6 April 1998 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
111(1)28-34   1948. 
Diagnoses of hybrid hummingbirds (Aves: Trochiiidae). 5. Probable 
hybrid origin of Amazilia distans Wetmore & Phelps 
Gary R. Graves 
Depart men I of Vertebrate Zoology. National Museum of Natural History, 
Smithsonian Institution. Washington. DC. 20560, U.S.A. 
Abstract.?Amazilia distans Wei more & Phelps, 1956, is believed to be a 
hybrid between Hylocharis eyamts and Amazilia fimbriata. The hybrid, col- 
lected in Estado Tachira. Venezuela, exhibits a blended mosaic of plumage 
characters of the parental species. External measurements of the hybrid fall 
between the character means; of the parental species which overlap in size. 
The unique holotype of Amazilia distans 
Wetmore & Phelps, 1956 was collected by 
Ramon Urbano at "El Salao" (300 m) near 
Burgua, Estado Tachira, Venezuela, on 17 
July 1954. Originally deposited in the Co- 
leccidn Omitologica Phelps (No. 60790). 
Caracas, the type was cataloged on 9 Oc- 
tober 1956, in the National Museum of Nat- 
ural History (USNM 461695), Smithsonian 
Institution. Collar et al.'s (1992) report of a 
second specimen in the Coleccion Phelps 
was based on a misreading of the Phelps 
card catalog (fide M. Lentino, N. Collar). 
References treat A. distans as a valid spe- 
cies (e.g.. Morony et al. 1975, Meyer de 
Schauensee & Phelps 1978, Hilly & Brown 
1986. Sibley & Monroe 1990, Collar et al. 
1992). Analyses reported here suggest that 
it represents a hybrid between Hylocharis 
cyanns and Amazilia fimbriata. I provide a 
detailed hybrid diagnosis employing the 
methods and assumptions outlined in 
Graves (1990) and Graves & Zusi (1990). 
Materials and Methods 
The holotype of Amazilia distans was 
sexed as male (testes drawn on original la- 
bel). The unstriated maxillary ramphotheca 
(see Ortiz-Crespo 1972) and brilliant plum- 
age of the specimen indicate that it is an 
adult in definitive plumage (Pigs. 1, 2). The 
unique appearance of A. distans cannot be 
attributed to mutation or developmental 
variation of any known taxon. Nor does it 
seem to represent a morphologically dis- 
tinctive or geographically isolated popula- 
tion of another species of Amazilia. Con- 
sequently, A. distans appears either to be a 
valid species or a hybrid. As hybrids have 
no standing in zoological nomenclature, the 
burden of proof lies with the taxonomist to 
reject conclusively the hybrid origin of A. 
distans before bestowing species status on 
it. I was unable to reject I he hypothesis of 
hybridity. 
Hybridization between species from dif- 
ferent subfamilies, Phaethornithinae and 
Trochilinae. is unknown (Graves 1990). As- 
suming a hybrid origin for A. distans, the 
pool of potential parental species ( = geo- 
graphic pool) can be limited to the species 
of trochiline hummingbirds (? ? 23; see 
Appendix 1) that occur regularly below 
1000 m elevation in the region immediately 
south and east of the Andes in Estado Tach- 
ira and Estado A pure. Venezuela (Phelps & 
Phelps 1958, Meyer de Schauensee & 
Phelps 1978. Hilty & Brown 1986). 1 com- 
pared A. distans directly with specimens of 
all hummingbird species in the collections 
of the National Museum of Natural History. 
Smithsonian Institution, paying particular 
attention to those listed in Appendix 1. 
Notes, photographs, and videotape of the 
holotype were compared with the extensive 
VOLUME III. NUMBER I 29 
table I.?Ranges and means (? one standard ile- 
viation) of measurements (mm) of representative spec- 
imens i.i.liilr male) of Hylm-harix cyanus, Amazitutfim- 
lustiiii, and the Hybrid, Hylwhans cvanus x Amazilia 
fiinhriaia i= Amazilia distorts Wctmore & Phelps. 
1956: USNM 461695). 
in =  I*) 
fi'tih mil*! 
Hybrid 
Win^ ehord 47.1-53.0 52.4-56.5 51 0 
49.8 ?15 54.7 t  1.4 
Bill length 14.8-18.5 17,3-22.0 IS,6 
16.9 ? I.I 19,8 ? 1.3 
Reetrix 1 24.1-27.4 26.2-30.1 26.6 
25.9 i  1.2 28.8 ? 1.0 
Reetrix 5 25.1-28.1 27.7-32.5 27.4 
26.7 ? 1.0 30.6 ? 1.4 
?Colombia <n  =  5). Venezuela (n = 4), Guyana 
(n = 3) 
"Colombia (n = 8), VenezueJa (n = 8). 
series of Amazilia and Hylocharis in the 
American Museum of Natural History. New 
York. 
Color descriptions were made under Ex- 
amolites (MacBefh). Measurements of wing 
chord, bill length (from anterior extension 
of leathers), and reetrix length (from point 
of insertion of the central rectrices to the tip 
of central and outermost rec trices) were 
taken with digital calipers and rounded to 
the nearest 0.1 mm (Table 1). Measure- 
ments and least squares regression lines 
were projected on bivariate plots to illus- 
trate size differences (Wilkinson 1989). 
The hybrid diagnosis was approached in 
a hierarchical manner. The presumed paren- 
tal species of A. distans were hypothesized 
through the comparative analysis of plum- 
age pattern and color, feather shape, and bill 
colon As a second step, the restrictive hy- 
pothesis was tested with the quantitative 
analysis of size and external proportions. 
Concordance of results is regarded as 
strong support for the hypothesis (Graves 
1990, 1993a, 1993b, 1996a; Graves & Zusi 
1990). Atavism or hybrid luxuriance has 
not been demonstrated in hybrid humming- 
birds (Banks & Johnson 1961. Graves 
1990). For brevity. A. distans will be re- 
ferred to as a hybrid in the remainder of 
this paper. 
Results and Discussion 
Several characters of the hybrid permit 
its parental species to be identified: (a) bill 
red tipped with black in life; (b) base of bill 
conspicuously swollen, nasal flanges un- 
feathered and exposed; (c) crown glittering 
bluish-green; (d) throat glittering bluish- 
green, chin and upper throat streaked with 
white; (e) indistinct white pectoral spot; (f) 
abdomen gray along midline; and (g) rec- 
trices black, innermost and outermost about 
the same length (Appendix 2; Fig. I, 2; Ta- 
ble 1). None of the potential parental spe- 
cies considered one at a time exhibits this 
suite of character states in definitive or sub- 
definitive plumage. 
The red bill of the hybrid appears to be 
the most useful character for initially nar- 
rowing the held of potential parental spe- 
cies. Adult males of several species in Ap- 
pendix 1 have pink or red mandibular (low- 
er jaw) ramphothecae (Lophornis delattrei, 
L. stictolophus, Chrysumnia oenone, Hy- 
locharis cyanus, Amazilia versicolor, A. 
fimhriata, and A. viridigaster), and some 
specimens of A. fimbriata have pinkish- 
brown maxillary ramphothecae (upper jaw). 
However, bright red maxillary ramphothe- 
cae are found in only three species, L. de- 
lattrel, L. stictolaphus, and Hylocharis cy- 
anus. Lophornis can be eliminated as pos- 
sible parents of A. distans because they 
possess elongated rufous crests and pre- 
dominately rufous rectrices. which would 
almost certainly be expressed in a hybrid. 
Hylocharis cyanus is thus identified as the 
parental contributor of the red maxillary 
raniphotheca of the hybrid. 
Identifying the second parental species is 
most easily accomplished by focusing on 
the plumage characters of the hybrid that 
are lacking in Hylocharis cyanus. Plumage 
of the head, chin, throat and upper breast 
of H. cyanus is glittering purple. The in- 
heritance  of  iridescence  in  hybrid  hum- 
\0 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
Fig,  I.    Lateral and ventral views of male Amazilia fimhriam (top), Hylmhuris cyanus (bottom), and llieir 
putative hybrid, A. dhtans Wetmore & Phetps (USNM 461695I, 
VOLUME 111, NUMBER 1 33 
Fig. 2.    Lateral view of head and hill of the type of AmuzitUt distorts Wemiore & Phelps (USNM 4AloV5). 
mingbirds is poorly understood (Graves 
1990, Graves & Zusi 1990). In this case, 
however, I assume that hybridization be- 
tween two purple-crowned species would 
not result in offspring with a bluish-green 
crown. The glittering bluish-green crown 
and throat of the hybrid suggest that the 
second parental species has iridescent green 
plumage in these areas, ruling out Klais 
guimeti (purple chin and upper throat) as a 
parental species. In another example, the 
rectrices of Chrysuronia oentme are shining 
coppery-gold on both dorsal and ventral 
surfaces, whereas the rec trices of the hybrid 
are black, similar to those of H. cyanus 
(bluish-black). Hybridization of C. oenone 
and H. cyanus would likely produce off- 
spring with bronze-colored or dark brown 
rectrices that are significantly paler, less 
melanized, than those of the hybrid. In a 
similar fashion. Campy lopterus falcatus 
(chestnut rectrices, thickened primary ra- 
chises), Colibri thalas.tinus and C. corus- 
cans (purple auricular tufts, banded rectri- 
ces), ChtorostHbon poortmani (shining 
golden-green tail), Chlorestes notatus (bril- 
liant bluish-green plumage from breast to 
undertail coverts), Chalybura buffonii 
(lengthened silky white undertail coverts). 
Heliomaster (ongirostris (tail spots, brilliant 
magenta gorget). Thalurania furcata (pur- 
ple lower breast, deeply forked tail), Heiiu- 
doxa leadbeateri (violet crown patch), Ster- 
noclyta cyanopectus (violet breast patch, 
white-tipped rectrices, heavy curved bill), 
Coeligena coeligena (brown plumage), 
Ocreatus underwoodii (racket-tipped rectri- 
ces, tibial "puffs"), Agtaiocercus kingi 
(greatly elongated rectrices with metallic 
bluish-green dorsal surfaces), and Chaeto- 
cercus jourdanii (rufous shafts of rectrices. 
rose throat), can be removed from the list 
of potential parental species because they 
exhibit plumage characters not expressed in 
the hybrid. By the process of elimination, 
the second parental species appears to be 
one of three species of Amazitia that are 
sympatric with Hylocharis cyanus in Taeh- 
ira. Venezuela (Appendix I). 
Wetmore & Phelps (1956:4) noted that 
the type of A. distans had the general ap- 
pearance of Amazjlia fimbriata. differing 
from that species "in the glittering blue 
foreneck and upper breast, and in possess- 
32 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
22 A 
A V      . 
20 A ^0*^? 
A A *f* 
IB -     ? ? 
** 
A 
A 
^--* ? s 
16 
* 
* 
24 26 28 30 32 34 
Length Reclrn 5 
Fig. 3. Bivariatc plots of selected measurements (see Table 1) of mate Hyttxharis cyanus (diamonds I. Ama- 
ziliti fimhritiia (triangles), ami their putative hybrid (tilled circle), A. distanx Weimore & Phelps (USNM 461695) 
Least squares regression lines are illustrated for comparison. 
ing a crown spot differing in color from the 
rest of the head .... the appearance of the 
specimen is so distinct from that of other 
species of the genus [Amazdia] that we 
have no hesttance in describing it as rep- 
resenting a new species." I concur with 
Wetmore and Phelps that A. fimbriata bears 
more than a fleeting resemblance to Ama- 
zilia distans in plumage pattern. In fact, the 
hybrid is nearly intermediate in appearance 
between Hylocharis cyanus and Amazilia 
fimbriata. Significantly, the hybrid lacks 
plumage traits that characterize A. versicol- 
or (e.g., dark subterminal band on the out- 
ermost rectrices) and A. viridif>aster (e.g., 
brown or buff undertail coverts). In conclu- 
sion, evidence gleaned from bill and plum- 
age characters suggest that A. distans rep- 
resents a hybrid of Hylocharis cyanus and 
Amazilia fimbriata. 
External measurements.?Measurements 
of avian hybrids fall within the mensural 
ranges exhibited by their parental species as 
a consequence of a poly genie mode of in- 
heritance (see Buckley 1982). External 
measurements of adult male Hylocharis cy- 
anus and Amazilia fimbriata overlap and 
the difference in character means (larger 
species divided by smaller) is modest: wing 
chord (9.8%) bill length (17.2%); rectrix I 
(11.2%); and rectrix 5 (14.6%). Consistent 
with the hypothesis derived from plumage 
color and pattern, measurements of ihe hy- 
brid fall between the character means of the 
parental species (Table 1, Fig, 3). Had the 
hybrid's measurements fallen outside the 
range of those of Hylocharis cyanus and 
Amazilia fimbriata, this particular hybrid 
hypothesis would have been rejected. 
In summary, both plumage and morpho- 
logical data are consistent with the hypoth- 
esis that Amazilia distans represents a hy- 
brid between Hylocharis cyanus and Ama- 
zilia fimbriata. These species overlap ex- 
tensively in Amazonia. For taxonomic pur- 
poses the Amazilia distans Wetmore & 
Phelps is available only for the purpose of 
homonymy. 
Berlioz (1929) described a supposed hy- 
brid specimen, Hylocharis cyanus X Ama- 
zilia fimbriata. prepared in the "Bahia" 
style and presumably collected in Brazil. 
Unfortunately, he failed to report the spec- 
imen's registration number or in what mu- 
seum the specimen was deposited. Later, he 
(Berlioz 1951:287 equivocated in his iden- 
tification, suggesting that the specimen 
might represent Hylocharis pyropygia (Sal- 
vin & Godman   1881), poorly known and 
VOLUME III. NUMBER I H 
somewhat   doubtful   species   from   Bahia, 
Brazil (see Sibley & Monroe 1990): 
"D'ailleurs. fame de connaitrc alors ties Hyl. pyr- 
opygia auihcniiqucs. j'avais primitive mcni decritce 
specimen . . . comme titan) probablcmcnt un hy- 
bride: Aityrtrinn \.\niiiTitiii\ iimhriahi nigrirtttttUi X 
ffylocharis eycuua. Sans rcjeter definitivement cettc 
hypothese. tres justifiable par I'apparence de 
I'Oiseau. il DM semble pourtant plausible, mainten- 
anl i|ue I'identification, com me espece il 1st mete, 
d'Hyl. pyrapygia s'est afftrmee par I'existenee de 
plusieurs specimens identiques, de considcrcr dub- 
iiauvcment vei Oiscau commc referable atisst it cettc 
demiere cspiee." 
To further complicate matters, Berlioz 
(1938) had proposed in earlier paper that 
Hylocharis pyropygia was actually a hybrid 
between Chlorostilbon aureoventris and 
Hylocharis cyanus. In any case, there ap- 
pears to be no previous verified examples 
of the hybrid combination reported here 
(Hylocharis cyanus X Amazilia fimbriata). 
Sight records.?Sight records of "Ama- 
zilia distans" in northwestern Venezuela 
and adjacent Colombia (see Hilty & Brown 
1986, Collar et al. 1992) are problematic, 
and, to my knowledge, none is supported 
by diagnostic photographs. Although these 
sightings may refer to Hylocharis X Ama- 
zilia hybrids, they more likely represent the 
manifestation of imaginations fertilized by 
the possibility of observing a narrowly dis- 
tributed endemic. Identification of hum- 
mingbird hybrids under field conditions is 
virtually impossible (Graves 1996b). 
Acknowledgments 
I thank Nigel Collar, Steve Hilty, Miguel 
Lentino. and David Wege for clarifying the 
status of Amazilia distans in the Coleccion 
Ornitologica Phelps. The manuscript was 
improved by the reviews of Richard Banks, 
Douglas Stotz. and Richard Zusi. I thank 
Leo Joseph and David Agro (Academy of 
Natural Sciences of Philadelphia) for loan- 
ing comparative material, and the curators 
and staff of the American Museum of Nat- 
ural History, New York, for permitting me 
to work in their collections. Finally, I thank 
Carl Hansen (Smithsonian photographic 
services) for providing good photographs. 
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North American hybrid hummingbirds.?Con- 
dor 63:3-28. 
tk-iliu/. J. I>>.,i>. In cas riouveau iThybridiie chey ie\ 
Trochllidtis.?L'Oiscau 10:340-343. 
 .   1938,  Notes critiques sur des Trochilides.? 
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 ,  1951,  Etude systernalique de quctques espfc- 
ccs liligieuses de Trochilides,?l.'Oiseau 21: 
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Buckley. P, A, 1982. Avian genetics. Pp. 21-1 10 in 
M Petrak. ed . Diseases of cage and aviary 
birds :r,.J ed I c.i and Febigcr. Philadelphia, 
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Collar, N. J., L. R Gonzaga, N. Krabbc. A. Madrono 
Nicto. L, G, Naranjo. T. A. Parker, 111, & D. C. 
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The ICBP/IUCN Red Data Book. 3rd edition. 
part 2. International Conned lor Bird Preser 
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 .   1993b. A new hybrid manakin iliixiphia pi- 
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 .    1996a.   Hybrid  wood  warblers, Dcndmint 
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dae: Tribe Parulini) and the diagnostic predict- 
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Meyer de Schaucnsee. R., & W, H. Phelps. Jr.   1978. 
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Appendix I 
Species of hummingbirds thai occur regularly below 
1000 111 elevation in southwestern Eslado Tachira and 
extreme western Estado Apurc. Venezuela: Campytop- 
terus fiilcatus, Colibri tftalajsttwt, C corvscans, Kluis 
guimtti, hophomis dtlattrei, /.. stictolophus, Cklorei- 
tes miututs, CM-orostilbon inrllixuRus, C pootimaiti. 
iiutlitraniti furcula. Hylorharix cyanus. CHtysUftMia 
in-nime. Amazilia wr\icnitir, .1 fimbriaia. A. viridi- 
gaster. Chalybura bufftmii. Hetiodoxa leadbcateri. 
Suntoctyu cytmopeaus, Codigtna coeligena. Ocrea- 
nix lauterwoodU, AgtaUtctmu kiniii. HeHomaster km- 
girostris, C'haenicercus jtmntanii. 
Appendix 2 
General comparative description of definitive plum- 
ages of male Hylociutris cyanus. Amazilia fimbriaia. 
and the hybrid. H. cytmus X A. fimbriaia i = Amazilia 
distant Wetmore & Phelps. 1956; USNM 461695). 
Descriptions of structural colors are unusually subjec- 
tive, as color seen by the observer varies according to 
the angle of inspection and direction of light. For ibis 
reason 1 use general color descriptions. 
The forecrown and crown (to a line drawn across 
the crown at I he rear of the orbits) of cyanux are glit- 
tering purple, bordered posteriorly by dark bluish- 
green on the hinderown. The hind neck, upper back, 
and scapulars are dark green, gradually turning to 
bronzy green and then coppery on the lower back and 
rump, respectively; the upper-tail covens arc purplish 
black- In fimbriaia the dorsal plumage {capital and spi- 
nal tracts) is primarily dark green, with bronze reflec- 
tions on the clown and upper-tail coverts. The dorsum 
of the hybrid is intermediate in appearance between 
tyanus and ftirtbiUna. but more closely resembling the 
latter species. The forecrown is glittering greenish-blue 
and the upper tail coverts are dark bronzy green. 
The sides of the head, throat, and upper breast of 
cyanus are deep glittering purple; exposed white feath- 
er bases on the chin impart a spotted or mottled an 
pcamnce. Fculhcrs of the lower breast, sides, and 
flanks arc dark brownish-gray tipped with a dark green 
disc: greenish leather lips are less apparent near the 
mid line. Vent leathers are white and the under-tail co- 
verts are dull hrownish-black (blue reflections in bright 
light). Feathers of the chin, throat, and upper breast of 
fimbriaia have glittering green discs (when viewed 
head-on): leathers are white ha sally, narrowly fringed 
with white. White feather margins and a few complete- 
ly white feathers form an indistinct spot near the center 
of the lower breast. The belly, sides, and flanks are 
green with an indistinct grayish-while stripe along the 
mid line. Vent feathers are white: under-tail coverts are 
dark gray (with greenish reflections) moderately mar- 
gined with white or pale grayish-white. The venter of 
the hybrid more closely resembles that of fimbriaia. 
Feather discs of the ehin, throat, and upper breast are 
bluish-green, a few are distinctly purple. Traces of the 
white pectoral spot of fimbriaia arc present (one com 
pletely white leather): under (ail covens are dark slate 
gray margined with dull white. 
The tail of ryartus is bluish-black. In fimhriata, the 
outer rcctrices (2-5) are dull bluish black: the outer 
margins of reetrices 2?4 are glossed with dark green. 
The central rectrices ill are dark green, becoming dull 
biuish-hlaek dislally. The tail of the hybrid is similar 
in color lo that of cyanus. but the outer margins of 
rectrices 2-4 are faintly glossed wuh bronzy-green: the 
basal two-thirds of the central rectrices (I * are glossed 
with bronzy-green. 
The maxillary ramphotheca is red. tipped with black 
in eyanus, and moderately to heavily mclanized (pink- 
ish-brown to black in life) in fimbriaia. Ramphotheca 
of the hybrid exhibits an intermediate amount of mel- 
anin; the specimen tag notes thai the bill was red with 
a black tip in life.