yellow, 7, 8, 13, 15, 19, 24, 35, 36,40, 89, 97yellow pahn, 1 1
2
yellow-tliroated, 106warbling vireo, 7, 8, 36, 40, 90warszewiczi, Dives dives, 201waterthrush, Louisiana, 7, 12, 40, 114northern, 113waxwing, Bohemian, 80cedar, 16, 40, 80western bluebird, 77western flycatcher, 39, 52, 55western kingbird, 49western meadowlark, 127western tanager, 40, 135white and gray warbling finch, 215white-banded mockingbu-d, 197, 208white-breasted nuthatch, 64white-collared seedeater, 145white-crowned sparrow, 36, 165white-ej'^ed vireo, 7, 14, 40, 82, 86white-headed marsh tyrant, 195, 197white-naped ant shrike, 197, 205white-rumped shrike, 38white-throated sparrow, 7, 41, 166white-winged dove, 176white-winged junco, 41, 160whitii, Poospiza nigro-rufa, 202widow pepoaza, 205Wilsonia canadensis, 123citrina, 122pusilla, 123pusilla chryseola, 123pusilla pusilla, 123Wilson's phalarope, 45warbler, 95, 123wood thrush, 7, 12. 13. 16, 36, 37, 39, 73wood warbler, 8, 9. 10, 22woodhewers, 10, 192, 193woodpecker, red-headed, 49worm-eating warbler, 7, 40, 92wren, 10, 11, 195banded, 178Bewick's, 35, 67, 178Carolina, 39, 68European, 67happy, 178house, 15, 39, 66marsh, 131North American winter, 67plain, 178
wren?Continuedrock, 68sinaloa, 178South American house, 197, 207superciliated, 206wrentit, 39, 65
xanthocephalus, Xanthocephalus, 127Xanthocephalus xanthocephalus, 127Xanthopsar flavus, 201Xanthornus angustifrons, 222decumanus, 219, 221, 222xanthornus, Myospiza humeralis, 202
viridis, 219Xenopsaris albinucha, 199Xiphorhynchus picus dugandi, 199Xolmis cinerea, 203, 205irupero, 205pyrope, 199
yellow bird, 27yellow finch, 213yellow palm warbler, 112yellow warbler, 7, 8, 13, 15, 19, 24, 35,36, 40, 89, 97yellow-bellied flycatcher, 53yellow-billed cuckoo, 4Syellow-breasted chat, 3, 7, 8, 13, 35, 40,120yellow-breasted marshbird, 194, 216, 217yellow-green vireo, 87, 180, 209yellow-headed blackbird, 13, 127yellow-rumped cacique, 219, 221ycllowthroat, 7, 8, 12, 16, 19, 21, 22, 36,40, 117Maryland, 35, 36yellow-throated atlapetes, 186yellow-throated vireo, 7, 8, 36, 40, 85, 86yellow-throated warbler, 106yncas, Cyanocorax, 177, 219
zaboria, Passerella iliaca, 167Zarhynchus, 220wagleri, 31, 219, 221Zenaida, 192asiatica, 176asiatica mearnsi, 176Zenaidura macroura, 46macroura marginella, 46Zouotrichia albicollis, 166capensis, 11, 194, 195, 196, 197, 214capensis argentina, 202capensis capensis, 202
276 U.S. NATIONAL MUSEUM BULLETIN 23 3
Zonotrichia?Continuedcapensis chilensis, 202capensis choraules, 202capensis hypoleuca, 202capensis matutina, 214capensis peruviensis, 215capensis pulcayensis, 202
Zonotrichia?Continuedcapensis subtorquata, 203, 214capensis venezuelae, 202leucophrys, 165leucophrys leucophrys, 166leucophrys oriantha, 166