Pelagic Studies of Seabirds
in the
Central and Eastern Pacific Ocean
WARREN B. KING, EDITOR
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SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 158
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S M I T H S O N I A N C O N T R I B U T I O N S T O Z O O L O G Y • N U M B E R 1 5 8
Pelagic Studies of Seabirds
in the
Central and Eastern Pacific Ocean
Warren B. King, Editor
SMITHSONIAN INSTITUTION PRESS
City of Washington
1974
ABSTRACT
King, Warren B., Editor. Pelagic Studies of Seabirds in the Central and Eastern
Pacific Ocean. Smithsonian Contributions to Zoology, number 158, 277 pages, 170
figures, 1974.—Seven papers by various authors on the pelagic distribution of sev-
eral seabirds in the central and eastern Pacific Ocean based largely on the re-
searches of the Pacific Ocean Biological Survey Program, 1963-1968. "Introduc-
tion," by Patrick J. Gould, introduces these and future papers in this series. He
discusses the methods and procedures used by the POBSP in gathering and recording
data on observations of seabirds, outlines the areas under surveillance, and pro-
vides a general account of the oceanography and marine biology of the areas under
discussion as a background to understanding the movements of seabirds in relation
to their environment. "Sooty Tern (Sterna fuscata)," by Patrick J. Gould, presents
the POBSP'S records of this most abundant tropical and subtropical Pacific species.
Its distribution at sea depends on erratic food availability, location of breeding
islands, breeding schedule, and postbreeding dispersal patterns. "Wedge-tailed
Shearwater (Puffinus pacificus)," by Warren B. King, gives data on the distribu-
tion of the northern, predominantly white-breasted and the southern, dark-
breasted morphs of this species. Subtropical populations migrate extensively, for
example between the Hawaiian Islands and the Pacific coast of Middle America;
tropical populations are apparently nonmigratory. "Black-footed Albatross
(Diomedea nigripes)," by Gerald A. Sanger, discusses the distribution and fre-
quency of sightings on a seasonal basis of this ship-following seabird, both in gen-
eral terms throughout its range and in detail in certain areas, for example, the
CalCOFI study covering an eight year period oft California and Baja California.
Its winter range overlaps largely with, but lies slightly to the south of, its summer
range. "Laysan Albatross (Diomedea immutabilis)," by Gerald A. Sanger, analyzes
observations of this species and relates its seasonal distribution and abundance to
its oceanographic environment. This species is more abundant in the western and
central Pacific, whereas the Black-footed Albatross is more abundant in the central
and eastern Pacific. "The Storm Petrels (Hydrobatidae)," by Richard S. Crossin,
summarizes the POBSP'S data on eighteen species or subspecies of storm petrels
based on sightings and collected specimens. Pelagic distribution is related to
breeding cycles, location of breeding sites, and marine environment. "Red-tailed
Tropicbird (Phaethon rubricauda)," by Patrick J. Gould, Warren B. King, and
Gerald A. Sanger, discusses seasonal distribution and abundance of this species
relative to its breeding cycle. This species disperses widely from its breeding is-
lands, for example, from the Hawaiian Islands to the Pacific coast of Middle
America. "Recoveries of Banded Laysan Albatrosses (Diomedea immutabilis) and
Black-footed Albatrosses (D. nigripes) in the Pacific Ocean," by Chandler S. Rob-
bins and Dale W. Rice, summarizes the seasonal distribution of pelagic recoveries
of 324 banded Laysan Albatrosses and 399 banded Black-footed Albatrosses. Dif-
ferent age groups of each species concentrate in somewhat different areas, and, al-
though range overlap between species is almost complete, each has its own distinc-
tive seasonal distribution pattern.
OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded
in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 4901. SERIES COVER DE-
SIGN: The coral Montastrea cavernosa (Linnaeus) .
Library of Congress Cataloging in Publication Data
Main entry under title:
Pelagic studies of seabirds in the central and eastern Pacific Ocean.
(Smithsonian contributions to zoology, no. 158)
"Seven papers by various authors . . . based largely on the researches of the Pacific Ocean
Biological Survey Program, 1963-1968."
Bibliography: p.
1. Sea birds—Pacific Ocean. 2. Pacific Ocean Biological Survey Program. I. King, Warren B.,
ed. II. Series: Smithsonian Institution. Smithsonian contributions to zoology, no. 158.
QL1.S54 no. 158 [QL694] 591'.08s [598.4'09164] 73-10383
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price $3.70
Contents
Page
INTRODUCTION, by Patrick J. Gould 1
Survey Areas 2
Methods and Procedures 4
Acknowledgments 4
SOOTY TERN {Sterna fuscata), by Patrick J. Gould 6
Introduction . 6
Behavior 8
Distribution and Abundance 13
Summary and Conclusions . 33
Appendix: Tables A C 46
WEDCE-TAILED SHEARWATER (Puffinus pacificus), by Warren B. King 53
Introduction 53
Distribution and Abundance . 56
Density and Distribution within Equatorial Currents . 56
Range of Sea Surface Temperatures and Salinities at Which Wedge-
tailed Shearwaters Were Observed 59
Specimen Records, Molt, and Band Recoveries 59
Discussion 62
Behavior 63
Summary 67
Appendix: Summary of Published Data on Wedge-tailed Shearwater
Distribution 92
BLACK-FOOTED ALBATROSS (Diomedea nigripes), by Gerald A. Sanger 96
Introduction 96
Distribution and Abundance 98
Specimen Records 98
Sighting Records 98
Band Return Information 103
Distribution off California and Baja California, 1951-1959 103
Abundance at Weather Station Victor 107
Analysis of Distribution . 107
General Considerations 107
Seasonal and Monthly Variations 109
Distribution in Relation to the Environment 110
Addendum 113
Appendix: Summary of Published Data on Black-footed
Albatross Distribution 126
LAYSAN ALBATROSS (Diomedea immutabilis), by Gerald A. Sanger 129
Introduction 129
Distribution and Abundance . 130
Specimen Records 130
Sighting Records 130
Annual Pelagic Cycle 134
iii
Page
Abundance at Weather Station Victor 134
Band Return Information 134
Analysis of Distribution 134
General Considerations 134
Distribution in Relation to the Environment 138
Addendum 139
Appendix: Summary of Published Data on Laysan Albatross
Distribution 152
THE STORM PETRELS (Hydrobatidae), by Richard S. Crossin 154
Introduction 154
Pelagodroma marina (Latham) 157
Oceanodroma furcata (Gmelin) 158
Oceanodroma leucorhoa leucorhoa (Vieillot) 158
Oceanodroma leucorhoa beali Emerson 165
Oceanodroma leucorhoa chapmani Berlepsch 169
Oceanodroma leucorhoa socorroensis Townsend 170
Oceanodroma homochroa (Coues) 176
Oceanodroma castro (Harcourt) 177
Oceanodroma tethys (Bonaparte) 179
Oceanodroma hornbyi (Gray) 183
Oceanodroma melania (Bonaparte) 183
Oceanodroma markhami (Salvin) 187
Oceanodroma tristrami Salvin 187
Halocyptena microsoma Coues 189
Oceanites oceanicus (Kuhl) 190
Oceanites gracilis (Elliot) 190
Fregetta grallaria (Vieillot) 190
Nesofregetta albigularis (Finsch) 193
Discussion 200
Appendix: Tables A-E 203
RED-TAILED TROPICBIRD (Phaethon rubricauda), by Patrick J. Gould,
Warren B. King, and Gerald A. Sanger 206
Introduction 206
Behavior 207
Specimen Records 210
Molt 212
Distribution and Abundance 213
Environmental Factors 216
Discussion 216
Appendix: Summary of Published Data on Red-tailed
Tropicbird Distribution 230
RECOVERIES OF BANDED LAYSAN ALBATROSSES (Diomedea immutabilis)
AND BLACK-FOOTED ALBATROSSES (£>. nigripes), by
Chandler S. Robbins and Dale W. Rice 232
Introduction 232
General Patterns of Distribution 236
Concentration Areas 238
Statistical Analysis of Geographic Range 238
Comparison of Distribution of Laysan and Black-footed Albatrosses 241
Discussion 242
LITERATURE CITED 272
iv
Pelagic Studies of Seabirds
in the
Central and Eastern Pacific Ocean
Introduction*
Patrick J. Gould
In 1963 the Smithsonian Institution initiated a
research project to study the ecology of certain
areas of the Pacific Ocean. The activities and ob-
jectives of this project, called the Pacific Ocean Bio-
logical Survey Program (POBSP) , have been sum-
marized by Humphrey (1965). The present paper
is the first in a series summarizing at-sea bird ob-
servations made by the POBSP, although a number
of papers have already been published incorporat-
ing some POBSP at-sea observations (Amerson, 1969;
Gould, 1967; Gould and King, 1967; King, 1967;
King, 1970; King and Gould, 1967). The following
introduction is rather lengthy so that subsequent
papers herein and elsewhere may avoid needless
repetition of material relevant to all of them.
POBSP efforts were concentrated primarily on a
4ys million-square-mile area of the central Pacific
between 10°S and 30°N, and 148°W and 180°. The
birds of this area have received the greatest atten-
tion, although plants, arthropods, mammals, fishes,
reptiles, and other forms have figured in the re-
search as well. The energies of the POBSP were di-
vided between periodic visits to the islands of the
Leeward Hawaiian chain, the Line group, the
Patrick J. Gould, Department of Zoology, University of
Arizona, Tucson, Arizona 85721.
•Paper Number 100, Pacific Ocean Biological Survey Pro-
gram, Smithsonian Institution, Washington, D.C. 20560.
Phoenix group, and observations in the open ocean.
Peripheral island groups such as the Tokelaus,
Marshalls, Gilberts, Wake, and the Pribilofs were
visited less frequently.
On island surveys POBSP personnel estimated the
breeding and roosting populations of each seabird
species, described the breeding status of each, made
representative collections of the plants and animals
(with special attention to vagrants), and marked
large numbers of as many species of birds and mam-
mals as possible. In the course of this work, POBSP
personnel have banded over 1,800,000 birds of 56
species. On two atolls, Johnston and Kure, POBSP
maintained continuous surveillance. A large pro-
portion of the birds on these islands was banded,
and uninterrupted breeding biology studies were
conducted.
Late in 1966, field work was expanded eastward
to include a survey area off southern California
and northern Baja California. Observers also ac-
companied many cruises (south to as far as 20°S
and east to as far as 135°W) of project EASTROPAC.
This latter project was an intensive oceanographic
investigation of the eastern tropical Pacific Ocean
by Chile, Ecuador, Mexico, Peru, and the United
States, sponsored and coordinated by the U.S. Bu-
reau of Commercial Fisheries.
Observations at sea have been made in the cen-
tral and eastern Pacific to determine the identity,
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
occurrence, and abundance of seabirds. Data on
atmospheric and oceanographic conditions were
collected concurrently on some cruises to provide a
broad ecological foundation. POBSP personnel made
continuous observations, normally from sunrise to
sunset, but sometimes around the clock, on cruises
along replicate tracks and straight-line transects in
all months of the year. On most island survey
cruises, personnel made observations en route to,
from, and between the islands. Furthermore, data
on the population and breeding phenology of sea-
birds from island surveys added to the understand-
ing of the distribution and densities of birds at sea.
In addition, the use of plastic leg streamers and
feather dye applied by island workers increased the
chances of assigning an island of origin to marked
birds observed or collected at sea.
SURVEY AREAS
Data were gathered systematically from the
north-central, south-central, and eastern Pacific dur-
ing all months of the year. In these areas, ships fol-
lowed replicate cruise tracks or concentrated their
efforts within a small area of ocean so that the
abundance and distribution of birds could be docu-
mented seasonally in great detail. Cruises also went
into peripheral areas but less regularly (Figure 1).
Although the seasonal movements of birds in these
peripheral areas cannot be shown in as much de-
tail, the resulting data broaden the total coverage.
The north-central Pacific is defined herein as the
area between 10°N and 30°N, and between 148°W
and 180°. The only islands within this predomi-
nantly tropical oceanic area are the Hawaiian group
and Johnston Atoll. This area is within the North
Pacific Trade Wind Zone which is characterized by
mild temperatures and remarkably constant winds
from the northeast, normally between 10 and 25
knots. Anticyclonic high pressure cells move from
west to east between 35°N and 50°N and generate
the trade winds. These cells break down occasion-
ally,, more frequently in winter than in summer, at
which times southerly and westerly winds bring
warm moist air and increased rainfall.
The north-central Pacific is within the large
North Pacific Central water mass. This is bounded
on the east by the southward flowing California
Current, the westward extension of which flows
into the North Equatorial Current. The southern
border of the North Equatorial Current forms a di-
vergence with the Equatorial Countercurrent be-
tween 9°N and 12°N depending on the season. The
Kuroshio Current and the North Pacific Current
border the water mass on the west and north, re-
spectively. The North Pacific Central water mass
in the Hawaiian Islands area has a high surface
salinity, up to 35.3 parts per thousand, decreasing
toward the south to 34.1 parts per thousand. Sur-
face water temperatures range in summer from
25°C in the north (26°N) to 27°C in the south
(10°N), and in winter from 20°C in the north to
25°C in the south. A summary of north-central Pa-
cific oceanography is found in Seckel (1962).
The flow of water through the Hawaiian Islands
is to the southwest. The large submerged bases of
the islands deflect the water and cause eddies to
form in the lee of the islands, which result in local
areas of nutrient turnover and enrichment (Sette,
1955). Seabirds are often associated with such
areas. The leeward Hawaiian Islands, Johnston
Atoll, and, to a lesser extent, the main Hawaiian
Islands, have large seabird breeding colonies. In
the spring and summer, when most of the species of
this area are breeding, high densities of seabirds
are found at sea near the islands. The oceanic areas
within 100 miles of these islands provide most of
the food resources that make possible the large col-
onies.
The south-central Pacific, as herein defined, ex-
tends from 10°N to 10°S and from 150°W to 180°.
Within this area are the Line Islands, the Phoenix
Islands including Howland and Baker, and the
Tokelau Islands. Northeast trade winds predomi-
nate in the northern part of this area, and southeast
trade winds predominate in the south. The narrow
zone of light, variable wind between the two trade
wind systems is called the doldrums. It is charac-
terized by low atmospheric pressure, warm, humid
air, and more abundant rainfall than in the trade
wind zones. In January the doldrums are farthest
south, being found at 5°N at 150°W and 5°S at
170°W. In July they are found between 5°N and
9°N (Riehl, 1954:13, fig. 1.9). The belt of high
rainfall (up to 118 inches per year) moves north
and south seasonally with the doldrums.
The oceanographic conditions of the south-cen-
tral Pacific are dominated by the equatorial cur-
rent system which includes the easterly setting
Equatorial Countercurrent, and the westerly setting
NUMBER 158
North Equatorial and South Equatorial currents.
The boundaries of these currents change seasonally
and annually (Barkley, 1962). They are strongest in
summer as the result of stronger and more constant
trade winds. In winter the width of the currents de-
creases and the surface flow is weaker. In general
the North Equatorial Current is north of 9°N, the
Countercurrent lies between 4°N and 9°N, and the
South Equatorial Current is south of 4°N. Surface
temperatures range between 26° and 29°C, and sur-
face salinities between 34.4 and 35.8 parts per thou-
sand. For a more thorough treatment of the ocean-
ography of the area see Barkley (1962). Ashmole
and Ashmole (1967) present an excellent review of
the general biology of birds and their food organ-
isms in the equatorial current system.
The uninhabited islands of the south-central Pa-
cific support large breeding seabird populations,
and pelagic areas close to islands maintain high
seabird densities. In addition, high seabird densi-
ties are normally found along the southern bound-
ary of the Equatorial Countercurrent where local
140"E 150' WO' 170'W 160" 150" 140' 130' 120' 1K>' t00 '
FIGURE 1.—Area covered by POBSP observations.
80' 70'W
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
concentrations of food organisms are caused by
convergence of that current with the South Equa-
torial Current (Ashmole and Ashmole, 1967:57).
The eastern Pacific is herein defined as the ex-
panse of ocean between 35°N and 20°S, and be-
tween the American Continental coast and 135°W.
Most of the islands in this area occur within 100
miles of the coast but a few are oceanic. The sur-
face water conditions of this area are dominated by
the California Current in the north and the Peru
Current in the south. These currents, especially the
latter, carry relatively low temperature surface wa-
ters toward the equator. This results in cooler sur-
face temperatures in this area than are found
farther west at the same latitudes.
METHODS AND PROCEDURES
Observers maintained daily watches on ships mov-
ing through areas of interest. When two or more
observers were available, watches began before sun-
rise and alternated every two to four hours until
sunset. If only one observer was present, one- or
two-hour rest periods were taken occasionally. Noc-
turnal observations were made whenever possible.
In no case was an inexperienced observer expected
to make identifications without the supervision of
an experienced observer. However, in 1963 all ob-
servers were relatively inexperienced and for this
reason the 1963 data (8 cruises) are included only
as supplemental material in this report.
All birds seen were recorded in a daily field log.
The following information was included: time of
sighting, identification (to species or subspecies
when possible), number of birds, direction of
flight, behavior, and special comments (e.g., de-
scription, association with other species, fish activ-
ity) . When weather conditions and ship schedules
permitted, specimens were collected to verify sight
identifications and to show the range of individual
birds and, by inference, of whole populations. All
specimens are in the collection of the National
Museum of Natural History, Smithsonian Institu-
tion, Washington, D.C. Records were kept of all
position fixes and of interpolated hourly positions.
On a few cruises bathythermograph and other
oceanographic recordings were also taken. Prelimi-
nary reports were made of each trip and these,
along with the raw data obtained, are on file at the
National Museum of Natural History.
Line transects provide the basis for data collec-
tion and analysis. Densities were calculated in
birds per mile (BPM) or birds per hour (BPH) . In
this report only the former value is used. Since the
majority of observations were made at a speed of
approximately 10 knots, it is necessary only to mul-
tiply all BPM figures by 10 to get an idea of BPH
values.
In order to store and analyze data, an electronic
data processing system was designed (King, Wat-
son, and Gould, 1967). This system can simultane-
ously analyze data pertaining to sighting, environ-
ment, and location and duration of observation.
The system was programmed to calculate and list
the abundance of each species. For each day of
each cruise, the total diurnal miles traveled and the
total number of a species seen were used to calcu-
late relative densities for the entire day. All sight-
ings were tied to the noon position of the ship.
The BPM units were plotted by month on maps,
one per month, for all data from January 1964
through April 1968. Contour lines were drawn on
the maps, connecting points of equal bird density.
In most cases a linear gradation of bird density was
assumed between any two points (i.e., noon posi-
tions) . Exceptions to this were when several posi-
tions with significantly different densities (greater
or less than the next contour increment) occurred
within a relatively small area. This may have been
because of different densities noted during a given
month or a given year, or because of different den-
sities noted among the four years for a given
month. In such cases, the contours were drawn ac-
cording to the arithmetic mean of the densities
within the area. Thus, the maps represent the
monthly average distribution and density for all
four years. All midday positions are indicated by
dots, and varying density is indicated by degrees
of shading.
ACKNOWLEDGMENTS
The following POBSP personnel and collaborators
contributed observations during the course of the
Program: Kenneth E. Amerman, A. Binion Amer-
son, Jr., Alan H. Anderson, J. Phillip Angle, Ken-
neth C. Balcomb, Frederick A. Blagden, David A.
Bratley, Robert L. Brownell, Jr., Walter Buhner,
David L. Burckhalter, Richard D. Chandler, Jane
P. Church, Roger B. Clapp, Richard S. Crossin,
NUMBER 158
Robert L. DeLong, Paul G. DuMont, Robert P.
Elliott, Charles A. Ely, John H. Fitch, Robert R.
Fleet, Douglas E. Gill, Patrick J. Gould, C. Doug-
las Hackman, Brian A. Harrington, Richard
Heiden, Norman N. Heryford, the late J. Vincent
Hoeman, David I. Hoff, Lawrence N. Huber,
Dayle N. Husted, Raymond R. Jillson, Cameron B.
Kepler, Warren B. King, Ralph D. Kirkpatrick,
Vernon M. Kleen, Philip N. Lehner, T. James
Lewis, Charles R. Long, James P. Ludwig, Peter
Marshall, Richard L. Maze, Robert W. McFarlane,
Richard W. Merrill, David L. Pearson, Robert L.
Pyle, Gerald A. Sanger, Ralph W. Schreiber, Philip
C. Shelton, Fred C. Sibley, Frank H. Smith, Jr.,
Dennis L. Stadel, Robert S. Standen, Robert A.
Sundell, F. Christian Thompson, Max C. Thomp-
son, Jeffrey P. Tordoff, Michael N. Trevor, Robert
Tuxson, George E. Watson, J. Douglas Whitman,
Kenneth J. Wilz, William O. Wirtz, II, George S.
Wislocki, and Paul W. Woodward.
Reginald Creighton and Warren Minami devel-
oped and operated the automatic data processing
program. Anne K. Poulson prepared most of the
illustrations. Mae H. Esterline gave editorial ad-
vice. All work was under the direction of Philip S.
Humphrey.
All the observations to be presented were made
by POBSP personnel as well as by many other collab-
orators. On innumerable occasions logistic and
technical support has been generously provided by
the United States Coast Guard, the United States
Navy, the Bureau of Sport Fisheries and Wildlife
and Bureau of Commercial Fisheries of the U. S.
Department of Interior, the State of California De-
partment of Fish and Game, the State of Hawaii
Division of Fish and Game, the Scripps Institution
of Oceanography, and the institutions and coun-
tries involved in the EASTROPAC investigations. We
are grateful to all the participants who have made
this series of papers possible.
Sooty Tern (Sterna fuscata)*
Patrick J. Gould
Introduction
SUMMARY OF PUBLISHED PELAGIC DISTRIBUTION.—
The Sooty Tern is one of the most numerous and
characteristic seabirds of the tropical and subtrop-
ical Pacific Ocean, occurring widely at sea during
all times of the year. Birds have been recorded
south to 40°S on both sides of the Pacific, and
north to southern Japan and southern Baja Cali-
fornia. Population estimates of breeding colonies
for mid-central Pacific Islands visited by the POBSP
indicate total numbers in that area to be in excess
of 30 million birds (Table 1). Data from the east-
ern Pacific are fewer and less precise but indicate
many thousands of birds are present. Vast numbers
occur throughout the Atlantic and Indian Oceans
as well.
Appendix Table A is a summary of published in-
formation on Sooty Tern distribution in the Pa-
cific Ocean. It can be seen that at-sea records are
spotty, both with respect to time of year and to
geographical area. It is apparent, however, that
Sooty Terns range widely at sea throughout the
tropical and subtropical Pacific. Morzer Bruyns
(1965) found them common to abundant in No-
vember within the Equatorial Countercurrent (6°-
8°N) across most of the Pacific. Although he re-
corded the largest numbers near islands and coastal
areas, he found them most consistently, on a day-
to-day basis, across the large open stretch between
145°W and 115°W. King and Pyle (1957) found
these terns most abundant near islands and coastal
areas. They observed birds only sporadically along
the northern edge of the Equatorial Countercur-
Palrick J. Gould, Department of Zoology, University of Ari-
zona, Tucson, Arizona 85721.
• Paper Number 68, Pacific Ocean Biological Survey Pro-
gram, Smithsonian Institution, Washington, D.C. 20560.
rent (ca. 10° N) in November between 156°W and
120°W, and from mid-October to mid-November
between Manzanillo, Mexico, and the Marquesas
Islands. In early December they recorded Sooty
Terns every day between the Marquesas and the
Line Islands.
Distributional extremes in the south Pacific are
represented by one specimen from Rio Valdivia,
Chile, ca. 40°S (Murphy, 1936:1132) and three
records along the Wellington coast of New Zealand,
ca. 40°S (Falla, et al., 1967:165). In the north Pa-
cific extreme records are from: the Alijos Rocks, ca.
25°N (McLellan, 1926:283), north of the leeward
Hawaiian Islands, ca. 33°N (POBSP) , and Japan,
35° N (Austin and Kuroda, 1953:450-451).
Factors influencing Sooty Tern distribution (e.g.,
feeding habits) have been studied by Ashmole
(1963a), and Ashmole and Ashmole (1967). In
the latter study they found that these terns fed
mainly on fish and squid between 2 and 8 centi-
meters in length. They suggest that Sooty Terns are
capable of utilizing food sources up to 700 miles
from breeding islands, and that Christmas Island
birds often feed at great distances from land during
the breeding season. Nocturnal feeding has been
documented by Morzer Bruyns and Voous (1965)
and by Gould (1967).
BREEDING PHENOLOGY.—At-sea distribution and
densities of Sooty Terns are greatly influenced by
the timing of breeding activities. A brief summary
of these activities is thus necessary to the under-
standing of data presented later in this paper.
Sooty Terns breed, or have bred, on almost all
islands in the tropical and subtropical Pacific be-
tween latitudes 29°N and 32°S. The timing of the
breeding cycle is apparently quite variable (Hutch-
inson, 1950; Chapin, 1954; Ashmole, 1963a). For
colonies within the Hawaiian Islands the breeding
NUMBER 158
TABLE 1.— Maximum number of Sooty Terns
recorded on islands in the central and eastern
Pacific
Island
CENTRAL PACIFIC
Hawaiian-Leeward
Kure
Midway
Number
48,000
353,000
Pearl and Hermes Reef 40,110
Lisianski
Laysan
Gardner Pinnacles
French Frigate Shoals
Necker
N'ihoa
Moku Manu
Manana
Johnston Atoll
Line Islands
Palmyra
Fanning
Christmas
Jan is
Maiden
Starbuck
Caroline
Phoenix Islands
Canton
Enderbury
McKean
Phoenix
Birnie
Hull
Howland
Wake
Marshall Islands
Taongi
Bikar
Taka
Eniwetok
Ailinginae
Jaluit
EASTERN PACIFIC
Isabel
Revilla Gigedos
Clipperton
IslasFrailesdelSur
Cocos
Culpepper
1,000,000
2,000,000
1,000
250,000
50,000
100,000
20,000
200,000
600,000
750,000
thousands
15,000,000
1,900,000
10,000
3,000,000
500,000
100
400,000
250,000
250,000
1300
3,000,000
375,000
1,750,000
20,000
7300
60,000
16,000
5,000
30
thousands
thousands
2,000
200
30
thousands
San Felix large numbers
Source
POBSP
••
"
*•
"
••
"
"
Amerson, 1969:23
Amerson, 1969:37
Amerson, 1969:50-51
Amerson, 1969:116
Amerson, 1969:141
Amerson, 1969:196
McLellan, 1926:283
Gifford, 1913:20
Stager, 1964:365
Wetmore, 1965:457
Hundley, 1962:114
Leveque, 1964a:39-40
Millie, 1963:566
cycle is annual and regular, the dates of peak lay-
ing generally falling within the same four-week
period in most years. Dates of egg-laying, however,
occur progressively later on the chain from Oahu
northwestward to Kure Atoll. On Manana, close to
Oahu, the peak of egg-laying occurs during the last
week in March or the first week in April. On Kure,
at the northwestern end of the leeward Hawaiian
chain, egg-laying begins in May.
On Johnston Atoll the peak of egg-laying comes
in the middle of March. Birds first appear over the
island at night, nearly three months prior to the
time of laying. Numbers swirling over the island at
night build up gradually to the time of egg-laying,
when birds are present throughout the day as well.
Maximum numbers on, or over, the island coincide
with the hatching peak in the middle of April.
Most fledging takes place in June. Fledglings gen-
erally leave the island by the first of August, and
most adults leave by the end of August. The John-
ston population is composed of approximately
300,000 breeding birds, and a roughly equivalent
number of subadults and nonbreeding adults. The
relative proportion of subadults and nonbreeders
to breeding adults increases from June to the end
of the cycle. Sooty Terns are virtually absent from
Johnston Atoll from mid-September to the end of
December (Shdton, in. prep.).
In the Line island group, the breeding cycle ap-
pears to be semiannual. Birds that successfully rear
a chick breed again in 12 months, but those that
fail nest again in only 6 months. The egg-laying
peaks are in December and June. This cycle has
been documented on Christmas Island by Ashmole
(1965) and appears to hold true for other islands
of that chain as well, although there may be excep-
tions or complicating factors in some populations.
The timing of the breeding cycles of Sooty Terns
on Wake Island, and in the Phoenix, Marshall, and
Gilbert chains, and on islands in the eastern Pa-
cific is not understood. Some islands may have two
or more individual colonies, each breeding at dif-
ferent times. Many may have a non-annual cycle.
A discussion of breeding cycles and associated prob-
lems may be found in Ashmole (1963a).
ACKNOWLEDGMENTS.—I would like to give special
credit to Warren B. King and Gerald A. Sanger who
have worked with me in analyzing all at-sea bird
data obtained by the POBSP and Philip C. Shelton
who has provided data and comments on the popu-
lation dynamics of Sooty Terns on breeding islands.
Charles A. Sklar plotted the majority of the noon
positions on the maps, and Helen H. Quinn typed
the final draft.
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE 2.—Sample size of POBSP Sooty Tern
observations
Observation
Sightings
Birds
1964 1965 1966 Total
1,547
19,070
1,665
20,738
782
11,287
3,994
51,095
I am indebted to William B. Robertson, Jr., and
George E. Watson for their critical reading of the
manuscript and their many helpful suggestions.
The many POBSP personnel and various cooperat-
ors without whose observations and help this paper
could not have been written have already been ac-
knowledged in the Introduction.
Behavior
In this section all data, except when specifically
stated otherwise, were collected within the follow-
ing parameters: (1) at sea over 50 miles from land,
(2) within approximately three-fourths mile of the
ship, (3) in the north-central Pacific Ocean, (4)
from 1964 through 1966, (5) from diurnal observa-
tions (sunrise to sunset). These parameters have
been purposely chosen. Observations near land
have been excluded because it was often impossible
to get a clear idea of what was happening when
birds were "too numerous to count": birds seem to
be everywhere, moving in all directions, joining
groups, leaving groups, flying high, flying low, etc.
In such situations it was impossible to follow indi-
vidual birds or flocks, or to understand behavioral
patterns and interactions. The parameter of three-
fourths mile from the ship was chosen because, al-
though Sooty Tern flocks could be seen at greater
distances, they could not be counted accurately, nor
could they be observed well enough for behavioral
studies beyond that distance. Moreover, single birds
cannot be observed at greater distances so that the
inclusion of distant birds would over-emphasize ef-
lects created by flocking. The north-central Pacific
was the most uniformly covered large area, and had
by far the largest number of observations made
within it; also, Sooty Terns breeding in this area
have an annual rather than semiannual cycle. Only
the years 1964, 1965, and 1966 were included be-
cause of the spottiness of coverage in the north-
central Pacific during other years. Within these
parameters a total of 51,095 birds in 3994 sightings
was recorded (Table 2).
At this point it seems advisable to define a few
special terms which will be used in the following
discussion. A "sighting" refers to a single bird or
two or more birds acting as a unit. A "flock" is con-
sidered to be the association of five or more indi-
viduals, "BPS" (birds/sighting) is a good index of
the gregariousness or flocking tendency of a species.
A "mixed" flock or sighting is one that contains
more than one species, while a "pure" flock or
sighting is one which contains only one species.
"Searching" birds are those actively hunting for
food, while "traveling" birds appear to be moving
towards a specific goal.
FEEDING.—Ashmole and Ashmole (1967) have
discussed the feeding ecology of Sooty Terns, con-
sidering particularly the kind of food taken and
how it is captured. Our observations are in general
agreement with theirs. Sooty Terns, searching for
food, generally remain from 10 to 20 meters above
the water surface. When the food source appears,
they descend, simultaneously, and begin wheeling
rapidly and erratically in circles. At this time there
does not appear to be any coordination between
individuals within a flock, although small groups
may act in unison for short periods. When the food
source descends, the flock rises to its original posi-
tion and follows until the food returns to the sur-
face or until it disappears. In a feeding flock work-
ing over a large area, terns in one section may be
flying high, following locally deep food, while those
in another section may be low and actively feeding.
"Air dipping" and "contact dipping" (Ashmole
and Ashmole, 1967) appear to be the preferred
feeding techniques, although "plunge to surface" is
frequently used if the food source remains near but
under the surface. The latter technique has been
recorded only once in the Sooty Tern literature
(Watson and Lashley, 1915). In POBSP observa-
tions, the "plunge to surface," although actually
causing the water to splash up and obscure the
bird momentarily, is never powerful, nor is it made
from any great height. It never results in complete
submergence of the bird, nor do the wings ever ap-
pear to cease beating. The feet do not seem to be
utilized.
FLOCKING.—Sooty Terns were recorded in sight-
ings of from 1 to 3000 individuals. The overall BPS
ratio was 13, the highest value for any seabird
NUMBER 158
TABLE 3.—Percent of sightings and numbers of
Sooty Terns in different sighting classes
Birds per
sighting
1
2
3
4
5
6
7
8
9
10+
1-4
5-55
56-105
106+
Percent of all sightings
1964
36
20
9
4
3
3
1
1
1
22
69
25
4
2
1965
15
21
9
5
4
2
1
1
1
21
70
?4
4
2
1966
1?
21
10
6
4
3
1
?
1
20
69
3
1
mean
35
21
9
5
4
2
1
1
1
21
70
25
4
2
Percent of all birds
1964
3
3
2
0.5
86.5
9
37
27
26
1965
1
3
2
2
?
1
1
1
1
84
10
3">
27
28
1966
?
3
2
2
86
9
in
16
45
mean
3
3
2
2
1
1
1
1
1
85
10
15
24
31
species regularly feeding over 50 miles from land.
Although 90 percent of all individuals were found
in flocks, flocks comprised only 30 percent of the
sightings in all years. Indeed, sightings of single
birds (35 percent) far outnumbered sightings of
any other group size. Singles and groups of two ac-
120
100
80
60
40
20
counted for 56 percent of all sightings (Table 3).
The POBSP data agree with Ashmole and Ash-
mole's (1967:97) statement that "most tropical sea
birds depend partly or entirely on schools of preda-
tory fish (mainly tunas) to drive their prey close to
the surface and so make it available." Although
Sooty Terns have been observed feeding in the
absence of predatory fish, many actively feeding
flocks were directly associated with such schools.
The sudden, and often relatively short-term, ap-
pearance of feeding tuna apparently places a pre-
mium on the ability of Sooty Terns to join feeding
flocks containing other species. Seventy-seven per-
cent of all Sooty Terns, and 24 percent of all Sooty
Tern sightings, were associated with one or more
seabird species (Table 4) . Almost all species nor-
mally occurring in the area were involved, but the
degree of their involvement was related to their
gregariousness and their status within the area. For
example, 70.6 percent of all mixed flocks containing
Sooty Terns also contained Wedge-tailed Shear-
waters (Puffinus pacificus). Conversely, King (p.
65, herein) found that 77 percent of all mixed
flocks containing Wedge-tails contained Sooty
Terns. Wedge-tails are the next most abundant
species in the area and have a high BPS ratio (King,
p. 64 herein). On the other hand, Sooty Shearwa-
V
VV —
V
V V i , . ^
VV
V
VV
VV
rfV
VV
VV
£/ > r"
^
FIGURE 2.—Schematic representation of a mixed feeding flock showing the general stratification
of selected species and their general pattern of movement while feeding.
10 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE 4.—Percent of association of Sooty Terns zoith other seabird species,
1964-1966
Species
Puffinus pacificus
Pterodroma externa . . . .
Gygis alba
Pterodroma nigripennis..
Fregata minor
Puffinus griseus
Anous stolidus
Puffinus puffinus
Sula sula
Bulweria bulwerii
Pterodroma neglecta . . . .
Sula dactylatra
Puffinus nativitatis
Phaethon rubricauda ...
Oceanodroma leucorhoa .
Sterna lunata
Stercorarius pomarinus ..
Puffinus carneipes
Pterodroma alba
Pterodroma phaeopygia..
Stercorarius longicaudus.
Fregata oriel
Pterodroma hypoleuca ..
Phaethon lepturus
Puffinus bulleri
Puffinus Iherminieri
Puffinus tenuirostris . . . .
Pterodroma inexpectata .
Sula leucogaster
Catharacta species
Anous tenuirostris
All sightings
16.4
7.4
4.8
S.9
3.3
1.1
1.0
1.0
1.0
0.7
0.7
0.6
0.5
0.5
0.4
0.4
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
Mixed Sightings
70.6
32.0
20.8
16.8
14.2
4.5
4.4
4.3
4.1
2.8
2.8
2.5
2.3
2.2
1.8
1.5
1.2
1.0
1.0
0.6
0.6
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.2
0.2
0.2
General at-sea status
abundant most of the year
common summer and fall
uncommon throughout year
common summer and fall
uncommon throughout year
abundant spring and fall migrant
rare throughout year
uncommon spring, summer and fall
common winter
uncommon spring, summer and fall
uncommon throughout year
common winter
uncommon spring, summer and fall
common throughout year
abundant winter
uncommon spring, summer, and fall
uncommon spring and fall migrant
rare spring and fall migrant
rare throughout year
rare summer and fall
rare spring and fall migrant
rare throughout year
rare throughout year
uncommon throughout year
rare spring and fall migrant
rare throughout year
abundant fall migrant
uncommon spring and fall migrant
rare throughout year
rare spring and fall migrant
rare throughout year
ters (Puffinus griseus) were abundant at certain
seasons and had a high BPS ratio, but were found in
•only 4.5 percent of all mixed flocks containing
Sooty Terns. This difference between two highly
flocking and abundant species is explained by the
fact that Wedge-tails are resident in the area while
Sooty Shearwaters are primarily passing through
on migration and rarely stop to feed.
The association of Sooty Terns with other sea-
bird species appears to be mainly one of a common
interest in the same food source. While within
mixed feeding flocks, Sooty Terns maintain a defi-
nite spatial position in accord with the feeding
abilities and techniques of all species involved.
(Figure 2) .
We have a number of records of Sooty Terns be-
ing harrassed by Pomarine Jaegers (Stercorarius
pomarinus), Long-tailed Jaegers (Stercorarius
longicaudus), Great Frigatebirds (Fregata minor),
and Lesser Frigatebirds (Fregata ariel).
The largest Sooty Tern flock ever recorded by the
POBSP occurred on 20 May 1966, some 200 miles
south of Oahu. On this day a feeding flock of
4300+ birds, including Wedge-tailed Shearwaters,
Pale-footed Shearwaters (Puffinus carneipes),
Christmas Shearwaters (Puffinus nativitatis), Manx
Shearwaters (Puffinus puffinus), Bulwer's Petrels
(Bulweria bulwerii), Great Frigatebirds, Brown
Noddy Terns (Anous stolidus), Black Noddy
Terns (Anous tenuirostris), and 3000+ Sooty Terns
was observed. The birds were concentrated over
eight to twelve Fin-backed Whales (Balaenoptera
physalus) and about 200 porpoises. The fringes of
the flock stretched for approximately three miles.
NUMBER 158 11
Although we have no direct information on how
much time individual birds spend feeding, search-
ing, or traveling, the fact that the great majority of
all birds observed were in mixed flocks, usually an
indication of current or recent feeding, suggests
that the greatest percent of their time is spent feed-
ing or actively searching for food, with the former
outweighing the latter. There is certainly a tend-
ency for Sooty Terns to occur in larger flocks
while feeding (Table 5) . Our observations indi-
cate that mixed, nonfeeding groups are composed
mostly of searching birds. Pure, nonfeeding groups
may be either searching or traveling; the activity
cannot always be determined. Pure flocks of up to
140 birds and mixed flocks of up to 125 birds have
been recorded traveling. Single birds and small
groups have been observed both searching (moving
slowly, dropping occasionally to the water surface,
and investigating other birds in the water), and
traveling. The distinction between searching and
traveling, however, sometimes breaks down (trav-
eling birds may stop to feed if the stimulus is strong
enough), or it is sometimes even meaningless
(many traveling birds may be headed for a distant
feeding flock).
It was difficult to obtain direct evidence on how
flocks form, how long they are maintained, and
what happens when the food source being utilized
disappears. In discussing the feeding behavior of
Brown Noddies and Sooty Terns, Watson (1908:
193) wrote: "The birds feed singly or in groups,
usually in groups. The group may be composed of
both noddies and sooties and may contain some-
times as many as 50 to 100 individuals. All during
the day groups of noddies and sooties may be seen
at work. As the minnows cease to jump above the
surface of the water, the group disbands and scat-
ters in every direction. An instant later, as an at-
tack is made upon the minnows in some other lo-
cality, the birds immediately rush there and renew
their feeding." POBSP observations include a num-
ber of isolated observations documenting various
stages in this process. The following entries, with
annotations enclosed in brackets, are abstracted
from the POBSP original daily log sheets. They are
arranged in a subjective order from "searching"
birds through "feeding" birds (including birds trav-
eling toward already formed feeding flocks), to
flocks "breaking up."
TABLE 5.—Total Sooty Tern sightings and numbers
in mixed and pure, feeding and nonfeeding, situ-
ations
Situation
Mixed
Feeding ..
Nonfeeding
Pure
Feeding ..
Nonfeeding
Mixed
Feeding . .
Nonfeeding
Pure
Feeding ..
Nonfeeding
Mixed
Feeding ..
Nonfeeding
Pure
Feeding ..
Nonfeeding
1964 1965 1966 Mean
Percentage of sightings
14
8
2
14
10
2
14
8
5
14
9
3
75 74 74 74
PerCe«»=><*** nt total numtv»r*
58
16
6
18
51
24
33
3
54
24
3
19
BPS
48
30
22
3
69
8
10
13
ratio
70
16
28
3
59
18
6
18
53
25
28
3
SEARCHING
05 March 1964. 0700 Hours. 16°48'N, 169°06'W.
3 ST [Sooty Terns], [flying at] ca. 30-40 feet. One bird
separated and circled a dead albatross in the water, then
joined other two.
08 March 1964. 1103 Hours. 14°50'N, 169°40/W.
1 ST. Investigated downed [dead in water] albatross and
continued NE.
07 June 1964. 1441 Hours. 18°11'N, 166°10'W.
2 ST. One shot [ship circled to retrieve downed bird]. At
1450 Hrs. 12 ST circled and looked over downed bird.
02 April 1964. 1612 Hours. 20°41'N, 159°ITW.
2 ST flying SW joined and drded with 6 ST circling at
1615 Hrs., then all 8 departed SW. No feeding was ob-
served.
04 July 1964. 0600 Hours. 16°40'N, 169° 1 8 ^ .
Hock of 26 ST and 1 WTS [Wedge-tailed Shearwater].
Original group of 14 joined by 6 then 6 more. Birds
were not actively feeding but flew around as if food
were near by.
FEEDING
10 May 1964. 1900 Hours. 15°04'N, 170°37'W.
30 ± ST. Very high, maybe 1000 feet up. Some of them
seem to be gathering to move on, but then descend sud-
12 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
denly as feeding flock. Big fish, probably tuna 5' or more
long and some about 3' long jump at least 6' clear of
water.
22 July 1964. 1110 Hours. 18°46'N, 150°59'W.
Feeding flock containing 90± ST, 2 WTS, 8 JFP [Juan
Fernandez Petrel, Pterodroma externa], 1 W'T [White
Tern, Gygis alba]. Three separate groups joined up,
each with about 30 ST.
11 March 1964. 1656 Hours. Near Johnston Atoll.
Feeding flock in formation started with 4 birds on their
way south starting to circle and dive. Within minutes, 8
other Sooties came in, seemingly from all directions to
join them. No fish action noted and feeding over area of
about 14 mile length (or diameter). [Ship continuing to
move at ca. 8 knots.] 1700 Hours: 25+ ST moving low
towards above flock. 1702 Hours: 40 ± ST at ca. 50' mov-
ing to join above? 1702 Hours: 10 ± ST low, moving
right under above. 1705 Hours: 2 ST moving low toward
above flock.
18 May 1965. 1500 Hours. 20°14'N, 154°02'W.
Feeding flock of 50 ST, 8 WTS, and two unidentified
shearwaters or petrels. Original flock of 20 joined by 10
individuals and then by group of 25 or so.
06 September 1964. 1645 Hours. 17°34'N, 167°03'W.
30 ± ST, 8 WTS, 1 GFB [Great Frigatebird]. Feeding
over fish jumping out of water. 1640 Hours: 13 ST at 50'
going to above flock. 1646 Hours: 10 ST, 1 GFB, circling.
1648 Hours: 11 ST flying towards 1645 flock. 1656 Hours:
8 ST flying towards 1645 flock.
12 May 1964. 0715 Hours. 15°30'N, 171°33'W.
Flock of 55 ±1 ST and 3 WTS. Actively feeding. Large
tuna-type fish jumping under flock. Flock was originally
only of about 30 birds but soon increased to final num-
ber. At one point flock broke up into two groups, one of
about 25, the other about 30. One group was soaring
around high on port side of ship, the other was low,
flying on starboard.
BREAKING UP
11 April 1964. 0825 Hours. 15°07'N, 171°24'W.
16±2 ST feeding. 3 birds left flock as we approached.
18 July 1964. 0905 Hours. 21°48'N, 162°27'W.
Flock of 50 ±10 ST, 6 WTS, 2 BFB [Blue-faced Booby,
Sula dactylatra], 1 WT, 1 GFB, feeding—but breaking
up into small groups. 091") Hours: flock of 30 ST, 10
WTS, 1 RFB [Red-footed Booby, Sula sula], 2 CIS
[Christmas Shearwater], and 1 WT, undoubtedly was
once part of last flock; we saw birds from last flock
join this one.
13 May 1964. 1705 Hours. 16°25'N, 17O°51'W.
17 ST, 5 to 50' [above water]. Not feeding, but appar-
ently looking for food source—group tended to split up
but constant movement was to E[ast].
Most shearwaters and gadfly petrels tend to sit
on the water in either compact or loose aggrega-
tions after heavy feeding. It is well known, how-
ever, that Sooty Terns are incapable of spending
long periods in such a fashion (Watson and Lash-
ley, 1915:39-41). Sooty Terns do, however, alight
occasionally at sea, either on a floating object or
actually on the water. All such POBSP records are
listed below. Omitting the bird knocked down by
shot and the three sitting on turtles or flotsam,
0.3 percent of all sightings and 0.16 percent of all
individuals recorded by the POBSP were on the
water. These estimates, however, are undoubtedly
low since most birds tend to rise before they can
be detected.
19 August 1965. 0920 Hours. 13°53'N, 173°01'W.
One Sooty Tern was knocked down by shotgun blast and
sat in the water for 12 minutes then flew at the approach
of the ship.
23 October 1965. 0940 Hours. 01°16'S, 173°38'W.
One adult and one immature Sooty together on water,
immature being fed by the adult.
23 October 1965. 1730 Hours. 02°00'S, 172°52'W.
One adult, one immature were collected while sitting on
the water.
10 November 1965. 17°5rN, 164°09'W.
In a feeding flock containing ca. 15 Sooty Terns (at least
four being immature), one adult and one young were
noted as "on water together."
September-October 1964.
"Three different times during the trip I saw Sooty Terns
sitting on the water. A total of 6 birds were observed,
always in twos. Each pair contained an immature bird
and an adult. In one case both the immature and the
adult were observed on the water. In the other two cases
just the immature was on the water with the adult hov-
ering overhead. In all cases the birds flew off as the ship
approached. I never saw them land on the water so I
can't say how long they stayed there. The longest I ob-
served them was about 5 seconds." (POBSP, Robert
Standen)
12 May 1965. 0744 Hours. 16°44'N, 162°16'W.
10 and 25 Sooty Terns. "Two separate flocks sitting on
the water. They were gliding around and at first ap-
peared to be Wedge-tails from their flight pattern. Birds
were flying and then sitting down again. They were not
feeding."
01 September 1967. 0930 Hours. 01°44'N, 98°04'W.
75 ± ST. All adults, seemed to have fresh plumage. Most
circling high 200'±, some close to water. About 8 of
them were sitting on the water.
14 June 1967. 1425 Hours. (Atlantic Ocean) 12°42'N,
81°06'W.
2 adult ST sitting on water with wings closed—quite
happy 10-15 seconds that I saw. (POBSP, Richard Chan-
dler)
February 1968.
"On February 13 both shipboard observers saw a single
flock of 22 adult Sooty Terns resting on the water about
10 miles south of Johnston. When first seen all were to-
gether on the water spaced two to six feet apart. As the
ship aproached two or three birds rose off the water and
NUMBER 158
began hovering over the remaining 20. These remained
on the water for at least another minute before the ship
scared them into flight. The time lapse between the
lust sighting and flushing was about two minutes, but it
was obvious that the birds had been there quite a bit
longer." (POBSI\ Brian Harrington)
07 July 1967. 0955 Hours. 18°35'N, 104°53'W.
One Sooty Tern sitting on a turtle.
10 July 1967. 1433 Hours. 17°O8'N, 101°05'VV.
One Sooty Tern standing on head of turtle.
18 August 1966. 1713 Hours. 32°06'N, 163°42'W.
One adult Sooty Tern sitting on fish ball [float].
DISCUSSION.—Sooty Terns occur over the entire
pelagic area of the north-central Pacific. They are
distributed primarily as singles and small groups
interspersed with a few small flocks and even fewer
large flocks. Over 90 percent of all individuals,
however, are found in flocks. The degree of flock-
ing is probably greatest in areas of food abundance.
Single birds and small groups generally appear to
be searching. Their flight is usually slow, indirect,
and often high above the water. They frequently
drop to just above the surface, apparently investi-
gating possible food items. When available food is
spotted the bird or birds descend and begin feed-
ing. This change in behavior pattern is distinct and
easily recognizable to the human eye. Other birds
within visual range probably can detect and
identify the new pattern and are attracted to it.
Birds heading towards a feeding flock fly in a rela-
tively fast and direct manner distinct from that of
searching birds. It is possible that this type of flight
may provide a clue to other birds which were not
aware of the newly formed feeding flock. Similar
behavioral differences are also found in other flock-
ing seabirds (e.g., Wedge-tailed Shearwaters) and it
seems probable that Sooty Terns could recognize
such behavioral changes in other species and act
accordingly.
As a feeding flock grows it becomes visible to
more distant birds. The eventual size of the flock
would thus be controlled, primarily, by the length
of time that food is available. The total number
of terns within range of the food supply would,
however, have a restricting effect, since distant
birds might be hard put to detect the presence of
food and to reach it before it disappeared. When
the food source disappears, Sooty Terns rise high
into the air and disperse, either by fragmenting
into two or more smaller groups each going in a
separate direction, or by all going in the same
direction but becoming widely separated. Subse-
quent fragmentation of groups or continued sepa-
ration of individuals may eventually result in the
dispersal of all birds over the ocean as individuals.
If another food source is discovered before a flock
has fragmented or separated completely, the group,
whatever size it has been reduced to, becomes the
nucleus of a new feeding flock. As the length of
time between feedings increases, sightings of single
birds should increase since flocks would have had
more time to disperse. The relative frequency of
sightings of single birds, as opposed to sightings of
groups, should thus provide an estimate of food
availability and tuna school density in a given
pelagic area.
Distribution and Abundance
Figures 17-28 (pp. 34-45) summarize monthly
POBSP Sooty Tern sightings in the Pacific Ocean.
They attempt to show gross distributional patterns
and in most cases tend to de-emphasize local or
short-term variations. Only at-sea sightings are in-
cluded, although these may include sightings
within a few miles of land. Sightings cover the
period January 1964 through April 1968, and con-
tour lines are drawn without regard to year. Den-
sities are recorded in BPM units.
NORTH-CENTRAL PACIFIC.—Sooty Terns are pres-
ent in the north-central Pacific throughout the
year. At least one bird was recorded during 74.5
percent of all days of observation from 1964
through 1966. Only during January 1964, Decem-
ber 1965, and August 1966, were birds seen on
fewer than 50 percent of all observation days
(Figure 3).
Densities throughout the year ranged from a low
of 0.0 BPM to a high of 54.5 BPM. Densities greater
than 10.0 BPM were uncommon and, with one ex-
ception, always occurred within 50 miles of land.
This exception, however, was the second highest
density ever recorded within the study area (27.1
BPM). The highest density figure, 54.5 BPM, is some-
what unreliable since observations on that day
covered only four miles and lasted somewhat less
than one hour (Table 6).
With the fledging of chicks in August, Sooty
Tern numbers near islands decrease markedly.
Lowest maximum densities near the Hawaiian Is-
lands and Johnston Atoll occurred in October
14 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
100
90
80
70
60
t
8 50
I
40
30
20
10
Average
J F M A M J J A S O N D
63 59 83 115 77 99 66 76 58 72 79 77
Days of Observation
FIGURE 3.—Percent of observation days on which one or more Sooty Terns were recorded in the
north-central Pacific during 1964-1966.
(Table 7). In the area as a whole, however, den-
sities were lowest in November and December,
even though densities near the Hawaiian Islands
and Johnston Atoll increased slightly. Densities
over 50 miles from land began increasing in June
with an influx of newly fledged birds. From June
through November, immature birds became in-
creasingly abundant and wide-spread throughout
the north Pacific. We have a few records which
indicate that newly fledged birds accompany their
parents when they leave the breeding colony, i.e.,
the six sightings of an adult and immature sitting
on the water listed in the behavior section. The
record of an adult feeding an immature over 100
miles from land on 23 October 1965 is certainly
conclusive.
Increasing densities in January and February,
particularly near breeding islands, were the result
of birds returning to these islands for the next
breeding season. From September through Decem-
ber, and especially during September and October,
densities in areas over 50 miles from land were
generally greater than those within 50 miles. This
was particularly noticeable in two widely separated
areas where at-sea densities reached as high as 9.0
BPM. The first area was 200-300 miles west-south-
west of Oahu. This is apparently a rich feeding
area favored by many species of seabirds, particu-
NUMBER 158 15
TABLE 6.—Date and location of all Sooty Tern
densities of 10.0 or greater BPM recorded within
the north-central Pacific, 1964-1966
(Observation = within 50 miles of "Location")
TABLE 7.—Maximum Sooty Tern densities (BPM)
in the north-central Pacific
Density
(BPM)
10.0
10.2
10.4
10.9
11.0
11.5
11.8
12.4
12.8
12.9
14.5
16.1
23.2
26.9
27.1
54.5
Location
Oahu
Johnston Atoll
Oahu
Oahu
French Frigate Shoals
Oahu
Laysan
Johnston Atoll
Oahu
Johnston A toil
Laysan
Johnston Atoll
Lisianski
Oahu
at-sea, 17°54'N,
158°48'W
Oahu
Date
6 Jun
5 Jun
5 Jul
5 Jun
17 Jun
4 May
20 Jun
13 Apr
13 Jul
31 Jan
5 Aug
5 Jul
14 Jul
31 May
20 May
2 Jul
66
66
66
64
64
65
66
65
64
66
65
65
65
65
66
65
Miles of
observation
28
141
23
73
108
40
39
117
51
22
80
127
33
104
117
4
larly those breeding in the leeward and main
Hawaiian Islands. The second was 700-800 miles
south-southeast of Oahu. This area may be occu-
pied by birds from more southerly breeding locali-
ties (e.g., Line Islands) as suggested by King
(1970:54), although it is somewhat north of the
Equatorial Gountercurrent which Ashmole and
Ashmole (1967:66) considered a likely feeding
ground for Christmas Island birds.
During this winter period, a strange pattern of
occurrence was found in the area between 50 and
300 miles southwest of Johnston Atoll. During the
day, Sooty Tern densities decreased through No-
vember and December to a low of 0.0 BPM in
January, and then increased again in February.
Nocturnal observations in the same area, on the
other hand, revealed few terns in November and
December, but large numbers in January and
February. This occurred in all three successive
years of our investigations in this area (Table 8).
Nocturnal counts were primarily of birds heard
near the ship. Densities listed in Table 8 are con-
servative, particularly with respect to diurnal sight-
ings, since birds can be seen at greater distances
than they can be heard. Although Sooty Terns are
often attracted to the ship's lights, particularly on
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Near Near 50+ miles
Hawaiian I. Johnston Atoll from land
4.8
6.7
6.9
5.6
26.9
11.8
54.5
14.5
1.0
0.1
1.0
1.5
12.9
5.0
7.9
12.4
7.2
10.2
16.1
2.8
3.5
02
1.3
2.3
4.9
6.7
8.0
6.4
27.1
3.9
9.4
8.0
9.0
7.1
2.6
5.0
TABLE 8.—Winter Sooty Tern densities 50-300
miles southwest of Johnston Atoll, 1963—1967
Year
1963-1964
1964-1965
1965-1966
1966-1967
Mean
1963-1964
1964-1965
1965-1966
1966-1967
Mean
Nov Dec Jan Feb
Birds per 100 miles of diurnal
observations
23 1 0 1
1 17 0 0
32
3
14
1
10
8
0
0
0
8
41
20
Birds per 100 miles of nocturnal
observations
2 0* 2 # 0#
13
9
1
2
» 2
0
5
3
62
5
32
30
23
47
40
•Months in which less than 100 miles of observations were
made.
stormy nights, they are still difficult to observe. The
chances of counting the same birds twice are much
greater at night than during the day. In this case,
however, most of the nocturnal birds appeared to
be traveling in a specific direction, rather than
circling the ship, thus reducing the chances of
duplicate recording.
Two additional features were also apparent.
First, there was a definite nocturnal activity cycle.
Sooty Terns were first heard about an hour after
sunset and increased in numbers to maximum
16
6
5
r
u
s
IEi3
2
1
-
-
-
-
- m
Ii
m11n1
II
i1
1I1
sXXS
I
ii1i
I
i
I
!iIi
g j JAN. - FEB.
[ | NOV. - DEC.
SUNRISE-0617-0790
SUNSET -1749 1912
I
I1
IIi
w
I1m1
1100 19-20 20 21 21-22 22-23 23-24 24-01 01-02 02 03 03-04 04-05 OJ-04 0600
to to
1 9 0 0 HOURLY PERIODS 0700
FIGURE 4.—Nocturnal abundance cycle for Sooty Terns from
50 to 300 miles southwest of Johnston Atoll during 1963-
1967.
densities between 2200 and 0200 hours. Numbers
then declined to zero about an hour before sun-
rise (Figure 4). This was especially noticeable in
January and February, but was also true in No-
vember and December. Second, a majority of the
nocturnal terns heard south and west of Johnston
Atoll was apparently moving north and northwest
towards the atoll, or towards other breeding islands
farther north and northwest in the Leewards. The
number moving in southerly directions was almost
nil. Unfortunately, adequate records for nocturnal
direction of movement are available only for Jan-
uary and February of 1966 (Figure 5).
A similar nocturnal-diurnal pattern occurred
on the breeding island at Johnston Atoll. Lowest
numbers of Sooty Terns occurred in October and
November when only a few individuals and small
flocks visited the island briefly and irregularly.
These were probably wandering pelagic birds that
happened to pass the island and were temporarily
attracted to it, primarily at night or just at dusk.
They rarely landed on the island. Potential breed-
ing birds were first observed at the island between
late November (1964—1965) and late December
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
(1963). In 1966 flocks first occurred near the island
during the first two weeks of December. These
birds first gathered offshore at night, then began
settling on the island in small groups. These groups
grew until much of the land was occupied. This
development took several weeks, generally lasting
through mid-February, during which no more than
a few wandering birds were over the island during
the day. All of those on the ground at night left
shortly before dawn. Finally, the birds began to
stay on the island during the day, after which
courtship and egg laying followed in quick succes-
sion (POBSP, Philip Shelton). Sooty Terns occurred
within 50 miles of the atoll in fair numbers during
the day throughout this period, especially in Jan-
uary and February.
Several causative and perhaps interrelated factors
have been suggested to explain the day-night differ-
ences in January-February densities. Although
none of these explanations is complete in itself,
one or more may provide part of the answer.
1. At this time of year Johnston birds are known
to avoid land during the day, and to be attracted
to it at night. Birds may react toward ships in the
same way, thus avoiding diurnal detection at sea.
2. Sooty Tern migration may be rapid and noc-
turnal. Birds may "pile up" in preferred feeding
areas during the day and complete the last leg of
their migration in a single night.
3. Most Sooty Terns may remain within 50 miles
of Johnston during the day even though they avoid
close approach to land.
4. The area southwest of Johnston is probably
very poor in available food. Terns leaving John-
ston before dawn may pass through the area before
sunrise and return through the area after sunset. A
lack of food would deter them from pausing within
the area.
5. The January and February nocturnal aggre-
gations may represent prebreeding swirls from
Johnston Atoll. W. B. Robertson of the National
Park Service (pers. comm.) informs me that early
prebreeding swirls at the Tortugas often do not
seem to be oriented toward the colony site. Instead
they may occur anywhere around the general area
and, quite possibly, well outside the area.
Although egg-laying commences in late February
on Johnston Atoll, at-sea densities of Sooty Terns
continued to increase through March in the sur-
rounding waters. This was consistent with a con-
NUMBER 158 17
169°3O'
16°45'
•Jr
^ 9
Johnston
A Atoll
WIND
Total °h for 271 bird*
. = 24OO position
Avg. 16 knots
5 1
2 7 8 1
FIGURE 5.—Nocturnal flight directions for Sooty Terns southwest of Johnston Atoll during Janu-
ary-February 1966. (Arrows indicate direction in percent, numbers indicate sample size.)
tinued increase of birds on the island. Maximum
island and at-sea densities were generally main-
tained through July, although some terns began
leaving Johnston Atoll in early June.
During the northern summer, densities in the
1-5 BPM range were common over 50 miles from
land, and ranged from 0.0-8.0 BPM. Densities up
to at least 26.9 BPM were recorded within 50 miles
of the breeding islands at this time. The largest
single concentration of Sooty Terns recorded by
the POBSP north of the equator, however, occurred
on 20 May 1966, at 17°54'N, 158°48'W, some 200
miles south of Oahu.
Repeated observations to the northeast of the
Hawaiian Islands illustrate the seasonal expansion
and contraction of Sooty Tern distributional limits
in the north central Pacific (Figure 6). During the
nonbreeding season, in particular November-De-
cember, birds were rarely recorded over 100 miles
northeast of Hawaii. With the return of the birds
and the beginning of nesting activities (March-
April), distributional limits were extended, and
by July-August, when chicks were being fed, birds
were found up to 600 miles northeast of Hawaii.
The northernmost sighting in the central Pacific
was of two adult-plumaged birds recorded at 33°
06'N, 164°08/W on 9 August 1966.
To summarize, at-sea densities of Sooty Terns in
the north-central Pacific Ocean are reflections of
breeding island densities. The annual cycle is repre-
sented by a fairly smooth curve, with lowest den-
sity in November-December and highest density in
June (Figure 7).
To clarify the distributional patterns of birds
18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
160'
FIGURE 6.—Seasonal variation in the distributional limits of
Sooty Terns northeast of the Hawaiian Islands.
within the central Pacific, the POBSP initiated an
intensive banding program. Since March 1963, over
1,200,000 Sooty Terns have been banded. These
include birds from nearly all major breeding col-
onies on the main and leeward Hawaiian, Line,
and Phoenix (including Howland) island groups,
as well as on Johnston and Wake atolls. Greatest
numbers have been banded on Johnston (over
250,000), Laysan (over 130,000), and Howland (over
100,000). Colored vinyl leg streamers were also
placed on birds from Johnston (orange) and How-
land (blue). A special effort was made on all POBSP
field trips, both at sea and on islands, to look for
streamered and banded birds. In addition, a pro-
gram of intensive advertisement of our efforts,
including appeals for help in locating banded and
streamered birds, was made throughout the in-
habitated areas of the tropical and subtropical
Pacific.
As of December 1968, we have processed 1027
interisland and at-sea recoveries and 339 at-sea
streamer sightings of Sooty Terns. These represent
WEST
170° 160°
M A M J
MONTHS, 1964-1966
N
FICURE 7.—Annual at-sea density cycle for Sooty Terns in the north-central Pacific.
NUMBER 158 19
CENTRAL PACIFIC OCEAN
\SLANOjs
»NUKUNONOt
mryyD IQO 20ST 355 «oo
FIGURE 8.—Distribution of banded and streamered Sooty Tern sightings.
20 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
110° IJ0° 130* 140° ISO* 160* 170° t»0° 130° 110° 110* 100* 90* to' 70*
FIGURE 9.—Interisland movements of Sooty Terns banded in the north-central Pacific.
less than 0.01 percent of the total number banded.
Over one-half of the interisland recoveries repre-
sent elapsed times greater than one year and 68
percent were short-distance movements within
island groups (e.g., between Kure and Midway
atolls). It is thus too early to attempt a detailed
analysis of the banding data. Since some of these
records provide insight into the confusing pelagic
dispersal of Sooty Terns, however, a brief summary
is presented here.
Two hundred and thirty-five orange-streamered
birds have been observed at sea (Appendix Table
B). All were in the central Pacific north of 11°N.
Similarly, orange-streamered birds have been seen
and handled on most islands in the same area, but
none have been observed on islands farther south.
No blue-streamered birds have been recorded north
of 02°N. Ninety-six percent of all orange-stream-
ered birds were recorded during the breeding sea-
son (March-August). Of these, 70 percent were
within fifty miles of Johnston Atoll even though
over 80 percent of all observation time in that gen-
eral area was spent over 50 miles from the atoll.
During the breeding season, four streamered birds
were sighted over 275 miles from Johnston (one
adult in August, 278 miles SE; one immature in
August, 287 miles SW; one adult in August, 392
miles SW; and one adult in March, 392 miles SW).
We have 10 records of 13 streamered birds feeding
at distances up to 225 miles from Johnston (April-
June). Recently fledged streamered birds have been
found over 100 miles from the breeding colony only
during August (3 birds: 180, 226, and 287 miles
SW). During the nonbreeding season (September-
NUMBER 158 21
February), three of a total of eight orange-streamer
sightings were over 50 miles from Johnston (two
in September, 394 and 481 miles NE; and one in
December, 299 miles ENE). The remaining five
were found in September, January, and February,
and were probably late departing or early arriving
birds.
Twelve banded birds (10 from Johnston, 1 from
Oahu, and 1 from Laysan) have been recovered at
sea (Appendix Table C). As with the streamer
sightings, all were from the central Pacific north of
11°N. All but three were recovered over 100 miles
from the site of banding. One immature banded on
Laysan in August was recovered four months later
1170 miles to the southeast. Another, banded on
Johnston in July, was recovered four months later
460 miles to the southwest. Figure 8 is a spatial
summary of all at-sea streamer sightings and band
recoveries.
The above data suggest that during the breeding
season, Johnston-based Sooty Terns may forage up
to 300 miles from the breeding colony, but that the
greatest numbers remain within 50 miles. At the
end of the breeding season, adults and immatures
disperse widely at sea and many disappear from the
north-central Pacific. Four late fall and early winter
orange-streamer sightings show dispersal from John-
ston of birds to the northeast (three) and to the
southwest (one). The one late fall record from
Laysan was to the southeast.
Figure 9 summarizes interisland movements of
Sooty Terns involving the main and leeward
Hawaiian, Johnston, and Wake islands. Unfortu-
nately, few of these recoveries involve known status
birds (e.g., breeding, nonbreeding), or elapsed times
less than the length of one breeding season. It is
thus impossible to connect the islands of banding
and recovery with meaningful directional arrows.
TABLE 9.—Interisland Sooty Tern movements occurring within six months of
banding
Banding and recovery
locations
Hawaiian banded :
Hawaiians
Leeward banded:
Leewards
Johnston
Japan
Philippines
Johnston banded:
Leewards
Japan
Philippines
Wake banded:
Johnston
Carolines
Japan
Phoenix banded:
Phoenix
Leewards
Line banded:
Leewards
North Pacific banded:
North Pacific
Western Pacific . . .
South Pacific banded:
South Pacific
North Pacific
Recovery month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2
-
1
_
2
1
-
3
!•
9
1
-
16
_
-
-
2
1 + 1
1 - 3
1
5 9 28 -
- 1 1 4
- 3 - 2
1
1 1
•Banded as locals or immatures.
22
Table 9 summarizes all recoveries made less than
6 months after time of banding. It is apparent,
however, that there is considerable interisland
movement between islands of the north-central
Pacific. Birds banded on Johnston regularly occur
on Wake and in the main and leeward Hawaiians
and vice versa. Similarly, much movement occurs
between islands of the south-central Pacific. A cer-
tain amount of interchange between these two
areas has been recorded, but our eighteen records
probably exaggerate its amount. The lack of
orange-streamer sightings in the southern islands,
and blue-streamer sightings in the northern islands,
particularly on frequently surveyed islands such as
Howland and Johnston, indicate that some of the
north-south band recoveries may be due to misread
band numbers. Unfortunately, none of the north-
south band recoveries have been substantiated by
the collection of the bird or the removal of its
band. The relatively large number of these north-
south records, however, indicate that such move-
ments may occur.
Twenty-eight poBSP-banded birds have been re-
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
covered in the western Pacific. Ten were reported
as being associated with typhoons, and three with
stormy weather. Another three were reported ex-
hausted when found. By comparing the dates and
localities of recapture with typhoon and tropical
storm tracks in the western Pacific (Joint Typhoon
Warning Center, 1965, 1966, 1967; DeAngelis, 1968,
1969), a total of 20 can be directly associated with
typhoons and tropical storms (Table 10). This
indicates that at least a majority of banded birds
recovered in Japan and the Philippines was driven
there by storms. By analyzing the origin and path-
way of these storms, it is possible to make assump-
tions as to the area these Sooty Terns were carried
from and thus determine at least part of their non-
breeding range.
Typhoons in the northwest Pacific appear to
originate in the area between 5°N and 20°N, and
between 170°E and the Philippines. The United
States Naval Oceanographic Office (1964:42) de-
scribes the typhoon tracks in this area as follows:
. . . the greater number of typhoons conform to the usual
tropical cyclone track pattern and move initially westward or
100 E
20
10
FIGURE 10.—Tracks of typhoons which blew banded Sooty Terns to the western Pacific.
NUMBER 158 23
TABLE 10.—Sooty Tern recoveries from the western Pacific
Recovery location
Leyte, Philippines
(ca. 11°N, 126°E)
Southern Honshu, Japan
(34°4O'N, 135°56'E)
Honshu, Japan
(37°4O'N, 139°J0'E)
Southern Leyte, Philippines
(ca. 10°N, 125°E)
Masbate, Philippines
(ca. 12°N, 122°E)
Isabela, Philippines
(prob. 1O°35'N, 124°E)
Near Ticao, Philippines
(12°3O'N, 123°5O'E)
Tarlac, Luzon, Philippines
(ca. 15°S0'N, 125°E)
Southern Honshu, Japan
(34°5O'N, 138°20'E)
Honshu, Japan
(35°I9'N, 139°22'E)
Honshu, Japan
(35°00'N, 1S8°2O'E)
Southern Luzon, Philippines
(ca. 15°N, 121°E)
Eastern Samar, Philippines
(12°N, 125°20'E)
Mawmawan, Philippines
(ca. 10°N, 124°E)
Philippines
(no location specilicd)
Southern Leyte, Philippines
(ca. 10°N, 126°E)
Toledo City, Philippines
(ca. 10°20'N, 124°E)
Negros Island, Philippines
(09°10'N, 123°10'E)
Southeast Luzon, Philippines
(13°3O'N, 123°10'E)
Northern Luzon, Philippines
(ca. 15°40'N, 121 °E)
Southeast Luzon, Philippines
(ca. 13°2O'N, 123°2O'E)
Southern Luzon, Philippines
(ca. 14°15'N, 121°15'E)
Eastern Samar, Philippines
(ll°40'N, 125°20'E)
Honshu, Japan
(35°20'N, 139°35'E)
Shikoku, Japan
(ca. 33°3O'N, 133°3O'E)
Shikoku, Japan
(ca. 33°3O'N, 133°3O'E)
Shikoku, Japan
(ca. 33°3O'N, 133°3O'E)
Negros, Philippines
(ca. 10°N, 123°E)
Date Remarks
Banding
location Date Age
7 Mar 65 tropical storm Vera off Leyte on 7 Mar 65; bird
exhausted by "typhoon" winds
7 Aug 65 typhoon Jean moved north over Kyushu 5 Aug
65; birds "typhoon-driven"
18 Sjp 65 typhoon Trix over eastern Honshu on 17 Sep 65
before typhoon Faye passed about 250 mi NE of islands
17 Dec 65 on 23 Nov 65
before as above; bird exhausted
22 Dec 63
before no typhoons or tropical storms since Faye passed
10 Mar 66 250 mi NE on 23 Nov 65
20 Mar 66 as above
20 May 66 typhoon Irma over SW Luzon on 18 May 66; bird
in wake of typhoon Irma
25 Sep 66 typhoon Ida passed over Honshu on 24 Sep 66;
birds "typhoon-driven"
25 Sep 66 as above; no recapture data
25 Sep 66 as above; bird "typhoon-driven"
4 Jan 67 no typhoons or tropical storms since Pamela on
27 Dec 66; raining
11 Jan 67 as above; bird exhausted
4 Feb 67 as above; bird in heavy rain in front of "ty-
phoon"
? Feb 67 as above; bird "storm-driven"
3 Mar 67 typhoon Sally passed over central islands on 3
Mar 67
4 Mar 67 as above; bird at height of typhoon Sally
4 Mar 67 as above; male bird
6 Mar 67 as above; bird weak
17 Oct 67 typhoon Carla passed over northern Luzon on
17 Oct 67; after typhoon Trining
3 Xov 67 typhoon Emma passed over southern Luzon on
3 Nov 67; stormy
4 Nov 67 as above; "typhoon-driven"
4 Nov 67 as above; bird after typhoon Welling
26 Apr 68 cannot be accounted for by typhoons or tropical
storms
3 Jul 68 last stages of typhoon Lucy passed about 250 miles
S of Shikoku on 2 Jul 68
28 Jul 68 typhoon Mary passed over Shikoku on 28 Jul 68
29 Jul 68 as above
25 Nov 68 typhoon Nina passed over Negros on 24 Nov 68
Johnston 8 May 64 local
Wake 1 May 65 nestling
Johnston II May 65 local
Laysan 9 Aug 65 adult
Johnston 26 May 65 local
Johnston 28 May 65 local
Johnston 7 Jun 65 local
Midway 27 Jul 65 nestling
Johnston 22 Mar 66 adult
Midway 12 Jun 66 breeding
adult
Lisianski 17 Jun 66 adult
Johnston 13 Mar 66 adult
McKean 19 Jul 64 adult
Johnston 15 Jun 66 adult
Wake 15 Jun 66 nestling
Howland 19 Jul 66 adult
Christmas 12 Mar 66 nestling
McKean 21 Sep 65 local
Howland 16 Aug 66 local
Midway 27 Jul 65 nestling
Johnston 14 Jun 67 local
Midway 22 Jul 64 local
Midway 8 Sep 64 immature
Laysan 6 Aug 65 adult
Johnston 8 Mar 64 adult
Johnston 20 May 68 local
Johnston 2 May 66 adult
Midway 13 Jun 66 adult
24 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
west-northwestward from the source region. Those that reach
higher latitudes, normally north of 15°N, have a tendency to
recurve and move in a northeasterly direction over or to the
east of Japan. A considerable number, however, travel almost
due westward and eventually dissipate over the Philippines
or the China coast. At the height of the typhoon season over
the western Pacific (July through October) the majority of
these storms passes to the north of the Philippines moving
toward Taiwan, the Japanese Islands, and the China coast.
. . . During the so-called slack season (December through
February) many continue on a westward course and enter
the South China Sea.
Figure 10 shows the typhoon and tropical storm
tracks that can be associated with POBSP band re-
coveries in the western Pacific. All originate in, or
immediately southeast of, the Philippine Sea, and
all pass through it. Thus, the Philippine Sea must
constitute at least part of the nonbreeding range
of north-central Pacific Sooty Terns. The only
typhoon that can be associated with birds from the
Line and Phoenix islands was Sally in 1967. This
was the most southern of all Sooty Tern-bearing
typhoons, and had the southwesternmost point of
origin. No northern birds were reported as a result
of this storm. Lane (1967), however, reports the
recovery of a Sooty Tern originally banded on
Roach Islet, Lord Howe, New South Wales, 28
November 1962, from southern Leyte, Philippines,
on 4 March 1967. This is the same recovery date and
area as two of our recoveries associated with
typhoon Sally. This suggests that the nonbreeding
ranges of south-central and north-central Pacific
terns are essentially allopatric. Unfortunately,
literature records from this area are scarce. Brink-
ley (in Bourne and Radford, 1961) recorded seven
birds in August at 22°N, 124°E. In late October,
Morzer Bruyns (1965) recorded two groups of 50
birds each at approximately 9°N, 131°E, three
groups of 40, 10, and 3, near 7°N, 142°E, and
possibly two birds at 7°N, 150°E. He did not, how-
ever, find any terns in late October or early No-
vember near the Palau, western Caroline, or
Marshall islands. Records for the timing of the
breeding cycle in the Carolines are lacking so that
we do not know whether the birds he observed
were of that population.
EQUATORIAL CENTRAL PACIFIC.—Sverdrup, et al.
(1942:709) point out that the Equatorial Counter-
current is remarkably well developed in the Pacific
Ocean, present at all seasons, lies always in the
northern hemisphere, and is farther north in the
northern summer. Barkley (1962:5) shows that the
borders of this current generally lie between 4°-
5°N and 9°-10°N. North of the Countercurrent is
the westward flowing North Equatorial Current,
while south is the westward flowing South Equa-
torial Current. Data from the Carnegie Expedition
(Sverdrup, et al., 1942:711) state that
within the Equatorial Countercurrent descending motion
takes place at the southern boundary and ascending motion
at the northern boundary, and between the Equator and the
Countercurrent descending motion takes place at the bound-
ary of the Countercurrent and ascending motion at the Equa-
tor. Thus, two cells appear with divergence at the northern
limit of the Counlercurrent and at the Equator, and with a
convergence at the southern boundary of the Countercurrent.
Ashmole and Ashmole (1967) have discussed the
distribution of seabirds with relation to the equa-
torial currents in the central Pacific. They make
several points which are relevant to the following
discussion: (1) Most tropical seabirds depend, at
least in part, on schools of fish to drive their prey
close to the surface. (2) Upwelling waters are gen-
erally rich in nutrients and zooplankton. (3) As
water moves away from divergence areas, phosphate
and zooplankton decrease and forage animals in-
crease. (4) In the equatorial current area fish schools
are generally most abundant within the Counter-
current. They (1967:107) conclude that "localized
concentrations of plankton and nekton produced
by convergence and sinking of surface waters at
'fronts' which have been suggested as exerting im-
portant effects on the distribution of surface schools
of tunas in the open ocean, may also provide favor-
able feeding grounds for many oceanic birds."
Other authors, among them King and Pyle (1957)
and Morzer Bruyns (1965) have shown some of the
effects of oceanic currents in the central Pacific on
the density and distribution of seabirds.
From January 1964 through 1967 twenty cruises
were made by the POBSP across the equatorial cur-
rents (0°-13°N) between 148°W and 180°. Surface
water temperatures ranged between 25.5° and
30.6°C with the majority falling between 27.0°
and 29.5°C. Barkley (1962) presented averaged
temperatures for this area of 27° to 28°C, and
averaged salinities of 34.30 to 35.40 ppt.
FIGURE 11.—Sooty Tern density in relation to equatorial cur-
rents in the central Pacific between longitudes 148°W and
180°.
IT:
70
J 110
a 130
J -
Q 210
230
250
H
Q
D
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0
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160' IS
WEST LONGITUDE
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WEST LONSITUDE
I I
i^«J-
DECEMBER
JANUARY
FEBRUARY
12* 11" 10" 9" 8" 7" 6" 5" 4" 3* 2" 1" 0"
NORTH LATITUDE
12 11 10 9 8 7 6 S 4 3 2 1 0
T
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170" 160'
WEST LONSITUDE
I f JUNE
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• AUGUST
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11 10" 9" 8" 7* 6" 5* 4' 3" 2' I* 0'
NORTH LATITUDE
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WEST LONGITUDE
1 4
 [J] SEPTEMBER
[|]| OCTOBER
• NOVEMBER
I
12 11 10 9" 8" T 6" 5" 4" 3" 2" 1" 0"
NORTH LATITUDE
NUMBER 158 27
Figure 11 shows latitudinal variation of Sooty
Tern densities plotted against the depth of the
20°C isotherm for five 1966 cruises. The slope of
this isotherm can be used as a rough indication of
the position of major currents. Figure 12 presents
density data for all 20 cruises on a seasonal and
monthly basis, while Figure 13 shows a composite
of all 1965-1966 densities and an average density
per each degree of latitude.
Ignoring areas under the immediate influence of
islands (i.e., areas within 50 miles of Howland,
Christmas, and Palmyra) Sooty Terns are more
abundant within the Equatorial Countercurrent
than in either the North or South Equatorial cur-
rents. The South Equatorial Current has greater
Sooty Tern densities than the North Equatorial
Current, possibly because of the more direct in-
fluence of islands and/or the convergence at its
northern border. It is within the convergence area
that greatest over-all densities have been recorded
(Figure 13). Our data thus support the assump-
tions reached by the Ashmoles. Our data also sug-
gest, but are too few to prove, a seasonal shift in
high densities from the convergence area (4°N-
5°N) in the fall, to the northern Countercurrent
area (7°N-9°N) in the spring. Intervening seasons
are intermediate, with greatest winter densities re-
corded in the area of 5°N to 6°N, and greatest sum-
mer densities in the area of 6°N to 7°N. The more
northerly position of high density in spring and
summer might be explained if many of the terns
in the Countercurrent area were part of the north-
ern islands' (e.g., Johnston Atoll) breeding popu-
lation. Unfortunately, there have been no band
returns or color-streamer sightings from this area.
It seems quite probable that Sooty Terns in the
equatorial currents are from islands in both the
north and south central Pacific and that the in-
fluence of each area varies with the season and
with the local breeding schedule.
Within the equatorial currents lie a number of
islands, most of which support large Sooty Tern
colonies. These include the Line Islands: Kingman
Reef (06°24'N), Palmyra (05°52'N), Washington
(04°43'N), Fanning (03°52'N), Christmas (01°51'N)
and Jarvis (00°23'S), and two islands often consid-
FIGI'RE 12.—Sooty Tern density across the equatorial central
Pacific.
ered part of the Phoenix group: Howland (00°
45'N), and Baker (00°13'N). The latter two islands
have been intensively investigated by the POBSP
with respect both to island and at-sea bird popula-
tions.
The POBSP observations show a very close rela-
tionship between the breeding schedule and den-
sities on Howland Island, and at-sea densities
within a 100-mile radius of it (Figure 14). Peak
at-sea densities occurred during each of the two
major egg-laying periods in 1966-1967. The large
numbers of birds at sea during September and
October 1965 while island populations were at their
lowest are thought to be due to birds from other
populations moving into or through the area. The
only evidence for this was the collection within
the area in October of three immature and one
adult Sooty Terns originally banded on Hull Is-
land three to eight weeks earlier. At-sea collections
and sightings of banded or color-tagged birds dur-
ing all other surveys were of Howland-marked
birds.
SOUTH-CENTRAL PACIFIC.—Pelagic observations
were conducted on 13 POBSP surveys to the south-
central Pacific from March 1964 through February
1967. During most of these trips many days were
spent in the Phoenix Islands. Twelve trips con-
tinued south to eastern Samoa and one to the Fiji
Islands. Two general cruise tracks were used, one
by way of the Tokelaus and Swain's Island, and
the other by way of Rakahanga and the Danger
Islands. Table 11 summarizes the distribution and
abundance of Sooty Terns during these trips. The
area of coverage was too restricted, and the timing
of observations too unevenly spaced to allow more
than the following brief summary.
Sooty Terns were abundant at all times of the
year on and around the Phoenix Islands. Highest
densities were recorded from September through
February, particularly October to December. An-
nual at-sea abundance cycles in this area, however,
cannot be evaluated because of the variation in
the timing of breeding cycles between the islands,
and because of the nearness of these islands to one
another and our inability to assign island origins
to birds observed at sea. These factors prevented
relating a daily at-sea density to a particular island.
Also May-September records are few while October-
April records are numerous. South of the Phoenix
Islands these terns became progressively less abun-
28 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
8* 7* 6* 5* 4*
NORTH LATITUDE
Daily Observations
Avsrage Density
12* 11* 10* 9* 8*
NORTH LATITUDE
FIGURE 13.—Summary of Sooty Tern densities across the equatorial central Pacific during 1965-
1966.
NUMBER 158 29
HOWLAND ISLAND
0
5 UJ
UJ -1
I U O(C >
mo
i^5 If S
3 I
i n n
•M'-L L
iOCCS ta.*W— ill —
525 - 5 5 s * III
I 8'
K j Diurnal density
^ Nocturnal density
Average Miles of Observations per Month
Diurnal = 690
Nocturnal 479
FIGURE 14.—Correlation of at-sea densities (within 100 miles o£ Howland) of Sooty Terns with
the breeding schedule and population fluctuations of Howland Island.
dant, being seen on fewer days as well as in smaller
numbers.
Movements of banded and streamered birds from
this area are summarized in Table 10, Appendix
Tables B, C, Figures 8, 10, and 15. These records
are discussed under the section dealing with north-
central Pacific banding results, and under the dis-
cussion of Howland Island in the equatorial central
Pacific.
EASTERN PACIFIC.—Surveys in the eastern Pacific
north of 30° N have been conducted from Decem-
ber 1966 through April 1968 off southern Califor-
nia and northern Baja California, generally on a
semimonthly basis. South of 30°N surveys have
been made in cooperation with EASTROPAC. POBSP
personnel recorded observations during nine
cruises. Three of these ran concurrently in January-
March 1967, one in June-July 1967, two concur-
rently in August-September 1967, one in October-
December 1967, and two concurrently in February-
April 1968. The survey pattern was based on
north-south cruise tracks along specific longitudes.
Two of these tracks (119°W, 112°W) were followed
five times each; two (105°W, 98°W) were followed
30 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
•c
NUMBER 158 31
TABLE 11.—Distribution and occurrence of Sooty Terns within 100 miles of south-
central Pacific islands from March 1964 through February 1967
Area
Days
observed
(No.)
Days
recorded
(No.)
Days
recorded
Average
density
(BPM)
Range of
density
(BPM)
Months of observations
Phoenix Islands
Tokelau I
Rakahanga I.
Danger I
Swains I. . . . . .
Wallis I
£. Samoa
Horn I
Fiji I
Total/average .
51 51 100 3.9 0.02-34.6 all except Jun and Aug
20 17 85 0.7 0.0-3.4 all except Jan and May
2 1 - 0 . 3 0.0-0.6 Jun
3 3 - 0.3 0.03-0.7 Mar and Jun
17 13 76 0.1 0.0-1.0 all except Jan, May, and Dec
2 2 - 0 . 6 0.04-1.2 Feb
15 4 27 0.1 0.0-1.1 all except Jan, May, Sep. and Dec
2 2 - 0 . 1 0.02-0.2 Feb
3 3 - 0 . 1 0.01-0.3 Feb
11? % 8? T? 0.0-34.6 all months
four times each; one (92°W) was followed twice;
and three (126° W, 96°W, 88°W) were followed
once.
Sooty Terns have never been recorded north of
26°N in the eastern Pacific, and POBSP personnel
have not found them north of 22°N. Our data
from the eastern Pacific are not complete enough
to show much in the way of annual trends. Ob-
servations, for example, do not exist for May and
December, and are minimal for January and April.
Figures 17 through 28 summarize all POBSP records
for the eastern Pacific (pp. 34-45).
Sooty Terns were generally common (1-5 BPM)
in the Equatorial Countercurrent, particularly
west of 110°W to 126°W, and along the Mexican
coast from Acapulco north to the Gulf of Califor-
nia. Densities greater than 5 BPM were recorded on
TABLE 12.—Date and location of Sooty Tern
densities (BPM) greater than 5.0 in the eastern
Pacific
Date
2 Feb 67
22 Feb 67
5 Jun 67
7 Jul 67
5 Sep67
9
22
17
18
7
Noon position
°38'N,119
°18'N,109
°56'N,102
°38'N,104
°42'N,112
°00'W
°17'\V
°55'W
°48'W
°06'W
Area
Equatorial Counter-
current
mouth of Gulf of
California
coast of Mexico
coast of Mexico
Equatorial Counter-
current
Density
8.8
7.8
18.5
6.1
9.0
only five days (Table 12). These were also either
along the Mexican coast or in the Equatorial
Countercurrent. We have never recorded Sooty
Terns north of 15°46'N except at the mouth of the
Gulf of California where birds have been seen
north of 21°49'N. Anthony (1898), Kaeding (1905),
Gifford (1913), and McLellen (1926) recorded Sooty
Terns as breeding on die Revilla Gigedo Islands
(19°N, 111°W) in the northern spring. However,
during four days of POBSP observations within 150
miles of these islands (11 February, 20-21 March, 15
September) no Sooty Terns were seen. Brattstrom
and Howell (1956) did not record this species there
in March or November.
Only in February and March were observations
made south of 20°S. During these two months Sooty
Terns were common (1-5 BPM^ in southern waters
from 5°S to 14°S in the more western area (119°W-
126°W), with scattered birds recorded to 19°48'S
at 121°3rW. In August, Sooty Terns were likewise
common from 5°S to 10°S, the southern limit of
our observations.
Equatorial currents were probably as influential
on Sooty Tern distribution and abundance in the
eastern Pacific as they are in the central Pacific.
There are, however, several important differences
between the two areas. These appear to be signifi-
cant in their effect on Sooty Terns. Wyrtki (1966,
n.d.) characterizes the Equatorial Countercurrents
east of 120°W as clearly developed from May to De-
cember and absent from February through April.
From May to December, west of 110°W, its bound-
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
11" 10* 9" 7"
NORTH LATITUDE
112*through 119*
NORTH LATITUDE
88* through 106*
FIGURE 16.—Sooty Tern density across the Equatorial Countcrcurrent in the eastern Pacific.
aries vary between 4°N to 6°N and 8°N to 12°N,
while east of 110°W there is a southward shift so
that at the end point the boundaries lie south of
4°N and 10°N. From February to April surface wa-
ter flow is to the west and northwest between the
South Equatorial and North Equatorial currents.
Figure 16 summarizes data from our nine cruises
across the Equatorial Countercurrent. The distri-
bution and abundance of Sooty Terns appeared to
change in response to changes in the Countercur-
rent as described by Wyrtki. In both seasons Sooty
Terns were found across the entire current area.
Density centers, however, differed markedly. During
the season when the Countercurrent was not pres-
ent, high densities were found only west of 110°W
(the two highest densities were at 119°W) and only
north of 9°N. (If the Countercurrent were devel-
oped, this position would be at its northern bound-
ary which is contrary to what would be expected
from the Ashmoles' discussion and from the ob-
served distribution of central Pacific terns.) Eastern
Pacific distribution, however, may be the result of
the west and northwest flow developed through
this area at this time of year. During the season
when the Countercurrent was clearly developed,
high densities were mainly at the convergence
along the southern border of the Countercurrent
(ca. 5°N). It is also pertinent to note that during
both seasons highest densities were recorded west
of 112° W where the currents are generally stronger
and well developed.
Sooty Terns appear to be present throughout the
year in the eastern Pacific. Our fragmentary data
suggest that during the spring (February-April)
greatest numbers occur west of 110°W, while dur-
ing the fall (August-November) high densities also
occur over much of the area east of 110°W. This
would be in accord with fall nesting on the Gala-
pagos Islands and Clipperton Atoll, and with a
westward dispersal at the conclusion of the breed-
ing season. Such an hypothesis for breeding stations
is consistent with central Pacific Sooty Tern dis-
tribution patterns. We would expect to see color-
streamered birds if central Pacific birds were mov-
ing into the area. Unfortunately, only a few birds
have been collected so that the chance of recover-
NUMBER 158 33
ing banded birds has been exceedingly small. It is,
however, possible that birds from French Poly-
nesia enter the area. This is suggested by the large
numbers of birds found from 5°S to 15°S, and
from 119°W to 126°W in February and March. All
traveling flocks observed at this time were heading
east.
Summary and Conclusions
Sooty Terns are abundant and widely dispersed
throughout the tropical and subtropical Pacific
Ocean. The perimeter of peripheral breeding local-
ities marks the normal limits of their pelagic dis-
persal. Within this area they may be found over
almost any part of the ocean at any time of the
year. The occurrence of Sooty Terns beyond the
normal limits of their range is generally the result
of major climatic disturbances, such as typhoons
and cyclones in the western Pacific, and possibly
of fluctuations in oceanic currents and water
masses. The regularity of stragglers in such areas
as Japan is due to the regularity of these disturb-
ances.
Sooty Tern densities fluctuate widely in both
space and time. Factors affecting these densities
are complicated, often interacting, and sometimes
obscured by the presence of two or more popula-
tions which are indistinguishable in the field. The
following factors are educed in this investigation,
but this list is not exhaustive:
Food Availability: Over a greater part of the
ocean, Sooty Terns are generally few and scattered,
with occasional high densities shifting from area
to area in response to an erratic food supply. In
such areas, tern densities vary directly with the
length of time food is available. In areas where
food is regularly available (e.g., the Equatorial
Countercurrent), tern densities are uniformly
higher.
Breeding Island Proximity: During the breeding
season Sooty Terns are island-oriented; highest
densities generally occur within 25 miles of breed-
ing islands. Individual breeding birds, however,
may forage up to 300 miles at sea away from breed-
ing colonies.
Breeding Schedule: At-sea densities vary directly
with the breeding cycles on nearby islands; highest
at-sea numbers occur at the peaks of the nesting
seasons. In the north-central Pacific (Hawaiian-
Leewards and Johnston), the at-sea density and
island nesting cycles are annual and regular. In
the south-central Pacific (Line and Phoenix is-
lands), breeding is semiannual or irregular, and
at-sea densities may be high at any time depending
upon the status of nearby breeding colonies.
Post-breeding Dispersal: During the nonbreeding
season birds may be rare or absent in some parts
of the Pacific. After the young fledge, Sooty Terns
become ocean-oriented, and densities near islands
decrease; birds appear to remain in the general
area of the breeding islands for up to a month be-
fore moving to nonbreeding areas. Central Pacific
Sooty Terns of all age groups disperse westward;
many north-central birds reach the Philippine Sea,
which constitutes at least part of their nonbreeding
range. Nonbreeding ranges, as well as breeding
ranges, of north<entral and south-central Pacific
Sooty Terns appear to be allopatric.
34 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
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SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
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38 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
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40 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
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Appendix
TABLE A.—Summary of published data on Sooty Tern distribution
Location Date Remarks Source
EAST-CENTRAL PACIFIC
Roca Alijos
Coast of Mexico
ca. 20°N
Between Manzanilla
and the Marquesas I.
Roca Partida
Oneal Rock
Isabel I.
Clipperton I.
Panama
7°46'S, 120°W
7°09'N, 81°08'W
7°N, 131°W
7°N, 125°W
7°N, 116°W
7°N, 101°W
7°N, 93°W
Pedro Gonzales I.
7°N, 82°3O'W
3°N, 93°30'W
2°50'N, 120°W
SOUTHEAST PACIFIC
Central and
South America
10°15'S, 101°53'W
10°30'S, 103°20'W
Independencia Bay,
Peru
San Felix
Near Mas Atierra
Near San Felix I.
100 mi S of
San Felix I.
Between Valparaiso
and the Juan
Fernandez I.
33°S, 74°W
Rio Valdivia, Chile
NORTHWF-ST PACIFIC
Japan and Taiwan
24 Apr 25 probably breeding, specimens taken
mid-Oct 53 abundant
24 Oct-24 seen occasionally
Nov 55
22 May 25 probably breeding, specimens taken
1925 some
24 May 25 thousands, large numbers of almost fully
grown young
Aug 58 estimated 2000 breeding
breeds on Islas Frailes del Sur and ranges the adjacent
waters of the Gulf of Panama and the open sea
4 Nov 55 flock of 25-30
28 Aug 64 many
9 Nov 60 groups of 1 and 40
10 Nov 60 one group of 50
11 Nov 60 groups of 1, 20, 20, and 10
13 Nov 60 one possible Sooty Tern
14 Nov 60 groups of 10-50 continuously through the
afternoon
7 Sep 61 one seen by D. R. Paulson
21-22 Dec? 1, more
4 Jan 63 3
8 Nov 55 flock of 14 associated with a convergence
front in the upper layer of the ocean
Hanna, 1926:28
King and Pyle, 1957:37
McLellen, 1926:283
Stager, 1964:365
Wetmore, 1965:456
King and Pyle, 1957:37
Jones, 1965:67
Morzer Bruyns, 1965:63-64
Wetmore, 1965:457
Mitchell in Bourne, 1965:37
Morris in Bourne, 1965:36-37
King and Pyle. 1957:37
recorded breeding from the Tres Marias and Revilla Gige-
dos south to the northern Galapagos Islands, also at San
Felix Island, Chile
28 Nov 62 1
27 Nov 48 1, in surface water temperature 27.4°C
13 Jan 25 many noted by Murphy, sighting coinci-
dent with a general warming of the
water in this area
18 Feb 35 Chapin noted moderate-sized flocks
19 Dec 13 Beck noted birds flying toward the island
10 Oct 62 some birds flying away from the islands
in the morning and toward the islands
in the evening
9 Oct 62 flock of 20 flying toward San Felix in
afternoon
7 Dec 13 observed feeding with shearwaters by Beck
5 Dec 13 4 specimens taken by Beck
2 Aug 1855 1 specimen
occasional summer straggler to southern Japan; breeds on
the Bonin, Riu Kiu, Senkaku Retto, and Marcus islands;
recorded also from Borodino Island and Formosa [Tai-
Murphy, 1936:1121
Worgan in Bourne, 1964:37
Fleming, 1950:181
Murphy, 1936:1132
Millie, 1963:566
Murphy, 1936:1132
Hachisuka, et al., 1958:222
46
NUMBER 158 47
TABLE A.—Summary of published data on Sooty Tern distribution—Continued
Location
Honshu, Japan
Izu I.
Honshu, Japan
" "
Shikoku
Kyushu
WEST-CENTRAL PACIFIC
26°57'N, 126°07'E
26°36'N, 121°20'E
25°26'N, 124°18'E
24°55'N, 122°01'E
22°N, 124°E
19°N, 163°05'E
135 mi W of Wake I.
Micronesia
14°30'N,113°43'E
9°N, 131°E
7°N, 142°E
Philippines
l°01'N, 119°01'E
0°02'N, 129°47'E
0°09'S, 159°50'E
0°44'S, 136°46'E
1°18'S, 138°35'E
4°22'S, 128°50'E
8°25'S, 119°42'E
8°30'S, 134°30'E
9°S. 123°E
SOUTHWEST PACIFIC
SW Coral Sea
15°10' 151°39'E
to 15°20'S, 151°41'E
15°57'S, 151°50'E
tol5°38'S, 151°39'E
16°10'S, 157°14'E
16°47'S, 152°27'E
to 17°03'S, 152°48'E
New Caledonia
19°44'S, 156°33'E
to 19°50'S, 156°33'E
20°02'S, 153°31'E
to 19°41'S, 153°36'E
20°26'S, 153°09'E
to 19°32'S, 153°05'E
20°48'S, 164°13'E
21°55'S, 173°21'E
22°07'S, 154°20'E
to22°18'S, 154°13'E
22°39'S, 166°28'E
23°21'S, 153°24'E
to 23°36'S, 153°26'E
26°16'S, 161°24'E
27 °S, 176°30'E
29°06'S, 154°01'E
Date
25 Apr 04 j
undated
10 Jul 04
24 Aug 07
4 Sep 50
undated
undated 2
31 May 29 :
10 Jun 29
30 May 29
12 Jun 29 1
16 Aug 60
18 Mar 60
6 Mar 45 (or 46)
Remarks
ilus two undated records
j
> or 6
lock of about 50 (species?)
flock of about 30
ew
1
arge flocks
I
found in the Mariana, Palau, and Caroline islands
19 May 29
27 Oct 60
29 Oct 60
flock of about 100
wo groups of 50
three groups of 40, 10, and 3
recorded from Siquijor and Sulu Islands
14 Aug 29
30 Jul 29
21 Jul 29
25 Jul 29
24 Mar 29
6 Apr 29
27 Sep 63
26 Sep 63
Hock of about 150-200 (species?)
dock of about 58 (species?)
several
many in flocks
.everal (species?)
airly common
many
scattered flocks
vast numbers breeding in this area
11 Sep 62
8 Sep 62
20 Aug 61
8 Sep 62
12 Dec 57
22 Aug 61
17 Aug 61
7 Sep 62
26 Nov 28
8 Jul 62
23 Aug 61
29 Nov 28
14 Sep 62
19 Dec 57
14 Feb 63
1 May 60
3
5
ca. 50
8
:> resent
6
3
ca. 200
arger flock far out (species?)
20
ca. 30
fairly numerous
10
one flock
2
7
Source
Austin and Kuroda, 1953:450-451
•• •• •• "
" " " " "
" " " •• "
" " " " "
Jespersen, 1933:206
..
Brinkley in Bourne and Radford, 1961:25
Mitchell in Bourne and Radford, 1961:25
Dixon and Starrett, 1952:271
Baker, 1951:161
Jespersen, 1933:206
Morzer Bruyns, 1965:63-64
" " " "
Delacour and Mayr, 1946:77
Jespersen, 1933:206
" " "
••
" " "
" " "
Mitchell in Boume, 1965:37
Hindwood, et al., 1963:28-30
Norris, 1967:46
" " "
" " "
Gibson, 1960:18
Norris, 1967:46
" " "
»t it »»
Jespersen, 1933:206
Norris, 1967:46
" " "
Jespersen, 1933:206
Norris, 1967:46
Gibson, 1960:18
Morris in Bourne, 1965:37
King in Bourne, 1964:37
48 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE A.—Summary of published data on Sooty Tern distribution—Continued
Location
29°54'S, 178°30'E
29°56'S, 156°37'E
SO°55'S. 155°17'E
OS Sydney
Lord Howe I.
New South Wales
New Zealand
Near Sydney
Sydney Harbor
Queenscliff
Near Sydney Head
Dorrigo
North I.
S4°S2'S, 172°31'E
CENTRAL PACFIC
Central Pacific
23°S0'N, 162°W
Honolulu
Oahu
Pearl Harbor
2O°23'N, 158°52'W
20°31'N, WWW
Marshalls
7°N, 159°W
7°N, 145°W
7°N, 1S8°W
7°N, 179°E
Gilberts
02°15'N, 169°17'W
Hull I.
8°40'S, 136°54rW
8°30'S, 156°30'W
Marquesas I.
to Palmyra I.
Marquesas I.
SOUTH-CENTRAL PACIFIC
10°08'S. 142°01'W
10o41'S, 172°22'W
11°44'S, 144°10'W
14°39'S, 174°27'W
18°07'S, 179°47rW
18°40'S, 176°21'W
20°57'S, 158°58'W
27°06'S, ffl"41'Vf
29°45'S. 176°57'W
31°35'S, 176°25rW
Date
23 Nov 64
25 Feb 29
20 Dec 57
17 Feb 29
Remarks
singles and small flocks in water tempera-
ture 70° F
few
present
1 specimen
regular breeding cycle beginning in September each year
undated
breeding on
lands
May 1892
undated
3 Feb 34
11 Dec 42
25 Jun 50
Feb-Apr
late Jul-Aug
30 Jul 61
reported as
rare straggler
Lord Howe, Norfolk, and the Kermadec is-
1 specimen
several specimens
1 immature specimen
1 bird observed
2 cyclone-driven birds, 1 collected
7 records following northerly gales
6
1 bird landed on ship
breeding or as having bred on every island
group except the New Hebrides and the Solomons
12 Apr 64
24 May 59
undated
27 May 60
26 May 60
13 Jan 60
Oct-Nov 64
Jun 66
Apr 67
5 Nov 60
7 Nov 60
8 Nov 60
3 Nov 60
Nov 64
27 May 59
28 May 59
1 Oct 28
6 May 64
early Dec 55
2 Oct 28
late Nov 55
5 Oct 28
2 Nov 28
6 Oct 28
8 Nov 28
13 Nov 62
8 Dec 57
21 Oct 28
13 Dec 28
14 Dec 28
15 Dec 28
present
50
many groups all around the coast
hundreds
5
30
occurred near and between breeding atolls
" " " " •• "
..
groups of 2 to 200, one group with im-
matures present
groups of 1 and 10
groups of I, 10, and 3
three groups of 100
20 seen between Makin and Maiana
1
ca. 1000 seen fishing in small groups
few
large flock over a school of tuna
observed daily at sea
fairly common
abundant in and around these islands
few
flock of about 10 (species?)
still a few (one possible flock of 50)
small flock
120
1
few (species?)
2 and 2
1 specimen
few
Source
Edgar, et al., 1965:42
Jespersen, 1933:206
Gibson, 1960:18-19
Jespersen, 1933:206
Hindwood, et al., 1963:30
Goddard and Hindwood, 1951:170
Falla, etal., 1967:165
Goddard and Hindwood, 1951:170
" " " " "
" »• ,» •, »,
" " " " "
Falla, etal., 1967:165
» .. » ..
Jenkins, 1962:33-34
King, 1967:76
Lamb in Bourne, 1966:33
Peakall. 1960:202
..
King in Bourne, 1964:37
.. ,.
Amerson, 1969:302
..
Morzer Bruyns, 1965:63-64
"
••
"
Amerson, 1969:302
Peakall, 1960:202
" "
Jespersen, 1933:206
Mitchell in Bourne, 1966:33
King and Pyle, 1957:37
Jespersen, 1933:206
King and Pyle, 1957:37
Jespersen, 1933:206
Worgan in Bourne, 1964:37
Gibson, 1960:18
Jespersen, 1933:206
..
.. .,
NUMBER 158
TABLE B.—At-sea sightings of streamered Sooty Terns
Date
JOHNSTON
1963
5 Aug
1964
5 Mar
••
11 Mar
14 Mai
••
• •
"
9 Apr
13 Apr
14 Apr
7 May
••
••
• •
••
8 May
10 May
15 May
"
••
••
7 Jun
8 Jun
••
••
»
• •
••
••
"
••
11 Jun
16 Jun
11 Jul
"
5 Aug
6 Aug
••
"
8 Aug
10 Aug
11 Aug
12 Aug
lime
STREAMERED
0704
1040
1110
1148
1400
1607
0659
0713
0719
0736
0837
0930
1431
1751
1520
1810
1630
1335
1002
1026
1146
1530
1600
1218
1428
1205
1315
1423
1603
1636
1713
0622
0720
0735
1151
1154
1157
1300
1304
1547
0714
0824
1345
1420
-•
0700
0702
0928
0933
1640
1650
1050
1250
So.
I
1
1
1
1
1
1
1
1
3
•)
1
1
1
1
:">
1
4
5
1
1
1
1
1
4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Behavior
flying E
flying E
feeding
not noted
flying N
not noted
flying SE
flying NNE
flying N
flying SSE
not noted
flying NE
flying NE
feeding
Hying NE
feeding
• •
flying NE
not noted
flying SE
flying E
flying SE
feeding
not noted
feeding
flying SE
flying NNE
flying SE
flying S
flying ENE
flying NNW
flying ENE
flying WSW
flying ENE
not noted
flying NE
flying SE
flying ENE
flying SE
flying NE
feeding
"
flying NNW
flying N
not noted
flying SE
flying E
not noted
flying NW
not noted
N lat.
15°45'
16°43'
16°41'
"
16°22'
16°40'
16°57'
••
••
••
"
14°07'
16°03'
15°26'
16°20'
17°05'
17°31'
16°54'
16°52'
16°47'
16°20'
16°16'
13°54'
15°36'
16°55'
16°59'
17°04'
17°09'
17°11'
18°05'
17°06'
16°59'
••
16°42'
••
16°36'
"
16°07'
15°32'
20° 02'
15°58'
16°05'
18°30'
16°54'
16°42'
16°41'
14°01'
14°26'
16°24'
14°42'
W long.
169°19'
169°21'
169°23'
169° 22'
169°21'
169°31'
169°39'
169° 36'
• •
"
171°49'
171°51'
173°24'
171°37'
171 °20'
169°16'
168° 08'
169° 00'
169° 05'
169° 46'
169°23'
169° 22'
169° 24'
170°02'
169°21'
169°11'
168° 58'
168° 47'
168° 44'
166°28'
I68°27'
168° 38'
168°41'
169°19'
169° 20'
"
169° 27'
169° 20'
169°57'
169°27'
170° 52'
170° 46'
M
165°03'
169°00'
169°23'
169°21'
170° 46'
172°31'
170°51'
173° 57'
Miles from
origin
55 SSE
9 ESE
8 SE
9 SE
25 SSE
5 S
14 NNW
13 NNW
"
"
211 SW
144 SW
187 SW
125 WSW
109 WSW
24 NE
90 NE
30 NE
24 NE
16 W
26 SSE
30 SSE
174 S
76 SSW
13 NE
23 NE
36 NE
48 NE
51 NE
177 ENE
63 NE
52 NE
50 NE
11 SE
10 SSE
39 SSE
79 SSW
200 N
91 SW
84 SW
••
278 NE
30 NE
7 SE
7 SE
180 SSW
226 SW
80 SW
287 SW
Age
adult
"
"
"
"
"
adult
'*
**
immature
adult
adult
immature
50 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE B.—At-sea sightings of streamered Sooty Terns—Continued
Date
1965
IS Apr
19 Apr
••
20 Apr
••
15 May
21 May
17 Jun
••
••
21 Jun
5 Jul
11 Jul
15 Aug
••
••
••
22 Aug
>•
"
••
••
••
••
"
"
"
8 Sep
••
10 Sep
1966
31 Jan
6 Mar
8 Mar
1 Apr
2 Apr
••
4 Apr
5 Jun
'•
••
"
Time
1507
1215
1630
0955
1345
1130
1415
0430
1045
»
1710
0956
1710
0740
"
1018
1143
1414
1418
1419 '
1451
1507
1508
"
1530
1630
1700
1905
0850
1700
1515
1745
0853
0852
0642
1754
0805
1215
1710
1024
1030
1430
0731
0733
0744
0756
0809
0821
0830
0837
0923
1027
1659
1849
1851
No.
2
1
4
10
9
2
3
5
1
17
2
5
12
3
3
11
1
18
3
4
2
Behavior
not noted
feeding
••
••
••
not noted
feeding
not noted
feeding
flying S
flying NE
feeding
flying SE
flying SE
flying NW
feeding
not noted
feeding
not noted
feeding
not noted
feeding
"
••
not noted
feeding
••
••
••
not noted
flying NE
flying N
flying NE
flying W
feeding
"
••
not noted
flying NW
feeding
flying S
••
not noted
feeding
•>
"
not noted
feeding
••
flying NE
flying E
N. lat.
16° 18'
15°37'
16°06'
17°28'
16° 17'
13°32'
18°50'
15°07'
15°22'
••
17°44'
17°07'
15°40'
16°54'
"
16° 32'
16°20'
16°43'
16°44'
••
16°46'
16°48'
"
16°50'
16°54'
16°56'
17°03'
19°47'
19°15'
16°43'
16°28'
16°34'
11°38'
16°47'
16°43'
15°05'
14°22'
13°40'
16°02'
16°03'
16°28'
16° 18'
••
16°17'
16°16'
16° 15'
16°14'
16°13'
16° 12'
I6°08'
16°02'
15°33'
15°23'
••
W long.
169°25'
17S°41'
173°O7'
170°Sl'
172°25'
169°49'
170°24'
169° 35'
170°14'
169°53'
168°06'
173° 39'
169°44'
169°34'
169° 30'
169°29'
"
169° 25'
169°23'
••
"
169°20'
169° 14'
169°12'
169°02'
161 °47'
163° 10'
169°3r
169°39'
170°53'
173°34'
167°21'
169°29'
170°25'
170°40'
171°O3'
171°11'
171°10'
171 °08'
169° 15'
••
169° 17,
169°19'
169°22'
169°23'
169°25'
169°26'
169° 34'
169°45'
170°45'
171°02'
171 °03'
Miles from
origin
28 S
225 SW
218 WSW
73 NW
172 WSW
195 S
137 NNW
97 S
93 SSW
••
63 NNW
83 NE
247 WSW
16 NW
"
13 SSW
25 S
2 S
1 S
"
5 E
8 E
"
11 ENE
17 ENE
20 NE
32 NE
481 NE
394 NE
2 SSW
19 SSW
80 W
392 SW
124 E
4 SSE
113 SSW
160 SSW
209 SSW
107 SW
106 SW
95 WSW
30 S
••
31 S
•>
32 S
33 S
34 S
38 S
45 SSW
101 SW
122 SW
••
Age
adult
"
••
immature
"
adult
"
immature
adult
••
"
adult
••
"
••
••
immature
adult
••
••
•>
••
••
••
••
••
••
••
n
-
••
-
adult
••
»
»
••
»
••
••
"
••
»
NUMBER 158
TABLE B.—At-sea
Date
1966
10 Sep
3 Dec
1967
8 Jan
12 May
1968
12 Feb
Time
1458
1016
1153
1429
1200
HOWLAND STREAMEREG
1966
14 Jul
17 Jul
20 Jul
••
"
••
••
21 Jul
••
M
14 Aug
••
15 Aug
16 Aug
17 Aug
••
••
••
••
••
••
••
••
••
••
19 Aug
16 Sep
19 Sep
••
20 Sep
••
22 Sep
23 Sep
"
••
16 Oct
12 Dec
1967
18 Jan
18 Feb
0832
0845
0846
0830
1017
1144
1617
1724
0936
1645
1649
1010
1025
0845
0930
0649
1659
0923
0948
1015
1044
1059
1117
1135
1204
1320
1330
1415
1440
1500
1515
0850
0808
1035
1425
1522
1543
1736
0430
1040
1710
1015
1652
1153
0836
No.
1
1
1
1
2
1
1
1
1
1
2
1
1
1
3
1
1
1
1
1
1
2
3
1
1
1
3
1
3
1
1
1
3
3
2
1
1
1
sightings of streamered
Behavior
flying N
feeding
not noted
feeding
flying S£
••
flying NW
flying NE
flying E
"
flying NW
flying S
not noted
feeding
flying W
feeding
••
••
••
not noted
••
••
flying ENE
flying NE
flying SE
feeding
flying NE
feeding
flying S
not noted
flying S
feeding
"
not noted
flying N
feeding
not noted
••
feeding
not noted
flying SE
flying E
feeding
N lat.
16°42'
18°44'
16°38'
18° 14'
16°35'
O°53'
0°54'
0°45'
0°41'
0°24'
0°14'
0°34'
0°41'
0°27'
0°38'
0°31'
0°30'
0°40'
0°34'
0°40'
0°42'
0°45'
0°44'
0°42'
0°40'
0°39'
0°38'
0°S7'
0°34'
0°26'
0°25'
0°22'
0°21'
0°20'
0°19'
1°28'
0°52'
0°29'
0°42'
0°52'
"
••
0°48'
0°18'
0°07'
l°05'
0°58'
0°45'
0°49'
Sooty Terns—Continued
W long.
170°13'
164°44'
169°11'
169° 12'
168°35'
176°44'
176°45'
176°31'
176°38'
"
176°36'
176°4r
176°40'
176°32'
176° 36'
176°35'
176°28'
176°40'
176°48'
176°47'
176°44'
176°48'
176°52'
176°57'
176°59'
177°O1'
177°04'
177°12'
177°22'
177°23'
177°30'
177°34'
177°37'
177°39'
177°OO'
176°47'
175°51'
176°26'
176°35'
176°37'
176°23'
176°27'
176°01'
176°46'
176°39'
177°35'
176°29'
Miles from
origin
42 W
299 ENE
19 ESE
89 N
54 E
8 NW
9 NW
7 E
7 S
24 S
34 S
15 SSW
8 SSW
22 SSE
10 SSE
18 S
15 S
14 SSE
12 SW
11 SW
4 SW
12 W
14 WSW
20 WSW
22 WSW
24 WSW
28 WSW
32 WSW
50 WSW
51 WSW
58 WSW
62 WSW
66 WSW
68 WSW
46 NNW
7 NW
52 SE
15 SE
7 NNE
6 N
••
8 S
32 SSE
54 SSE
17 NNW
11 N
56 W
9 E
Age
"
••
"
"
"
"
adult
"
••
••
"
••
"
"
••
••
••
••
"
••
"
••
adult
••
••
••
*•
••
"
••
••
••
immature
adult
••
••
••
51
52 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE C.—At-sea recoveries of banded Sooty Terns
(table based on distance between banding and recovery localities; ? uncertain, - not noted)
Original data
Date Age Location Date
9 May 66
14 Aug 66
9 Apr 66
21 Jul 66
-•
Recovery
Age
adult
"
-
adult
data
Sex
$
$
-
$
Elapsed months
15.2
18.4
14.3
8.7
17.6
0.3
Miles
HOWLAND ISLAND
2 Feb 65 adult
1 Feb 65
19 Jul 65
2 Feb 65
12 Jul 66
18 Jul 66
12 Oct 64
2 Feb 65
1 Feb 65
23 Jul 64
12 Jul 66
19 Jul 66
21 Jul 66
17 Aug 66 immature
1 Feb 65 adult
21 Jul 66
9 Oct 64
1 Feb 65
12 Jul 66
2 Feb 65
HULL ISLAND
26 Sep 65
24 Sep 65 immature
25 Sep 65
JOHNSTON ATOLL
8 Jul 66
3 Feb 64 adult
30 Jan 64
8 Jun 64
27 Apr 65
I Aug 63
25 Jul 63
22 Jul 64
II Feb 64
21 Apr 66
LAYSAN ISLAND
9 Aug 65 immature
MANANA, OAHU
20 Mar 64 adult
1°OO'N-175°47'W
0oH'N-176°30'W
0°12'N-176°36'W
0°15'N-176°40'W
O°17'X-176°3rW
1°17'N-176°34'W
O°42'N-176°17'W
0°47'N-176°59'W
0°48'N-176°59'W'
l°OrN-176°39'W
O°44'N-176°27'VV
O°38'N-I76°34'\V
O°44'N-176°27'W
0°50'N-176°26'W
lear Howland
0o27'S-177o31'W
0°34'N-176°20'W
O°O2'S-176°37'\V
O°14'N-175°52'W
11°57'N-
16°18'X-
I5°44'X-
14°36'N-
18°58'X-
18°49'X-
18°43'X-
14°59'X-
17°42'N-
16°44'N-
175°49'W
172°57'W
172°2O'W
171°03'W
170°16'W
170°24'W
17O°31'W
170°37'W
169°47'W
169°11'W
ll°09'N-140°53'W
at sea, Hawaiian
area
15 Jul 66
17 Jul 66
13 Jul 66
9 Dec 66
22 Apr 67
23 Sep 66
18 Sep 66
19 Sep 66
23 Sep 66
17 Jul 66
17 Jan 67
20 Oct 65
22 Oct 65
17 Oct 65
22 Nov 65
13 Nov 66
20 May 65
18 Apr 65
16 Apr 65
21 May 65
16 Apr 65
20 Apr 65
8 Jan 67
before 6 Dec 65
mid-Oct
adult
?
adult
adult
immature
adult
adult
adult 9
immature $
$
9
adult
0.1
21.1
17.5
17.4
28.5
4.9
9.1
2.1
1.0
19.6
2.1
21.3
15.5
0.2
2S.5
0.8
0.9
0.8
1.9
4.2
15.6
14.6
10.3
0.8
21.7
21.9
8.8
14.3
8.6
3.9
31.0
52 EXE
38 S
35 S
33 S
32 S
28
22
22
21
17
13
12
11
12
5
N
ESE
W
VV
W
N
ESE
SSE
ESE
ENE
1 W
400
390
370
360
460
202
175
158
141
135
132
124
60
18
XW
xw
NW
NW
sw
wsw
wsw
svv
NNW
XX W
NNW
SW
NNW
E
1,170 SE
0 to 400
Wedge-tailed Shearwater {Puffinus pacificus)*
Warren B. King
Introduction
The material contained in this report was gath-
ered in the course of intensive biological investiga-
tions in the central and eastern Pacific by the
Pacific Ocean Biological Survey Program (POBSP),
Smithsonian Institution, Washington, D. C Hum-
phrey (1965) has given a general summary of the
activities and objectives of the program, and Gould
(pp. 1-5) has discussed the methods and materials
and areas of coverage of the program.
At-sea work began in 1963 and was concluded
in 1969. This report is one of a series of studies of
the pelagic distribution of Pacific seabirds. By the
end of 1968 POBSP personnel observed 81,740
Wedge-tailed Shearwaters during 2747 days (26,457
hours) and 259,710 miles of observation.
The Wedge-tailed Shearwater (Puffinus pacificus)
is an abundant, wide-spread species in the tropical
and subtropical Pacific and Indian oceans; it may
be encountered far from land most of the year. In
the central Pacific its population is approximately
one-half million birds (Table 13). It also breeds on
numerous islands in the western Pacific from the
Bonin, Volcano, and Pescadore islands in the
north, along the east coast of Australia to Monta-
gue Island near Bass Strait in the south-. In the
eastern Pacific it breeds only on San Benedicto Is-
land of the Revilla Gigedo group.
Its marine range is only slightly larger than its
breeding range in the Pacific, although in the In-
dian Ocean its marine range appears to extend
farther north than its breeding range (Bailey, 1968).
In the eastern Pacific it has been recorded from
Warren B. King, International Council for Bird Preservation,
Smithsonian Institution, Washington, D.C. 20560.
Baja California south to the Gulf of Guayaquil,
Ecuador. In the western Pacific it has been recorded
from the Izu Islands south of Japan to the South
China Sea and the Tasman Sea.
The northernmost records are a sighting (POBSP.
TABLE 13.—Maximum estimates by POBSP
(1963-1968) of Wedge-tailed Shearwaters on
islands in the central Pacific*
Island
Kure
Midway
Pearl and Hermes Reef
Lisianski
Laysan
Gardner Pinnacles
French Frigate Shoals
Necker
Nihoa
Islets of the Main Hawaiian group
Johnston
Christmas
Canton
Phoenix
McKean
Taongi
Bikar
Taka
Eniwetok
Wake
Number
6,250
3,000
22,400
60,000
200,000
100
13,600
2,000
25,000
70,000
2,500
6,000
40
10,000
500
12,000 +
6
12
3
6
• Paper Number 70, Pacific Ocean Biological Survey Pro-
gram, Smithsonian Institution, Washington, D.C. 20560.
•Estimates are of birds "using" the islands, including
breeding birds, nonbreeders, and, in some cases, chicks. Esti-
mates of nocturnal burrowing birds are notoriously inaccu-
rate so that many of these estimates may be low by 100
percent or more. On the basis of total number of birds
handled in one year during banding operations on islands on
which coverage was thorough (Kure, Johnston), roBSP experi-
ence indicates that most initial estimates should be doubled
or trebled. Above estimates, however, give a good idea of
order of magnitude of the populations.
53
54 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
Paul Woodward) at latitude 35°26'N, longitude
164°17'W in August 1966 and a typhoon-driven
bird found 30 September 1959 in Fukui, Japan, near
the Sea of Japan at latitude 36° N (Anonymous,
1960). The southernmost record is a U.S. Fish and
Wildlife Service (USFWS) band return record from
Cook Strait, New Zealand, on 8 November 1965;
the light-phase bird had been banded as an adult
19 September 1963 on Johnston Atoll by POBSP per-
sonnel. Another Wedge-tailed Shearwater, also
light-phase, was reported by Falla (1962) from
Makara, Wellington, also in Cook Strait. On tenu-
ous grounds Falla assigned this bird to one of the
north Pacific light-phase breeding islands, rather
than the Shark's Bay, Western Australia, breeding
grounds where light-phase birds occur as well.
Murphy (1951) recognizes two subspecies, P. p.
pacificus Gmelin, an all-dark form from the Kerma-
dec Islands, Norfolk Island, and Kandavu Island
of the Fiji group, and P. p. chlororhynchus Lesson,
a slightly smaller form, from all other islands in
the Pacific and Indian oceans. The latter occurs in
both light-phase and dark-phase morphs, and oc-
casionally in an intermediate form. The light-phase
morph predominates in all breeding colonies north
of 10°N except the Marianas, where only dark
birds occur, and in the Revilla Gigedos. These
breeding grounds include:
island or group latitude
San Benedicto 19° N
Main Hawaiians 19°-22°N
Northwestern
Hawaiians 23°-28°N
Johnston Atoll 16°N
Northern Marshalls 11°-14°N
Bon ins, Volcanos 24°-27°N
Pescadores 20 °N
longitude light-phase
pop- <%)
110°W 33 or less
154°-160°W 97
162°-179°VV 99 +
169°W 95
162°-170°E 93
140°-142°E 99 +
119°E 99?
Light-phase birds make up about one percent of
the Phoenix Islands' population. Light-phase birds
have not been reported in any other breeding col-
onies in the south Pacific. The figure of 33 percent
light-phase birds for the Revilla Gigedos comes
from Murphy's (1951:9) comment that "in certain
colonies, as at the Revilla Gigedo Islands, both
dark- and white-phase birds are found together in
a respective ratio of about two to one." The com-
ment was probably paraphrased from Anthony
(1898:313), who was speaking of the birds "about"
San Benedicto and Socorro Islands, not particu-
larly of the birds "on" either island. Anthony's
(1900:251) statement that "by far the greater num-
ber were in dark plumage," refers to breeding birds
on San Benedicto, and Loomis (1918:143) quotes
Bunnell's notes which say that "the white-breasted
ones were a very small proportion of the total
number" just offshore or on the island of San
Benedicto. At the risk of reading information into
these comments, it would seem that the proportion
of light- to dark-phase birds on San Benedicto may
be smaller than one to two.
BREEDING PHENOLOGY.—The breeding season is
from April to November in northern subtropical
Pacific breeding localities, and October to May in
southern subtropical localities. Birds are most
abundant at sea near their breeding areas during
these months. When the birds of the year fledge,
young and old alike disperse from the general vi-
cinity of the breeding islands, so that numbers en-
countered nearby at sea are only a small fraction
of those seen during the breeding season. The
routes of dispersal are not yet known.
Birds from tropical Pacific breeding stations are
often present near their breeding islands year
round, and their breeding cycle may extend beyond
the eight months of the subtropical breeders.
In the Hawaiian group, Johnston Atoll, and the
northern Marshalls, the Wedge-tailed Shearwater
breeds synchronously on an annual cycle. Birds ap-
pear first on their breeding islands at night in early
March. In the Hawaiian group maximum numbers
occur in May, although on Johnston Atoll num-
bers increase gradually to an August peak. Eggs are
laid in mid-June. Nonbreeders visit the islands
sporadically and usually account for more than half
the population on an island at any given time.
Eggs hatch in early August and by mid-August the
chicks are left alone in their burrows during the
day. By early November neither breeding nor non-
breeding adult birds visit the island, and by the
middle of November the young have fledged and
no birds remain. From September to November
large flocks are often encountered off the shore of
breeding sites. Birds presumably form such flocks
prior to migration.
The gonadal development cycle of light-phase
birds was determined on the basis of measurements
of 75 males collected at sea in all months but Janu-
ary and of 79 females from all months but January,
October, and November (Figure 29). Gonadal de-
NUMBER 158 55
15r
E
E
Ovary length
Left testis length • •""" yy
Ovary width
Left testis width
Largest ovum
J F M A M J J A S O N
FICURF. 29.—Monthly gonad dimensions of light-phase Wedge-tailed Shearwaters collected at sea.
velopment apparently begins with the birds' return
to the vicinity of their breeding islands and reaches
a peak by May, a month before eggs are laid. After
May, gonads decrease in size, but the decrease stops
between July and October during which gonad
sizes hold constant; thereafter they shrink rapidly
to minimum size during winter. There is little indi-
cation from the data of any distinction between
adults and subadults on the basis of gonad size. An
exception was that two of four birds collected on
the equator in April had gonads very much smaller
than the mean dimensions, suggesting they might
have been subadults. The other two, and several
others taken later in the year south of 10°N latitude
where subadults might be expected to be found,
showed gonadal development not appreciably dif-
ferent from monthly averages.
Birds from Christmas Island breed on a schedule
similar to that of Hawaiian birds although it is
somewhat more prolonged (Schreiber and Ash-
mole, 1970), but it is not known if the birds disperse
after breeding.
In the Phoenix Islands the breeding cycle is an-
nual but the peaks are not clearly defined (POBSP) .
The cycle is five months ahead of the cycle in the
Hawaiian group. Breeding birds arrive at their is-
lands in September and eggs are laid in late No-
vember or early December. Peak populations are
found on the islands at this time, although more
than half of the birds present are nonbreeders. Eggs
hatch in early February and by March the adults
visit the islands only sporadically at night to feed
their chicks or to roost. Most adults leave the is-
lands in early May, followed by most of the fledged
young two weeks later. By early June few birds are
left on the islands except small roosting popula-
tions which remain during the nonbreeding season.
The breeding cycle of San Benedicto Island ap-
pears to be roughly synchronous with that of the
northwestern Hawaiian group on the basis of the
only available information: two egg dates, 31 May
and 26 July (Anthony, 1900:252; Loomis, 1918:
142).
SUMMARY OF PUBLISHED PELAGIC RECORDS.—The
appendix summarizes the status of the Wedge-
tailed Shearwater in the Pacific Ocean. Because few
observers are familiar with the distinguishing char-
acteristics of this species, many of the pelagic rec-
ords are ambiguous; they could refer to one or more
species that resemble either light- or dark-phase
Wedge-tailed Shearwaters.
In the eastern Pacific Wedge-tailed Shearwaters
have never been identified with certainty south of
the Gulf of Guayaquil (latitude 3°S) (Le've'que,
1964b:53-54). They have been reported several
times along the Middle American coast from Pan-
ama to Mexico near Manzanillo. Murphy's (1958)
record of both light- and dark-phase birds off north
56 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
era Baja California in December is exceptional;
they have not otherwise been reported north of
21 °N (Loomis, 1918), fully 500 miles farther south.
Records from the eastern Pacific have been obtained
mainly in the northern spring and fall.
Morzer Bruyns (1965) saw Wedge-tailed Shear-
waters over the Equatorial Countercurrent across
most of the Pacific in November, dark-phase west
of the Line Islands, and mixed from there east;
King and Pyle (1957) found them in the Counter-
current between the Line Islands and Mexico in
October.
In the southwest Pacific several authors (Jesper-
sen, 1933; Fleming, 1950; Gibson, 1960; Mitchell,
in Bourne, 1965; Morris, in Bourne, 1965; Norris,
1967) have noted scattered individuals or small
groups of dark-phase birds between Samoa and
Australia throughout the year.
ACKNOWLEDGMENTS.—In addition to all the co-
operators who have made this paper possible (p.
5) special thanks are due to Gerald A. Sanger and
Patrick J. Gould who were closely involved in
analyzing the data. The latter was almost solely
responsible for the section entitled "Density and
Distribution within Equatorial Currents."
I am also indebted to William R. P. Bourne,
Roger Bailey, and George E. Watson for their criti-
cal reading of the manuscript and their many help-
ful suggestions and comments.
Distribution and Abundance
Figure 34-57 (pp. 68-91) show monthly densities
of Wedgetailed Shearwaters in the central and east-
ern Pacific based on POBSP observations between
1963 and 1968. Densities are expressed in terms of
birds per linear mile of observation, and located on
the monthly map at the ship's noon position. Areas
of similar daily densities are contoured to show the
relative abundance of the species in all areas of the
Pacific where POBSP observations have been made.
In cases where parallel ocean transects were made
on cruises spanning two months, the contouring
takes into account the distribution and abundance
reflected in adjacent areas even though the data
came from different months. Because of their geo-
graphical and, often, phenological distinctness,
light-phase and dark-phase birds are treated sep-
arately.
DENSITY AND DISTRIBUTION WITHIN
EQUATORIAL CURRENTS
The Equatorial Countercurrent is an eastward-
flowing current, bounded on the south by the west-
ward-flowing South Equatorial Current and on the
north by the westward-flowing North Equatorial
Current or the California Current Extension, de-
pending on the longitude.
Sverdrup, et al. (1942:709) point out its salient
features, i.e., it is a well-developed, northern hemi-
spheric phenomenon, whose boundaries fluctuate
with the seasons, moving north with the northern
summer. Data from the Carnegie Expedition dis-
cussed by Sverdrup, et al. (1942:709-711) show that
at latitude 140°W the countercurrent lies between
3°N and 10°N. Due to a distinct transverse circu-
lation superimposed upon the major flow direction,
a divergence occurs at the northern boundary of
the countercurrent and at the equator, while a con-
vergence occurs at the southern boundary. They
speculate, on the basis of the plankton collections
of the Carnegie Expedition, that divergences are of
high productivity. Similarly, convergences concen-
trate plankton and organisms that feed on plank-
ton along narrow fronts (Ashmole and Ashmole,
1967). Other authors, e.g., Murphy (1936) and
Morzer Bruyns (1965), have noted some of the ef-
fects of oceanic currents on density and distribu-
tion of birds.
In the central Pacific Wedge-tailed Shearwaters
may be found throughout the current areas. In
general the dark-phase population predominates in
the area south of 10°N, the area generally covered
by the Equatorial Countercurrent and the South
Equatorial Current. The dark-phase population
moves north in conjunction with the northward
movement of warm waters during the northern
summer months.
North of the countercurrent, light-phase birds
predominate, although small numbers may some-
times be encountered as far to the south as the
equator or farther. These may represent migrants
or nonbreeding visitors since they occur primarily
during the nonbreeding period of the light-phase
population.
CENTRAL PACIFIC.—From January 1964 through
February 1967, sixteen cruises were made by the
POBSP across these equatorial currents in the area
bounded by longitudes 165°W and 180°. Surface
57
15
North
Equatorial
Current Equatorial Countercurrent
Degrees North Latitude
FIGURE 30.—Density of Wedge-tailed Shearwaters in relation to latitude across the equatorial
currents in the central Pacific (165°W to 180°), all months, 1966. (Shaded bars -= dark phase;
white bars = light phase.)
water temperature ranged from 25.5° to 30.6°C
throughout the period of study; the vast majority
of samples fall between 27 °C and 30°C. Lowest
temperatures were generally found north of the
countercurrent and highest temperatures south.
Within the countercurrent temperatures remained
remarkably constant.
Small densities of Wedge-tailed Shearwaters were
recorded throughout the current area at all times
of the year; a few notable concentrations occurred
between 4°N and 7°N in winter and spring, and
at 9°N in July. A July peak, composed of 99 per-
cent dark-phase birds, occurred during the period
of northward movement of the dark-phase popu-
lation. A concentration in the fall at 15°N can
best be explained in terms of the attraction of
Johnston Atoll, a nearby breeding site. Unlike
Sooty Terns, whose pattern of distribution in the
Equatorial Current area does not conform to any
boundaries (Gould, p. 32 herein), Wedge-tailed
Shearwaters appear to be most abundant within
the borders of the Equatorial Countercurrent. This
is best exemplified by Figure 30, in which all the
data from 1966 are combined. Data from 1966 were
used because data were complete enough to permit
identification of the countercurrent on the basis of
water temperature samples.
EASTERN PACIFIC.—In the eastern Pacific the
Equatorial Countercurrent is generally well defined
east to 90°W longitude from June through Decem-
ber, but diffused or absent during the rest of the
year. Its southern boundary remains relatively sta-
ble at 4°N to 6°N; its northern boundary fluctu-
ates between 8°N and 12°N. It is farthest north
during the northern summer (Wyrtki, 1966; n.d.).
Figure 31 shows densities for six cruises through
58 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
5.0
4.5
4.0
3.5
_» 3.0
8.2.5
5 2.0
1.5
1.0
.5
6.08
15 14 12 10
m
8 7 6 5
Equatorial Countercurrent
Degrees North Latitude
FIGURE 31.—Density of Wedge-tailed Shearwaters in relation to latitude across the Equatorial
Countercurrent in the eastern Pacific (97°W to 126°W), 1967. (Shaded bars = dark phase;
white bars = light phase.)
the area bounded by 97°W and 126°W during
1967. Surface water temperatures show a different
pattern for these cruises than for the central Pa-
cific cruises. Temperatures remained between 25.5°
and 28.8°C in latitudes south to ca. 6°N. At 6°N,
temperatures began to drop rapidly; at ca. 2°N
readings were between 23.8° and 25.7°C, dropping
in one instance to 20.7°C near the equator at
97°W.
Both color phases occur within this area, and, al-
though the data base is too small to provide a com-
plete picture, it appears that light-phase birds (pos-
sibly nonbreeding sojourners from the central Pa-
cific) predominate in the northern winter, while
dark-phase birds (possibly from the Revilla Gigedo
population) predominate during the rest of the
year.
All large concentrations were found between
4°N and 10°N. In February and March highest
densities were near 10°N. Due to the unstable con-
dition of the countercurrent at this time, its bound-
aries cannot be defined clearly. In June and July
highest densities were from 4°N to 5°N, corre-
sponding fairly closely with the southern boundary
of the countercurrent; smaller concentrations were
found at 7°N and from 10°N to 11°N, the former
being just north of the southern boundary of the
countercurrent, and the latter just south of the
northern boundary. In the fall (September) only
one large concentration was noted, at 8°N, some-
what south of the northern boundary of the coun-
tercurrent. In the eastern Pacific, especially in the
northern summer when the Equatorial Counter-
current is strongest, Wedge-tailed Shearwaters
NUMBER 158 59
reach highest densities near and within the borders
of that current.
RANGE OF SEA SURFACE TEMPERATURES AND
SALINITIES AT WHICH WEDGE-TAILED SHEARWATERS
WERE OBSERVED
The Wedge-tailed Shearwater is distributed
throughout most of the tropical central and eastern
Pacific Ocean, and, thus, it is not surprising to find
that the range of sea surface temperatures and
salinities at which the species was observed is
roughly as broad as the recorded temperatures and
salinities of the area. Sea surface temperatures were
recorded on a sufficiently large number of cruises to
provide a substantial amount of data from which
to draw conclusions; salinity determinations were
far fewer, and the data are less conclusive.
The water samplings within five minutes of the
hours of 0800, 1000, 1200, 1400, and 1600 were as-
sumed to give a fairly accurate measure of the
temperature and salinity for one hour before and
one hour after the hours mentioned. All sightings
made one hour before to one hour after were as-
signed the temperature and salinity values of said
hours. Since each sample covers two hours of ob-
servation, the ratio of birds to samples divided by
2 yields a bird per hour of observation figure.
TEMPERATURE.—Sightings made when no sea
surface temperatures were taken, or more than one
hour before 0800 or after 1600, account for slightly
more than one-half the data. Temperature correla-
tions apply to 34,073 of 82,000 Wedge-tailed Shear-
waters observed during the study. Table 14 shows
the number of birds observed in conjunction with
each whole degree of temperature centigrade, the
number of water samples at each temperature, and
the ratio of birds to samples.
Table 14 suggests that Wedge-tailed Shearwaters
showed no great sensitivity to temperature as long
as it was above 21 °C. The lowest sea temperature
at which Wedge-tailed Shearwaters were observed
was 15.0°C. Two individuals were seen at this re-
markably low temperature; otherwise the lowest
temperature was 20.8°C, and the highest was
33.0°C.
SALINITY.—Far fewer salinity measurements were
made, too few to show anything but the range of
salinities over which Wedge-tailed Shearwaters
were observed. Table 15 shows the number of birds,
TABLE 14.—Relative abundance of Wedge-tailed
Shearwaters at various sea surface temperatures
Temperature (°C)
20
21
22
23
24
25
26
27
28
29
30
31
Total
Number Number of
of birds water samples Birds/Sample
0
13
502
278
5,193*
1,618
11,642
6396
5,579
1,185
1,398
69
34,073
56
66
75
98
133
445
853
900
814
340
276
14
4,070
.00
.20
6.56
2.84
39.05
3.64
13.65
7.33
6.85
3.49
5.07
4.93
'Includes a single sighting of 3500 individuals. This sight-
ing is unusually large, and accounts for the inflated birds/
sample figure at 24°C.
TABLE 15.—Wedge-tailed Shearwaters observed at
various sea surface salinities
Surface salinity
(parts per thousand)
33.0-33.3.
33.3-33.7..
33.8-34.1 .
34.2-34.5
34.6-34.9
35.0 +
Total
Number Number of
of birds water samples Birds/Sample
4
18
17
84
158
87
368
4
11
31
46
49
38
179
1.00
1.64
0.55
1.83
3.22
2.29
the number of samples, and the birds per sample in
each of six salinity ranges. Table 15 shows a fairly
even spread across the recorded salinity range, with
a tendency toward greater abundance at salinities
34.6 parts per thousand and above. The lowest re-
corded salinity at which Wedge-tailed Shearwaters
were seen was 32.60 parts per thousand; the highest
was 36.54 parts per thousand.
SPECIMEN RECORDS, MOLT, AND BAND RECOVERIES
SPECIMEN RECORDS.—The POBSP secured speci-
mens of Wedge-tailed Shearwaters at sea in both
60 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
30°
N
20°
10°
0°
0°
s
180°
•
•
•
•
•
»
\
•
170* \
it
•
 T
•
I-
•
- •
DS
•
•
-
r.
i •
-
! |
160
•A-
•
:
•sir
•
*
•
.
>
1
•
L
•k
(
1
|
i
o
150
1
N
 it
10*
0*
120 W
12C*
s
1
<.
110
>
5,i
, \
v S
r
IK)'
H
i
|
s.
00
no
V\
30"
20
FICURE 32.—Distribution of light- and dark-
phase Wedge-tailed Shearwater specimen rec-
ords: left, in the central Pacific; right, in the
eastern Pacific.
the central and eastern Pacific. Table 16 lists the
numbers of specimens of the two color phases col-
lected each month. Figure 32 shows the location; by
degree squares, where specimens were obtained;
color phases are differentiated.
TOPOGRAPHY AND SYNCHRONY OF MOLT.—Pri-
mary molt proceeded distally from one locus. It was
far more symmetrical than rectrix molt. The pri-
maries on either wing were almost invariably at
identical stages of growth. Growth differentials of
one-half of a feather length were noted rarely. In
distal primary molt (primaries 7 to 10) only one
feather was replaced at a time. Growth of a distal
primary was nearly completed as the next one be-
gan to grow. Several inner primaries can be re-
placed simultaneously.
Rectrix molt was most intense during later pri-
mary molt. It was only marginally symmetrical,
usually more in the number and spacing of replaced
feathers than in their position. For example, rec-
trices 2 and 4 might be growing on the left, and
rectrices 3 and 5 on the right. Rectrix replacement
followed no fixed sequence. Usually one or two,
and up to five, of the six rectrices on each side were
replaced simultaneously.
Contour feather molt probably started at the
same time as, but was more protracted than, pri-
mary molt. Head and nape feathers were replaced
first, followed by scapular and rump feathers. New
head and nape feathers of light-phase birds were
gray and soft; old ones were browner and coarser.
Newly replaced scapulars had conspicuous pale
scallops at their tips. These pale scallops were most
conspicuous in light-phase birds in December (pre-
sumably first-year birds), slightly less so in adults
in April. Most December light-phase birds had gray
vermiculations on the crissum, flanks, and sides,
similar to those of adult Pink-footed Shearwaters
NUMBER 158 61
TABLE 16.—Specimens of Wedge-tailed Shearwaters collected by the POBSP each
month
Area and
color phase
CENTRAL PACIFIC
Light phase
Dark phase
EASTERN PACIFIC
Light phase
Dark, phase
Total
Jan
0
- 3
-
_
3
Feb
3
3
-
1
7
Mar
1
2
3
6
Apr
12
20
-
_
32
May
32
7
-
39
Jun
25
17
1
43
Jul
18
10
-
1
29
Aug
30
2
-
32
Sep
24
10
-
34
Oct
2
5
4
1
12
Nov
1
11
-
12
Dec
16
3
-
19
Total
164
93
8
3
268
(Puffinus creatopus). Such vermiculations were
present infrequently in light-phase birds from other
months.
First-year birds probably retain their juvenal
plumage for 15 months. Adults molt primarily dur-
ing their nonbreeding season, although replace-
ment of contour feathers extends throughout the
breeding season. Since adults and subadults are
present together on islands, and most likely also
at sea, most age-classes were probably sampled in
the POBSP collections. Thus, it is likely that molt
occurs simultaneously in all age-classes after the
first year.
SCHEDULE OF MOLT.—Light-phase Birds: No
light-phase birds were collected at sea in January.
Few were seen in the central Pacific, but they were
common in the eastern Pacific. In early February in
the eastern Pacific POBSP personnel (Woodward,
pers. comm.) reported that they had noticeable
gaps in their primaries, indicative of molt of the
inner primaries. The three central Pacific speci-
mens from February had no molt of remiges, rec-
trices, or contour feathers; two had gray vermicula-
tions on flanks and abdomen. These three were
probably first-year birds with 3-month-old plumage
since March and April specimens, presumably
adults growing their 9th or 10th primaries, were
in the midst of rectrix replacement and had re-
placed head, nape, and some scapular contour
feathers. Some March specimens collected on the
northwestern Hawaiian Islands were completing
growth of their 10th primaries. In April seven of
twelve specimens taken at sea had completed remex
and rectrix molt, but all were still replacing con-
tour feathers. In May only one of 32 specimens had
not completed flight feather molt, but contour
feather molt was continuing in the scapulars and
on the rump. No flight feather molt occurred on
any bird from June to December. However, all six-
teen December specimens had fresh plumage, in-
cluding remiges and rectrices with a silvery sheen
and prominent white scalloping on scapular and
lower back feathers. (The scalloping was noticeable
from a considerable distance at sea.) Their remiges
had broad vanes and blunt tips with small sharp
central points, similar to those of May specimens,
indicative of unworn feathers. There was no indi-
cation of remex replacement in the small sample of
October and November birds, so I conclude that
the December birds, which were all from the cen-
tral Pacific, were fledglings and that adults and sub-
adults had already left that area. Although the
date of onset of molt is not known, adults and sub-
adults might have already started to molt their
worn plumage by December. These December birds
were the only ones that followed ships regularly
(see "Behavior").
Dark-phase Birds: The molt cycle in dark-phase
birds is more complex than it is in light-phase
birds because of the geographical and temporal
overlap of populations at sea. There was some rec-
trix or remex molt in 40 out of 96 birds, and in all
months but May. Using the clear-cut molt cycle of
the light-phase birds as a model, it is difficult to
explain the molt cycles of dark-phase birds. Phoenix
Islands' birds lay eggs in November and December;
they should start flight-feather molt in May and
complete it in October. Many specimens conform to
this schedule. Five of 17 June birds were growing
primaries 4, 5, or 6; 7 of 10 July birds were grow-
ing primaries 6, 7, 8, or 9; several August birds and
7 of 10 September birds were growing primaries 9
62 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
or 10, and all 5 October birds had completed or
nearly completed molt.
Christmas Island birds lay eggs in June and July.
They would be expected to begin molt in Novem-
ber and to complete it in April. Seven birds col-
lected in November were growing primaries 3 to 7;
two January birds were growing primary number
8; 17 of the 20 April birds and all May birds had
completed molt of flight feathers. These birds con-
form to the Christmas Island schedule.
There are still a number of dark-phase specimens
that conform to neither of these schedules. The
large number of birds molting at all times of the
year suggests two explanations: either most birds
are from local populations (e.g., Line and Phoenix
islands) and are present around their breeding is-
lands a greater part of the year and molt is more
protracted than in their subtropical, light-phase
counterparts, or the central Pacific is invaded by
postbreeders from other populations. The two
theories are not mutually exclusive. I suspect both
are true.
BAND RECOVERIES.—Between 1963 and 1969
POBSP personnel banded 75,285 Wedge-tailed Shear-
waters, 65,806 in the Hawaiian Islands, Johnston
Atoll, and the northern Marshall Islands, and 9,479
in the Line and Phoenix islands. Nineteen banded
birds were recovered at sea by August 1969. Three
had been banded on Johnston Atoll; the remainder
had been banded on islets off the northeast coast
of Oahu.
The only significant recovery is the southernmost
record from Cook Strait, New Zealand, described
in the introduction. Recoveries of birds banded on
Johnston Atoll were within 300 miles southwest or
northwest of Johnston Atoll. Birds banded on islets
off Oahu were recovered within 100 miles in all di-
rections of Oahu. All recoveries were made between
April and October—the breeding season.
On 11 October 1964 a bird that had been marked
with an orange plastic leg streamer on Johnston
Atoll was seen at latitude 9°25'N, longitude
152°55'W, about 1250 miles southeast of its place
of marking. Although it is tempting to suggest that
this is evidence for migration, individuals doubtless
range thousands of miles searching for food, so that
this location might well be included within the
possible foraging range of the Johnston Atoll
population.
DISCUSSION
In the central Pacific light-phase distribution and
abundance at sea were quite evidently tied to the
breeding cycle of the birds on the Hawaiian Islands
and Johnston Atoll. During the northern winter
light-phase bird abundance was lowest and, al-
though there was a poorly defined density center at
the Equatorial Countercurrent, for the most part
the few birds that were recorded were scattered. In
February light-phase birds were virtually absent
from the central Pacific north of 10°N (7 individ-
uals in 4 years). Data from March showed birds re-
entering that area, and from April through Novem-
ber a typical distribution pattern prevailed with
only minor irregularities; maximum densities dur-
ing this period were recorded consistently within
100 miles of the breeding islands.
In the eastern Pacific the timing was reversed.
Light-phase birds were most abundant from Octo-
ber to February (a maximum of 10.6 BPM south of
Guatemala in February), and least abundant from
March to September. Greatest densities were re-
corded between 6°N and 12°N, the area of the
Equatorial Countercurrent, and the normal light-
phase range did not appear to extend very much
farther north or south. The northern limit ap-
peared to be approximately 25°N latitude.
I conclude that the eastern Pacific is a major win-
tering ground for light-phase birds from the Ha-
waiian group. I suspect they migrate there along
the Equatorial Countercurrent and return via the
North Equatorial Current.
The at-sea distribution and abundance of dark-
phase birds cannot be tied as readily to their breed-
ing cycles. In the first place the two populations
that breed in the central Pacific do so at opposite
seasons. (Increasing density in the eastern Pacific
concurrent with the beginning of the breeding sea-
son on Christmas Island suggests that the bulk of
eastern Pacific dark-phase birds in the northern
summer do not come from Christmas Island.) Sec-
ondly, both populations number in the tens of
thousands, rather than hundreds of thousands as
does the Hawaiian population. Thirdly, there are
many more dark-phase colonies across the Pacific
than there are light-phase colonies. Thus, assigning
islands of origin to any group of dark-phase birds
encountered at sea is, at our present level of knowl-
edge, only conjecture.
NUMBER 158
Several tendencies in dark-phase distribution are
worth noting. The first is the repeated association
of high densities with the Equatorial Countercur-
rent area, not only in the central Pacific but also in
the eastern Pacific. The second is the extent and
timing o£ the northward penetration of dark-phase
birds. This penetration began in April at the same
time that light-phase birds were once again becom-
ing numerous to the north. It increased in scope
and intensity to a peak in July and August, during
which time dark-phase birds were found nearly as
far north (to ca. 23°N) as light-phase birds. Num-
bers decreased thereafter until there were almost
no dark-phase birds to be seen north of 10°N dur-
ing December, January, and February. In other
words, the distribution and abundance pattern of
dark-phase birds north of 10°N in the central Pa-
cific paralleled that of light-phase birds.
A parallel situation occurs in the Indian Ocean
(Bailey, 1968). During the northern winter, the
breeding season for Wedge-tailed Shearwaters in
the western Indian Ocean, the birds are distributed
most abundantly along the Equatorial Countercur-
rent. In summer, when the countercurrent weakens
or is absent, birds move north to the Bay of Ben-
gal and the Arabian Sea in substantial numbers.
In the eastern Pacific light-phase and dark-phase
birds occupied roughly the same area, but they
reached maximum abundance at different times of
year. Both phases reached greatest densities between
the Equatorial Countercurrent and the coast of
Mexico near Manzanillo. Light-phase birds gen-
erally were not seen south of 4°N, whereas dark-
phase birds were seen occasionally as far south as
POBSP observations were made (to latitude 20°S in
some months). Light-phase birds were most abun-
dant between October and February; dark-phase
birds attained highest densities from June to Sep-
tember. It is likely that a few birds of both phases,
probably nonbreeders, were present throughout the
year in the eastern Pacific.
The implication of an abundance cycle in the
eastern Pacific of dark-phase birds similar to that of
light-phase birds, although several months out of
phase, is that dark-phase birds from yet unspecified
breeding sites perform an annual translongitudinal
migration also. Even if all the dark-phase birds en-
countered in the eastern Pacific were from the
Revilla Gigedos, which is quite unlikely, they must
be making an extensive migration, for there are
fewer dark-phase birds to be found in the eastern
Pacific from October to May than from June to
September.
Several sources (Jespersen, 1933; Dixon and Star-
rett, 1952; MacDonald and Lawford, 1954; Morzer
Bruyns, 1965) indicate the presence in the western
tropical Pacific between New Guinea and the Mari-
anas, and in the Philippine Sea, of large numbers
of dark-phase Wedge-tailed Shearwaters from April
to October. POBSP personnel saw light-phase birds
between the Tokelau and Samoan islands at 12°S
latitude in February. Dixon and Starrett (1952)
also suggest that light-phase birds are present, at
least south of the Marianas, in January and Febru-
ary although these may have been any of several
other species, especially Streaked Shearwater (Cal-
onectris lencomelas). Thus there may be in the
western Pacific a situation directly analogous to
that of the eastern Pacific in which both phases are
present but with abundance peaks in different sea-
sons.
Behavior
FEEDING.—Wedge-tailed Shearwaters have been
observed feeding on the surface, under the surface,
and in the air. The method most frequently noted
by POBSP observers, at least for diurnal flocks, was
"contact dipping," to use the terminology of Ash-
mole and Ashmole (1967). Second in frequency
was "feeding on the surface," third was "air dip-
ping," and fourth was "air diving."
In contact dipping birds flew close to the sur-
face, wings held back as if to hover, sometimes
touching the surface with outstretched feet. Head
and neck were plunged down several inches into
the water. Forward momentum was regained by
vigorous wing beats and foot paddling. Usually
when a fish was caught it was eaten without inter-
rupting flight although birds stopped on the sur-
face occasionally, presumably to swallow heavy
prey. This was the only method of feeding observed
at night (Gould, 1967), although it is likely that
feeding on the surface was used too.
Feeding on the surface was often accomplished
from a sitting position but sometimes a surface dive
was employed, although rarely forcefully enough to
submerge a bird completely under water. Wing tips
and tail usually remained out of water.
Air dipping was seen infrequently. It involved
64 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
70 T
1 2 3 5 610 11-25 26-50 51100 101
Number in Sighting
FIGURE 33.—Number of Wedge-tailed Shearwaters per sight-
ing in a sample of 1000 sightings in which this species was
recorded.
pursuit of a Hying fish above the surface of the wa-
ter, sometimes accompanied by vigorous foot strokes
for increased speed.
Air dives were rarely observed. They involved a
dive into the water "just about like the boobies"
(POBSP, Dayle Husted). No further description is
available.
There were no observations to indicate that birds
swim any distance under water, in spite of adapta-
tions for this purpose such as laterally compressed
tarsi and compact plumage (Kuroda, 1954; Storer,
1960).
FLOCKING.—Figure 33 shows the number of
Wedge-tailed Shearwaters counted or estimated per
sighting in a random sample of 1000 sightings in
which the species was observed. A sighting is de-
fined here as the observation of one or more birds
acting as a unit. Occasionally it was difficult to de-
cide whether birds seen at the same time were asso-
ciated or not. This was especially true close to
breeding areas where streams of birds of several
species could be seen coming and going at the same
time.
Most sightings (66.9%) were of single birds.
Progressively fewer sightings were made of larger
groupings. Only 0.3 percent of sightings contained
100 or more birds. However, the largest number
seen in one sighting was 3500. This was part of a
large milling mass of birds near Kaula Rock. Of 70
flocks containing 100 or more Wedge-tailed Shear-
waters, the mean number for that species was 307.
Fifty out of 70 (71.4%) flocks of more than 100
Wedge-tailed Shearwaters were within one day's
travel (100 miles or less) of the Hawaiian Islands.
ASSOCIATION WITH OTHER SPECIES.—Casual ob-
servations at sea suggest that birds of some species
tend to occur individually, others tend to associate
frequently with other members of the same species,
and still other species tend to occur in mixed-
species aggregates. Wedge-tailed Shearwaters usu-
ally travel singly or in small groups, but feed most
frequently in large mixed-species flocks.
Data on association of Wedge-tailed Shearwaters
in all sightings between 1963 and 1969 were ana-
lyzed to determine the relative tendency for the spe-
cies to occur alone or in conjunction with other
species. Data showed that Wedge-tailed Shearwaters
associated with members of other species in 57.8
percent of the sightings, and were alone or with
other Wedge-tailed Shearwaters in 42.2 percent of
the sightings (Table 17).
To understand why more Wedge-tailed Shear-
waters were seen in mixed-species aggregates than
alone, it is important to look at the behavior of the
respective groups. The categories of behavior for
which information was recorded systematically in-
cluded sitting on the water, feeding, searching, fol-
lowing the ship, displaying, parasitism, dispersing,
and traveling. The behavior of birds at sea, how-
ever, is sometimes difficult to characterize. Search-
ing and dispersing are closely related to feeding.
Searching implies that a flock of birds has formed
and is about to feed when schooling fish break the
surface. Dispersing implies that a flock was feeding
a short time before observation, but inability to
TABLE 17.—Sightings of Wedge-tailed Shearwaters
in association with other species and alone
Status
Associated
Unassociated
Total
Average number
Number of Number of of birds per
birds sightings sighting
47,276
34,561
81,837
3^25
14,743
17,968
14.66
2.34
4.56
NUMBER 158 65
TABLE 18.—Number and percentage of sightings in
which various species were observed feeding with
Wedge-tailed Shearwaters (n = 1285)
Species
Puffinus pacificus (alone)
Sterna fuscata
Anous stolidus
Gygis alba
Sula sula
Pterodroma externa externa
Fregata minor
Pterodroma hypoleuca nigripennis
Sula dactylatra
Puffinus puffinus neweHi
Sula leucogaster
Puffinus griseus
Bulweria bulwerii
Pterodroma externa cervicalis
Sterna lunata
Anous tenuirostris
Fregata ariel
Pterodroma neglecta
Puffinus nativitatis
Oceanodroma leucorhoa
Stercorarius pomarinus
Puffinus carneipes
Puffinus Iherminieri
Pterodroma alba
Phaethon rubricauda
Procelsterna cerulea
Stercorarius longicaudus
Diomedea immutabilis
Phaethon lepturus
Number Percentage
85
994
241
239
213
192
112
104
90
75
45
43
43
40
31
30
28
26
24
20
17
15
15
13
11
10
8
7
7
6.6
77.4
18.8
18.6
16.6
14.9
8.7
8.1
7.0
5.8
3.5
3.3
3.3
3.1
2.4
2.3
2.2
2.0
1.9
1.6
1.3
1.2
1.2
1.0
0.9
0.8
0.6
03
0.5
find more surfacing fish was resulting in disintegra-
tion of the flock. Wedge-tailed Shearwaters were
not known to display at sea, nor were they subject
at sea with any regularity to parasitic attacks by
jaegers (Stercorarius spp.), skuas (Catharacta
skua), or frigatebirds (Fregata spp.).
Wedge-tailed Shearwaters not actively involved
in any other behavioral activity were assumed to be
traveling. Thus, it is not surprising that in only
2172 sightings (12.1%) was a behavior noted other
than that of traveling.
Of behavioral categories other than traveling,
feeding was probably of greatest significance, be-
cause, next to traveling, the greatest number of
sightings were of feeding birds (1285 sightings). An
additional 295 sightings were noted as searching
and 16 were dispersing. Significant interspecific re-
lationships can be shown best by analyzing the spe-
cies content of the 1285 sightings of feeding birds.
I disregarded searching and dispersing birds in this
analysis because of the possibility that these behav-
iors were misinterpreted by the observers. Table 18
lists the number and percentage of sightings in
which various species were in feeding association
with Wedge-tailed Shearwaters. Wedge-tailed
Shearwaters fed without other species present only
6.6 percent of the time; 93.4 percent of the time
they fed in association with other species, especially
Sooty Terns (Sterna fuscata).
In mixed feeding flocks in the tropical Pacific
Ocean, Wedge-tailed Shearwaters and the noddies
(Anous spp.) fly lowest, usually no higher than 10
meters above the water. Boobies (Sula spp.) usu-
ally fly between 10 and 30 meters and Sooty Terns
and White Terns (Gygis alba) fly between 20 and
60 meters above water level. Frigatebirds can be
found substantially higher, perhaps as high as 120
or 160 meters. These are the approximate levels at
which these species fly during the periods when the
schooling fish are not surfacing. The longer the
periods between surfacing, the higher the Sooty
Terns and frigatebirds tend to fly, and the more
dispersed the typical feeding flock becomes. When
fish once again break the surface it is difficult for an
observer to tell which component of the flock spots
them first, but an observer quickly learns to watch
for a characteristic flash of white as the Sooty Terns
bank from horizontal flight, exposing their white
underparts against the sky, in a dive toward the
surfacing fish. It is visible to an observer perhaps a
mile or more away, appearing like snowflakes danc-
ing on the horizon. The presence of frigatebirds
over the terns confirms the suspicion that a flock
has gathered and is or has been feeding.
Wedge-tailed Shearwaters utilize a modified
dynamic soaring technique in flight, less efficient
than the soaring of albatrosses because of higher
wing loading and lower aspect ratio. However, they
take advantage of the differentials in windspeed at
different elevations over the waves caused by sur-
face friction, and are, therefore, more or less tied
to the air layer in which windspeed differentials are
greatest. Sooty Terns and frigatebirds, on the other
hand, either soar statically or propel themselves by
constant wingbeats, and are not tied as closely to
the surface of the water.
Sooty Terns are in a good position to act as the
"eyes" of the flock, both because they are high
66 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
above the water and because their greater abun-
dance permits a greater area of ocean to be kept
under surveillance for surfacing fish. If human ob-
servers can take advantage of the Sooty Terns' dives
to the surface as an indication of feeding activity,
it is not unreasonable to suspect that birds do the
same. Although the behavioral pattern of Sooty
Terns may bring increased numbers of other spe-
cies to the feeding area, competition for food is
probably minimal because food is superabundant
for the short periods when it is available.
The ephemeral nature of the food supply sug-
gests that, up to a point, more, rather than fewer,
birds help to make the supply of food more readily
available. Ashmole (1963, postscript) suggested
that although tropical seabirds may be limited in
their abundance by the availability of food, their
effect on the abundance of the food organisms is
probably negligible. This is probably also true in
areas of food concentration (for example, in the
upwellings of the Peru current, where birds' search
efficiencies are undoubtedly much higher than for
tropical oceans as a whole), where breeding adap-
tations permit more rapid growth of offspring and
population sizes commensurate with predictable
abundance of food (see Nelson, 1968, for a com-
parison of breeding adaptations of boobies within
and without such an area of predictable food abun-
dance) . Seas surrounding breeding islands in areas
without unusual food abundance may support sea-
bird concentrations large enough to cause competi-
tion for available food resources. In the face of such
competition some species, such as Sooty Terns and
Wedge-tailed Shearwaters, can, if necessary, exploit
seas at greater distances from their breeding islands
than can others, e.g., noddies and boobies. Travel-
ing greater distances for food places more impor-
tance on the role of search time in the species' en-
ergy budget than in birds of areas of food abun-
dance, and the resulting breeding strategies tend to
be more conservative, e.g., fewer offspring, longer
incubation stints, and longer fledging periods.
Of significance is the relatively low percent of
participation in feeding sightings of the Sooty
Shearwater Puffinus griseus, Bulwer's Petrel Bul-
weria bulwerii, Leach's Petrel Oceanodroma leuco-
rhoa, and the two tropicbirds Phaethon spp., all
of which are more abundant than is suggested by
Table 18. The first species, and its traveling com-
panion the Slender-billed Shearwater Puffinus
TABLE 19.—Sightings of sitting birds that included
Wedge-tailed Shearwaters (n=465)
Species
Puffinus pacificus (alone)
Pterodroma externa
Anous stolidus
Puffinus puffinus newelli
Sula sula
Puffinus puffinus auricularis or P. p.
opisthomelas
Sula leucogaster
Puffinus griseus
Pterodroma hypoleuca nigripennis. .
Sula dactylatra
Number Percentage
382
34
9
7
6
4
3
3
3
3
82.2
7.3
1.9
1.5
1.3
0.9
0.6
0.6
0.6
0.6
tenuirostris, seldom stops to feed in the tropics dur-
ing its transequatorial migrations. The other species
are all more or less solitary feeders.
SITTING ON WATER.—Wedge-tailed Shearwaters
frequently sit on the water during the day. Of 465
sightings of sitting birds which included Wedge-
tailed Shearwaters, 382 (82.2%) sightings were of
Wedge-tailed Shearwaters only. Other species most
frequently associated with Wedge-tails were Juan
Fernandez Petrels Pterodroma externa externa, and
White-necked Petrels P.e. cervicalis. These petrels,
not readily distinguished from one another on the
water, were frequently seen sitting on the water
singly and in rafts up to ten birds during the
months of June to October undergoing heavy molt.
They were frequently joined by Wedge-tailed Shear-
waters. Table 19 gives the frequency with which
other species were seen to sit on the water with
Wedge-tailed Shearwaters.
Wedge-tailed Shearwaters seem to sit on the wa-
ter most frequently under two conditions. The first
is in association with flocks in which individuals
have finished feeding and are resting on the water
in small rafts. The second is evidently prior to mi-
gration. Rafts of up to 700 or more Wedge-tailed
Shearwaters have been seen, mainly near the Ha-
waiian Islands in November when the young of the
year are fledging; the age-structure of the rafts is
not known.
FOLLOWING SHIPS.—Wedge-tailed Shearwaters
were recorded following ships 20 times. I will omit
an analysis of the other species involved in these
sightings because of the difficulty in determining if
an individual bird was actually following, or if it
NUMBER 158 67
passed aft of the ship, turned, and ran with the ship
and the other birds for a short while. Also, if the
ship provided the stimulus that led the birds to fol-
low, then the association of the various species
would be purely accidental.
There can be no doubt, however, that Wedge-
tailed Shearwaters occasionally followed ships for
30 minutes or more. They followed ships most read-
ily in November and December in the vicinity of
the Hawaiian Islands, and the birds that followed
always seemed to have very fresh plumage. They
may have been fledglings, attracted to the ship be-
cause of food smells emanating from it. Normally
Wedge-tailed Shearwaters did not follow ships, al-
though they did not seem to avoid them as did
some other species, e.g., Sooty and Slender-billed
Shearwaters.
Summary
The Wedge-tailed Shearwater breeds on numer-
ous islands in the tropical and subtropical Pacific
Ocean. The infrequent sightings of the species at
sea belie the fact that it is abundant and wide-
spread. Some of its subtropical populations per-
form extensive migrations. Birds from the Ha-
waiian Islands, for example, probably migrate
south to the Equatorial Countercurrent and then
east to the coast of Middle America during their
nonbreeding season. Molt takes place during the
nonbreeding season and is nearly completed when
the birds return to the central Pacific to breed.
Tropical populations are present at sea near their
breeding islands most of the year, and may not mi-
grate.
Consistently high densities of birds were recorded
in the vicinity of the Hawaiian Islands, in the equa-
torial current area between latitudes 4°S and 10°N,
and off the coasts of Middle America. Light-phase
birds were abundant in the central Pacific during
the northern summer and all but absent during the
northern winter; the cycle of abundance was re-
versed in the eastern Pacific. The abundance of
dark-phase birds paralleled that of light-phase birds
in the central Pacific, but alternated with light-
phase birds in the eastern Pacific. Within the equa-
torial currents birds were most abundant near the
boundaries of the Equatorial Countercurrent.
Wedge-tailed Shearwaters are gregarious when
feeding, but more solitary when traveling. Three-
quarters of the sightings in which this species was
noted feeding contained Sooty Terns; Wedge-tailed
Shearwaters may rely on the conspicuous diving be-
havior of the Sooty Terns to help them locate food.
68 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
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Appendix
Summary of published data on Wedge-tailed Shearwater distribution
Location Date Remarks Source
NORTHEAST PACIFIC
Vancouver, B. C.
EAST-CENTRAL PACIFIC
Off N Baja California
Off Manzanillo, Mexico
20°59'N, 111°57'W
19°37'N, H1°H'W
Rcvilla Gigcdos
Rcvilla Gigcdos
16°55'N, 07°23'N to
97°48'W, 112°55'W
Off Cape San Lucas.
Mexico
Off Xayarit, Mexico
Off Nicoya Peninsula,
Costa Rica
11°N, 90°55'W
Off Darien, Panama
10°18'N, 121°04'W
Clippcrton
9°46'N, 93°S0'\V
7°58'N, I08°25'W
7°N. 131 °W
7°N, 123°W
7°N, 109°W
7°N, 101°VV
7°N, 93°W
W of Panama
S of Panama
4°N, 96°30'W
3°24'N, 84°12'W
l°40'N. 86°W
l°30'N, 108c30'W
0°30'S, 120°W
NW coast of South
America
NW of Galapagos I.
Gulf of Guayaquil
6°22'S, 117°O8'W
SOUTHEAST PACIFIC
13°34'S, 103°;>9'W
23°28'S, 127O31'W
not noted hypothetical, based on 1 specimen,
questionable data
16 Dec 56 light and dark seen
24 Oct 55 8
23 Jul 05 a few
2"> Jul 05 common
not noted thousands
not noted breeds
28 Scp-18 Oct seen daily
05
not noted recorded
not noted recorded
8 Fcb 38 3 specimens, 20 miles S of Cabo
Blanco
17 Nov 56 many, all light
5 Mar 41 2 specimens at sea 5 km NW of
Enscnada, Guayabo
13 Oct 55 came aboard ship
not noted 3 specimens, 7 seen in caves and on bank
of lagoon
6 Dec 56 seen
27 Oct 55 I
9 Nov 60 25 dark, 1 pale
10 Nov 60 1 dark
12 Xov 60 1 dark, 3 pale
13 Xov 60 2 dark
14 Xov 60 10-20 dark and 10-20 pale
not noted seen
not noted seen
25 Apr 64 1 of this species or P. natwitatis
23 Nov 58 1
3 Sep 56 3
27 Apr 64 1 of this species or P. natwitatis
29 Apr 64 1 of this species or P. nativitatis
not noted occurs regularly
7 Aug 62 1 specimen
14 Mar 62 seen in numbers, light phase
23 Nov 57 1 light, probable
29 Mar 50 2 possibles, dark
9 Jul 48 3 possibles, dark
Godfrey, 1966:23
Murphy, 1958:104
King and Pylc, 1957:35
Loomis, 1918:142
Anthony, 1900:250-251
Brattstrom and Howcll, 1956:111-112
Loomis, 1918:142
Blake, 1953:10
Slud, 1964:31
Murphy, 1958:104
Wctmore, 1965:42
King and Pylc, 1957:35
Loomis, 1918:142
Murphy, 1958:104
King and Pylc, 1957:35
Morzcr Bruyns, 1965:58
Harrison in Bourne, 1959:13
Mitchell in Bourne, 1966:19
Leveque, ct al., 1966:84
Mitchell in Bourne, 1966:19
I^veque. et al., 1966:84
Lcvequc, 1964b:53-54
Gibson. 1960:16
Laird, 1951:176-177
Fleming, 1950:175
92
NUMBER 158 93
Summary of published data on Wedge-tailed Shearwater distribution—Continued
Location Date Remarks Source
NORTHWEST PACIFIC
Off Izu I. not noted not uncommon Austin and Kuroda, 1953:305
WEST-CENTRAL PACIFIC
Bonin and Volcano I. not noted
Marcus
Pescadores
Pescadores
Philippine Sea
15°57'N, 113°12'E
Philippines
Marianas
Marianas
Marianas
Carolines
7°N, 141°E
7°N, 150°E
7°N, 157°E
7°N, 157°E
10°S, 151°30'E
Off S coast of New
Guinea
New Guinea
New Guinea and
Celebes
Solomons
not noted
not noted
not noted
Apr 52
10,15,28 Jan 61
not noted
22 Aug 45
Jan-Fcb 46
not noted
not noted
29 Oct 60
30 Oct 60
31 Oct 60
1 Nov 60
4 Oct 63
3 Oct 63
not noted
Jul 29
not noted
"Comes to land in late Mar. or Apr., some
remaining until end of Nov. After breed-
ing, a few stray northward to the waters
off Japan."
may still breed
seen in May
breeds
this species or P. carneipes, sometimes in
large numbers
probables seen
a few stragglers
flocks of 21 and 41 (dark-bellied?) 100
miles S\V from Sariguan, Marianas
white-bcllicd birds, possibly this species,
off southern Marianas
breeds Aug
breeds
tlark phase in numbers up to 10
up to 6 dark at Helen Shoal
1 dark at Ngatik I.
0 dark N of Kusaie I.
several
1
1
this species or P. carneipes, very numer-
ous from X point of Celebes, easterly
toward the waters N of New Guinea
breeds
King, 1967:118
Cheng, 1955:6
Murphy, 1951:9
MacUonald and Lawford, 1954:19-20
Mitchell »>i Bourne and Radford, 1962:16
Dclacour and Mayr, 1946:21
Dixon and Starrett, 1952:269-270
Baker, 1951:65
Murphy, 1951:2
Morzcr Bruyns, 1965:58
Mitchell in Bourne, 1965:19
Rand and Gilliard, 1967:29
Jespersen, 1933:196
Murphy, 1951:2
SOUTHWEST PACIFIC
I7°S, 158°E
Near New Caledonia
23°46'S, 151°18'E
New Caledonia
New Caledonia
26°16'S, 161°24'E
27°3O'S, 154°30'E
30°55'S, 155°17'E
lasnian and Coral Seas
East Australia, Lord
Howe and Norfolk I.
Off Sydney, Australia
Off Sydney, Australia
37°41'S, 134°E
Makara, New Zealand
1
well represented
$ probables, dark
several, all dark
breeds
usually 1 or 2 in sight
24 Oct 63
18 Dec 57
16 Nov 61
Nov 28
not noted
19 Dec 57
26 Oct 63 2
20 Dec 57 some in sight all day, once in hundreds
Aug 61-Scp 62 numerous dark-phase sightings
not noted breeds Sep to Dec
21 Dec 57 seen
27 Oct 63 2
19 Apr 57 1 dark
26 Jan 62 1 specimen, white-breasted
Mitchell in Bourne, 1965:19
Gibson, 1960:18
Semple in Bourne and Radford, 1962:16
Jespersen. 1933:1%
Delacour, 1966:20
Gibson, 1960:18
Mitchell in Bourne, 1965:19
Gibson, 1960:18-19
Norris, 1967:37-38
Mathcws and Iredale, 1921:26
Gibson, 1960:19
Mitchell in Bourne, 1965:19
Gibson, 1960:12
Falla, 1962:278-279
CENTRAL PACFIC
N, E, and W of
Hawaiian I.
Feb 64-Jun 65 Abundant Mar-Nov, uncommon Dcc-Feb King. 1970:25
94 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
Summary of published data on Wedge-tailed Shearwater distribution—Continued
Location
Hawaiian I.
Hawaiian I.
Off Pearl Harbor, Oahu
150 to 350 miles WSW
of Johnston Atoll
Off Oahu
Wake
13°S0'N, 180°
Marshalls
9°55'N, 164°48'W
9°43'N, lM°5lrW
9°04'N. 143°49'W
Christmas I.
7°N, 179°E
7°N, 180°
7°N, 166°W
7°N, 152°W
7°N, 146°W
7°N, 138°W
(N of Marquesas )
6°N, 153°W
Jaluit
Phoenix
4°-02°30'S, 169°-155°E
Marquesas
SOUTH-CENTRAL PACIFIC
New Hebrides
11°S, 177°W
11°S, W W W
Samoa
Samoa
Tonga
14°30'S, 176°E
14°47'S, 170*35^
Fiji
Fiji
Tuamotus
Henderson
16°S, 178°W
16°09'S, 176°42'E
17°57'S, 169°52'E
Society
18°28'S, 172°48'W
19°30'S, 177°3O'E
19°30'S, 178°E
2O°O2'S, 175°01'W
Near Papeete, Tahiti
Near Fiji
24°S, 166°30'E
25°S, 176°30'E
Australs
Date
27 Apr 45
28 Apr 45
29 Apr 45
not noted
24 Dec 61
30 Apr 45
24 May 59
not noted
1 May 45
not noted
26 May 59
6 Oct 55
4 Oct 55
not noted
3 Nov 60
4 Nov 60 (E)
4 Nov 60 (W)
6 Nov 60
7 Nov 60
8 Nov 60
9 Dec 63
2 Nov 60
not noted
Oct 51
not noted
not noted
30 Mar 63
8 May 64
Nov 28
not noted
not noted
16 Nov 63
27 Feb 63
not noted
Nov 28
not noted
not noted
10 May 64
9 Dec 57
10 Dec 57
not noted
6 Dec 57
12 May 64
2 Feb 63
25 Feb 63
28 Nov 57
24 Mar 59
14 May 64
3 Feb 63
not noted
Remarks
11 S of Oahu
14 S of Oahu
5 near Johnston Atoll
breeds May-Nov
200 light, 3 dark
33
5
migrant (bred formerly)
2
breeds
8 of this species or P. carneipes
flock of 20
came aboard ship
breeds Feb-Nov
two groups of 200 dark
2 dark
2 dark
6 pale
3 dark
110 dark, 1 pale
1
10 dark
breeds all months
small numbers of this species or P. car-
neipes between Niutao Atoll and the
Admiralty I.
breeds
breeds Jan-Jun
3
1 of this species or P. nativitatis
several, all dark
breeds
breeds
several
1 in hand
breeds
several, all dark
breeds
breeds
1 of this species or P. nativitatis
occasional
seen
breeds
small flock, dark birds, 1 light
1 of this species or P. nativitatis
I probable
1 in hand
dark birds seen, possibly this species
seen
several
1 probable
breeds
Source
Cogswell, 1946a:47
Cogswell, 1946a:47-48
Cogswell, 1946a:48
Richardson, 1957:16
King in Bourne, 1964:19
Cogswell, 1946a:48
Peakall, 1960:199
King, 1967:111
Cogswell, 1946b:53
Amerson, 1969:295
Peakall. 1960:199
King and Pyle, 1957:35
" " "
Schrciber and Ashmole, 1970:368
Mdrzer Bruyns, 1965:58
" " " "
" »
" " •• "
" " •• »
Mitchell in Bourne, 1965:19
Mdrzer Bruyns, 1965:58
King, 1967:93
MacDonald and Lawford, 1954:19
Murphy, 1951:2
King, 1967:105
Morris in Bourne, 1965:19
Mitchell in Bourne, 1966:19
Jespersen, 1933:195-196
Murphy, 1951:2
Davidson, 1931:217-218
Mitchell in Bourne, 1965:19
Jenkins in Bourne, 1965:19
Murphy, 1951:2
Jespersen, 1933: 196
Murphy, 1951:2
>. >.
Mitchell in Bourne, 1966:19
Gibson, 1960:18
» »
Murphy, 1951:2
Gibson, 1960:17
Mitchell in Bourne, 1966:19
Morris in Bourne, 1965:19
Jenkins in Bourne, 1965:19
Gibson, 1960:17
Dixon in Bourne, 1959:11
Mitchell in Bourne, 1966:19
Morris in Bourne, 1965:19
Mnrnhv IQR1-9
NUMBER 158 95
Summary of published data on Wedge-tailed Shearwater distribution—Continued
Location Date Remarks Source
26°15'S, 176°56'W 14 Mar 47 50-60 Fleming, 1950:172
26°28'S, 176°32'W 15 Mar 47 scattered group of 15 " " "
30 °S, 175°30'E 4 Fcb 63 1 probable Morris in Bourne, 1965:19
Kermadecs not noted breeds Oct-early Jun Falla, et al., 1%7:42
Kermadecs not noted breeds Dec-May Sorensen, 1964:70
33°S, 176°30'E 5 Jun 63 2 Morris in Bourne, 1965:19
Black-footed Albatross (Diomedea nigripes)*
Gerald A. Sanger
Introduction
The material contained in this report is a sum-
mary of all at-sea observations of the Black-footed
Albatross (Diomedea nigripes) by the POBSP in
the central and eastern Pacific Ocean. Literature
records, scattered northern Pacific POBSP records,
and data obtained from POBSP island surveys are
included for general background information.
Humphrey (1965) gave a general summary of the
objectives of the program and Gould summarized
the areas surveyed and the methods and materials
used in data collection and analysis. The reader is
referred to these papers for more details.
The Black-footed Albatross is probably the most
often seen and best known of the truly pelagic
northern Pacific birds. It has been the subject of
more papers on distribution and habits at sea than
any other northern Pacific seabird. In recent years,
intensive research relating to albatross interference
with aircraft operation at Midway Atoll has been
conducted. While the breeding grounds research
has been most fruitful (Rice and Kenyon, 1962a,
1962b; Robbins, 1966), the at-sea studies, because
of their general lack of temporal and seasonal
scope, have given only general ideas of the overall
distribution and ecology.
Rice and Kenyon (1962a: 383) conservatively
estimated the world's population of Black-foots at
300,000 birds during the period 1956-1958. Rob-
bins (1966:9) noted a sharp decrease in the nesting
population at Sand Island, Midway Atoll, through
1963, but felt that there was not enough informa-
Geiald A. Sanger, National Marine Fisheries Service, North-
west Fisheries Center, 2725 Montlake Blvd. East, Seattle,
Washington 98112.
tion available on prebreeding and older "unem-
ployed" ( = not breeding) birds for a direct com-
parison with Rice and Kenyon's 1957-1958 popu-
lation estimate.
BREEDING.—The Black-footed Albatross breeds
mainly in the leeward Hawaiian chain (Rice and
Kenyon, 1962a). A small colony (ca. 20 birds) exists
on Torishima, in the Izu Islands, south of Honshu,
Japan (Aronoff, 1960).
The leeward Hawaiian Islands support breeding
Black-footed Albatross populations as shown in Ta-
ble 20. The breeding cycle (see Rice and Kenyon,
1962b) is nearly identical from island to island and
from year to year. Table 21 summarizes this infor-
mation. Breeding birds begin returning to their
islands late in October. Eggs are laid between the
middle of November and the first week of Decem-
ber; they are incubated for 66 days, and most of
the chicks have hatched by the end of January. At
TABLE 20.—Largest numbers of breeding Black-
footed Albatross populations (all derived from
POBSP data except for Kaula, which is from
Rice and Kenyon, 1962a: 377)
Location
Kure
Midway
Pearl and Hermes Reef
Lisianski
Laysan
French Frigate Shoals
Necker
Nihoa
Kaula
Number of birds
1,150"
24.000*
9,000'
4,000b
40,000"
3,100+'
375«
100«
50-
• Paper Number 72, Pacific Ocean Biological Survey Pro-
gram, Smithsonian Institution, Washington, D.C. 20560.
' Recorded.
b
 Estimated.
96
NUMBER 158 97
TABLE 21.—Timing of Black-footed Albatross
activities at breeding grounds (adapted from
Rice and Kenyon, 1962b)
Activity
Arrival
Egg-laying
Incubation
Hatching
Departure of fledged chicks
Period
6 Oct-6 Nov
3 Nov-SO Nov
peak - 21 Nov
x—65.6 days
15 Jan-7 Fcb
peak=25-26 Jan
Juii-inid-Jul*
•Parents cease visiting breeding grounds when chicks are
fledged, but no sooner.
least one parent is present with the chick continu-
ously through mid-March, when the guard state
terminates. During April and May breeding birds
are mostly at sea and return only briefly to feed
fledging young, liy June only young birds are pres-
ent all day; breeding adults return only long
enough to feed their young. Most young have
fledged and departed the islands by the middle of
July, and toward the end of July all birds are at
sea.
SUMMARY OF PUBLISHED PELAGIC OBSERVATIONS.
—The Black-footed Albatross is an abundant and
commonly seen species throughout much of the
northern Pacific Ocean. At sea it ranges from the
coasts of China, Japan, and Russia eastward to con-
tinental North America, and from the southern
Bering Sea and the Gulf of Alaska southward to
18°N off North America, occasionally to 10°N in
the central Pacific, and to 19°N off Asia.
The appendix summarizes published data on
Black-footed Albatross distribution. Papers on ob-
servations from the eastern half of the northern
Pacific outnumber those on other areas by a wide
margin; a few of these papers warrant discussion.
McHugh (1955) made a detailed analysis of
Black-foot distribution off North America in 1949-
1950. In 1949 a progressive northerly distributional
shift occurred in the spring. The population center
lay relatively close to shore off southern California
in March, close to shore north of San Francisco in
April, and off Oregon and Washington in May,
when the center showed a tendency to withdraw
from the coast and to disperse over a larger area.
Summer months generally showed a decrease in
number of birds, and a somewhat irregular distri-
bution. Birds were present in low to moderate den-
sity (x = 11-20 birds/sighting, from stopped ship)
in an area off the southern California Channel Is-
lands in August, resulting in the highest abun-
dance of the year there. In October there was a
high overall density of birds, with a broad, heavy
concentration some 200 miles off southern Oregon
and northern California. By November the popu-
lation center had shifted southward far off central
California, and overall density had diminished con-
siderably. The 1950 distribution patterns were not
clear, but the abundance peak for the entire area
was in Mardi; there was evidence of a southerly
shift of heavy concentrations of Black-foots from
southern Oregon-northern California in May, to
central California in June.
In the period June-September of 1937 and 1938,
Black-footed Albatrosses were concentrated in a
cold tongue of water off the California Channel
Islands (Miller, 1940). There were commonly 12-
15 birds at oceanographic sampling stations in the
cold tongue, but never more than five or six at sta-
tions outside this area. None were seen in the Santa
Barbara channel. Miller (1942) showed that most
Black-foots followed his ship for only a few miles.
Of 25 birds marked with paint, 12 followed the
ship for 20 miles, seven for 30 miles, three for 40
miles, and only one for 60 miles.
In 1945 Thompson (1951) observed the distribu-
tion of D. nigripes between Pearl Harbor, Hawaii,
and San Francisco, California. Most months showed
an increase in abundance as the California coast
was approached, except in June, when there was
fairly even pelagic distribution, and late November,
which showed a bimodal distribution with peaks at
ca. 125°W and 150°W, and minimums at 140°W
and 155°W. There appeared to be an inverse cor-
relation between surface water temperatures and
albatross numbers. This easterly increase was asso-
ciated with passing from the North Pacific Central
Water (Sverdrup, et al., 1942) into the California
Current between 130°W and 155°W. The maxi-
mum number of birds seen at any one time was 45
at 130°W in October. A parallel increase in alba-
tross and jellyfish abundance was observed, which
Thompson (1951) believed was a similar response
of the two organisms to the same environmental
conditions.
The Black-footed Albatross was the most com-
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
monly seen and abundant species during seven
cruises off Washington and Oregon in 1964-1965
(Sanger, 1970). They were present on 94 percent of
the 88 days spent in the area and accounted for 53
percent of all birds seen. Maximum abundance and
occurrence were in the summer, and minimums
were in the winter. Peak abundance occurred in
August 1965 when albatrosses were 2.5 times as
abundant as in the previous August. Minimum
abundance was in January 1965. Generally, num-
bers increased with distance from shore, although
the maximum number seen at a single sighting
(78) occurred just 40 miles off northern Washington
in August 1965. Generally there was no difference
in abundance or distribution between the areas off
Oregon and Washington. For data lumped for all
seven cruises there was a general increase in abun-
dance with air temperature and surface water
temperature (range: 6°-18°C.). There was no ob-
served relation between albatross numbers and sur-
face salinity, with birds found in salinities ranging
from greater than 33 parts per thousand (%«,) far
offshore to 15%o just off the mouth of the Columbia
River. There appeared to be no relationship be-
tween albatross numbers and rate of primary pro-
ductivity, although the largest number of birds in a
single sighting (78) occurred in water with the high-
est primary productivity rate of all cruises. These
data have been incorporated with the POBSP records
and are included on the distribution maps.
The literature suggests that Black-footed Alba-
trosses are less abundant, or less frequently encoun-
tered, in the western than in the eastern Pacific.
For example, Starrett and Dixon (1946) noted a
general absence of albatrosses from the southwestern
portion of their range between June 1945 and Feb-
ruary 1946, and MacDonald and Lawford (1954)
noted that flocks of Black-foots were generally
smaller in the western Pacific than the eastern Pa-
cific in 1951 and 1952.
ACKNOWLEDGMENTS.—In addition to the many
cooperators mentioned by Gould (p. 5 herein), a
number of other people gave significant aid with
this paper. Warren B. King, Robert L. Pyle, and
especially Patrick J. Gould, offered useful advice
on early drafts. Elizabeth Anthony and Charles
Sklar assisted in analyzing the CalCOFI data,
which was made available to the Pacific Program
through the generous cooperation of Carl L.
Hubbs and Robert L. Wisner of the Scripps Institu-
tion of Oceanography. Furthermore, the mass of
CalCOFI data, which is the single most intensive
pelagic record ever assembled for the species, would
not have been possible without the cooperation of
the many CalCOFI sea-going personnel who dili-
gently recorded the sightings. Among these were
Robert Counts, David Kramer, James Thrailkill,
and Andrew Vrooman, all of the National Marine
Fisheries Service, La Jolla, California. To all
of these people I express my sincere appreciation.
Distribution and Abundance
SPECIMEN RECORDS
Table 22 summarizes Black-footed Albatrosses
collected at sea by POBSP personnel. Most were
from the central Pacific; a few were from the west-
ern Aleutians and the coast of southern California.
SIGHTING RECORDS
Figures 66-77 (pp. 114—125) are monthly maps of
the average Black-footed Albatross distribution for
January 1964 through November 1967. Relative
abundance, i.e., average number of birds per sight-
ing for each day, is indicated by different degrees
of shading. Because of the ship-following habits of
the Black-footed Albatross and a consequent dis-
parity in field recording techniques for this species,
it was impossible to estimate the actual abundance
in the standard units of birds per linear mile of
travel. The disparity in field recording techniques
was mainly a failure of observers to record the num-
ber of birds at set time intervals; some observers
recorded hourly counts and others recorded at
irregular intervals, or whenever the Black-foot den-
sity changed. However, the relative abundance was
determined by using a unit of mean number of
birds per sighting (BPS) for each day the species was
seen, thus eliminating discrepancies in abundance
due to variations in recording techniques.
Three principal areas received consistently good
seasonal coverage of Black-footed Albatross distri-
bution: the central Pacific, off the southern Cali-
fornia coast to about 126°W, and off the coasts of
Washington and northern Oregon to about 140°W.
Relative abundance in the former two areas is mu-
tually comparable in every way. In the latter area,
however, many counts were made from a stopped
NUMBER 158
TABLE 22.—Black-footed Albatross specimens collected at sea by POBSP personnel
Location
47°18'N,173°13'E
47°03'N, 173°16'E
33°23'N,122°18'W
33°23'N, 122°18'W
21°23'N,167°37'W
20°58'N,158°06'W
20°56'N,158°33'W
20°49'N,158°52'W
20°23'N,161°07'W
19°28'N, 162°11'W
18°2S'N,165O12'W
18°01'N, 166°H'W
17°20'N,164°12'W
16°50'N, 169°50'W
16°38'N, 169°38'W
14°46'N,160°44'W
12°20'N,167°41'W
USNM
number
503266"
503267"
497772'
497773d
496723
493513
492911
492910
lost
493917
494145
496198
493819
495791
493512
494144
495792
Sex
_
-
9
9
9
9
S
9
9
9
9
S
9
$
S
9
Body weight
(gm)
3110++
3110+ +
-
-
2527
2802
3200
2100
2533
2900+
_
-
2610
-
2857
3000 +
2006
Gonad size
(mm)
_
-
18 x 8
18 x 8
20 x 10
23 x 15
26 x 17
30 x 14
19 x 11
25 x 17
45 x 35
27 x 5
20 x 4
22 x 25
-
14i/2x7i/2
16 x 6
11 x 6
15 x 10
Date
9 Oct 65
9 Oct 65
21 Jan 67
21 Jan 67
22 May 65
3 Jan 64
3 Dec 63
3 Dec 63
4 Jan 64
4 Feb64
9 Dec 64
9 Dec 64
6 Jan 64
15 Jan 65
12 Feb 64
8 Mar 64
22 May 65
Collector
R. DeLong
R. DeLong
B. Harrington
B. Harrington
D. H usted
-
R. Fleet
R. Fleet
-
V. Hoeman
R. Standen
M. Thompson
C. Kepler
D. H usted
-
V. Hoeman
R. Merrill
99
* Banded, U. S. Fish and Wildlife Service Number 737^*5577 (adult, sex unknown, 8 Nov 63,
Green Island, Kure Atoll).
b
 Banded, U. S. Fish and Wildlife Service Number 697-73041
1
 Banded, U. S. Fish and Wildlife Service Number 757-26257 (local, sex unknown, 12 Jun 66,
East Island, French Frigate Shoals).
d
 Banded, U. S. Fish and Wildlife Service Number 767-42423 (nestling, sex unknown, 19 Mar
63, Crass Island, Pearl and Hermes Reef).
ship, a fact that may make the counts seem large
compared to the other areas due to the increased
attraction stopped ships have for Black-foots. All
mileage figures refer to statute miles.
January Distribution (Figure 66): The densest
concentration of birds occurred in the central Pa-
cific across a broad front at ca. 25°N, between
148°W and 157°W; however, there were no ob-
servations along the leeward Hawaiian Islands.
Black-foots occurred in most of the area off Cali-
fornia farther than 75 miles off the coast, and in
areas farther than 100 to 200 miles off the coasts of
Oregon and Washington.
February Distribution (Figure 67): In the central
Pacific, birds were seen in fair numbers as far south
as 11°N, 151 °W, although they were peculiarly
absent a few longitudinal degrees in either direc-
tion. Concentrations were still found across the
front at 25°N; no observations were conducted in
the Leewards. Scattered birds were seen south to
13°N, 170°W, although there was a conspicuous
absence of Black-foots at similar latitudes between
153°W and 168°W. Off California, overall densi-
ties decreased from January; a few birds were ob-
served within 30 miles of the coast. Scattered birds
were seen between northern Washington and 53 °N
in the Gulf of Alaska; these sightings apparently
represent the northernmost winter records for the
species.
March Distribution (Figure 68): During March,
observations were extended westward along the lee-
ward Hawaiian Islands. Correspondingly, ex-
tremely dense concentrations of Diomedea nigripes
were seen in areas near the breeding islands. A
maximum of 56 BPS was seen near Laysan Island.
No Black-footed Albatrosses were seen south of
31 °N in the area off California; a few birds were
encountered within 25 miles of the coast. No ob-
servations were conducted off Washington or Ore-
gon.
April Distribution (Figure 69): Due to two
cruises between Hawaii and North America, cover-
100 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
age this month was quite broad in area, although
the Leewards area was not included. A localized
concentration of 10-20 BPS was found some 100
miles north of the main Hawaiian Islands, but the
bulk of the Black-foot population was seen north
of 25°N. A relatively small concentration of birds
was centered at 148°W, 28°N, but between here
and northeastward to 130°W, distribution was re-
markably uniform. Off southern California, overall
densities remained essentially unchanged from
March; scattered birds were seen within 25 miles of
shore. Between the area off southern California
and Oregon, distribution is largely speculative, be-
cause noon positions were so far apart. However,
there apparently was a broad band (5° wide) of
5-10 BPS density off northern California and Ore-
gon between ca. 127°W and 132°W, with lesser
densities to either side. The densest concentrations
this month occurred off Washington and northern
Oregon.
May Distribution (Figure 70): The most evident
feature of May distribution in the central Pacific
was the continued northward withdrawal of the
population to 20°N. A lone bird was encountered
at ca. 13°N. Concentrations were centered at French
Frigate Shoals, and some 450 miles northwest of the
main Hawaiian Islands. Distribution off California
was quite uniform at 2-5 BPS across most of the
area. There were no observations off the Washing-
ton-Oregon coasts.
June Distribution (Figure 71): A continued
northward withdrawal of the population in the
central Pacific was evident this month; the southern
limits were at 21 °N, 160°W, although two widely
scattered individuals were seen at the 16°N parallel.
The species was observed along the Leewards as
far west as Lisianski Island. Off southern Califor-
nia, the overall density diminished greatly. A bi-
modal distribution was evident off Washington and
Oregon, with concentrations of birds found rela-
tively close to shore off northern Oregon and 400
miles off northern Washington.
July Distribution (Figure 72): The Black-foot
population continued to move northward, with
28° N marking the southern range limits. Ten to
twenty BPS densities were seen some 1000 miles due
west of San Francisco, with an apparent density de-
crease toward the southern California coast. A bi-
modal distribution was noted off southern Califor-
nia. Concentrations of 10 to 20 BPS were seen
within 75 miles of the coasts of Washington and
Oregon.
August Distribution (Figure 73): In the central
Pacific, Black-foots were found still farther north
than during the previous months. Overall abun-
dance off southern California declined slightly. Dio-
medea tiigripes was very abundant off the Washing-
ton and Oregon coasts; about half of the region
was populated with birds in 10 to 20 BPS densities
and a general increase in abundance with distance
from shore was noted.
September Distribution (Figure 74): In the cen-
tral Pacific two widely separated individuals were
sighted near Midway Atoll and at 04°S0'N, 174°W;
the latter sighting is the southern record for the
species, excluding the two strays in the southern
hemisphere (Oliver, 1955:181). Overall abundance
off southern California decreased markedly; a few
Black-foots were seen within 20 miles of shore. A
region near the western Aleutians was censused this
month and low concentrations were encountered
over most of the area. There was no observation
off the Washington-Oregon coast.
October Distribution (Figure 75): Only one Dio-
media nigripes was found in the central Pacific this
month, near Gardner Pinnacles; however, areal
coverage was scanty. Farther north, among and
south of the western Aleutians, low densities were
still encountered over most of the area. Overall
abundance off Washington and Oregon diminished
markedly from August, and Diomedea nigripes
numbers were distributed erratically in the region
off southern California.
November Distribution (Figure 76): The species
had again returned in some numbers to the central
Pacific area, south to 19°N. There was a pro-
nounced decrease in overall abundance off Califor-
nia, while the region off Washington and Oregon
showed an increase in Black-foots between 134°W
and 139°W.
December Distribution (Figure 77): The popu-
lation level in the central Pacific increased to an
observed all-time high this month. As would be
expected, maximum concentrations were found
among the leeward Hawaiian breeding islands. Off
California, overall density showed an increase over
November, and two days of observations off the
Washington-Oregon coast revealed a few birds off
Oregon but none within 50 miles of the Washing-
ton coast.
NUMBER 158 101
- 35'
40°
35°
30°
25°
20°
V*'
\
\
\
\
\
\
\
\
\
\
-
-
125°
' 1 '
\
\ \\ N\\
V
\
\
\
\
\
1
CAPE
MEN0OCIN0
\
" V\
120°
1
BLACK
LOCATION
N
SAN
FRANCISCO
N
\
N
POINT
s CONCEPTION
• \ ^ \
\
i
115° 110°
, . . . . 1
^% A 1 f\ S\ ^^ •
CALCOFI
FOOTED ALBATROSS DATA
OF BLOCKS (AFTER McHUGH,1955)
-
N
S
\
SAN /
• DIEGO /
. \ X . . . i
- 40°
- 30"
- 25"
125° 120° 115° 110s
FIGURE 58.—Location of area blocks for analysis of CalCOFI Black-footed Albatross distribution.
BLOCK 10
BLOCK 13
£ 10
J ! J J
Z
~ BLOCK 16
y • ,N ? r MJ F M A M J J A S O N D J F M A M J J A S O N O J J F M A M J J A S O N D
1951 1952 1953
BLOCK 10
I J
BLOCK 13
20-i
s BLOCK 16
<20-i
10-
? • . , 1 I *, ? \
J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S 0 N 0
BLOCK 10
a: BLOCK 13
* 10"
M t i -V4-*
S ^ BLOCK 16
20
f^  i—i—i—r
i F M A M J J A S O N D J F M A M J J A S O N O J F M A M J J A S O N O
1957 1958 1959
NUMBER 158 103
BAND RETURN INFORMATION
Robbins and Rice (pp. 232-271 herein) made a
detailed analysis of at-sea band returns of Black-
footed and Laysan albatrosses including POBSP rec-
ords. No young Black-foots were captured in the
leeward Hawaiian Islands during their first winter
of life, but some were captured within a couple of
hundred miles of both Japan and the United
States. As the birds grew older (through their
fourth summer), there was an increasing tendency
for band recoveries to occur farther north and east
in summer, and closer to the Leewards breeding is-
lands in winter. Once the birds reached breeding
age, there was only a slight tendency for more re-
coveries to occur off North America in summer
than off Japan. The relative chances of a tagged
bird being caught in either area are unknown.
There are a number of POBSP band returns from
various breeding islands from birds that were
originally banded on other breeding islands. Thus,
this species exhibits some interisland movement;
the individuals involved are probably prebreeders.
DISTRIBUTION OFF CALIFORNIA AND
BAJA CALIFORNIA, 1951-1959
In 1949, an interagency oceanographic research
program known as the California Cooperative
Oceanic Fisheries Investigations (CalCOFI) "was
established as a broad and thoughtful inquiry into
the environment and the biology of the California
Current system" (Ahlstrom, et al., 1967:5). As a
regular part of routine survey cruises, the number
of Black-footed Albatrosses congregating around
the ships was counted at each sampling station.
Black-foot distribution has been analyzed for only
the first two years of these data (McHugh, 1955),
although the albatross counts continued through
April 1959. Data subsequent to 1950 are analyzed
and discussed here for the first time.
McHugh's (1955) method of analyzing the data
was, for the most part, used herein. The survey
area was divided into the same series of blocks
(Figure 58), and the monthly average of the num-
ber of Diomedea nigripes counted at each station
«*-
FIGURE 59.—Real time graphs of the BPSt for inshore
blocks: a, 1951-1953; b, 1954-1956; c, 1957-1959. (Numbers
on graphs indicate number of stations contributing to BPSt.)
within a block was calculated as mean number of
birds per station (BPSt), using the maximum num-
ber of birds seen at any one time during a station
and including "zero counts." McHugh (1955) dis-
cusses the reasons for averaging the counts from
stations within the blocks, rather than considering
individual counts at each station. An atlas-type
presentation of monthly distribution maps such as
McHugh (1955) used would be impractical in this
paper because of the large amount of data involved.
Therefore the blocks were divided into three north-
south strips, inshore (blocks 4, 7, 10, etc.), inter-
mediate (blocks 5, 8, 11, etc.), and offshore (blocks
6, 9, 12, etc.). The seasonal changes in abundance
within individual blocks have been analyzed, as
well as changes within the entire strips.
SEASONAL CHANGES IN ABUNDANCE WITHIN AND
AMONG INDIVIDUAL BLOCKS.—Seasonal fluctuations
in birds per station were examined in blocks with
the most intensive coverage. These were blocks 10,
13, and 16 in the inshore strip, and 11, 14, and 17
in the intermediate strip. Blocks 12 and 15 in the
offshore strip were also considered in this manner
because of their proximity to the other blocks, al-
though their coverage was poor. Real time graphs
of the BPSt in the inshore blocks are presented in
Figure 59, in the intermediate blocks in Figure 60,
and in the offshore blocks in Figure 61. In the in-
shore blocks (10, 13, 16) a north-south density cline
is quite evident, as are seasonal cycles in abun-
dance, with peak numbers occurring in late spring-
early summer, especially in block 10. A study of
the intermediate blocks (11, 14, 17) shows that Dio-
medea nigripes was generally more abundant there
than closer inshore. Also evident during most of
the period is a north-south population cline (re-
gardless of year or season) and seasonal abundance
cycles, with maximum numbers occurring in late
spring and early summer. Figure 61 indicates that
the highest numbers of Black-footed Albatrosses in
the entire area may have occurred farthest off the
coast. However, the scanty coverage, both in time
and in number of stations, precludes direct com-
parisons with the blocks closer to shore.
OVERALL DISTRIBUTION AND ABUNDANCE.—Tem-
poral changes in albatross abundance within each
of the north-south strips are presented as con-
toured density real time diagrams (Figure 62) . By
simultaneously examining the diagrams for all
three strips it is possible to see changes in distribu-
20-
lfr
o
§ 0
BLOCK 11
* BLOCK 142O
S- 10-
S BLOCK 17
« 20-
10-
j T M A M j ) A S 6 N 6 j F M A M j j A S 6 N 6 i F M A M i i A S 0 N 0i iJ
1951 1952 19b3
BLOCK 11
J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O H D
20-
10-
o
£ o
BLOCK 11
i 1 1 r—i 1 r
£ BLOCK 14
u, BLOCK 17
3 20-.
10-
v' . 1 t/\f
^ * * i" i A S 6 N 6 j F M A M j j A S T o N 0 j F M A M j j A S 6 N 6
1957 1958 1959
NUMBER 158
BLOCK 12
105
J F M A M J j A S O N 0 J F M A M J J A S O H D J F M A M J J A S O N D
•1951 -1952 -1953
* 1 9 5 4 * 1955 "1956
o l 9 5 «
FIGURE 61.—Real time graphs of the BPSt for offshore blocks 1951-1956 and 1958.
(Numbers on graphs indicate number of stations contributing to BPSt.)
tion and to infer movement among the three areas.
There are a number of salient features to the distri-
bution and abundance evident in each of the strips.
Inshore Strip (upper diagram in Figure 62):
Seasonal cycles in abundance are apparent for most
years, especially north of Point Conception, Califor-
nia. Black-foots occurred in concentrations of 5 to
10 BPSt mostly between April and July; other
months they were absent, or present in concentra-
tions of 5 BPSt or less. Off southern California they
were generally absent most of the year, but a few
birds showed up sporadically. The year 1958 was
unique in that Black-foots occurred in this area con-
tinuously from March through September (except
for June), although mostly in densities of 1 BPSt or
less. In strong contrast, Black-foots occurred during
most months north of Point Conception and off
northern Baja California.
Concentrations as high as 10-20 BPSt occurred
only north of Point Conception; indeed, south of
here densities of 5 BPSt or less occurred most of the
time. Also quite evident each year was an absence
FIGURE 60.—Real time graphs of the BPSt for intermediate*
blocks: «, 1951-1953; b, 1954-1956; c, 1957-1959. (Numbers
on graphs indicate number of stations contributing to BPSt.)
of birds between 24°N and 30°N in late summer or
early fall. This could be due to either a northward
migration, or a progressive northward withdrawal
to seaward from these latitudes. This phenomenon
culminated in a complete withdrawal from the in-
shore strip in the fall and winter of 1952-1953
and 1955-1956.
Intermediate Strip (middle diagram in Figure
62): The most striking feature here is that Black-
footed Albatrosses were continuously present in at
least part of this zone for the entire 100-month
period (no stations were occupied in October and
November 1956). There appeared to be a trend for
maximum density to occur between April and July,
although in 1955 Black-foot densities of 10-20 BPSt
lingered until October north of 32°N. Relatively
few birds were found in the strip in August through
March. Densities of greater than 10 BPSt were rarely
encountered south of ca. 32°N; when they did oc-
cur, usually as somewhat anomalous groups, it was
from June through August (e.g., at 30°N in August
1952 and June-July 1954). Evident in most years in
varying degrees was an exodus from, and return to,
the area south of 30° N, from late summer to early
winter in the same manner as in the inshore strip.
This movement generally started in September
south of 25° N and progressed northward to 30°N,
J F M A W J J A S O M D I F H » H i 1 » j 6 » 6
S l P O t P E R S T A T
• E23 ED • •
NUMBER 158 107
where it peaked in October or November. In De-
cember and January low numbers of Diomedea
nigripes returned to the southern end of the strip
but another brief evacuation from the southern-
most degrees usually followed. This phenomenon
occurred every year for which data are available,
except 1958-1959.
At or south of 25°N anomalous patches of 5-10
Bpst densities frequently occurred from June
through August; examples of this were observed in
July-August 1953, June 1955, June-July 1956, and
June 1957.
Offshore Strip (lower diagram, Figure 62): As
seen in the figures, coverage in the offshore strip
was quite spotty compared with those closer to
shore, but a few salient features of distribution and
abundance are evident. Densities of more than 20
upst occurred with greater frequency in this strip
than in either the inshore or the intermediate zones.
There also seems to be a tendency for high densi-
ties to occur farther south in this strip than in the
other two. These high densities occurred quite er-
ratically, and with no apparent evidence of the cy-
cles which were displayed in the other two strips.
Discussion: South of Point Conception, the rela-
tive abundance among the three strips indicates a
general increase in abundance with distance from
shore, but north of here there is no consistent pat-
tern. A more uniform pattern of distribution among
the strips is evident, and sometimes there is even a
decrease in abundance with distance from shore.
Indeed, north of Point Conception, maximum
densities among the strips occurred within the in-
shore strip in June and/or July of 1952, 1953, 1955,
and 1956.
ABUNDANCE AT WEATHER STATION Victor
Personnel aboard the USCGC Winnebagq kept a
record of albatross numbers seen while the ship was
positioned at Ocean Weather Station Victor (34°N,
164°E) from 26 February through 19 March 1967.
Figure 63 presents the results of this record. The
most birds seen at any time during the day (upper
graph) ranged from a low of 2 on 17 March to highs
FIGURE 62.—Contoured density real time diagrams of BPSt
in inshore, intermediate, and offshore blocks: a, 1951-1953;
b, 1954-1956; c, 1957-1959.
of 31 birds on 1 March and 30 birds on 12 March.
There appeared to be a cycle in numbers of birds,
changing from low to high numbers at 5-7-day in-
tervals. The bottom graph of Figure 63 shows that
the maximum number of birds usually occurred in
the afternoon (1600), but never occurred in the
morning (0800).
Analysis of Distribution
GENERAL CONSIDERATIONS
Two major trends in the distribution of Black-
footed Albatrosses are evident. First, there is a ma-
jor latitudinal population shift coincident with the
breeding season, i.e., the birds are in the southern
part of their pelagic range in winter (breeding sea-
son), and in the northern part of their range in
summer (Figure 64). This is especially evident in
the central Pacific. However, because there is con-
siderable spatial overlap between the two ranges,
and some birds are well north as early as April and
as late as October, there are Black-foots throughout
most of the absolute range at any given time of the
year. Secondly, the evidence suggests that this spe-
cies is predominantly an eastern Pacific bird, al-
though a part of the population regularly occurs
west of 180°. For example, the numbers of birds
seen in single sightings in the northeastern Pacific
are far in excess of similar counts for the north-
western Pacific. Examples of this are: 70 birds 40
miles off San Francisco Bay (McHugh, 1950); 125
birds some 1000 miles southwest of San Francisco,
and 53 Black-foots 465 miles off Oregon (Yocom,
1947), 78 birds 40 miles off northern Washington
(Sanger, 1970); and 100 Black-footed Albatrosses at
Unimak Pass in the Aleutians (ca. 165°W, 54°N)
(Arnold, 1948). Although similar counts for the
western Pacific are scarce, those available show far
lower numbers; Kuroda (1955) saw a maximum of
11 birds 240 miles east of Hokkaido during his sum-
mer observations, and Wilhoft (1961) had a maxi-
mum cumulative daily total of only 70 birds, some
100 miles northwest of Luzon in the Philippines.
Furthermore, a general scarcity of Black-foots has
been noted in the western Pacific at various seasons
(Starrett and Dixon, 1946; Aronoff, 1960). Trans-
Pacific observations (MacDonald and Lawford, 1954;
Nakamura, 1963) have revealed generally more
Black-foots in the eastern Pacific than in the west
108 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
30
25
20
15
10
(A)
Birds seen at
. . . . 0800hours
— 1200 hours
— —1600 hours
26 27 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
February March
1967
FIGURE 63.—Fluctuation in Black-footed Albatross numbers at Ocean Weather Station Victor
(WOCN. 164°00'E).
Seasonal Variation in the Range of
Black-Footed Albatross
E D Summer (July)
£Z2 Winter (February)
HOE 130 150 170 170 150 130 110
FIGURE 64.—Seasonal variation in the range of the Black-footed Albatross.
TON
(although Austin and Kuroda [1953:299-300] stated
that this albatross is common off Japan from April
to November, and Hamilton [1958] observed that
in June 1955 they were more abundant between
Japan and 180° than east of there). Perhaps the
most convincing evidence that the majority of the
population prefers eastern Pacific waters is ob-
tained from banding studies. Robbins and Rice
(pp. 237-238) reveal that band recoveries of pre-
breeding young showed a marked tendency to occur
in the eastern half of the Pacific in all seasons, as
did those for adults during winter. In summer, how-
ever, band recoveries of adults occurred with nearly
equal frequency off North America and Asia. The
relative chances for recovering banded birds in
these two areas of the Pacific are unknown.
SEASONAL AND MONTHLY VARIATIONS
Starting in late fall, adult birds begin arriving at
the breeding grounds. This would explain, at least
in part, the sharp reduction in the number of
Black-foots off Washington and Oregon between
August and October. The regular late summer-early
fall reduction in numbers off southern California
and Baja California may be partly due to adult
birds leaving for the breeding islands. Except for
copulation, breeding activities do not require the
simultaneous presence of both parents. "Incubation
spans" range up to 18 days, and "guard spans" last
about 21/2 days (Rice and Kenyon, 1962b). When
the guard stage ends in late February, both parents
leave the island, returning only briefly to feed the
110 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
fledging young. Thus, even during the breeding
season, about half of the breeding birds are at sea.
It is uncertain how far parents range from breed-
ing sites, but they probably remain within 1500 to
2000 miles. Evidence to this effect is a dramatic
buildup at sea during the breeding season in areas
near the main Hawaiian Islands, some 1500 miles
east and southeast of the major breeding areas on
the Leewards. Robbins and Rice (Figure 148)
indicate a host of band returns of adult birds from
December through March between 155°E and
170°W, along the latitude of 30°N, and very few
elsewhere. This further suggests the tendency for
adults to range as indicated above. The Black-foots
that occur off Washington, Oregon, and southern
California in winter are probably largely nonbreed-
ing immatures, but it is physically possible for the
parents to range for food as far away from the
breeding grounds as the North American Pacific
Coast and return to the breeding grounds within
two to three weeks.
Although parent birds are gathering food for the
young, and presumably for themselves, they appar-
ently exist under a progressive nutritional deficit
during the breeding season. Frings and Frings
(1961) noted that the weight of adult Black-footed
Albatrosses decreased by about 8 percent over a two-
week period in early egg-laying and nesting stages,
presumably because of a reduction in heavy fat de-
posits which birds have prior to that time.
Woodward (POBSP) shows a dramatic decrease in
the number of nonbreeding Black-foots during
March and April on Kure Atoll. By late February
most breeders are away from the atoll most of the
time. The general exodus of birds from breeding is-
lands which takes place in March and April may
explain the regular April-May ingression of birds
into the area off California as noted in the Cal-
COFI data. McHugh's (1955) 1949 distribution
data certainly suggest a northeastward movement
away from the breeding grounds, followed by, and
coincident with, a northward movement paralleling
the coast. The timing of this movement corresponds
to the subsequent CalCOFI data reported here.
After the young albatrosses are fledged in early
July, the adults stay away from the breeding
grounds permanently and disperse throughout their
range. Their distribution is probably governed by
the distribution of food organisms, concentrations
of which, at least in the case of immature birds, are
possibly found only by random searching.
Overall movements, as indicated earlier in the
literature review, show that some birds are in the
area of the Aleutians as early as May (Gabrielson
and Lincoln, 1959:74), and as late as November
(Kenyon, 1950). There seems to be no clear-cut
trend in the winter movements in the far northeast
Pacific. Rice and Kenyon (1962a) estimated that
about 14 percent of the Black-foot population (one-
and two-year-old birds) winter at sea.
DISTRIBUTION IN RELATION TO THE ENVIRONMENT
CURRENTS AND WATER MASSES.—The southern
limits of Black-foot distribution generally coincide
with the southwestern sweep of the California Cur-
rent in the eastern Pacific Ocean off Baja Califor-
nia and the North Equatorial Current in the cen-
tral Pacific Ocean. Although there are few data
available for the western Pacific it seems likely that
Black-foots usually do not range south or west of
the North Pacific or the Kuroshio Currents, which
may explain the scarcity of birds reported by Star-
rett and Dixon (1946). La Touche (1934) and
Cheng (1955) both stated that this species occurs
off China. It is common in the Bering Sea in sum-
mer, considerably north of the major northerly
currents, the West Wind Drift and the Alaskan
Stream. In winter the species apparently does not
range very far north of the Kuroshio-Oyashio con-
vergence in the northwest Pacific, nor of the sub-
arctic current (ca. 50°-55°N) in the northeastern
Pacific.
Thompson (1951) found that Black-foots tended
to be more abundant in the California Current off
California than in eastern North Pacific Central
Water. Within the California Current, Miller
(1942) found Black-foots concentrated within
"tongues" of cold water off the southern California
Channel Islands. Sverdrup, et al. (1942) explain that
these tongues are caused by intense upwelling of
deep water along the coast which are swept south-
ward along the surface by the California Current.
The point of upwelling in Miller's description
would have been at Point Conception, California.
Reid, et al. (1958:30) note that upwelling along
the North American coast is seasonal, being
"strongest off Baja California in April and May, off
southern and central California in May and June,
NUMBER 158 111
off northern California in June and July, and off
Oregon in August." Thus, while the initial increase
in abundance of Black-foots close to the central
California coast (north of Point Conception) is cor-
related with the departure of adults and nonbreed-
ing birds from the breeding islands in March and
April, it seems quite possible that this high density
of Black-foots is prolonged by the enriching process
of upwelling in May and June. Further, the de-
crease in upwelling off the central California coast
in July might well be a factor in the reduction in
Black-foot numbers usually noted at this time.
Farther north off Oregon, upwelling also occurs
close to the coast in August, and Black-footed Alba-
trosses are apparently concentrated there then
(Gerard Bertrand [Oregon State University], pers.
comm.). The large concentrations of birds found
by Yocom (1947) are well within the California Cur-
rent, but the observed abundance was probably dis-
torted by the fact that his ship spent several days
in the same location, thus creating a strong attrac-
tion factor.
Sanger (1970) observed a concentration of 78
Black-footed Albatrosses relatively close to shore
over the continental shelf in August 1965, but over
an 18-month period there was a general increase
in abundance with increasing distance from shore;
however, observations in nearshore areas may have
been inadequate for a direct comparison with off-
shore data. P. W. Martin (1942) implied an abun-
dance of Black-foots off British Columbia in sum-
mer over offshore banks. The large concentration
of birds observed in Unimak Pass in the Aleutians
(Arnold, 1948) could well have been coincident with
local island-induced upwelling or tidal currents. In
the western Pacific, Kuroda (1955) saw his highest
numbers of Diomedea nigripes in the coastal waters
off Honshu, approximately west of the Kuroshio-
Oyashio convergence, in June and July.
SURFACE WATER TEMPERATURE.—There has been
much discussion on the relationship between Black-
footed Albatross distribution and surface water tem-
peratures. Kuroda (1955) considered the species to
be warm water adapted in his study of the birds be-
tween Japan and the western Bering Sea. Thomp-
son (1951) observed a seeming inverse correlation
between temperature (mostly 15°-25°C) and alba-
tross numbers between Oahu and California.
Hamilton (1958), Wilhoft (1961), and Nakamura
(1963) all present temperature data which are in-
conclusive. In oceanic waters off Washington and
Oregon, relatively high surface water temperatures
(range over 18-month period, ca. 6°-17°C) were
associated with relatively large numbers of Black-
foots, and low temperatures were associated with
small numbers (Sanger, 1970). In the central Pa-
cific near the main Hawaiian Islands, King (1970:
91) observed Black-foots in low densities when sur-
face water temperatures were greater than 23°C
(range of ca. 22°-27°C).
The POBSP data correlating water temperature
and albatross occurrence show no clear-cut trends
for individual months; sample sizes (number of
days of observation) are often small and the data
are therefore insufficient to present graphically. In
most months the data apparently simply reflect the
range of surface temperatures encountered on the
cruises. The only month that indicates a trend at
all is March, which shows an inverse correlation
between Black-foot numbers and water tempera-
tures from 20° to 28°C. This is in line with tem-
perature data of King (1970) and Sanger (1970),
which suggest that the species is most often found
in relationship to surface water temperatures rang-
ing from ca. 14° to 22°C.
A detailed analysis of the relationship of alba-
tross abundance and water temperatures in the
CalCOFI area is beyond the scope of this paper;
however, a few brief generalizations can be made.
Ten-meter water temperatures were obtained at the
same time the albatross counts were made (Cali-
fornia Marine Research Committee, 1963). The
warmest temperatures generally occurred off south-
ern California and Baja California in September
and October, followed by rapid cooling through
March. Off southern Baja California (ca. 26°30'N
in the inshore strip), the 10-year mean October IO-
meter temperature was 23°C; it can reasonably be
assumed that the surface temperature was warmer
by a few, perhaps several, degrees. Thus, the usual
fall evacuation by Black-foots from the zone south
of 30°N in the inshore and intermediate strips may
have been the result of a negative reaction by the
birds to increased water temperatures. Similarly,
the fact that the birds consistently reentered this
zone in winter may have been a result of cooling
water temperatures. Just off Point Conception
(CalCOFI station 80.60), the coldest 10-meter tem-
peratures occurred between February and May (10-
year mean ca. 12.5°C), and the warmest from Au-
112
120 140 160 180 160
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
120 100 80
120 140
FICURF. 65.—The area bounded by the surface isotherms of 14° and 22°C
(after Muromtsev. 1958).
gust through October (10-year mean ca. 17.5°C).
The peak Black-foot numbers occur just north of
here as the water temperature is warming (in June),
although the entire annual range of temperatures
is within the "preferred" temperature range noted
above.
The apparent disparity in abundance of the
Black-footed Albatross between the western Pacific
(fewer birds) and the eastern Pacific (more birds)
may possibly be explained by the species' apparent
preference for a certain range of surface water tem-
peratures. It was noted above that Black-foots were
most often found within a surface temperature
range of ca. 14° to 22°C. Assuming that the species
disperses randomly within, and actively associates
with, waters in this temperature range, one would
expect to find more birds in the eastern Pacific than
in the western Pacific. Figure 65, the average sum-
mer surface temperature in the North Pacific (after
Muromtzev, 1958), shows that the region encom-
passed by the isotherms of 14° and 22°C is more
than two times as large east of 170°W than west of
that meridian. Thus, if the Black-foot indeed does
actively associate within a 14° to 22°C surface wa-
ter temperature range, one would expect most of
the population to be found in the eastern north
Pacific.
The absolute range of surface water temperature
in which this species has been observed is from
3.4°C in the Gulf of Alaska in March 1967 (Uni-
versity of Washington data), to 30°C in the western
Central Pacific in August 1960 (Wilhoft, 1961).
SURFACE SALINITY.—King (1970) observed an ap-
parent direct relationship between Black-foot num-
bers and surface salinity in the central Pacific
(within a range of ca. 33.5%, to 35.0%,). He felt,
however, that this resulted from the fact that,
within his study area, the species' geographic range
occurred north of waters with a lower surface salin-
ity. Off the Washington and Oregon coasts there
was no observable relationship between Black-foot
numbers and surface salinity (Sanger, 1970), al-
though Black-foots were occasionally found in sa-
linities far below normal sea water salinities (e.g.,
14.98%.).
AIR TEMPERATURE.—Air temperatures are closely
correlated with ambient surface water temperatures
in the ocean. One would expect, therefore, to find
similar relationships between Black-foot numbers
and these two parameters, and this indeed is the
case. King (1970:89) observed a pronounced inverse
correlation between air temperatures and Black-
foot numbers from 16° through 29°C. Few birds
were seen at temperatures warmer than 22°C, and
none above 27 °C. Sanger (1970) noted a direct re-
lationship between air temperature and Black-foot
abundance within a range of 7° to 18°C, and
Kuroda (1960) believed that within an overall
range of 7.0° to 22.5°C the species preferred air
temperatures from 17° to 22.5°C.
NUMBER 158
WEATHER CONSIDERATIONS.—Wind is probably
the most significant feature of the weather affecting
albatross distribution. Since albatrosses are depend-
ent upon the wind for mobility, it stands to reason
that they would avoid, or be found in lesser num-
bers in, areas with wind velocities insufficient or
marginal to maintain their sailing flight. The aver-
age wind velocity decreases as the equator is ap-
proached and the doldrum wind conditions are en-
countered; this fact no doubt plays a significant role
in limiting the southern distribution of the Black-
footed Albatross. High winds apparently have little
or no adverse effect on the Black-foot, since the
species has been noted sailing in winds as high as
113
70 knots (80 MPH) with no apparent ill effects
(Sanger, 1970).
Addendum
After this paper was written in 1968, the impor-
tant paper of V. P. Shuntov (1968) came to my at-
tention. It is in general agreement with the findings
reported here that the Black-footed Albatross is pri-
marily a species of the eastern north Pacific, but
with some of the population occurring in the west-
ern part. Shuntov indicates the Black-foot ranges in
summer and autumn into the Sea of Okhotsk and
north into the western Bering Sea to the Gulf of
Anadyr, but not as far south in winter as our rec-
ords in the central Pacific indicate.
114 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
NUMBER 158 115
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124 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
NUMBER 158 125
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Appendix
Summary of published data on Black-footed Albatross distribution
Location Date Remarks Source
NORTHEAST PACIFIC
Point Barrow, Alaska
Gulf of Alaska and
Bering Sea
Between Unalaska and
the Pribilofs, Bering
Sea
llnimak Pass, Aleutians
Bristol Bay, Alaska
From S of Shumagin I.
(Alaska), W into south-
ern Bering Sea at
75 mi N Seguam I.
From 47 mi NVV Semiso-
pochnoi I., Aleutians,
to 30 mi W Cape
Spencer, Alaska
Southern Bering Sea
000 mi SE Unalaska to
the Farallon I. off
San Francisco
Great Circle route, San
Francisco to Yokoha-
ma, return via Hono-
lulu to Los Angeles
Off British Columbia
and in Gulf of Alaska
British Columbia
Off British Columbia
60 mi inside Str. of Juan
de Fuca, Washington
51°44'N, 138°48'W-
49°5G'\, 128°16'\V
Washington
Trans-Pacific and off
Washington
5-11Jul 1898 the authors note, without comment, 11 Gabrielson and Lincoln, 1959:74
specimens reportedly collected here;
since the expedition during which these
birds were collected was in the north
Pacific 5-11 July 1897, it seems possible
that specimens were collected then and
not a year later at the extremely extra-
limital site of Point Barrow
May-Oct
Jul 47
9Jun43
no date
8-11 Jun43
some present in this area
100 at once
ranges nearly to 58°N in this region
continuous between these points
20Jun-10 Aug continuously seen in this area
43
Oct 47, Nov 48,
May 49
Nov 48 continuously in sight, following ship; up
to 10 seen at once
Aug 59, Mar 61 abundance slightly higher in NE Pacific
than NVV; maximum at once, 11 at
155°W on Great Circle route, 14 at
164°E on return
Sep 52-May 54 seen each of live cruises, most common
Sep-Oct, least common Nov-Dec
no date in pelagic waters; numbers increase as
spring progresses, a tendency to flock
in summer
Apr-late Sep "constant companion of fishermen on off-
shore banks"
no date 1
25 Jul 44-27 4-10 seen daily
Jul 55
14 Apr-30Oct "a common migrant or wanderer"
"well offshore"
Jun 55 numbers ranged from 0 at 180° to ca.
7.5/hr off Washington; mean daily
abundance 8.5 over six days E of 180°
Kenyon, 1950:98
Arnold, 1948:556-557
Murie, 1959:35
Arnold, 1948:556-557
Kenyon, 1950:98
Kenyon, 1950:97
Nakamura, 1963:239-245
Poole, 1966:71
Godfrey, 1966:20-21
Martin, 1942:27
Poole, 1966:71
Motoda and Fujii, 1956, t.3
Jewctt, et al., 1953:66
Hamilton, 1958:160-162
126
NUMBER 158 127
Summary of published data on Black-footed Albatross distribution—Continued
Location Date Remarks Source
48°27'N, 126°32'W-
43°08'N, 179°08'W
Cobb Scamount, 290 mi
off Washington
Off Washington and
Oregon
Central California to
northern Washington
Southern California to
northern Washington
Off Washington and
Oregon
100 mi off Washington
Oregon
Off central and northern
California
130° W off San Francisco
EAST-CENTRAL PACIFIC
California
Off southern California
Southern California
9-20 Aug 55
Aug50
1964-1965
1949-1950
Dec 48
1963
Feb-MarSl
apparently reg-
ular summer
visitors
1949
Oct 45
apparent in-
crease during
summer
1949
Jun-Sep 1937,
1938
34°40'N, 129°50'W
34°00'N,131°31'W
34°OO'N,131°31'W
32°N(ca.), 132°34'W
31°40'N,136°00'W
Baja California
Mexico
Off Mexico at 22°N,
109°W
NORTHWEST PACIFIC
Along Aleutians between Oct, Nov 47
Unalaskaand 175°£
Between Kiska and Attu, Jun 43
and the USSR
Japan Apr to Nov
(year?)
Off Hokkaido Dec (year?)
43°05'N, 175°42'E 22Aug55
42°57'N, 171 °04'E 23 Aug 55
24 Feb-19 Mar
45
10Apr-l May
45
24May-15 Jun
45
Jul59
22-27 Jun 45
1949-1950
not noted
15Jun 54
seen daily, up to 12 following ship at
once
presence of Black-foots briefly mentioned
comprehensive seasonal data; see text
herein
comprehensive seasonal data; see text
herein
5-15 followed ship within 30-175 mi off
the coast
presence off coast to I30°W during all
seasons
present from here to Hawaii
not abundant off Oregon
increasing abundance over previous 20-
odd years noted
45 seen at once is maximum of period
"especially along the edge of the conti-
nental shelf throughout the length of
the state"
increasing abundance over previous 20-
odd years noted
concentrated offshore of Channel Islands
in "cold tongue" of water; commonly
12-15 birds at oceanographic stations in
cold tongue but never more than 5-6
outside this area; none seen in Santa
Barbara Channel
abundant, maximum of 65 seen at once
abundant, maximum of 50 seen at once
abundant, maximum of 95 seen at once
cumulative total of 30 near here
abundant, maximum of 73 seen at once
comprehensive seasonal data; see text
herein
off Baja California and in the Revilla
Gigcdo I.
seen south to here
a few seen
absent
common offshore in summer
none seen
2 seen in distance
2 seen in distance
Motoda and Fujii, 1956, t.3
Powell, et al., 1952:52
Sanger, 1970:342-349
McHugh, 1955:375-381
Kenyon,1950:98
Sanger, 1965:1
MacDonald and Lawford, 1954:14-15
Gabrielson and Jewett, 1940:80
McHugh, 1950:153
Thompson, 1951:228-229
Grinnell and Miller, 1944:40
McHugh, 1950:153
Miller, 1940:231-232
Yocom, 1947:518
Wilhoft, 1961:258-260
Yocom, 1947:518
McHugh, 1955:375-381
Fricdmann, et al., 1950:15
Poole, 1966:71
Kenyon, 1950:98
Arnold, 1948:556-557
Austin and Kuroda, 1953:299
Kuroda, 1963:234
Motoda and Fujii, 1956, t.3
128 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
Summary of published data on Black-footed Albatross distribution—Continued
Location Date Remarks Source
42°51'N, 162°08'E-
42°45'N, 151°28'E
Off Honshu and
Hokkaido
25-27 Aug 55 none recorded here
Formosa Channel
Western Pacific
West Pacific area
16°05'N,119o02'E
New Hebrides to Solo-
mons to western
Carolines and from
Okinawa to Saipan
Saipan to Pearl Harbor
Philippines to Pearl
Harbor
SOUTHWEST PACIFIC
New Holland
(Australia)
Dusky Sound, N.Z.
CENTRAL PACIFIC
Washington to Oahu
San Francisco to
Honolulu
Honolulu to
San Francisco
4 Jun-
14 Jul 54
Japan to Washington Jun 55
Between Torishima I. Apr 58
and Tokyo
Honolulu to Yokohama May 20
32°39'N, 160°37'E 16 Sep 64
34°36'N, 141°31'E Apr 51
WEST-CENTRAL PACIFIC
China coast
fairly concentrated close to shore; rare N Kuroda, 1955:292
to 200-300 miles off southern Kamchat-
ka; maximum number of 11 just N of
Hokkaido
from Japan to 180°, mean daily abun- Hamilton. 1958:160-162
dance was 155 over four days, vs 8.5
over six days from 180° to Washington
occurred relatively infrequently Aronoff, 1960:277
present from a day out of Honolulu to a La Touchc, 1934:430
day before arriving Yokohama
I Jones, 1965:71
westernmost record of authors MacDonald and Lawford, 1954:15
winter-spring "Off the China coast during the winter Cheng, 1955:5
and spring; in the Taiwan Straits at
the end of the year, according to Swin-
hoe."
year round common in Formosa Channel La Touchc, 1934:430
1951-1952 flocks generally smaller in W Pacific than MacDonald and Lawford, 1954:14-15
in E
Jun45-Feb46 general absence noted Starrett and Dixon, 1946:268-270
Aug 60 daily total of 70+ birds Wilhoft. 1961:258-260
Mar, Apr 45 none Thompson, 1951:233
21 Apr 45
Oct45
no date
July 1884
Feb-Mar51
May 20
first seen at 15°40'N, 176°20'E
none
specific location not indicated, specimen Oliver, 1955:181
collected
vagrant specimen collected by A. Reischek
present near Hawaii, with maximum of
18, N of Maui
present to two days out of Honolulu
1000 mi SW San Jul 64
Francisco
San Francisco to Aug 45
Eniwctok
Southern California to Jul 59
Hawaii
North of leeward Mar 51
Hawaiian I.
24°22'N, 163°30'W 25 Aug 60
Philippines to Pearl Oct 45
Harbor
25 Jan-1 Dec 45 during most months abundance increases
as California coast is approached; see
text herein
125; maximum ever seen in single sight-
ing at sea
last seen at 35°N, 151CW
numbers generally low
most plentiful mid-March; maximum of
60, 600 miles NW of Hawaii
daily total of 50 +
none
MacDonald and Lawford, 1954:14-15
La Touche, 1934:430
Thompson, 1951, 228-231
Yocom, 1947:518
Thompson, 1951:233
Wilhoft, 1961:258-260
MacDonald and Lawford, 1954:14-15
Wilhoft, 1961:258-260
Thompson, 1951:233
Laysan Albatross [Diomedea immutabilis)*
Gerald A. Sanger
Introduction
The material contained in this report is a sum-
mary of all at-sea observations of the Laysan Alba-
tross (Diomedea immutabilis) gathered by the Pa-
cific Ocean Biological Survey Program (POBSP) in
the central and eastern Pacific Ocean. Literature
records, scattered northern Pacific POBSP records,
and data obtained from POBSP island surveys are
included for general background information.
Humphrey (1965) gave a general summary of the
program's objectives and Gould (pp. 1-5 herein)
summarized the areas surveyed and the methods
and materials used in the data collection and
analysis. The reader is referred to these papers for
more details.
An estimated 1.5 million birds constituted the
world population of Laysan Albatrosses {Diomedea
immutabilis) in 1956-1958 (Rice and Kenyon,
1962a: 383). Although the Laysan is five times as
abundant as the Black-footed Albatross {Diomedea
nigripes) there has been a grossly disproportionate
lack of information on the pelagic habits and distri-
bution of the former species at sea. The Laysan
Albatross is a shy bird, usually not strongly at-
tracted to ships. Consequently, it has been seen and
studied at sea far less than the gregarious, inquisi-
tive Black-foot. Indeed, until 1950 Laysans were
quite erroneously thought to range only to 40°N,
but Kenyon (1950) showed them to range as far
north as the southern Bering Sea. Recent papers
which mention scattered sightings at sea (e.g.,
Hamilton, 1958; Kuroda, 1955) have expanded our
Gerald A. Sanger, National Marine Fisheries Service, North-
west Fisheries Center, 2725 Montlake Blvd. East, Seattle,
Washington 98112.
• Paper Number 71, Pacific Ocean Biological Survey Pro-
gram, Smithsonian Institution, Washington, D.C. 20560.
knowledge, but they also glaringly exposed our ig-
norance of gross distribution and movements. Pe-
lagic observations of the POBSP in the central Pa-
cific, off southern California, northern Baja Cali-
fornia, and in the Aleutians, plus a seasonal study
off Washington and Oregon (Sanger, 1970), have
gone a long way toward providing an understand-
ing of movement in rather small areas of the north
Pacific Ocean. Moreover, large-scale banding studies
by the U.S. Fish and Wildlife Service and the POBSP
have revealed much about the qualitative distribu-
tion of known-age birds at sea.
BREEDING.—The Laysan Albatross presently
breeds exclusively in the Hawaiian Islands (Table
23). The population is centered in the Leeward
chain, but a small population breeds irregularly on
Niihau and a nesting was recorded on Moku Manu
off Oahu (Richardson, 1957:16). Fisher (1967,
1971) contributed to our knowledge of the Laysan's
breeding biology on Midway Atoll. Rice and
Kenyon (1962a, 1962b) gave an account of gen-
eral breeding distribution and phenology. The
breeding pattern follows that of the Black-footed
Albatross, but is 10 to 14 days later in starting and
finishing. Breeding birds return to the islands the
first week in November, eggs are laid at the end of
November or early December, chicks hatch at the
end of January or early in February, and all birds
have fledged and headed out to sea by the second
week in August. The proportion of nonbreeding
birds on the islands is the same as that of the Black-
footed Albatross, about 75 percent.
SUMMARY OF PUBLISHED PELAGIC OBSERVATIONS.—
The Laysan Albatross is an abundant species
throughout much of the north Pacific Ocean, al-
though rare or uncommon in some parts of its
range. Its at-sea range is from the Japanese coast
to 150°W and, in winter, almost to the North
129
130 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE 23.—Laysan Albatross breeding populations
Location
Largest number Number of
of breeders' breeding pairs'1
Kure
Midway
Pearl and Hermes Reef
Lisianski
Laysan
Gardner Pinnacles . . .
French Frigate Shoals
Necker
Nihoa
Niihau
TABLE 24.—Recent specimen records of Laysan
Albatrosses off North America
3200*
no,oood
30,000"
8,000"-
10,000
300,000"-
500,000
14C
1,000"
1,650"
38l
no data
350
100,055
17,750
30,000
130,000
2
584
2,500
500
500
• POBSP and U.S. Bureau of Sport Fisheries and Wildlife
data.
bFrom Rice and Kenyon (1962a:369). A discussion of the
disparity between these two sets of figures is beyond the
scope of the present paper. The estimates are presented
merely to give the reader an idea of the general population
size of Laysan Albatross. A more accurate and detailed evalu-
ation of populations will be presented in island accounts cur-
rently under preparation (POBSP) .
c
 Recorded.
" Estimated.
American Pacific Coast; from the southern Bering
Sea and the Gulf of Alaska south to about 28° N
in the eastern Pacific, 13°N in the central Pacific,
and about 30° N in the western Pacific.
Available data on the life history of the Laysan
Albatross prior to 1962 have been summarized
(Palmer, 1962:126-130). The previously known
marine range and published pelagic records are
summarized in the appendix. Information on Lay-
san distribution adjacent to coastal North America
south of Alaska is scanty or nonexistent in major
area references (e.g., Godfrey, 1966; Grinnell and
Miller, 1944), but a number of recent papers (e.g.,
Holmes, 1964), supported by a mass of POBSP
sightings, show that the Laysan Albatross is indeed
common in this area from late fall through early
spring. Winter storms are notoriously severe in the
northeast Pacific and this fact has no doubt dis-
suaded bird observers from venturing into the
region at this time.
Since the Laysan Albatross is a reasonably dis-
tinctive bird, and the only species normally rang-
ing in the north Pacific with which it could be con-
fused (Diomedea albatrus) is extremely rare
(Sanger, 1972), the sight records as a whole are
Area Date
13Jul60
Remarks
dead specimen on
beach
dead specimen on
beach
caught alive from
a fishing vessel
Source
Fredrich,
1961:500
McAllister,
1954:211
Stager,
1958:404-
405
Northern Oregon
coast
Northern Oregon 30 Jan 53
coast
Five mi off S. 6 Feb 58
California
probably quite valid. Supporting the sight obser-
vations off North America are three recent speci-
men records (Table 24).
ACKNOWLEDGMENTS.—Many people in addition
to those mentioned by Gould (p. 5) helped make
this paper possible. Warren B. King and Patrick J.
Gould were especially helpful in offering useful
criticism on early drafts. George E. Watson read
the final draft. Richard H. Fleming initiated the
bird observation program for University of Wash-
ington Department of Oceanography cruises, which
resulted in many sightings; these cruises were sup
ported by various research grants from the U.S.
Office of Naval Research and the U.S. Atomic
Energy Commission. Robert L. Wisner, Scripps In-
stitution of Oceanography, kindly assembled the
California Cooperative Oceanic Fisheries Investiga-
tions sightings.
Distribution and Abundance
SPECIMEN RECORDS
Three Laysan Albatrosses have been collected at-
sea by POBSP personnel. Two were taken south of
the western Aleutians and the third in the central
Pacific. Pertinent data for these specimens are listed
in Table 25.
SIGHTING RECORDS
Figures 81-92 (pp. 140-151) show average
monthly Laysan Albatross distribution in the Pa-
cific Ocean as determined by POBSP sightings. The
relative abundance is indicated by a unit of mean
number of birds per sighting per day (BPS). In ad-
dition to POBSP sight records (1964-1968), sightings
during a number of earlier University of Washing-
NUMBER 158 131
TABLE 25.—Laysan Albatross specimens collected at sea by the POBSP
51
44
13
Location
°19'N,172°
°25'N,173°
°53'N,171°
46'E
O2'E
O5'W
USNM
number
496197
503268
496720
Sex Body weight
(gin)
p
3110
?
Gonad size
(mm)
12x3,11x3
?
11x5
Date
4 Oct 65
13 Oct 65
1 Feb 66
Collector
R. DeLong
R. DeLong
R. Crossin,
D. Husted
ton Department of Oceanography cruises are in-
cluded on the maps. These cruises occurred in the
Gulf of Alaska in September 1955, May 1956, and
April 1957, and in the Aleutians to 173°28'E in
August-September 1957. Since the distribution of
the Laysan has been so poorly understood in north-
eastern Pacific waters, these sightings are listed in
detail in Table 27, as well as on the maps.
Laysan Albatrosses were also noted during the
CalCOFl oceanographic cruises off California and
Baja California from 1951 through 1959 (for details
of these cruises see the Black-footed Albatross ac-
count, Sanger, this volume). These are listed in
Table 26.
January Distribution (Figure 81): In the central
Pacific, only scattered individuals were observed
southwest of the main Hawaiian Islands to
17°15'N. Birds were undoubtedly abundant in the
Leeward Islands, but no trips were made to that
area. The species was relatively common and abun-
dant (up to 4.0 BPS) off southern California. It was
also seen commonly off Washington and Oregon,
and occurred in densities up to 7.3 BPS about 600
miles off northern Oregon.
February Distribution (Figure 82): The fre-
quency of sightings in the central Pacific increased
over January (the southernmost sighting occurring
at 13°02'N), but the species was still seen on only
a minority of all days. A vagrant was noted at
8°30'N by Thompson (1951). Sightings off southern
California decreased, with birds being seen on only
four days. The northernmost winter record was
noted at 53°00'N, 141°30/W in the Gulf of Alaska,
on 6 February 1967.
March Distribution (Figure 83): Laysans were
observed rather frequently in the central Pacific,
and, although scattered birds reached almost 17°N,
they were uncommon south of 20°N. One bird,
possibly a vagrant, was recorded at ll°30'N,
151°04rW. Observations were conducted along the
Leewards for the first time; birds were found in
densities of up to 2.3 BPS. They were seen on only
four days off southern California, the southernmost
record being at 28°49'N. None were observed in
the Gulf of Alaska during five days spent north of
50°N, but scattered individuals were recorded off
Washington and Oregon in 1963.
April Distribution (Figure 84): In the central Pa-
cific Laysans were uncommon south to 17°30'N,
but relatively common from 23°N to at least 35° N.
They were noted on three days off southern Cali-
fornia and were seen only at distances greater than
450 miles off Washington and Oregon. They were
recorded north to 55 °N in the Gulf of Alaska
(1957).
May Distribution (Figure 85): Only a single Lay-
san was seen south of 24°N (18°25'N, 155°28'W)
TABLE 26.—Laysan Albatross sightings (one bird
each) during CalCOFl Cruises, 1951-1959
Date
22 Feb 51
20 Jan 53
10 May 53
17 Jun 53
10 Aug 53
12 Aug 53
4 Sep 53
9 Sep 53
10 Sep 53
23 Jan 54
1 Feb 54
19 Mar 54
13 Oct 54
15 Jul 56
6-7 Nov 56
8 Dec 56
1 Feb 58
10 Apr 58
24 Apr 59
32e
28'
31'
37'
40'
44'
51'
41'
40'
24'
33°
25'
32'
40'
29'
30'
33'
36'
33'
34'
Location
09'N, 125°15'W
'42'N, 116°37'W
'35'N, 118°30'W
'37'N, 123°37'W
'30'N, 149°45'W
=20'N, 150°18rW
W N , 158°40'W
'20'N, 155°13'W
300'N, 155°00'W
3OO'N, 132°00'W
28'N, 133°26'W»
'18'N, 125°00'W
5O4'N, 120°39'W
W N , 159°00'W
'26'N, 119°45'W
'25'N, 117°45'W
'00'N, 120°21'W
303'N, 122°02'W
'39'N, 122°12'W
'20'N, 122°O1'W
•Two birds.
132 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE 27.—Miscellaneous sight records of Laysan Albatross from the eastern
North Pacific, (observers, except one, from University of Washington)
Date
28 Sep 49
3 Sep 55
4 Sep 55
6 Sep 55
5 May 56
7 May 56
8 May 56
8 May 56
8 May 56
8 May 56
9 May 56
9 May 56
9 May 56
9 May 56
12 May 56
13 May 56
29 May 56
1 Jun 56
8 Aug 57
9 Aug 57
9 Aug 57
13 Aug 57
14 Aug 57
15 Aug 57
15 Aug 57
16 Aug 57
16 Aug 57
17 Aug 57
18 Aug 57
18 Aug 57
18 Aug 57
20 Aug 57
20 Aug 57
24 Aug 57
25 Aug 57
25 Aug 57
Location No. of birds
38°OO'N,
53°38'N,
50°58'N,
51°06'N,
50°43'N,
50°12'N,
50°02'N.
50°02'N,
50°01'N,
50°00'N-
5O°O2'N
51°15'N,
52°02'N,
52°05'N,
52°31'N,
59°17'N.
59°34'N,
54°36'N,
50°01'N,
50°22'N,
50°32'N,
50°52'N,
50°42'N,
50°4O'N,
49°44'N,
49°3O'N.
49°2O'N,
49°35'N,
51°08'N,
51°13'N,
51°19'N,
51°24'N,
52°39'N,
52°42'N,
51°11'N,
51°02'N,
51°02'N,
123°45'W
161°28'W
161°09'W
152°4O'W \
133°48'W
142°39'W
144°12'W 5
144°21'W
144°45'W \
145°02'W-
144°56'W
145°03'W
145°02'W
145°02'W
145°02'W
144°59'W 5
144°3O'W
152°46'W
144°57'W
177°38'W 1
177°29'W 5
177°35'W
177°12'E
177°18'E S
174°29'E 1
173°29'E S
173°28'E 5
173°28'E
174°41'E 1
174°32'E 5
175°05'E 5
175°35'E 1
180°00'
179°41'W 1
173°2O'W 1
171°45'W 1
171°45'W 1
i
>
>
1
I
>
>
Observer
R.C. Miller*
unknown
"
CM. Love
" • •
• • "
•* "
G.H. Allen
CM. Love
" "
H.Jackson
G.H.Allen
unknown
'•
CM. Love
P. McCrery
H. Jackson
P. McCrery
G.H.Allen
P. McCrery
E. Linger
R. Rubinstein
P. McCrery
R. Rubinstein
P. McCrery
R. Rubinstein
E. Linger
P. McCrery
R. Rubinstein
E. Linger
P. McCrery
R. Rubinstein
E. Linger
Remarks
letter of 21 Jan 66 to Sanger
Operation NORPAC
i . • •
bird stayed with drifting
ship for 7.5 hours
I.G.Y. Expedition
" "
" "
" "
" "
" "
" "
•• "
••
" "
"
" "
"
" "
in the central Pacific, but the species was still com-
mon in the Leewards. In 13 days of observations off
southern California, Laysans were seen on only two
days. A single bird was recorded as close as 200
miles off the Washington coast, but most were west
of 140°W. In the Gulf of Alaska (1956) the species
was seen as far north as 59°34'N, this apparently
being the northernmost record for the species.
June Distribution (Figure 86): Laysans were com-
mon in relatively low densities (less than 3.2 BPS) in
the Leewards, but were not seen in the remainder
of the central Pacific. None were observed off south-
ern California, and one was seen in the Gulf of
Alaska (1956).
July Distribution (Figure 87): Our records show
only one sighting in the entire Pacific this month,
at 26°15'N, 174°00'W near Lisianski Island.
August Distribution (Figure 88): In the central
Pacific there were but two birds sighted in the Lee-
wards (near Pearl and Hermes Reef), and two more
at 35°N. None were seen off southern California
and only one was observed off Washington, about
750 miles off the coast. In the Aleutians (1957), Lay-
sans were common just south of the islands be-
tween longitudes 171°W and 173°E. Two were
noted one day in the southern Bering Sea at ca.
52°40'N, 180°.
NUMBER 158 133
TABLE 27.—Miscellaneous sight records of Laysan Albatrosses from the eastern
North Pacific, (observers, except one, from University of Washington) —continued
Date Location No. of birds Observer Remarks
25 Aug 57
13 Sep 57
14 Sep 57
2 Apr 57
3 Apr 57
13 Jan 61
16 Jan 61
27 Jan 62
10 Oct 62
1 Mar 63
1 Mar 63
9 Mar 63
11 Mar 63
15 Oct 66
15 Oct 66
16 Oct 66
16 Oct 66
18 Oct 66
19 Oct 66
20 Oct 66
23 Oct 66
24 Oct 66
24 Oct 66
26 Oct 66
27 Oct 66
30 Oct 66
13 Nov 66
14 Nov 66
19 Dec 66
21 Dec 66
27 Sep 67
29 Sep 67
29 Sep 67
5 Oct 67
6 Oct 67
7 Nov 67
51°02'N,
52°58'N,
51°53'N,
55°30'N,
54°20'N,
'48°10'N,
46°22'N.
46O41'N,
42°21'N,
48°14'N,
48°13'N,
45°34'N,
44°16'N,
47°04'N,
46°53'N.
47°OO'N,
47°OO'N,
47°OO'N,
47°OO'N,
46°55'N,
46°55'N.
47°OO'N.
47°OO'N.
47°OO'N,
47°00'N.
47°3O'N,
48°00'N,
47°45'N,
48°10'N,
46°03'N,
53°S0'N,
52°3O'N,
52°07'N,
50°00'N,
47°33'N,
48°25'N,
171°45'W
15O°34'W
150°42'W
139°0O'W
135°OO'W
126°42'W
129°30'W
126°40'W
125°25'W
126°46'W
127°45'W
129°30'W
127°24'W
130°08'W
13O°31'W
132°1O'W
132°OO'W
132°00'W
132°OO'W
132°12'W
132°OO'W
132°03'W
132°0O'W
132°00'W
132°00'W
129°45'W
131°52'W
131°55'W
125°41'W
126°4O'W
162°00'W
"l60°00'W
159°2O'W
137°OO'W
133°OO'W
129°18'W
P. McCrery
E. Linger
unknown
CM. Love
K. Light wood
CM. Love
J. Nickerson
R. Robeck
D. Armand
J. Nickerson
D. Armand
R. Robeck
D. Armand
R. Robeck
D. Armand
V. Wyatt
J. Nickerson
V. Wyatt
ca. 35 mi off Cape Alava,
Washington
•California Academy of Sciences.
September Distribution (Figure 89): None were
seen in the central Pacific or off southern Califor-
nia; one was seen some 35 miles off central Cali-
fornia (Robert C. Miller, California Academy of
Sciences, pers. comm.). The species was common in
the western Aleutians and in the western Gulf of
Alaska (1955, 1957).
October Distribution (Figure 90): None were
seen in the central Pacific nor off southern Califor-
nia again this month. Off Washington and Oregon,
however, Laysans were common in densities of up
to 4.0 BPS. One was noted 75 miles off Washington,
but most were much farther offshore. South of the
western Aleutians, they were common and ex-
tremely abundant. A center of abundance was
noted at ca. 45°N, 173°E, where densities of 20 and
30 BPS were recorded on two consecutive days.
These are high records for pelagic areas away from
breeding islands.
November Distribution (Figure 91): One bird
was observed in the central Pacific near Kaula Rock
(21°45'N, 160°30'W), but no surveys were con-
ducted in the Leewards. Single birds were seen on
three days off southern California and the species
was common to abundant to 138°W in areas far-
ther than 150 miles off the Washington and Oregon
coasts.
December Distribution (Figure 92): Laysan Alba-
134 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
trosses were abundant (up to 10.0 BPS) in the west-
ern Leewards, but only scattered sightings were
made south to 13°37'N in the central Pacific. Only
on 3 out of 33 days were they seen off southern
California. Off Washington and Oregon, single
birds were noted on two out of an unspecified num-
ber of days; one was a scant 35 miles off Cape
Alava, Washington.
ANNUAL PELAGIC CYCLE
The appearance of Laysan Albatrosses in pelagic
areas of the central Pacific in late November cor-
responds to their arrival on the breeding islands.
Numbers increase at sea around the breeding is-
lands in December and scattered birds are recorded
to almost the southern limits of their central Pa-
cific range. From December through May they are
seen, though uncommonly, in pelagic areas south
to 13°N, with February being the month of peak
abundance south of 20°N and the month of most
southerly penetration. Birds begin to leave the cen-
tral Pacific in May and by July and August there
is only an occasional bird seen in the northern
Leewards. They are unrecorded in September and
October. This seasonal shift in distribution is il-
lustrated in Figure 78. It can be seen that this
north-south shifting of birds is synchronized across
the central and eastern Pacific. The northern range
limits also retreat southward in winter, but this is
neither as pronounced nor as well documented as
it is in the central Pacific.
The occurrence of Laysan Albatrosses in the Gulf
of Alaska also appears to be cyclic, with spring be-
ing the season of maximum abundance and north-
ward penetration. A few birds occur in the southern
part during winter. As spring approaches they move
northward and by May can be found in the north-
ernmost part of the Gulf. As summer approaches,
they move westward out of the Gulf, and are found
with any regularity only west of 160°W; most of
, the population apparently occurs west of 180°.
Thus, the westward movement out of the Gulf of
Alaska corresponds to the late spring movement
away from British Columbia, Washington, and
Oregon (Sanger, 1970).
ABUNDANCE AT WEATHER STATION Victor
Figure 79 presents counts of Laysan Albatrosses
made by personnel of the USCGC Winnebago at
Ocean Station Victor (34°N, 164°E), from 26
February through 19 March 1967. The maximum
number of birds seen at any time during the day
(upper graph) ranged from none on 17 March to a
high of 27 on 15 March. Most counts revealed no
more than 14 birds. The maximum number of
birds during the day usually occurred in the after-
noon (1600), although the high counts were in the
morning on three days. This suggests that Laysans
were less inclined toward a regular daily activity
cycle than Black-footed Albatrosses, who never dis-
played maximum numbers in the morning in the
same area.
BAND RETURN INFORMATION
Routine monitoring of banded birds during sur-
veys of the breeding colonies on the leeward Ha-
waiian Islands has documented numerous inter-
island movements of Laysans. Most of these involve
birds moving the short distance between Kure and
Midway Atoll, or between Kure and other Leeward
locations. Only one bird has been recaptured on
land away from the breeding islands. This speci-
men, banded as an adult on Kure Island, was re-
covered on Mejit Island (ca. 10°30'N, 171°00'E),
Marshall Islands, on 20 May 1965 (Amerson, 1969:
293), but must be regarded as a stray in this extra-
limital location. This represents the southernmost
specimen record for this species.
The POBSP Laysan Albatross band returns are be-
ing integrated with those of the U.S. Fish and Wild-
life Service (Robbins and Rice, p. 234, herein).
Pertinent highlights of this information are sum-
marized here. Recoveries of subadult birds (through
the fifth year of life) suggest that they are more in-
clined to be scattered longitudinally than adult
birds, but most recoveries were west of 180°. More
than half of the summer adult recoveries occurred
between 170°E and 180°, in and just south of the
western Aleutian Islands. Almost all of the summer
adult recoveries were from north of 40°N between
Japan and the Aleutians. In winter, the adult re-
coveries were mainly south of 40°N, scattered be-
tween Honshu, Japan, and Midway Atoll.
Analysis of Distribution
GENERAL CONSIDERATIONS
Two major trends are apparent in the gross dis-
tribution of the Laysan which are similar to those
NUMBER 158 135
45
40 -
30 -
25
30
25 -
20 -
15 -
10 -
•
-
-
1 1
4 4 4 4
If 1
\l •+- Southern Distribution -*- \
U Point 1
jJIPlllIJi )|[|
/ ~ x -<— Southern Observational -*- ,
v
 Limit
' x '
X
' X '
X
1 1 1 * 1 1 1 l' 1 1
J F M A M J J A S O N O
Months
EASTERN PACIFIC
-
-
pr \
\y Point \
Vagrant Sightings 171°F
• 163°33'W ' N-«-Southern Observational
' v Limit
1 X
/ x
1 1 1 1 l/ 1 >l 1 1 1 1
V
1
J F M A M J J A S O N
Months
CENTRAL PACIFIC
FIGURE 78.—Seasonal and latitudinal shifting of Laysan Albatrosses in the central and eastern
Pacific Ocean.
136 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
30
25
20
15
10
5
0
Birds seen at
••••0800 hours
1200 hours
— -1600 hours
10 11 12 13 14 15 16 1726 27 28 1
February
18 19
KK.IRE 79.—Counts of Laysan Albatrosses made by personnel of the USCGC Winnebago at
Ocean Weather Station Victor (34°\, 164°E) 26 February through 19 March 1967.
Seasonal Variation in the Range of
Laysan Albatross
E 3 Summer (August)
EZ3 Winter (February-March)
72 Spring-Gulf of Alaska
•£23 Area of apparent non-
breeding concentrations
no E 130 ISO 170 170 ISO 130 110
FIGURE 80.—Seasonal variation in the range of the Laysan Albatross.
of the Black-footed Albatross. First, there is a ma-
jor latitudinal population shift concurrent with
the winter breeding season (Figure 80). In sum-
mer, they are fairly far north in the Pacific, appar-
ently concentrated off the Kuriles and in the Aleu-
tian Islands. During the winter breeding season,
their range shifts considerably farther south (to
13°N). Rare birds have been seen at 11°N (King,
1970:9) and 8°30'N (Thompson, 1951) in the cen-
tral Pacific Ocean. The second major distributional
feature is that the Laysan is predominantly a west-
ern and central north Pacific species, in contrast to
the Black-footed Albatross which has a more even
or eastern distribution.
The movements of breeding adults and older im-
matures are directed toward the breeding grounds
in late fall, and away from the breeding grounds
and toward feeding areas early the following sum-
mer. Moreover, about half of the breeding birds are
away from the breeding grounds at any given time
during the breeding season; indeed, the recovery
of a breeding bird over 2000 miles away 23 days
after being banded on its nest shows that breeding
birds can range well away from the breeding
grounds (Kenyon and Rice, 1958). Curiously, the
breeding season range is much broader than that of
the nonbreeding season. In winter, Laysans are un-
common to common off North America from north-
ern Baja California to southern British Colum-
bia, and off Japan as far south as Kyushu. These
138 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
birds are no doubt mostly prebreeding immatures,
but probably include some adult breeders. Kenyon
and Rice (1958) demonstrated the amazing ability
of this species to cover vast distances in relatively
short periods of time, despite adverse weather con-
ditions.
Banding returns indicate that the postbreeding
dispersal of adults and fledged young takes them
northwestward from the breeding grounds. POBSP
sightings for September and October 1964-1965 in-
dicate that maximum numbers of Laysans may oc-
cur in the Aleutians in late summer and early fall.
Therefore, the occurrence of Laysans off Japan in
summer may be because of a curvilinear migration
route to the Aleutians.
DISTRIBUTION IN RELATION TO THE ENVIRONMENT
CURRENTS AND WATER MASSES.—As in the case of
the Black-footed Albatross, the gross distribution of
the Laysan Albatross (Figure 80) is similar to the
distribution of certain major currents and water
masses. Winter distribution seems generally to par-
allel the circulation of the north Pacific cyclonic
currents, but individuals wander north of the West
Wind Drift and south into the Equatorial Counter-
current. Concentrations of birds in summer are ap-
parently mostly within the western Subarctic and
Alaskan Gyres, and north of the West Wind Drift
(see Dodimead, et al., 1963, for descriptions of these
currents and water masses). Summer distribution
seems to conform to the Kurilo-Aleutian surface
water mass (Muromtzev, 1958:248) with some birds
being found in the western part of the "Alaska Bay
( = Gulf) surface water." Distribution off Japan
(Kuroda, 1960; Robbins and Rice, pp. 236-237,
herein) relates well to the Kuroshio-Oyashio con-
vergence, with no birds being found in the warm
Kuroshio Current in summer.
SURFACE WATER TEMPERATURE.—The maximum
surface water temperature tolerated by most of the
population seems to be about 21° to 24°C
(70°-75°F) in the central Pacific in winter. In sum-
mer, individuals occur as far south as 35°N, where
the surface temperature would again be in the 21°
to 24°C range (Muromtzev, 1958, fig. 112). How-
ever, the surface water temperatures in the western
Aleutians, where most of the population appar-
ently summers, is moderately cold, about 8° to
10°C (Muromtzev, 1958, fig. 112). Kuroda (1960)
suggested that the Laysan is the most cold-adapted
albatross in northwest Pacific waters. When the
Laysan occurs off Washington and Oregon in win-
ter, the surface water temperature generally ranges
from 8° to 10°C. Within an observed annual range
of about 7° to 17°C in this area, Laysans were
found to occur most often in relatively low tem-
peratures, and only three times (all during the same
cruise) in water warmer than 14°C (Sanger, 1970).
King (1970) noted that albatrosses (both Laysan
and Black-foot) were seldom found in water
warmer than 23°C in a survey area east and south-
east of the main Hawaiian Islands (the data from
which are included in this report). As long as the
birds are within their physiological temperature
tolerances, distribution will probably be dictated
by the distribution of preferred food organisms and
not by water temperature per se.
AIR TEMPERATURE.—The limits of the Laysan's
range seem to parallel the isotherms of about 5°
and 24°C regardless of season. The 24°C (75°F)
isotherm lies at about 20°N latitude in March and
at about 40° N latitude in August in the central
Pacific (U.S. Navy, 1956). Both of these latitudes ap-
pear to be the southerly limits of most of the Lay-
san population during the respective seasons (see
Figures 81-92). The temperature tolerance of this
species is conjectural at this point, but the species
has been seen in temperatures ranging from 4.8°C
in the Gulf of Alaska in February 1967 to as high
as ca. 26°C in the central Pacific (King, 1970:89).
Kuroda (1960) observed that Laysan Albatrosses
preferred 13° to 15°C temperatures within a range
of 6.2° to 22.5°C in the summer in northwest Pa-
cific waters. In waters off Washington and Oregon,
Laysans were encountered most often when the air
temperature was less than 10°C in an annual range
of 6.6° to 18.0°C (Sanger, 1970).
SURFACE SALINITY.—The distribution of Laysans
indicates that they occur in waters with moderate
to high salinities, and only rarely in low salinity
water (less than 32.5-33.0%o). The surface salinity
in areas of Laysan Albatross concentrations, i.e.,
west of 180° and north of 40°N, generally ranges
from 33-34%o (Muromtzev, 1958:374). Seasonal data
from off Washington and Oregon show that, in-
deed, Laysans may avoid relatively low salinity
water (Sanger, 1970). In summer, when Laysans are
well away from the coast, salinity of less than
32.5%o (resulting from runoff from the Columbia
NUMBER 158 139
River) has been traced westward to nearly 132°W
off Oregon (Budinger, et al., 1964:52). Coinci-
dentally, there is no such offshore area of low surface
salinity in the northwest Pacific. In winter, prevail-
ing south and southwesterly winds off the Washing-
ton-Oregon coasts tend to hold river runoff within
a relatively few miles of the coast (Budinger, et al.,
1964:69), allowing a maximum eastward invasion
of oceanic water toward the coast via the California
Current. It is at this time that maximum abun-
dance of Laysan Albatrosses occurs in the area and
they occur closest to shore (see Figures 81, 91). In
the central Pacific, albatrosses tended to be found
in higher salinity water within a range of 33.9%o
to 35.2%o (King, 1970:96).
WEATHER CONSIDERATIONS.—As in the case of
Black-footed Albatrosses (see p. 113), wind is
probably the most significant feature of the weather
affecting Laysan distribution. The doldrum wind
conditions no doubt play a significant role in limit-
ing the southern distribution of the Laysan Alba-
tross.
Addendum
After this paper was completed in 1968, two im-
portant papers on the pelagic distribution of Lay-
san Albatrosses were published, those of V. P.
Shuntov (1968) and Fisher and Fisher (1972). Gen-
erally, these authors indicate the same distribution
patterns reported here, but with certain notable
exceptions.
Shuntov, using sightings at sea, has Laysans rang-
ing much farther north in winter than our data
indicate, to about 59°N in the Gulf of Alaska, and
to about 55° N in the western Bering Sea. Also, con-
trary to our sightings and those in the literature,
Shuntov has Laysans ranging south to only about
21 °N in the central Pacific. In summer, he shows
Laysans ranging well into the Sea of Okhotsk and
north in the western Bering Sea to the Gulf of
Anadyr.
The Fishers' paper is based on 109 captures at
sea of birds banded on Midway Island and most of
the sightings noted in the literature; omitted for
unknown reasons are Sanger's (1970) records off
Washington and Oregon. These omissions cast
some doubt on the validity of the graphs (Fisher
and Fisher, 1972: figs. 3, 5, 7) portraying average
monthly longitudinal and latitudinal movements,
as does the lack of statistical treatment of the data
in the graphs. The inclusion of standard deviations
of the means shown in the Fishers' figures 3 and 5
would have given an idea of how representative the
means really are. Puzzling is the contention (Fisher
and Fisher, 1972:8) for "a probable similarity in
the distribution of tunas and albatrosses in the
North Pacific. . . ." The facts are that tuna
range far south of the southern limit of the Lay-
san's range (cf., Rothschild and Uchida, 1968),
and that Laysans range far north of the northern
limits of tuna distribution. The northern part of
the tuna range and the southern part of the Lay-
san's range merely overlap. Fisher and Fisher's
(1972:16) curious reference to Seckel's (1970) dis-
cussion of weather-sea surface interactions in the
area from 0° to 35°N, and 130°W to 170°W, for
documenting "turbulence and many eddies be-
tween 35° and 40°N and 140° to 160°E," and their
erroneous view that warm oceanic waters have low
salinity (Fisher and Fisher, 1972:17, 23), suggests
that more rigor might have been applied in dis-
cussing oceanographic matters. The question raised
by the authors of whether their data reflected the
distribution of albatrosses or of persons recapturing
albatrosses never was convincingly answered, espe-
cially in view of the disparity in the distribution of
albatrosses and tuna (and therefore tuna fishermen).
Longline tuna fishing is by far the most susceptible
means of capturing albatrosses at sea because the
birds actively go after the baited hooks. These and
other flaws notwithstanding, the Fishers have pre-
sented an important, useful document, all the more
so because they have given evidence for differences
in the at-sea distribution of young and adult Lay-
san Albatrosses.
140 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
NUMBER 158 141
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142 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
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NUMBER 158 143
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144 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
NUMBER 158 145
146 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
NUMBER 158 147
148 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
NUMBER 158 149
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150 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
NUMBER 158 151
Appendix
Summary of published data on Laysan Albatross distribution
location Date Remarks Source
NORTHEAST PACIFIC
Various sites in the May-Oct
Aleutians, three Gulf
of Alaska sightings
230 mi £ Kodiak I., IS Oct 48
Alaska
Various sites in Aleutians Jun, Jul
90 mi S of Aleutians at 28 Mar 51
49°51'N, 178°22'W
Off Vancouver I. 25 Dec 52
10 Dec 53
Off Washington, Oregon 24-27 Fcb 58
and Vancouver I.
Off Washington and May 64-Nov 65
Oregon
100 mi off Washington Fcb 51
to Oahu
50°N, 173°W 23 Scp 54
48°N, 150°W to 30 mi
NW of Farallon I.
47°15'N, 126°45'W
Along 47° Nat 155° and
178°W
45°36'N, 124°S6'W
45°14'N, 127°31'W
44°45'N, 132°00'W
44°10'N,135°45'W
44°10'N, 132° W
41 °N. 137°30'W-
24°30'N, 155°W
40°32'N, 138°17'W
39°40'N, 139°W
37°37'N, 124°53'W
30 Nov-6 Dec 48
1 Dec 45
Aug 59
1 Oct 63
16 Mar 63
16 Dec 63
15 Dec 63
30 Nov 45
16-20 Jan 60
29 Nov 45
29 Nov 45
25 Jan 45
EAST-CENTRAL PACIFIC
North America when not
breeding
Within 45 mi of central Feb-Mar 58
California coast
California, far offshore Oct-Apr
from Cape Mendocino
to San Nicolas I.
possible confusion of early records with
Short-tailed Albatross
individual followed ship for several
hours; ship's captain quoted as often
seeing Laysans in same area
sight and specimen records; possibility
of several Short-tailed Albatross
sightings being Laysans
1, apparently the northernmost record
for the central North Pacific at this
early date
2 at 48°N, 133°W, was closest sighting
to North America
3 at 49°N, 133°W, were the most teen
off North America at this latitude;
generally scarcer in NE Pacific than
NW Pacific
6 sightings of 1-3 individuals, 60-100
mi off northern Washington and
southern Vancouver I.
comprehensive seasonal data; see text
herein
seen less often and in fewer numbers
than Black-footed Albatross
12 this date; place was maximum for
general area; seen north of 52 °N
several times
seen every day during this period; 1
collected 40 mi off northern Califor-
nia
1
155°W, apparently near eastern limits
of summer range
1
2
1
1
2
"Two or three were always present"
only southern range limits, i.e, Baja
California, specifically mentioned
11 sightings 8 Feb-29 Mar as close as
18 mi offshore
rare or casual visitant; specimen col-
lected San Nicolas
Murie, 1959:39-40
Kenyon. 1950:100
Gabrielson and Lincoln, 1959:75
MacDonald and Lawford. 1954:16
Poole. 1966:71-72
Sanger, 1965:1-2
Sangcr, 1970:342-343, 349-352
MacDonald and Lawford, 1954:15-16
Poole, 1966:71-72
Kenyon. 1950:100
Thompson, 1951:234
Nakamura, 1963:239-245
Sanger, 1965:1-2
Thompson, 1951:234
Agnew, J. H. in Bourne, 1961:12
Thompson, 1951:234
Vaurie, 1965:19
Holmes, 1964:302-303
Grinnell and Miller, 1944:41
NUMBER 158 153
Summary of published data on Laysan Albatross distribution—Continued
Location Date Remarks Source
Baja California to
Oregon
Feb-Apr 49
no dateSan Geronimo,
Cuadalupe and San
Martin, Baja
California
34°N, 131°30'W 17 Mar 45
31 °47'N-35°3rN, within 31 Mar-5Apr
100-300 mi of shore
31°45'N, 129°W
NORTHWEST PACIFIC
SE of Kamchatka Penin-
sula
49
26 Mar 60
16Aug?
45ON,155°E 22 Oct 53
Off Pacific coast of Hon- early spring-
shu and Hokkaido late autumn
Off Hokkaido, Kuriles, Jun,Jul54
and Kamchatka
40°N, from 165°E to
172°W
Coastal Honshu, Japan,
from ca. 35 °N to
38°30'N
Off Japan
36°N, 141°E
Off Japan 35°37'N,
142°59'E
Off Japan
34°56'N, 157°OO'E
30°N, 154°E
29°N, 146°E
CENTRAL PACIFIC
33°N, 166°E-23°30'N,
162°W
26°S0'N,151°3O'W
22°N, 170°W
N, S, and E of Hawaii
17°44'N,159°56rW
17°3O'N,171°2O'W
8°S0'N,163°35'W
6-8Jun55
Dec 62
Apr, May 51
10Jun53
apparently
May 51
not specified
22Aug60
Mar 61
22 Mar 60
9-12 Apr 61
12 Apr 60
Mar 61
1964-1965
22 May 59
22 Apr 45
1 Feb45
several sightings by people on oceano-
graphic cruises; unspecified positions
and numbers
formerly fairly common but not re-
cently seen
McHugh, 1950:153-154
Friedmann, et al., 1950:15
2 stayed near the stopped ship for most Yocom, 1947:510
of one day; crew members saw other
white-bodied albatrosses in the area
prior to 1945
scattered singles and doubles
1
1 obtained in Kamchatka waters
25, maximum number seen at single
sighting; generally more common in
western Pacific than other areas
regular and not uncommon visitor; not
as plentiful as Black-foot
maximum number 14 ca. 240 mi S
southern tip Kamchatka; other sight-
ings mostly scattered singles; none
seen in western Bering Sea; suggested
temperature preference is 7°-8°C
maximum numbers (2.5 per hr) seen at
180°
second in abundance only to Rissa tri-
dactyla; winter banding returns for
coastal Japan; suggests wintering birds
are nonbreeding young
more common here at this time than in
NE Pacific in previous February
6, closest sighting to land during 5
trans-Pacific trips
westernmost and southernmost position
at which sighted
suggests main summer range off Japan
as N of 40°N; main winter range S of
35°N (quoted by Kuroda, 1963:234)
only time species seen during 36 days
at sea, including 2 days off southern
and central Japan
1
1
regular occurrence in area implied
McHugh, 1950:153-154
Agnew, J. H. in Bourne, 1961:12
Dementev and Gladkov, 1951:347
Poole, 1966:72
Austin and Kuroda, 1953:300
Kuroda, 1955:292
Hamilton, 1958:160-162
Kuroda, 1963:234
MacDonald and Lawford, 1954:16
Poole, 1966:71-72
MacDonald and Lawford, 1954:16
Yamashina, 1942:247 [in Japanese]
Wilhoft, 1961:260
Nakamura, 1963:241-243
Mitchell, J. B. in Bourne, 1961:12
Lamb, K.D.A. in Bourne, 1961:12
2 Agnew, J. H. in Bourne, 1961:12
1 Nakamura, 1963:241-243
see text herein King, 1970:9
1, apparently southernmost record for Peakall, 1960:199
month
3 Thompson, 1951:234
1, southernmost record for species " " "
The Storm Petrels (Hydrobatidae)
Richard S. Crossin
Introduction
The family Hydrobatidae consists of a group of
morphologically similar species distributed over
most of the pelagic waters of the earth. At least 15
species and a variable number of subspecies (de-
pending upon the reviewer) are found in the areas
of the Pacific Ocean covered in the present work.
Many of these species are included in the genus
Oceanodroma which contains groups of sibling spe-
cies, often only separable with some difficulty in the
hand, and presenting considerable problems to the
observer in the field. The pelagic ranges, as well as
other aspects of the life histories of most of the
Pacific forms, are little known; for some species
even the breeding grounds are unknown. Austin
(1952) discusses the taxonomy and breeding stations
of most north Pacific species but deals little with
pelagic distribution or other aspects. Palmer (1962)
covers those hydrobatids that occur in North Amer-
ican waters, but the pelagic distribution maps are
inadequate. In many cases lack of knowledge of
pelagic distribution of a species is admitted by
placing a large question mark in an area. For other
species range maps are presented with little or no
information given as to the type of records (speci-
mens, sightings) used to determine the distribution
area shown. Murphy (1936) discusses the forms
found in waters off the South American continent,
as well as many species found to the north. Despite
the considerable ornithological work since these vol-
umes were written, there has been little or no new
information gained regarding many species of
hydrobatids considered therein.
Richard S. Crossin, Neotropical Ornithological Foundation,
J719 North Huachuca, Tucson, Arizona 85705.
* Paper Number 84, Pacific Ocean Biological Survey Pro-
gram, Smithsonian Institution, Washington, D.C. 20560.
The major reason for lack of positive knowledge
regarding Pacific Ocean hydrobatids is the logistics
problem with which the student of these seabirds
must contend; the Pacific is a vast area where ports
are few and far between, and shipping is primarily
restricted to large commercial or military vessels.
Harrison (1962) had a rather exceptional oppor-
tunity of making seabird observations while aboard
Royal Navy ships. King and Pyle (1957), Szijj
(1967), and others have gained information while
on trans-Pacific research cruises. The unique op-
portunities of consistent area observation available
to the Smithsonian Institution's Pacific Ocean Bio-
logical Survey Program (POBSP) during the course
of field work from 1963 to 1968 have added a wealth
of new information not only on Pacific hydrobatids,
but on Pacific seabirds in general.
In this paper I shall not attempt to summarize
all information available from other sources on the
forms of hydrobatids under consideration. Rather
I shall present the recently acquired POBSP data,
with inclusion of previous data only when it seems
necessary for cogency. The POBSP data on Pacific
hydrobatids covers essentially four categories: (1)
pelagic distribution, (2) breeding biology, (3) molt,
(4) taxonomy. As might be expected, unequal
amounts of information in these categories were
acquired for the various species concerned. These
data are presented in the species accounts.
Throughout the course of POBSP studies, a variety
of vessels were utilized: United States Department
of Interior, Bureau of Commercial Fisheries ships;
United States Navy vessels; Scripps Institution of
Oceanography research vessels; United States Coast
Guard ships; leased fishing ships; and others. POBSP
observers normally worked in rotating two-man
teams who were on watch constantly during day-
light hours and occasionally at night. On cruises
154
NUMBER 158 155
with only a single POBSP observer aboard, he usu-
ally observed from dawn to dark with intermittent
breaks. All bird sightings were recorded with ac-
companying pertinent data. The recording of time
of day at each sighting permitted interpolation of
latitude and longitude positions from the ships'
cruise charts. Weather and oceanographic condi-
tions were coupled to each sighting when possible,
and all information was later transferred to mag-
netic tape from which rapid summations of data
for single species or species groups could be drawn
for analysis. For a more comprehensive view of the
Automatic Data Processing program, see King, Wat-
son, and Gould (1967). As field work was performed
for the most part on a year-round basis, migrational
patterns, seasonal movements, and other factors can
be analyzed to determine variations present in sea-
sonal timing and areas utilized by the various spe-
cies concerned. During the course of POBSP activities
some 12,574 observations covering 27,140 individ-
uals of the family Hydrobatidae were recorded.
Regular and periodic surveys of islands used for
nesting within the area of investigation allow for a
more complete understanding of the pelagic obser-
vations. Specimen collecting accompanied pelagic
observations whenever feasible. Artificial oil slicks
(see Murphy, 1936:8) were often put out specifically
to attract hydrobatids.
During the course of the study 650 specimens of
11 hydrobatid species were collected. Most speci-
mens collected and observations made were of the
various subspecies of the Leach's Storm Petrel
(Oceanodroma leucorhoa). The means, with stand-
ard errors and standard deviations, are given in
Appendix Tables A to E for all standard measure-
ments of the POBSP specimens of leucorhoa races, as
well as of other species. All wing measurements are
of the chord. In comparing chord measurements
with measurements of the flattened wing on storm
petrels, I find extremely little difference between
the two.
AREA COVERED BY POBSP.—Gould (Figure 1)
shows the approximate outlines of the areas sur-
veyed during all POBSP cruises from August 1963
through April 1968. All portions of those areas were
not comparably surveyed in regard to total coverage
or to time of year. Without question, certain areas
received consistent and by far more regular cover-
age than other areas, which were surveyed only once
or very irregularly. By and large, the area surveyed
falls into two major regions: the central Pacific
and the central eastern Pacific (hereafter referred
to as the eastern Pacific). The former was surveyed
almost constantly from 1963 to 1967. The latter was
surveyed intensively during 1967 and 1968. Inter-
mittent cruises were also run in the Alaskan area.
FIELD IDENTIFICATION.—As a group, the various
white-rumped and dark-rumped storm petrels in
the Pacific present as great an identification prob-
lem to the field worker as any two groups of sibling
species known. I have no doubt that each species
has its peculiar identifying characters and that un-
der ideal conditions most individuals might be
properly identified to species, but sightings in the
field are seldom under ideal conditions. In fact, it
is unusual when weather, lighting, distance and
other factors are satisfactory for positive identifica-
tion. Most sightings are assigned to species only by
inference and deduction.
In 1965 Wilson's Storm Petrels (Oceanites ocean-
icus), a totally unexpected species, were collected
for the first time in the central Pacific. No doubt
some were seen during late 1963 and 1964, but were
erroneously recorded as Leach's (Oceanodroma leu-
corhoa) or Harcourt's Storm Petrels (Oceanodroma
castro). Continued collecting after 1965 with the re-
sultant procurement of scattered specimens of Wil-
son's, plus a detailed survey of migration in the
central Pacific (Huber, 1971) have shown that these
birds apparently move through the Pacific (Mar-
shall Islands area, at least) in considerable numbers,
and are scattered throughout the central Pacific in
small numbers during the migratory period. Any
purely visual identification made of storm petrels
in an unknown area is, in my opinion, speculative.
In the central Pacific, identification problems
were greatest for Leach's, Harcourt's, and Wilson's
Storm Petrels, all white-rumped forms. The latter
two were present in fewer numbers than Leach's.
Random collecting performed throughout the area
allowed for a fairly good estimate of the percentage
of each species present.
In the eastern Pacific the situation was consid-
erably different in that both white-rumped and
dark-rumped forms were present. Although more
species were involved, the majority of these were
sufficiently diverse to allow reasonably accurate
field identification. General collecting proved even
more fruitful here than in the central Pacific, as
certain forms, such as the two races of the Gala-
156 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
120° 110° 100° 90°
FIGURE 93.—POBSP sightings and specimens of Pelagodroma marina.
10
70°
pagos Storm Petrel (Oceanodroma tethys), are read-
ily separable in the hand. Thus in a situation such
as this, the ideal is realized in that a collected speci-
men not only provides positive identification of the
species, molt, food, and gonadal information, but
allows for designation of the at-sea range of a spe-
cific geographic race.
Hence, despite the problems connected with field
identification of hydrobatids, observations made
during the POBSP surveys can be discussed with a
considerable degree of assurance for the following
reasons: (1) the observers concerned had an extra-
ordinary opportunity to gain experience in field
identification during extensive periods of work at
sea under every conceivable condition, and (2)
most at-sea observations were backed by random
collecting; this constant procurement of specimens
throughout various areas provided a constant check
on visual observations.
ACKNOWLEDGMENTS.—The following made impor-
tant observations and collected field data pertinent
to hydrobatids during the program; without their
contributions, this paper could not have been writ-
ten: A. Binion Amerson, Jr., Richard D. Chandler,
Roger B. Clapp, Robert L. DeLong, Patrick J.
Gould, C. Douglas Hackman, Brian A. Harrington,
Lawrence N. Huber, Dayle N. Husted, Warren B.
King, Horace Loftin, Max C. Thompson, and Paul
W. Woodward. (For a more complete listing of
POBSP personnel and objectives of the Pacific Pro-
gram, see Gould, pp. 1-5, herein.)
I also wish to thank the following individuals
who aided the writing of this paper in their respec-
tive ways. Philip S. Humphrey, as Principal Investi-
gator of the Pacific Program, offered valuable ad-
vice and encouraged the writing of the present
work. Dean Amadon of the American Museum of
Natural History in New York and Joseph R. Jehl,
Jr., of the San Diego Natural History Museum
made available the hydrobatid specimens in their
charge. Carl L. Hubbs of Scripps Institution of
Oceanography generously offered me the use of his
field notes and preliminary consolidated data on
hydrobatids from the eastern Pacific islands, espe-
NUMBER 158 157
FIGURE 94.—POBSP sightings of Oceanodroma furcata. (Breeding localities are largely from
Palmer, 1962).
daily Guadalupe. Oliver L. Austin, Jr., reviewed
the manuscript and offered valuable suggestions.
Ralph Browning donated his time and effort to
performing much of the tedious work of measuring
specimens. Anne K. Poulson prepared the illustra-
tions.
Pelagodroma marina (Latham)
WHITE-FACED STORM PETREL
PELAGIC DISTRIBUTION.—Most POBSP pelagic rec-
ords of this basically southern hemisphere hydro-
batid are from west of the Galapagos Islands. Prac-
tically all sightings fall within a triangular area
with points at 5°N, 112°W; 8°S, 112°W, and 3°S,
100°W (Figure 93). Two adult females were col-
lected by the POBSP on 24 August 1967 at 6°19'S,
111°55'W. Three other specimens taken in the east-
ern Pacific (two near the Galapagos, one near Ecua-
dor) are mentioned in Murphy (1936:768). LeVeque,
et al. (1966) report a specimen collected in Septem-
ber 1930 about 100 miles southwest of the Gala-
pagos, and two sightings in August 1960 and seven
sightings in July 1961 about halfway between the
Ecuadorian mainland and the Galapagos.
The similarity of south Atlantic (Tristan da
158 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
Cunha Islands) and south Pacific (Australia-New
Zealand) subspecies makes it difficult to assign ori-
gin to specimens collected near the Galapagos.
Murphy (1936:768), while implying that some form
of this species was probably resident in the eastern
Pacific, left the question of origin open. Most likely
these eastern Pacific records pertain to members of
the Australian-New Zealand populations, which
migrate to the South American coast and follow the
Peru Current north and west through the Galapa-
gos region. The large number of records west of the
Galapagos in August and September (84% and
14%, respectively, of total POBSP sightings for those
months) indicate a buildup prior to the return to
the Australian-New Zealand breeding grounds
where egg-laying takes place in late October. The
condition of our August specimens (in terminating
stages of complete molt and with moderate fat) is
in accord with the condition of other procellarii-
forms prior to a prebreeding migration. Murphy
(1936) and Palmer (1962) summarize the known
biology of the species.
Oceanodroma furcata (Gmelin)
FORK-TAILED STORM PETREL
PELAGIC DISTRIBUTION.—This species was ob-
served commonly on all POBSP cruises in the central
and eastern Pacific north of 40°N (Figure 94). A
region of high density off the California coast be-
tween 31 °N and 36°N probably consists of birds
from the northern California or Oregon popula-
tions. An obvious straggler was observed on 22
February 1968 feeding on refuse behind a ship in
the company of several Black Storm Petrels (Ocean-
odroma melania) near the southern tip of Baja
California. POBSP collected only a few specimens of
nominate O. f. furcata near the Aleutian Islands;
thus most of our pelagic sightings are not referable
to race.
Oceanodroma leucorhoa leucorhoa (Vieillot)
LEACH'S STORM PETREL
PELAGIC DISTRIBUTION.—The nominate race of
Leach's Storm Petrel is distributed in its at-sea
range over much of the Pacific Ocean with a de-
cided center of abundance in the central Pacific.
Measurements of normally used characters of all
specimens collected (Figure 95) in this area are com-
pared with known breeding O. I. leucorhoa from
the Alaskan area in Appendix Table B. It can
easily be seen that central Pacific birds fall well
within the range for nominate leucorhoa. As a
whole, the specimens are comparable both in meas-
urements and other more subtle morphological
characters with nominate leucorhoa from the
breeding grounds. However, because of the diffi-
culty involved in separating nominate leucorhoa
from O. I. beali, the presence of a small percentage
of the latter in the central Pacific is not to be ex-
cluded.
Oceanodroma I. leucorhoa attains greatest winter
densities in a broad belt along the equator. Num-
bers drop rapidly to the south, and south of 12°S
only an occasional individual is sighted. Waters to
the north of this equatorial high-density area pre-
sent problems of seasonal density specification.
High density in small sectors north of the equa-
torial complex is probably due to several factors,
among which are local, temporary, high concentra-
tions of food. Additionally, late fall and early
spring migrants may tend to mass at certain points
in the northern sector of the wintering grounds be-
fore moving on south or north, as the case may be.
Birds are found throughout the central Pacific win-
tering grounds throughout the year, with decided
buildups of wintering birds as would be expected
(compare Figure 96 "Summer" with Figure 97
"Winter").
The number of summering birds is considerable,
but their age status is uncertain. In the Atlantic
population of the nominate race, birds presum-
ably do not breed until three years of age, but two-
year old birds may return to the colony during the
breeding season (Wilbur, 1969). Wilbur (1969) im-
plies that first-year birds might fly over the colony
without entering it; he apparently has no positive
evidence for this in the form of banded birds.
Huntington (pers. comra.) informed me that of
eleven breeding birds banded as nestlings, the
youngest were four years old; of thirteen banded
birds mist-netted over the colony, breeding status
unknown, the youngest were three years old. There
may be considerable individual variation among
one- and two-year old birds in regard to their re-
turn to the breeding colony.
The only other explanation for the large num-
ber of birds that summer in the central Pacific is
NUMBER 158 159
180
FIGURE 95.—Localities of collected specimens of Oceanodroma leucorhoa leucorhoa in the central
Pacific.
that for some reason, some adults do not return to
the breeding colony every year. Both Huntington
(1963) and Wilbur (1969) record that approxi-
mately 50 percent of birds banded while nesting
one year are found nesting the following year. Un-
less we assume some birds were missed in the study
plots or had moved elsewhere, this seems to be an
exceptionally high mortality rate. Possibly some
adults that successfully raise a chick one year do not
return to the breeding grounds the following year.
The migrational pattern of nominate leucorhoa
is largely obscured by the high densities of sum-
160
170 W 160'
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
150° 140° .
150° 140°
FICURE 96.—Summer densities (May, June, July, August) of Oceanodroma leucorhoa leucorhoa.
NUMBER 158 161
160 E 170 180" 170 W 160 150 140°
 o
—130
20'
10"
20
Birds per square mile
.01 -.10
if!-11--20
•1.21 +
20
10°
,20
140°160° 170 180 170 160° 150°
FIGURE 97.—Winter densities (November, December, January, February) of Oceanodroma
leucorhoa leucorhoa.
mering birds, and is more readily ascertained by
field observations of flocking birds rather than by
actual increases or decreases in recorded density.
The spring migration north begins in March and
probably occurs sporadically throughout April,
since April densities in the central Pacific are still
far greater than in mid-summer when most breed-
ing birds are on the breeding grounds. The fall mi-
gration south is also largely obscured by summer-
ing birds, but definite density increases are noted
southward to the high-density equatorial center as
early as September. At this time of year breeding
birds would still be expected on the breeding
grounds or at least in more northerly latitudes.
These early fall buildups in the equatorial area
may either be of birds that have experienced nest-
ing failures, and thus have left the breeding
grounds earlier than the successful breeders, or of
prebreeders that have spent the summer farther
north and have returned to more southerly latitudes
for the winter. As it is virtually impossible to dis-
tinguish immature prebreeders from adult breed-
ing birds when the latter's gonads are in a winter
quiescent stage, collected specimens from these sea-
162
20
10°
s
10"
130
110°
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
100° 90
"140°
1 bird
5 birds
30"
Islobela I., A -
Galapagos j
Islands
10"
120°
10°
no 100° 90°
FIGURE 98.—Localities of collected specimens of Oceanodroma leucorhoa leucorhoa in the eastern
Pacific Ocean.
NUMBER 158 163
sons do not lend information as to their recent
breeding activities.
Movements and distribution of the nominate
race throughout the eastern Pacific are less clear
because of the difficulty of separating individuals
from the abundant O. I. beali, which winters promi-
nently along the western American coast. A few
specimens from the eastern Pacific are clearly refer-
able to nominate leucorhoa by their greater size;
collecting localities of these are shown in Figure 98.
Aside from POBSP specimens, Loomis (1918:182)
mentions three specimens collected south of the
Galapagos Islands whose measurements indicate
their allocation to the nominate race. Palmer (1962:
227) mentions examples of the nominate form taken
off the coast of Ecuador. Comparatively, the num-
bers of these eastern representatives are low and
the equatorial high-density area between 170°W
and 175°E is, if not the center of winter abun-
dance, one of the most important of such centers.
TAXONOMY.—Considerable taxonomic work was
performed on available POBSP specimens during the
course of this study in the hope that the ability to
distinguish races of at-sea collected specimens would
allow for a clearer picture of their respective at-sea
ranges. In some cases this was possible, but many
individuals cannot be designated unconditionally to
a particular race. Concerning the Pacific races of
Leach's, Austin (1952:400) stated: "On dimensions
alone these are all weak races. Despite significant
differences between the means of some characters,
fewer than half the individuals of many of the
recognized subspecies are distinguishable." Despite
the recently collected large series of most of the
races concerned, we are no better off in regard to
solving these problems. Austin's (1952) arrange-
ment of the various Pacific subspecies of Oceano-
droma leucorhoa is followed here. The unusual
situation concerning O. I. socorroensis at Guada-
lupe Island and the possible need for revision of
the taxonomy of that population is discussed be-
yond.
In working with fresh series of recently molted
birds of all populations, I find that little signifi-
cance can be attached to the oft-mentioned char-
acter of a lead bloom to the plumage of the north-
ern races, which is supposedly most prominent in
nominate leucorhoa. All races in very fresh plum-
age show this particular bloom but with consid-
erable individual variation, and this particular cast
is lost quite rapidly, both in living birds and in
museum specimens. Freshly molted series of either
O. I. chapmani or O. /. socorroensis show this char-
acter as prominently as newly molted nominate
leucorhoa from the Alaskan area, although the
overall plumage is admittedly considerably darker
in the southern races. Juvenile socorroensis from
Guadalupe are especially prone to show this par-
ticular character, but drastic differences exist be-
tween new and old plumage. When the plumage
is several months old the entire feather coat in all
races is of a washed-out brown hue in addition to
its ragged condition, with hardly a trace of the rich
charcoal present in new featheration. Body contour
feathers, as well as flight feathers, are badly worn
at the end of a plumage sequence. Of the flight
feathers, primaries appear to take the most wear.
In contour feathers, those about the head and neck
appear most subject to wear and at the beginning
of a new molt sequence these are often no more
than ragged portions of the original appendages.
Only in the case of exceptionally large individ-
uals of O. I. leucorhoa, and exceptionally small in-
dividuals of O. I. socorroensis, can birds of the leu-
corhoa complex be segregated with any degree of
certainty. As is evident from the measurements in
Appendix Table B, nominate leucorhoa from the
Alaskan area is the largest of all races. While the
average individual of the nominate race has a gen-
erally more massive bill, this subtle difference is
useful only in direct comparison of specimens, and
does not lend itself meaningfully to mensural appli-
cation.
MOLT.—Members of the nominate race of Leach's
that enter the central and eastern Pacific from
northern breeding grounds, as well as year-round
semipermanent residents there (nonbreeders), are
already undergoing a pronounced primary molt by
July. This continues in some individuals through-
out the fall and winter (to December or even later).
In a large percentage of birds the entire primary
molt has been accomplished by November, and in
exceptional individuals by October (Figure 99).
For many others this molt may not terminate until
April. It cannot be determined whether individuals
finishing primary molt from, say, February through
April, are birds that have a very prolonged cycle or
whether they are individuals that began molt very
late in the year. Primary molt can be clearly ascer-
tained and follows a set pattern of replacement of
164 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
100
90
80
70-
60-
5 50
s.
40
30
20
10
July
N=6
I I Old
3 Molting
Non-molting
FIGURE 99.—Seasonal molt stages in Oceanodroma leucorhoa leucorhoa. The percentages of new,
growing, and old primaries and rectrices are calculated from direct count of all birds in each
respective sample; narrow portion of bar equals nonmolting percentage of sample, wide portion
of bar equals molting percentage of sample, (n = sample size.)
new feathers from the innermost to the outermost
primaries with corresponding feather pair members
of each wing coincident or very closely attuned.
Most individuals of chapmani and socorroensis, re-
turning to the breeding islands, were in terminal
stages or had very recently completed a body and
primary molt. Some individuals were still growing
the outermost (tenth) primary as defeatheration of
NUMBER 158 165
the brood patch and gonadal enlargement were oc-
curring. We took no specimens of either beali or
leucorhoa on any breeding grounds except for
willetti ( = beali) on the Coronados Islands.
Rectrix molt, like the preceding, is already well
along in our July sample of O. I. leucorhoa, and is
for all practical purposes, finished by November.
Only a few isolated individuals show any evidence
of rectrix molt during the period from January
through May. There seems to be no set pattern of
rectrix molt except that opposite members of a pair
of tail feathers are generally molted at the same, or
at nearly the same time.
Investigation of the molt pattern of the second-
ary feathers was less satisfactory because of the dif-
ficulty of working with study skins in these small,
long-winged birds. In general, it appears that the
outer secondaries begin to molt at about the time
the first primaries shed, and molt then proceeds
progressively toward the body. Secondary molt is
closely parallel to primary molt and is usually ter-
minated before the last primary has finished grow-
ing.
Extensive body molt of the contour feathers in
the nominate race begins in November and is ap-
parent in a decreasingly smaller number of indi-
viduals through April. Body molt is generally dis-
tributed over most of the body; the crown and
throat regions and the primary and greater coverts
are the last areas to replace feathers. The various
races of Leach's show certain variations in molt pat-
terns.
No doubt much of the variation in molt between
individuals of the nominate race can be attributed
to differences between juvenile, immature, and
adult breeding birds. However, I cannot satisfactor-
ily separate immature birds from adults on the
wintering grounds after the latter's gonads have
regressed, except for truly adult females, which
form only a small part of our sample. The more
extensive lighter margins of the coverts and the
scapulars, and the wrinkling of the nostril area in
study skins, which are supposed to be good charac-
ters for separating juvenile birds from older indi-
viduals, are not positive determinants and at any
rate these differences disappear within the first year
of life. Hence, the monthly samples shown in the
molt graphs are unquestionably made up of a va-
riety of age classes.
Oceanodroma leucorhoa beali Emerson
BEAL'S STORM PETREL
PELAGIC DISTRIBUTION.—Our at-sea observations,
backed by routine collecting of specimens through-
out the eastern Pacific (Figure 100), have deter-
mined that O. I. beali winters throughout a broad
area south of the breeding grounds from north-
central California (northern limit of recurrent
POBSP cruises) to at least 20°S. South of 10°S de-
creasingly lower densities are recorded. Within this
extensive area the distributional picture is some-
what confused because of the admixture of certain
other white-rumped forms, such as a scattering of
identifiable nominate leucorhoa, O. I. socorroensis
and two races of Galapagos Storm Petrels (O. tethys
tethys and O. t. kelsalli). Nevertheless dense winter-
ing populations of beali are found off both central
and southern California and throughout a broad
area from ca. 26°N to ca. 8°S, between 90°W and
120°W (Figure 101). Although not readily apparent
from the density distribution maps, these are the
areas most heavily surveyed by the POBSP. Hence,
as is often the case, graphic display of geographical
distribution of an organism more often tends to
show distribution of the researcher rather than of
the organism. The POBSP has not surveyed to the
west or south of the areas involved in EASTROPAC
cruises. Our summer cruises in the eastern Pacific
only extend to ca. 5°S; densities of O. I. beali are
fairly high to that point (Figure 102).
It may be noted that the density figures in the
O. I. beali pelagic distribution charts are consid-
erably higher than those for O. I. leucorhoa in the
central Pacific. Despite the fact that more forms are
involved in the eastern area, actual eastern Pacific
densities for all races of leucorhoa are roughly
three times greater than those recorded in the cen-
tral Pacific. Since the magnitude of observations
under varying conditions in both areas would elimi-
nate, or render insignificant, any temporary varia-
tions in the data gathering, the differences in
density consistently recorded between these two
areas must be regarded as real.
TAXONOMY.—Austin (1952) synonymizes both
O. I. beldingi from the northern California coast,
and O. /. willetti from the Coronados Islands, with
O. I. beali. Hence, O. I. beali applies to all Leach's
Storm Petrels breeding along the North American
west coast from extreme southeastern Alaska to the
166
130 W
20
10
130e
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
100° 90° .
• 1 bird
• 5 birds
40
30°
l.abela I.. '
Galapagos
Islands
120° 110° 100°
FIGURE 100.—Localities of collected specimens of Oceanodroma leucorhoa beali.
10"
10
90°
20 -
130
20
70"
FIGURE 101.—Winter densities (November, December, January, February, March) of
Oceanodroma leucorhoa beali.
168 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
13C w 70"
 0
50
10°
0°
Birds per square mile
.01 .20
40-
30
130° 120° 110° 100° 90° 80°
FIGURE 102.—Summer densities (May, June, July, August) of Oceanodroma leucorhoa beali.
Coronados Islands* just south of the United States-
Mexican border. Although this eliminates the con-
fusion involved in attempting to recognize more
than one form along the United States west coast,
many individuals in this complex cannot be dis-
tinguished from nominate leucorhoa to the north;
a considerable number of individuals from the
Coronados population cannot be distinguished
from either dark-rumped O. I. chapmani from the
San Benitos Islands (along the west-central coast
NUMBER 158 169
•o I
FHUJRE 103.—Seasonal molt stages in Oceanodroma leucorhoa beali. (See Figure 99 for explana-
tion of symbols.)
of Baja California), or O. I. socorroensis of Guada-
lupe Island.
BREEDING BIOLOGY.—A number of authors record
the nesting of O. I. beali along the western North
American coast; among these are Grinnell and
Daggett (1903), Willett (1915), Howell (1920),
Bailey (1927), E. W. Martin (1938), and Campbell
and Stirling (1968). The consensus of these reports
is that beali nests from at least April through Sep-
tember. Eggs are recorded from June to August,
and young from July to September. An exception-
ally early record of the Coronados Island popula-
tion ( = willetti of the 1957 A.O.U. Check-list) is that
of a three-quarter grown downy young taken 27 Ap-
ril 1929 (specimen in the San Diego Natural His-
tory Museum). Other specimens from the Corona-
dos in that institution were collected between 6
July and 5 September. A few of the September
birds are small downy young that probably would
not have left the island until October. The POBSP
captured three dark-rumped birds of the Coronados
population in a mist net on the night of 30 June
1968 on Center Island. No nests were found; the
population at that time could not have exceeded
100 birds.
MOLT.—The molt sequence of O. I. beali is
graphically demonstrated in Figure 103. From our
collected samples, beali appears to have a larger
percentage of individuals undergoing primary molt
during the prebreeding months (February-May)
than O. I. leucorhoa. Fall primary molt (probably
concerned with immatures) is terminated more
rapidly than in O. I. leucorhoa. Rectrix and body
molt are basically the same in beali and nominate
leucorhoa.
Oceanodroma leucorhoa chapmani Berlepsch
CHAPMAN'S STORM PETREL
PELAGIC DISTRIBUTION.—The pelagic distribution
of this form is little known, and POBSP surveys have
not been informative. Although the race is charac-
terized by the fact that all members have a dark
rump, its presence at sea is difficult to determine
because it is indistinguishable from dark-rumped
birds of both the Coronados and Guadalupe Island
populations present in the same area. Although
we have a considerable number of sightings of dark-
rumped birds from both the northern cruise areas
and the southern EASTROPAC areas, it is impossible
to assign racial designation to these sightings. An
admixture of collected specimens of dark-rumped,
intermediate, and white-rumped birds of small size
from the eastern Pacific are in most cases definitely
assignable to socorroensis. It is not possible by
measurements to separate definitely all dark-rumped
socorroensis from chapmani. We have collected
few, if any, chapmani at sea. On the basis of the
170 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
limited number of small, dark-rumped specimens
taken, however, it may be that this race winters
much closer to the coast than do beali, leucorhoa,
or socorroensis.
BREEDING BIOLOGY.—This dark-rumped form of
Leach's breeds predominantly or exclusively on the
San Benitos Islands off west-central Baja California.
During a POBSP survey of these islands from 26 to 29
April 1968, birds were plentiful on all three islands.
At that time they were calling from the air, as well
as occupying empty burrows and cavities among
the rocks. No eggs were found. Several adults were
discovered fatally impaled upon the spines of the
rampant cholla cactus (Opuntia sp.). A later June
survey noted 14 such individuals on one slope.
During a 25 to 27 June 1968 survey, most birds
were still calling from empty nest sites; some 20
percent of the population were on fresh to heavily
incubated eggs, but no chicks were found. The
birds occupy every feasible habitat on the islands
for nesting, with possibly the talus slopes and rocky
areas preferred. In these habitats they are in com-
petition for nest sites with the Black Storm Petrel
and Least Storm Petrel (Halocyptena microsoma).
Some chapmani used abandoned Cassin's Auklet
(Ptychoramphus aleutica) burrows, but a number
were noted digging their own burrows. DeLong
(POBSP) records that "despite the apparent weakness
of the bony structure of the legs, they dig with
great fervor and make the soil fairly fly."
The species' nocturnal and secretive nesting
habits make it extremely difficult to arrive at more
than a rough estimate of the population size. For
the June 1968 survey this was set at 50,000 birds
for the island group.
Oceanodroma leucorhoa socorroensis Townsend
SOCORRO STORM PETREL
PELAGIC DISTRIBUTION.—O. I. socorroensis were
found at sea as far north as 35°N and south to
10°N. A considerable number of specimens were
taken southeast of the breeding island of Guada-
lupe. As socorroensis cannot be distinguished in the
field with any degree of certainty, all records are
based on collected specimens (Figure 104). In late
February 1968 near 10°N, and between 100°W and
110°W, sizeable concentrations of socorroensis were
recorded in mixed flocks composed of Oceanodroma
tethys tethys, Oceanodroma leucorhoa beali, and a
few large specimens that are best referable to O. I.
leucorhoa. No socorroensis were collected below
10°N, although extensive collecting was done
throughout the cruise in these longitudes to 20°S.
The western limits of the pelagic distribution are
unknown. From our evidence, apparently socor-
roensis does not range as widely from the breeding
grounds, nor as far from the coast, as do beali or
leucorhoa.
TAXONOMY.—This race is the smallest and most
variable in rump color of all forms of leucorhoa in
the Pacific. The characters of greatest use in sep-
arating this from other races are wing and bill
length, and the overall slightness of the bill.
Weights, when available, are also useful in dem-
onstrating the small size.
A series of 109 POBSP specimens from the summer
breeding population show a range of wing length
from 135 mm to 150 mm with a mean of 141.89.
Austin (1952) records 25 socorroensis with wing
length ranging from 141 mm to 157 mm, and with
a mean of 148.8 ± .88. Another series of winter
breeding birds composed of POBSP specimens as well
as specimens from the San Diego Natural History
Museum contains 19 males with a wing length
range of 141 mm to 150 mm, and 18 females with
a range of 140 mm to 147 mm. With this overall
range of from 140 mm to 150 mm for both sexes
(although close to the 135 mm to 150 mm range
for summer socorroensis) the winter birds tend to
be slightly larger, although there is complete over-
lap between winter and summer birds. Considering
all birds of both winter and summer populations
from a sample of 146 birds, the range is 135 mm
to 150 mm. This large sample should totally blan-
ket Austin's sample of 25 birds, but his series shows
considerably larger measurements in both range
and mean. His sample apparently contains both
winter and summer Guadalupe birds and also ap-
parent stragglers (probably of O. I. beali) taken off-
shore Guadalupe. For example, several obvious
beali (by their worn plumage and measurements)
taken offshore in winter were found in the series
of socorroensis in the San Diego Museum.
The winter breeding population on Guadalupe
of slightly larger birds is in need of considerable
investigation. If this population is sufficiently dif-
ferent to warrant subspecific recognition, the ap-
propriate name would be Oceanodroma leucorhoa
NUMBER 158 171
130° W no"
N
20
10
100
-140°
• 1 Bird
Breeding locality
30"
10
130 120 110 100
FIGLRE 104.—Localities of collected specimens of Oceanodroma leucorhoa socorroensis.
kaedingi. For convenience, I will refer to the win- ing population, socorroensis. Besides their slightly
ter breeding birds as "kaedingi" to differentiate larger size, kaedingi are, in part, further distin-
them from the currently recognized summer breed- guishable from socorroensis by rump color. All 37
172 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
FIGURE 105.—Variation in rump color of Oceanodroma leucorhoa socorroensis from Guadalupe
Island.
winter-breeding kaedingi examined are white-
rumped, the amount of white ranging from 2
through 4 on a scale of 0 to 5 measuring the amount
of white in the rump. The series of 37 showed the
following scale figures: 2 (14%), 3 (40%); interme-
diates between 3 and 4 (11%); and 4 (35%). Thus
an average bird of this population would have
rump color of slightly over 3, about comparable to
that of O. I. beali. Summer socorroensis, on the
other hand, have rump color ranging from cate-
gories 0 through 5, or from pure dark to pure
white rumps (Figure 105). Austin's (1952:401) state-
ment characterizing rump color of socorroensis,
"rump patch variable, almost always with some
white, but never as much as in typical beali," is
not quite true. As discussed in the breeding biology
section, 90 percent of the birds breeding on Islote
Negro in June 1968 had pure dark rumps. Con-
versely certain individuals taken off Islote Afuera
have a pure white rump; even the feather shafts are
white (as in Oceanodroma castro), a condition that
rarely occurs in any race of leucorhoa. Obviously
these differences between socorroensis and kaedingi
are insufficient to permit racial designation of most
individuals taken away from the breeding island,
so at present it is useless to attempt to recognize
these two populations as taxonomically distinct.
These differences, however, are neither more nor
less than those displayed by most named subspecies
of leucorhoa. A small- to average-sized O. I. chap-
mani from the San Benitos Islands would be in-
distinguishable from a dark-rumped socorroensis
from Guadalupe Island, as would a large chapmani
be indistinguishable from a dark-rumped "willetti"
(=beali) from the Coronados. Unfortunately we
are dealing with populations that show few external
morphological differences. Nevertheless the winter
breeding population at Guadalupe, whether it is
recognized as a distinct race or not, undoubtedly
differs physiologically from the summer popula-
tion. Despite equalizing ocean temperatures, Guada-
lupe is at a fairly high northern latitude (29°N)
with a considerable difference between summer and
winter temperatures. The possibility exists that
food items available to the young in the surround-
ing waters differ considerably between winter and
summer. To my knowledge kaedingi is the only
hydrobatid (besides Oceanodroma tristrami) in the
northern hemisphere that nests in the northern
winter.
BREEDING BIOLOGY.—Oceanodroma leucorhoa so-
corroensis breeds only on Guadalupe Island, some
200 miles west of Baja California, Mexico. The
POBSP surveys, as well as numerous surveys by Carl
NUMBER 158 173
Hubbs of Scripps Institution of Oceanography and
other parties, have shown that at least the bulk of
the storm petrel population is now restricted to
breeding on tiny offshore islets free of introduced
predators. The two best surveyed among these islets
are Islote Negro and Islote Afuera near the Mexi-
can settlement at the southern tip of the main
island. We have indirect evidence that a sizeable
population may still breed on the main island
proper, but the actual nesting area has not been
discovered.
This race of Leach's has presented some of the
most puzzling problems of all forms studied. Be-
tween 22 and 23 June 1968 the populations on
both Islote Negro and Islote Afuera were surveyed.
On Islote Negro the estimated population of sev-
eral thousand birds, judged by several hundred
handled at the nest sites, was composed almost
without exception of dark-rumped birds. On Islote
Afuera, only about a mile and a half away, we
estimated more than 90 percent of the population
were white-rumped. There appeared to be no mor-
phological difference except rump color between
the two populations. This was inferred not only
from living birds, but from the series of skins col-
lected at the time. Vocalization recordings of in-
dividuals from both populations were taken, but
these have not yet been analyzed. Suffice to say that
the field workers could discern no differences in the
calls of the two populations. To complicate mat-
ters even more, a series of about 50 birds collected
aboard ship on the night of 28 June immediately
off the southeast coast approximately 10 miles from
these islets, contained individuals with every con-
ceivable rump color from white through completely
dark. Many of these were not in breeding condition,
but a considerable number of birds with interme-
diate-colored rumps had heavily vascularized brood
patches, indicating that eggs or young were already
present. Had these birds been part of the popula-
tions on either Islote Negro or Afuera, it seems cer-
tain that they would have been noticed. Hence, this
population was suspected of nesting somewhere on
the main island. Huber spent about eight hours
about the cliffs and among the pines on 29 June,
but found no breeding storm petrels.
No explanation is offered regarding the allo-
patric distribution on adjacent islets of these popu-
lations. That chance would be operative in segre-
gating these color morphs appears to be a mathe-
matical improbability, especially in view of the
number of individuals involved. The total exclu-
sion of an influx of birds of opposing rump colors
can hardly be plausible. For the present, this con-
fusing issue must await a more detailed study.
The nesting stages of the populations on these
islets on 22 and 23 June 1968 were as follows:
Islote Negro: The summer breeding population
on Islote Negro was estimated to be about 4000
birds. Storm petrels were found nesting over the
entire islet, but definite concentrations were found
wherever large masses of volcanic rocks were pres-
ent, these apparently being the most favored sites.
Lesser numbers were found nesting in soil burrows,
excavated by Black-vented Shearwaters (Puffinus
puffinus opisthomelas) or Cassin's Auklets, and un-
der dense mats of plant material. The storm petrels
themselves also excavated a considerable number
of burrows in the hard-packed soil. The tiny en-
trance holes to many extensive burrows indicated
that only storm petrels could have dug them.
Varying amounts of plant material in the form
of seed pods or dried stems (usually of the intro-
duced ice plant, Mesembryanthemum sp.) were
used for nest linings. Nests in rocky areas usually
had very little nest lining, the eggs being deposited
on the sparse soil or on the rocks in some cases. The
population on Islote Negro at this time was ap-
proaching its egg-laying peak with an estimated 20
percent of the nests containing fresh eggs. Only a
single egg out of about 30 examined showed ad-
vanced incubation. The majority of the popula-
tion appeared to be paired with completed or par-
tially completed nest sites.
An occasional fresh egg was found lying on the
ground outside nest cavities. These were presum-
ably inadvertently kicked out by the shearwaters or
murrelets, both of which utilized the larger nooks,
and rock or soil crevices. Many old storm petrel
eggs, presumably of the winter breeding popula-
tion, were noted in and about active nest sites. It
appeared that the two populations frequently uti-
lized the same nest sites. This seems reasonable, as
practically every good nest site was occupied by the
summer breeders.
Birds vocalized continuously through the night,
with a calling frenzy shortly after full dark. Most
birds called from burrows; a few called on the
wing.
All birds examined (a minimum of 500) on Islote
174 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
Negro had dark rumps. The most white noted on
any bird was a few feathers at the sides of the
rump. In these individuals the feathers were more
gray than glaringly white.
Islote Afuera: Islote Afuera supported about 25
percent fewer birds than Islote Negro. The nesting
cycle was roughly in the same stage, with a some-
what higher percentage of nests with eggs. This
may have been due to the considerably less nest
construction necessary, as the vast majority of birds
on Islote Afuera occupied natural pockets and crev-
ices in the lava rock instead of excavating burrows
in the sparse soil.
At least 90 percent of the birds on Islote Afuera
were white-rumped. Other than rump color, no
differences could be detected between the popula-
tions of the two islets. Except for the following rec-
ords of immatures, we have few data pertaining to
later aspects of the breeding season of O. I. socor-
roensis. Huey (1930) records a juvenile with con-
siderable down still adhering to the plumage that
came aboard ship about a mile off Guadalupe on
the evening of 27 September 1929, and another with
completely downy underparts that came aboard
ship 28 September, 26 miles north of Guadalupe.
The POBSP found flying young with down on ven-
tral regions sitting around burrows at night on 21
October 1967 on Islote Negro. The latest date for
young of this population is a male juvenile with
completely downy underside that flew aboard a
ship off northeast anchorage, Guadalupe, on 12
November 1954. The three specimens mentioned
above are in the San Diego Museum of Natural
History. From the above records it can be surmised
that young socorroensis leave the islands through-
out the fall and hence overlap with the winter
breeding population, at least from September
through November.
Measurements of a series of 20 eggs of the sum-
mer breeding populations of Islotes Negro and
Afuera are given in Table 28. Eggs of socorroensis
are white with a wreath of fine reddish brown dots
about the large end. The small size of socorroensis
is reflected in the egg dimensions when compared
to those of other races of Leach's Storm Petrel.
WINTER BREEDING POPULATION (O. /. kaedingi
Anthony).—More confusing is the status of the
winter breeding population that arrives on the same
islets before all the summer breeders leave (see
Hubbs, 1960). No POBSP survey was made during
TABLE 28.—Egg measurements of three subspecies
of Leach's Storm Petrel (Oceanodroma leucorhoa)
(data for O. I. leucorhoa and O. I. beali are from
Palmer, 1962)
Measurement
Length
with SD
(n = 20)
Breadth
with SD
(n = 20)
O. /. leucorhoa O. I. beali O. I. socorroensis
(Bay of Fundy) (NW U. S. coast) (Guadalupe Island)
3S.01±l.06
23.58 ±0.57
S1.46±1.S1
23.21 ±0.78
29.76 ±0.72
22.19 ±0.74
the height of the breeding season of kaedingi, and
we have few specifics pertaining to its cycle. It ap-
parently begins coming to the islets in August, and
thus at least a portion of the two populations over-
lap, as not all the summer breeders have left the is-
lets by this time. On 21 October 1967 on Islote
Negro, three pairs were noted during a mid-day
survey of the islet. Approximately 30 minutes after
sundown birds began appearing, and within an
hour an estimated 100 birds were calling from the
air and about 400 from rock crevices and burrows.
Previous mention is made of socorroensis juveniles
recorded at this time.
Specimens of juvenile kaedingi in the San Diego
Museum of Natural History indicate the extent of
the breeding season. J. R. Henderson took a three-
quarters downy young from a burrow on 31 Janu-
ary 1950 and Carl Hubbs collected similarly sized
young under a boulder on Islote Afuera on 11 Feb-
ruary 1957. A juvenile with completely downy
belly was taken aboard ship by Hubbs at northeast
anchorage on 1 March 1965. A POBSP survey found
on Islote Negro on 29 April 1967 one large juvenile
with down on the venter. It apparently represented
the last of the 1966-1967 winter season kaedingi.
The June 1968 POBSP survey found about ten fully
feathered chick mummies on Islote Afuera (presum-
ably birds of the winter breeding population). Only
one of these had a dark rump. All previously col-
lected winter birds were white-rumped.
The conditions that cause two or more popula-
tions of the same species, or of different species, to
utilize the same geographical area for nesting at
different times of year appear to be the presence
of vast uniform feeding grounds, coupled with very
limited land space for breeding. Much the same
NUMBER 158 175
100
90-
80
70
60-
c
» 50-
£.
40-
30-
20-
10-
New YZAGr I I Old olting Non-molting
FICURE 106.—Seasonal molt stages in Oceanodroma leucorhoa socorroensis.
(See Figure 99 for explanation of symbols.)
situation occurs at islands across the equatorial
Pacific where two or more colonies of the same
species breed on the same island at different times
of the year. This is most noticeable in the Phoenix
and Line groups with the Sooty Terns (Sterna
fuscata) because the colonies are exceedingly large.
However, species that are found breeding all
months of the year, yet with a known changeover
of marked individuals (such as the White Tern,
Gygis alba) must be doing the same thing, only
in a less dramatic way. How these species arrive at
such "shift-work" utilization of an island is little
known, but the factors bringing about such a situa-
tion are obvious. Aside from a shortage of actual
physical space on these small islands, and the pos-
sibility of insufficient food in the surrounding wa-
ters to support the entire population at any one
time of year, the social stresses between individuals
would prohibit reproduction if all birds were to
occupy the same area at one time.
MOLT.—Our samples, except for late summer, are
too small and disjunct in regard to time of year to
be especially meaningful. Data are graphically
demonstrated in Figure 106. For the most part, molt
sequence closely parallels that of O. I. beali.
PREDATION.—Aside from the ever-present danger
to storm petrels posed by the Western Gull' (Larus
occidentalis) (primarily avoided by the strictly noc-
turnal habits of the hydrobatids), Burrowing Owls
(Speolyto cunicularia) appeared to be the greatest
threat to these small Procellariiformes. In order to
study predation, numerous remains of owl-eaten
storm petrels were collected on Islote Negro during
the April 1968 survey and again during the June
1968 visit. Although little of quantitative value can
be determined from this study because of the wind-
scattered remains, etc., predation was considerable.
In April 1967 a downy young storm petrel was
found, partially eaten, at the end of a burrow, indi-
cating the possibility that the small owls may enter
occupied storm petrel burrows and attack the
young. At least one pair of owls each were noted on
176
130'V 120 110 100
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
90° 80°
130° 120 110° 100° 90° 80°
FIGURE 107.—POBSP s ightings of Oceanodroma homochroa.
Islote Negro and Islote Afuera. During June 1968
the owls were largely feeding upon downy young
Xantus' Murrelets (Endomychura hypoleuca), which
were hatching in great numbers and trying to make
their way to water.
Oceanodroma homochroa (Coues)
ASHY STORM PETREL
PELAGIC DISTRIBUTION.—The POBSP records of
this species are few, with low numbers of scattered
sightings from ca. 7°N to 47°N; all sightings are
along the western North American coast (Figure
107). The most pelagic sightings are of two birds
near 13°N about 480 miles from the coast. The
only concentration we recorded was off the Baja
California coast between 28°N and 29°N during
August 1967.
Uncertainty concerning the pelagic range of this
species results primarily from difficulties in sep-
NUMBER 158 177
arating it in the field from closely similar dark-
rumped Oceanodroma leucorhoa races such as O. I.
chapmani, O. I. socorroensis and O. I. willetti
(— O. I. beali). It probably occurs in rather low
numbers compared with its closely allied forms.
BREEDING BIOLOGY.—A POBSP survey around San
Miguel Island in the Channel Islands off the Cali-
fornia coast 14 and 15 May 1968, found small num-
bers of birds on both Castle Rock and Prince Islet,
all in empty nest cavities in rock crevices among a
colony of Cassin's Auklets. Flight calls of the storm
petrels were heard shortly after full dark, but it was
impossible to make an estimate of the population
size because of the din of surf and calling auklets.
The few birds examined at this time had bare or
defeathering brood patches.
On another survey of San Miguel from 28 May
to 7 June 1968, birds were still courting; one egg
each was found on Castle Rock and Prince Islet.
The maximum estimate at that time was 100 birds
for the San Miguel population. A bright moon at
the time seemed to retard the arrival of the birds
on the islets and reduced their activity. Perhaps the
Western Gulls take advantage of the moonlight to
prey upon these petrels as the Great Black-backed
Gulls (Larus marinus) and Herring Gulls (L. argen-
tatus) prey upon Leach's Petrels in the Bay of
Fundy (Gross, 1935). Gross notes that on moonlit
nights very little storm petrel activity occurs.
In the Coronados Islands Joseph Jehl of the San
Diego Natural History Museum collected a few
Ashy Storm Petrels in a mist net on Center Island
the night of 17 May 1968, but POBSP recorded none
during a 30 June to 1 July 1968 visit. No evidence
of nesting was found on either visit; apparently
very few individuals utilize the Coronados. Orr
(1944) gives an excellent summary of what little is
known of the breeding biology of this species along
the California coast.
From a series of 20 birds collected at San Miguel
Island, two show considerable amounts of whitish
feathers at the sides of the rumps. This is interest-
ing, not only from the standpoint of the relation-
ship of homochroa to leucorhoa, but from the fact
that selection for dark rumps seem to have affected
all hydrobatid forms along the middle western
North American coast (an area of excessively high
gull predation?).
Oceanodroma castro (Harcourt)
HARCOURT'S (or MADEIRAN) STORM PETREL
PELAGIC DISTRIBUTION.—The pelagic range of
Harcourt's Storm Petrel in the Pacific is rather ex-
tensive, as indicated in Figures 108 and 109. The
sightings recorded probably represent only a small
fraction of the actual birds seen, as those shown
represent only sightings considered positive. The
more extensively white rump of Harcourt's as op-
posed to Leach's could often be used to separate
these two forms at close range, but undoubtedly
the majority of birds of this species were recorded
by POBSP personnel only as "unidentified white-
rumped storm petrel." Despite the difficulty of dis-
tinguishing Harcourt's from other white-rumped
forms (especially Leach's and Wilson's), specimens
of Harcourt's collected at various points through-
out the pelagic range lend credibility to the obser-
vations.
In the central Pacific birds were recorded com-
monly south and southwest of the Hawaiian Is-
lands to 4°S, with one sighting south of 8°S. Birds
were also common to the west and northwest of the
Hawaiian Islands and it is likely that the species
ranges beyond the boundaries shown in the north-
west sector as birds were observed practically to the
limits of POBSP cruises in that area. Although it can-
not be determined from the collected specimens,
central Pacific records probably represent birds
from the Hawaiian population (dubiously distinc-
tive O. c. cryptoleucura).
Harcourt's distribution in the eastern Pacific is
even more extensive than that recorded in the cen-
tral Pacific. Sightings were recorded from near
Panama west to 120°W and from 25°N to south of
13°S. While it might be logical to assume that east-
ern Pacific records are attributable to the Gala-
pagos Islands population, we cannot, in fact, assign
origin to them. The species obviously ranges so
widely at sea that sightings at any point could be
of birds from any one of the Pacific breeding sta-
tions. Three specimens taken near the Galapagos
are most probably referable to the breeding race of
that island group (O. c. "bangsi"), but as Austin
(1952) demonstrates, none of the named Pacific sub-
species of this form are separable.
BREEDING BIOLOGY.—The available breeding data
for this species are summarized by Palmer (1962).
The POBSP was unable to add further information
of its breeding status in the Hawaiian Islands.
NUMBER 158 179
130 W
• 1 bird
• 5 birds
O Specimens collected
20
130° 120° 110° 100° 90° 80°
FIGURE 109.—I»OBSP sightings and specimens of Oceanodroma castro in the eastern Pacific.
court's Storm Petrel during a day of collecting on
25 June 1966 just off Kauai Island near the Waimea
Canyon area, where I saw a considerable number
of birds and collected one specimen, a female with
ovary enlarging, but not yet in breeding condition.
Birds appeared to be both going to and leaving the
island throughout the day, but we could not ap-
proach the shoreline closely enough to determine if
the birds went to land. The population on Kauai,
as judged by the number of specimens and sight-
ings, cannot be large.
MOLT.—The data from the ten specimens col-
lected by POBSP are given in Figure 110. Briefly, our
May and June birds collected in the central Pacific,
as well as March birds collected near the Galapagos,
are in new plumage without molt except for ter-
minal stages in the rectrices of the May birds. Octo-
ber and November central Pacific birds are in inter-
mediate primary and body molt with very worn,
but unmolting, rectrices. Oddly enough, a Gala-
pagos bird collected in late July is in exactly the
same stage of primary molt as two November speci-
mens from the central Pacific.
Oceanodroma tethys (Bonaparte)
GALAPAGOS STORM PETREL
PELAGIC DISTRIBUTION.—The Galapagos Storm
20
130° 120° 110° 100° 90° 80°
FIGURE 109.—I»OBSP sightings and specimens of Oceanodroma castro in the eastern Pacific.
court's Storm Petrel during a day of collecting on
25 June 1966 just off Kauai Island near the Waimea
Canyon area, where I saw a considerable number
of birds and collected one specimen, a female with
ovary enlarging, but not yet in breeding condition.
Birds appeared to be both going to and leaving the
island throughout the day, but we could not ap-
proach the shoreline closely enough to determine if
the birds went to land. The population on Kauai,
as judged by the number of specimens and sight-
ings, cannot be large.
MOLT.—The data from the ten specimens col-
lected by POBSP are given in Figure 110. Briefly, our
May and June birds collected in the central Pacific,
as well as March birds collected near the Galapagos,
are in new plumage without molt except for ter-
minal stages in the rectrices of the May birds. Octo-
ber and November central Pacific birds are in inter-
mediate primary and body molt with very worn,
but unmolting, rectrices. Oddly enough, a Gala-
pagos bird collected in late July is in exactly the
same stage of primary molt as two November speci-
mens from the central Pacific.
Oceanodroma tethys (Bonaparte)
GALAPAGOS STORM PETREL
PELAGIC DISTRIBUTION.—The Galapagos Storm
180 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
October - November
N--3
New 1223Growing L .J Old 1H3 Molting on-molting
FIGURE 110.—Seasonal molt stages in Oceanodroma castro. (See Figure 99 for explanation of
symbols.)
Petrel is one of the few white-rumped species in the
Pacific that can be identified with a fair degree of
certainty under most field conditions. The ex-
tremely large, prominent, wedge-shaped white
rump, and alternately fluttering and bouncy flight
are good characters for distinguishing most individ-
uals from Oceanodroma lencorhoa, the species reg-
ularly recorded with O. tethys over much of the
latter's pelagic range. When I first encountered
tethys at sea, and l>efore I learned some of its more
subtle characters, I had difficulty making on-the-
spot distinctions between it and equally small, ex-
ceptionally white-rumped O. I. socorroensis. Part
of this difficulty arose from the fact that both forms
were in extremely ragged plumage at the time. It
may be noted that specimens of both races of O.
tethys had medium-gray oil (uropygial) glands, as
opposed to the creamy white oil glands of all races
of O. leucorhoa and of O. castro.
Supposedly, the nominate race (O. /. tethys)
breeds in the Galapagos from April through Sep-
tember^). The POBSP pelagic specimens of this race
are confined to August 1967 and March and April
1968. During the latter period concentrations were
especially prominent in a broad band along the
equator from about 3°N to 2°S between longitudes
97°W and 105°W. August specimens were taken at
12°N, 120°W. A June specimen in the San Diego
Natural History Museum was taken at 15°N,
101 °W. Huey (1952) reports a specimen taken by
J. R. Pemberton in March 1938 at Roca Partida in
the Revilla Gigedo Islands south-southwest of Baja
NUMBER 15* 181
130° W 120
1.01 +
Specimens collected
O. tethys tethys
• lb ird
• 5 birds
O. tethys kelsctlli ¥•
120 110 100 90
FIGURE 111.—I*>BSP sightings and specimens of Oceanodroma tethys.
80 70
California (ca. 19°N). In this same publication
Huey reports a male of this race in nonbreeding
condition (testes 3 x 2 mm) taken from a colony of
Oceanodroma leucorhoa kaedingi on Guadalupe
Island off Baja California in January 1950. The
bird was found in a nest cavity with a downy young
kaedingi. For whatever reason the bird came to the
island, Hubbs (1960) is incorrect in regarding this
as constituting a breeding record for the Galapagos
Storm Petrel at Guadalupe. I have examined this
specimen at San Diego and, except for a short,
heavy bill and slightly small wing for O. t. tethys, it
corresponds well to that form. This locality, at
roughly 29°N, apparently marks the northern
limit for the nominate race.
The second-named form of this species, O. tethys
kelsalli (Lowe), breeds on the Pescadores and San
Gallan Islands off the coast of Peru. Northernmost
POBSP records of this race are of two individuals
collected on 6 August 1967 at 23°03'N, 118°24'W.
Moffitt (1938) reports 12 specimens collected at
22°30'N, 112°39'W on 22 July 1905 and another
specimen taken at 16°45'N, 110°28'W on 22 Sep-
tember 1933. These birds had traversed northward
through most of the recorded pelagic range of the
nominate race. Our pelagic sight records (Figure
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
Primary Rectrix
1 March-2 April
N=36
Body Primary Rectrix
11 August
Body
New E22 Growing C H Old I Molting
FIGURE 112.—Seasonal molt stages in Oceanodroma tethys tethys.
(See Figure 99 for explanation of symbols.)
I l l) cannot be qualified to race as the two named
forms are separable only on mensural differences.
The pelagic ranges of the two races show consid-
erable sympatry.
Other POBSP specimens of O. /. kelsalli were col-
lected in the Gulf of Panama during August 1968
and June and August 1969. Large numbers of O.
tethys were observed in the gulf from August
through November 1968 and June through August
1969. Although only a relatively few specimens
were collected, all are definitely referable to O. t.
kelsalli. On this basis, it is reasonable to assume
that most Gulf of Panama wintering O. tethys are
of the race kelsalli. From November on, tethys is
absent from the Panama gulf waters, when it is ap-
parently replaced by the Black Storm Petrel and
the Least Storm Petrel.
MOLT.—Considerable variation in molt is dis-
played in two series of O. t. tethys collected at sea.
A series of 36 taken between 1 March and 2 April
falls essentially into two categories:
1. Molting: As shown in Figure 112, 44 percent
of the birds in this sample are molting in both pri-
maries and rectrices. There was no exact correlation
in the progress of molt between these two plumage
areas. A few birds still molting the primaries had
completed their rectrix molt and vice versa. Hence,
although only 44 percent of the sample is involved
in each case, the total number of individuals con-
cerned in these combined categories equaled 50
percent of the sample. In practically every case, pri-
mary and/or rectrix molt was accompanied by
body molt.
2. Nonmolting: The remainder of the sample
NUMBER 158 183
(50%) not in primary or rectrix molt, was, for the
most part, in old, but relatively unworn plumage,
indicating that molt had occurred within the previ-
ous few months. Definition of plumage condition
in rectrices or remiges of birds not in molt is some-
what subjective. When molting, a distinction is
easily made between new and old feathers, pri-
marily because the feathers being replaced are obvi-
ously old and show considerable wear and discolor-
ation.
The majority of birds in both molting and non-
molting categories were adults, judging by gonadal
condition. None was in breeding condition, al-
though several may well be considered either to
have begun gonadal enlargement or retrogression.
The nominate race of O. tethys is supposed to have
a complete postbreeding molt from July through
October (Murphy, 1936:730). It appears from our
sample that the duration of the molt cycle is much
more extensive. If tethys has a molt cycle similar
to races of O. leucorhoa, a large number of birds
would be expected to terminate a molt just prior to
the advent of a breeding cycle.
The small series of five birds collected in August
are all in finishing stages of complete molt, or in
very new plumage. A combination of immatures
and adults is represented, judging by gonads. This
series substantiates Murphy's (1936:730) statement
concerning a postbreeding molt from July through
October, but half of the large series taken in March
and April certainly do not correspond to this pat-
tern. Obviously we need to know the ages and times
of breeding cycles of individual birds before it will
be possible to draw conclusions concerning the molt
cycle of the species.
Oceanodroma hornbyi (Gray)
HORNBY'S STORM PETREL
PELAGIC DISTRIBUTION.—The few POBSP records
of sightings and specimens of this southern hemi-
sphere hydrobatid were recorded in August 1967
in the Peru Current southeast of the Galapagos Is-
lands along the South American coast (Figure 113).
Three specimens taken at 3°38'S, 87°01'W were
adult females with medium fat, ovaries between 3
and 5 mm, granular. I have no data for a fourth
specimen taken south of the above area at 9°29'S,
82°05'W. Murphy (1936:741-743) limits the species
to the Peru Current roughly between Valparaiso,
Chile, and the equator.
The breeding grounds of O. hornbyi are still im-
precisely known, but Johnson (1965:108) cites four
points of evidence that strongly indicate it nests
inland along the Chilean and Peruvian coasts.
These are summarized as follows: (1) In 1894, Dr.
Darapsky found a fully grown immature specimen
(with patches of down still adhering) in a hole in
the hills of the coast ranges of the port of Taltal,
in the southern Antofagasta Province (specimen in
the National Museum of Santiago). (2) In 1923,
Wetzel found mummified nestlings in holes in the
canyon of the Loa River at the point where it
crosses the nitrate desert inland from Tocopilla.
(3) Another mummified specimen was found in De-
cember 1923 in the nitrate fields of Santa Luisa de
Taltal, 30 miles from the coast at an altitude of
5000 feet. (4) The Koepckes took several specimens
at night in the streets of Lima, Peru. Some of these
had abundant down patches on the abdomen.
Oceanodroma melania (Bonaparte)
BLACK STORM PETREL
PELAGIC DISTRIBUTION.—Abundant observations
of this species were made on POBSP cruises along the
western American coast from about 38°N to the
equator. Sightings below the equator (to 7°S) were
few, as were those in the extreme northern sector
and at extreme distances from the coast (Figure
114). There was a pronounced movement into the
Gulf of Panama during November, which presum-
ably indicates a southward movement after the
breeding season. The species was common in the
gulf area until June, during which time the Least
Storm Petrel was also abundant. Most sightings
along the California coast are summer records, but
a few birds were recorded above 34 °N in Decem-
ber. At sea the Black Storm Petrel is a swift flyer.
During collecting activities off the Baja California
coast, the birds appeared to have no problem in
outdistancing our skiff, which was moving at an
estimated 25 knots.
BREEDING BIOLOGY.—Coronados Islands: During
a POBSP survey on 1 and 2 May 1968, Black Storm
Petrels began coming in over the cove on North
Island precisely at full dark. Their appearance was
in exact correlation with the termination of West-
ern Gull movements and one may be certain that
184 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
100 W 80°
20'
N
ltf
10'
S
20'
70° .
20
• lbird
O specimen collected
100 90
FIGURE 113.—POBSP sightings and specimens of Oceanodroma hornbyi.
the timing of these activities is not coincidental.
Storm petrel aerial movements and vocalizations
were most intense during the first few hours after
dark and had essentially stopped by midnight. An
increase in flying birds was noted near the beach at
about 0100; this possibly represented birds leaving
the island. Two characteristic calls were noted: an
aerial call described by most field workers as "puck,
puckaroo," and a variable "twitter" uttered only
from nest cavities. This latter call may continue for
many minutes. The nest sites on North Island were
invariably in deep recesses under large boulders
NUMBER 158 185
130 W
• 1 bird
• 10 birds
• 20 birds
f Breeding localiti
110" 100° 90°
FICURE 114.—POBSP sightings of Oceanodroma melania.
that prevented investigating the nests in most cases.
A few such large "fortresses" harbored more than
one pair. The four to six nests that could be exam-
ined at this time contained both members of the
pair, but none had eggs or young. Individuals
taken in a mist net had bare or defeathering brood
patches. During a visit on 30 June 1968, a few birds
were noted on Center Island and a chick, estimated
to be only a few days old, was found on North Is-
land. In the San Diego Natural History Museum a
series of downy nestlings, ranging in size from small
to large, are recorded from the Coronados from 13
August to 5 September.
San Benitos Islands: On a POBSP survey from 26
to 29 April 1968, these petrels were noted coming
in over the islands at night, with a peak of aerial
movements and vocalizations during the first three
hours of darkness. Little activity was noted for the
remainder of the night. No evidence of nesting was
recorded at that time. During a survey from 25 to
27 June 1968, a sample of nest sites examined
showed that birds were on fresh- to medium-incu-
bated eggs, with a few individuals still calling from
as yet empty nest cavities. The preferred nesting
sites of this species seemed to be under large boul-
ders on talus slopes. In some cases Least Storm
186 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
Petrels were found nesting in the same burrows
with the Blacks. The Black Storm Petrels were
found on all three islands in the San Benitos group,
with greatest densities on West Island. A popula-
tion estimate for the island group at that time was
10,000+ birds. A prime mortality factor was the
abundant cholla cacti throughout the nesting area.
Birds flying about in the dark were often impaled
upon the spines; on one slope several Black Storm
Petrels were found dead in this manner (see com-
parable data on Oceanodroma leucorhoa chap-
mani).
120 W
' 1 bird
• 5 birds
• 10 birds
O specimen collected
20
120
20
110 100' 70°
FIGURE 115.—POBSP sightings and specimens of Oceanodroma markhami.
NUMBER 158 187
Oceanodroma markhami (Salvin)
MARKHAM'S STORM PETREL
PELAGIC DISTRIBUTION.—Most POBSP pelagic
sightings of this species are in August and Septem-
ber along a broad equatorial front from the South
American coast west through the Galapagos area to
105°W (Figure 115). A group of more northerly
sightings off the coast of Baja California may well
represent erroneous identifications attributable to
the very similar Oceanodroma melania. I doubt if
the two species can be distinguished in the field,
and melania would certainly be the more expected
form in these northern waters. It may be noted,
however, that Murphy (1936:740) cites Loomis
(1918:174) as having recorded markhami at 13°
28'N, 108°52'W, and just south of Cocos Island,
5°33'N, 87°00'W. Two specimens were collected
by POBSP along the South American coast. Both in-
dividuals taken on 6 August 1967 at 00°18'N, 81°
51'W were females with small gonads (and oviducts
never used), light fat and heavy contour molt.
The breeding grounds of this species are still un-
known. Murphy (1936:739) records several females
with fully formed eggs in the oviducts taken by
Rollo Beck in early June, 75 to 80 kilometers off
the Peruvian coast. He further states that the only
islands off the Peruvian coast not thoroughly in-
vestigated were the Hormigas de Afuera, which
because of their exceedingly low elevation seemed
a doubtful nesting site. He suggests the possibility
of their nesting inland in the Andes. Johnson
(1965:107) notes that Carlos Reed collected a speci-
men on 1 December off Antofagasta, Chile (23°S)
that still had traces of down on the head and ab-
domen. He also records an immature specimen with
abundant down on the breast and abdomen taken
between Pica and Matilla, some 30 miles inland
from the port of Iquique, Chile.
Oceanodroma tristrami Salvin
SOOTY STORM PETREL
PELAGIC DISTRIBUTION.—The POBSP pelagic sight-
ings of this species are from various positions around
the Hawaiian Islands, with concentrations near the
Hawaiian Leewards (breeding sites), as would be
expected (Figure 116). A disjunct, high-density con-
centration was also recorded between 44°N and
45°N near 173°W. The latter records may pertain
to tristrami populations from the Bonin or Izu
islands, or possibly to Oceanodroma matsudairae
from the Bonin Islands. It is extremely doubtful if
tristrami could be differentiated from O. matsu-
dairae in the field. No specimens are available to
clarify which of the two species were seen here, but
even if specimens were available, distinctions could
not be made between the Hawaiian and Bonin Is-
land populations of O. tristrami.
BREEDING BIOLOGY.—Sooty Storm Petrels have a
disjunct breeding distribution, with populations at
Torishima in the southern Izu Islands (Austin,
1952), the Bonin Islands, and the Hawaiian Lee-
wards. The specific localities in the Leewards are
Laysan, Pearl and Hermes Reef, and Midway. Rich-
ardson (1957:19) mentions the possibility of their
breeding on Necker but gives no details. Bryan and
Green way (1944:96) record the species on Nihoa.
Clapp and Woodward (1968:10) report recent
POBSP records on Kure Atoll and French Frigate
Shoals. The latter cite the collection of three speci-
mens with definitely enlarged gonads on Kure (one
each on 1 January 1964, 1 March 1965, and 12 De-
cember 1965). The January 1964 bird was one of
two observed digging a burrow. Two other birds
were observed digging a burrow on 2 April 1964,
and one examined in the field between 30 Decem-
ber 1966 and 5 January 1967 had a completely bare
brood patch. Others were seen on Kure between
November and January during the years 1963 to
1967. Three specimens collected 1 to 3 January
1967 have greatly enlarged gonads. On 14 March
1967, one very small downy chick and another
about three-quarters grown were found in shallow
burrows under the grass on Whale-Skate Island,
French Frigate Shoals. Amerson noted a fledgling
here in early June 1967. I believe it very likely that
the species will eventually be found nesting on
Lisianski Island, which has an extensive habitat
comparable to that which supports a sizable popu-
lation on Laysan. From this latter island POBSP col-
lected three specimens on 22 October 1966 with
considerably enlarged gonads. Willett (1919) re-
ports egg-laying on Laysan from 1 to 15 January.
Inadequate POBSP winter surveys in the Leewards,
plus the very secretive nature of this storm petrel
on the breeding grounds, make it difficult to obtain
a clear picture of the breeding cycle. From available
data it appears that the species is to be found on
188 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
170 E 180 170 W 160 150
40"
N
30"
20
10
• 1 bird
• 5 birds
•10 birds
^f breeding localities
40
30
20
10"
170' 180* 170* 160' 150
FIGURE 116.—POBSP sightings of Oceanodroma tristrami.
NUMBER 158 189
120 W
120 110 100 90
FIGURE 117.—POBSP sightings of Halocyptena microsoma.
70
the breeding grounds during an extended period
from at least October to May. Apparently Decem-
ber and January are peak egg-laying months; both
young and adults are gone from the islands by mid-
May.
Halocyptena microsoma Coues
LEAST STORM PETREL
PELAGIC DISTRIBUTION.—At sea this species is
usually distinguishable from other dark-rumped
forms by its tiny size. Although it is normally a
more coastal form, it was sighted by the POBSP as far
as 600 miles off the Mexican mainland. Large num-
bers are found in the Gulf of Panama during the
winter months (December to April). There appears
to be replacement between this species and Oceano-
droma tethys in the Gulf of Panama. Oceanodroma
tethys is very abundant from June to November,
but completely disappears in the latter month
when H. microsoma begins showing up in numbers.
A small number of Black Storm Petrels are, how-
ever, present during the time the Least is abundant.
Other than the concentrations in the Gulf of Pana-
ma, the majority of POBSP sightings of the Least
Storm Petrel was along the coast of Baja California
and the Mexican mainland (Figure 117).
BREEDING BIOLOGY.—The Least Storm Petrel
breeds on the San Benitos Islands and on various
other islands in the Gulf of California. During a
POBSP survey of the San Benitos on 28 April 1968,
the only Least noted was one that came aboard
ship offshore. During the 25 to 27 June 1968 survey
here, Leasts were abundant on all three islands of
the group. Nesting was primarily restricted to rock
outcrops and talus slopes, and nests were invariably
in rock crevices. Occasionally more than one pair
were found in suitable cavities and some birds were
nesting in the same cavities with the much larger
Black Storm Petrels. A few eggs of the Least were
found, but most of the birds in June were still in
early stages of nest site selection and courting. An
190 SMITHSONIAN CONTRIBUTIONS 1O ZOOLOGY
estimate for Halocyptena during the June survey
was ca. 15,000 birds for the island group. As men-
tioned in the sections on O. melania and O. I. chap-
man i, Halocyptena were adversely affected by the
abundant cholla cacti on the islands and several
birds were found impaled on the spines.
On islands in the Gulf of California, the Least
Storm Petrel is frequently mentioned as nesting in
association with the fishing bat (Pizonyx vivesi).
Maya (1969), who studied this bat in the Gulf, felt
that a lizard (Cnemidophorus sp.) preyed upon the
young storm petrels and that the lizards were less
prone to inhabit cavities where the bats lived. On
Isla Partida (in the northern part of the Gulf of
California) R. D. Ohmart (pers. comm.) saw no
predation by the lizards on very small storm petrel
chicks left unattended by their parents during the
daytime. Once after removing an adult storm petrel
from its nest, he saw a large scorpion carry away
the egg. Ohmart did not feel that the presence of
the bat offered any particular advantage to the pet-
rel. It appeared to him that the Least and Black
Storm Petrels and the fishing bat clumped to avoid
excessive heat and gulls, and possibly to gain in
relative humidity. Both eggs and small downy
chicks of the Least Storm Petrel were found on Isla
Partida from 12 to 21 June 1968. Nests were be-
neath rocks on the ground or in cavities among
rock piles.
Oceanites oceanicus (Kuhl)
WILSON'S STORM PETREL
PELAGIC DISTRIBUTION.—The POBSP pelagic rec-
ords indicate extremely widespread distribution of
this species in the Pacific, with two decided centers
of abundance (Figures 118 and 119). The equatorial
central Pacific records are practically all confined
to October and November; all are of adults with
somewhat enlarged gonads and very heavy fat, and
in all probability represent birds returning to the
Antarctic breeding grounds. An April specimen
from this area is probably a straggler from an ap-
parent postbreeding migration that moves north
through the Marshall Islands in the spring (Huber,
1971). Our surveys give no clue to northward extent
of this movement, nor to the distribution or activi-
ties of the birds between April and October.
Large numbers are recorded in the Peru Current
along the northwestern coast of South America dur-
ing August. A fair number of stragglers are re-
corded throughout the eastern Pacific to at least
31°N. In view of this, the various coastal California
records in August (1910, 1935, and 1959) summar-
ized by Nisbet and McCaskie (1960:141) seem not
too unusual considering the species' wide dispersal.
It should be emphasized that the POBSP sight rec-
ords shown are only those of fairly positive nature;
undoubtedly many more birds were observed which
were recorded only as "unidentified white-rumped
storm petrel."
Oceanites gracilis (Elliot)
GRACEFUL STORM PETREL
PELAGIC DISTRIBUTION.—Most POBSP sightings of
this species were during September near the Gala-
pagos Islands. Other cruises were run about the
islands during other times of the year, especially
March and April, and relatively few birds were
seen. Most of our September sightings were within
a hundred miles of the Galapagos (Figure 120).
Loomis (1918:181) states that "they were never ob-
served far from land, the greatest distance being
about 50 nautical miles." Murphy (1936) has no
record of its breeding, but it has been taken just
offshore of several of the Galapagos Islands and un-
questionably breeds there.
The race O. g. galapagoensis obviously restricts
itself to the cold waters of the Peru Current just to
the west of the Galapagos. The nominate race O. g.
gracilis appears to be restricted to the Peru Current
between Valparaiso, Chile, and Santa Elena, Ecua-
dor (Murphy, 1936).
Fregetta grallaria (Vieillot)
WHITE-BELLIED STORM PETREL
PELAGIC DISTRIBUTION.—The primary distribu-
tion of this species in the area covered by POBSP
was along 85°W from 06°S to 15°S. Two scattered
sightings were recorded at 09°45'S, 117°43'W, and
02°17'N, 104°W (Figure 121).
Murphy (1936:762) recorded that R. Beck took a
specimen of Fregetta grallaria titan at 04°20'S,
NUMBER 158 191
50°
N
170 E 170°W 160 ISO'o
50
40
20
10
• 1 bird
• 5 birds
O 1 specimen collected
40°
20
10
10
150°17<r 180° 170° 160°
FIGURE 118.—POBSP sightings and specimens of Oceanites oceanicus in the central Pacific.
(? = doubtful information.)
192 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
• 1 bird
• 5 birds
• 20 birds
O Specimen collected
FIGURE 119.—POBSP sightings of Oceanites oceanictu in the eastern Pacific.
93°30/W on 11 June 1906, and further stated that
no less than ten other examples were seen in the
same vicinity during the next few days. The race
F. g. titan is recorded as breeding at Rapa Island
in southern Polynesia. Whether our sightings per-
tain to the race F. g. titan, or to the nominate F. g.
grallaria which breeds at Mas Atierra and Santa
Clara of the Juan Fernandez Islands is unknown,
since no specimens were collected.
NUMBER 158 193
70°
20
Bird
Birds
10
90° 80°
FIGURE 120.—POBSP sightings of Oceanites gracilis.
70"
Nesofregetta albigularis (Finsch)
WHITE-THROATED STORM PETREL
PELAGIC DISTRIBUTION.—This species was widely
distributed in the Pacific along equatorial latitudes.
The vast majority of sightings in both the central
and eastern Pacific is confined to areas between
10°N and 10°S (Figures 122 and 123). Concentra-
tions about the Phoenix and Line islands in the
central Pacific are easily referable to the breeding
populations of those areas. The equally great con-
centrations recorded in the eastern Pacific west of
the Galapagos Islands are of unknown origin, but
most probably from the breeding stations in the
Marquesas Islands and Christmas Island. It should
be pointed out that our data represent a consider-
able range extension to the known pelagic range.
TAXONOMY.—To my knowledge this species does
not vary throughout its considerable range, and no
subspecies have been proposed. Except for Oceano-
droma tristrami, N. albigularis is approximately the
largest storm petrel in the Pacific area (Appendix
Table A). Most POBSP specimens are from the Phoe-
nix and Line islands (Christmas Island) popula-
tions.
In the Phoenix group, the majority of birds are
of the color morph usually described for the species,
i.e., dark upperparts and chest band, with white
rump, throat and belly. On both Phoenix and Mc-
Kean islands, however, every conceivable color vari-
194
120 W
10°
N
110° 100
— I —
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
90° 80° 70° „
0°
20
liobclo I..
, Galopogos Itlandi
20°
70°120 100 90 80°
FIGURE 121.—FOBSP sightings of Fregetta grallaria.
ation between the normal form and totally dark in-
dividuals may be found (Figure 124). The "Samoan
Storm Petrel" ("Fregetta moestissima" Salvin),
known from the unique type taken offshore the
Samoan Islands, is considered by Murphy and Sny-
der (1952) to be nothing more than an entirely
melanistic example of Nesofregetta albigularis. The
appreciably larger dimensions (especially wing)
than those of any specimens from the Phoenix,
Line, Marquesas or New Hebrides islands indicates
it may be from a distinct population, possibly
breeding somewhere in the Samoan Islands. Bourne
(1957) indicates that the unique, all dark specimen
of Fregetta fuliginosa (Gmelin) from Tahiti (speci-
men subsequently lost) was probably closely allied
to the Samoan form. On Christmas Island about
half the population of Nesofregetta albigularis
shows some dark flecking on the white underparts,
but completely melanistic birds have not been seen.
BREEDING BIOLOGY.—Published data on the
breeding biology of this species is virtually non-
existent and thus I have entered POBSP data in con-
siderable detail in comparison to other species
whose breeding biologies are well known. The
breeding range of Nesofregetta albigularis extends
from the Line Islands (Christmas Island) and Phoe-
nix Islands (Phoenix and McKean islands) in the
central Pacific south to and including the Samoan
Islands (?), Marquesas Islands, Fiji Islands, and the
New Hebrides Islands. The POBSP surveys covered
only the more northern parts of its range, i.e., the
Line and Phoenix islands. Since our surveys were
fairly complete for the Phoenix group, it is un-
likely that N. albigularis breeds on islands other
than McKean and Phoenix, although we have sev-
eral sightings of birds flying over Enderbury Island
(25 to 27 September, and 9 to 10 October 1966). A
specimen was collected on Howland Island on 24
October 1938, but we have no recent sightings.
In the Line Islands, however, islands such as
Maiden and Starbuck are quite large and our cov-
erage was insufficient to rule out the possiblity of
birds breeding in those areas. On Maiden Island
one bird was noted at night on 31 March 1967.
Several islets in the lagoon were not thoroughly
investigated and might be utilized by this species
NUMBER 158 195
180° 170° 160°
FIGURE 122.—POBSP sightings of Nesofregetta albigularis in the central Pacific.
for nesting. Other possible breeding areas are the
Gilbert, Society, Tuamotu and Marshall islands
(King, 1967:42).
The choice of breeding sites on the three central
Pacific islands investigated was much the same.
Areas supporting bunch grass (Lepturus sp.), large
clumps of weeds (Boerhaavia sp.) or Sesuvium, in
combination with an abundance of loose rocks,
were utilized in practically all cases in the Phoenix
Islands. Extensive areas of rocky coral slabs with-
out vegetation, as well as areas of continuous short
grass or small annuals, were avoided. Old fallen
rock walls which were constructed by the early col-
onists on the Phoenix Islands were often used as
196
130"W 120" 110 100
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
90° 80° 70°.
10
20'
120° 110° 100° 90 s 80°
FIGURE 123.—POBSP sightings of Nesofregetta albigularis in the eastern Pacific.
10
-
2
.
0
70°130°
FICL'RE 124.—Color variation in Nesofregetta albigularis from the Phoenix Islands.
NUMBER 158 197
nest sites, although standing walls devoid of vege-
tation were much more prone to be utilized by Bul-
wer's Petrel (Bulweria bulwerii). On Christmas Is-
land most nests on the small islets were under
clumps of overhanging grass (Lepturus), in pockets
in coral rock shelves also usually sheltered by grass,
or in depressions under Sesuvium. Regardless of
nest site, the actual nests were similar in all cases.
The few pieces of nest material (grass, weed stems,
feathers, etc.) invariably present were most likely in
the nest cavities to begin with; such material is
probably manipulated to some extent, but to my
knowledge no material is ever carried into the nests
by the birds. Incubating birds are usually hidden
from view within nest cavities, but an occasional
individual will nest in rocks in such a manner that
it can be seen. Schreiber (POBSP) noted that tails of
incubating birds were often visible in the shallow
nest cavities on the islets in Manulu Lagoon,
Christmas Island. Under large, extensive grass or
weed clumps, the birds usually retreat to the most
concealing portion. The nest cavities may be
slightly enlarged under clumps of vegetation, but I
have never noted any extensive digging performed
by this species. Storm petrels often utilize nest cavi-
ties dug out by the abundant Audubon's Shearwater
(Puffinus Iherminieri) on McKean and Phoenix is-
lands.
On Christmas Island the nesting areas are pri-
marily limited to five tiny islets in Manulu Lagoon.
These are separated by expanses of water from the
main island. A few birds nest on the islets of^Motu
Tabu, Motu Upua, and on at least one islet in Isles
Lagoon. Utilization of these retreats is probably a
direct result of feral cat predation on the main is-
land:
From banding and recapture data Schreiber
(POBSP) estimated the total population using Christ-
mas Island in 1967 at 350 to 450 birds, although
this estimate is probably low. Table 29 summarizes
the stage of nesting and nest contents recorded in
Manulu Lagoon by POBSP and others.
From the above data it can be inferred that the
peak egg period on Christmas Island is from Sep-
tember through November, but obviously some por-
tion of the population is nesting at all times of
year. This seasonal spread of nesting apparently
allows a greater number of birds to utilize the
available nesting area than would be possible if
TABLE 29.—Surveys of nesting Nesofregetta albigu-
laris in the Manulu Lagoon area, Christmas Island,
Line Islands
Date
Jan 59
Feb 21
Mar 65
Apr 59
Jun 65
Jul 67
early Aug 67
late Aug 67
Oct 65
Nov 64
early Nov 67
late Nov 67
late Dec 67
Xest contents Source
20 occupied nests (contents?) Gallagher (1960:494)
eggs and young present Murphy (1924:12)
30 nests, eggs and chicks POBSP
1 small, 2 nearly fledged Gallagher (1960:494)
chicks
few nesting POBSP
3 eggs, 1 small downy chick
14 eggs, 3 chicks
21 eggs, 5 chicks
50 (eggs and small chicks)
26 eggs, 5 chicks
54 eggs (including 11
abandoned), 9 chicks
37eggs (including 6 newly
abandoned), 9 chicks
(including 5 dead)
6 eggs, 25 chicks
nesting were limited to a specific time of the year
for all individuals. One adult, with an egg, banded
on 25 August 1967, on Islet # 2 in Manulu Lagoon
was found incubating an egg on Islet # 1 on 28
November 1967. This meager evidence suggests that
the species will renest within the same year, and,
furthermore, a specific nest site is apparently not
adhered to. Another adult in an empty nest cavity
on 29 August 1967 was incubating an egg there on
4 November 1967; yet another incubating an egg
on 17 August 1967 was still incubating on 4 Novem-
ber 1967. The egg in the latter case was probably
infertile, but these examples give an idea of the
extensive periods that the birds spend on the breed-
ing islands.
Our data for the Phoenix Islands are less com-
plete because of the extremely short surveys made,
but the available evidence shows that on McKean
and Phoenix, as on Christmas Island, some portion
of the population is nesting during every month of
the year. Tables 30 and 31 present POBSP data for
McKean and Phoenix islands.
Variation and inconsistencies in the data are due
partly to different observers and to the extremely
inadequate surveys in most cases. It is nonetheless
evident that considerable variation is to be found
on the same island for a given month during differ-
ent years (Table 30, February 1964 and 1965). De-
spite these differences, considering the data as a
198 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE 30.—POBSP surveys of Nesofregetta albigu-
laris on McKean Island, Phoenix Islands
TABLE 31.—POBSP surveys of Nesofregetta albigu-
laris on Phoenix Island, Phoenix Islands
Date
Number Population
banded estimate Nest contents
6-7 Feb 65 94
16-20 Feb 64 9
17-19 Apr 66
30Apr-lMay66 -
13-15 Jul 68
18-20 Jul 64
23-25 Jul 66
14-30 Oct 68
(thorough
survey)
18-22 Oct 64
24-28 Oct 63
56
13
500
25-30
500 +
1000
1000 adults,
200 eggs,
200 chicks
no data
750
30 adults
100
100 + .7
collected
large number beginning
to nest
no eggs or young found
no eggs
1 egg
sample of 23 nests: 12
eggs, 11 chicks rang-
ing from ca. 4 days
old to fully feathered
no data
10 eggs, few small and
large downy nestlings
1 egg, 3 large chicks
no data
1 egg found
whole, there appears to be a breeding peak on Mc-
Kean from April through at least July or August,
with a definite low in October and probably later.
For Phoenix Island we do not have data from
monthly surveys in successive years, but certainly
the high nesting populations recorded from October
through December do not correspond to the breed-
ing situation on McKean. This lack of conformity
to a set seasonal or annual cycle has been noted for
most species on the equatorial islands. Our surveys
indicate that the populations on one island appear
to operate independently from those on other is-
lands, regardless of the apparent ecological simi-
larities of the islands or their geographic proximity.
On McKean Island there appears to be a definite
separation in the timing of nesting of Nesofregetta
albigularis and Bulweria bulwerii. This was quite
apparent during two fairly extensive surveys in July
and October 1968. During July, N. albigularis was
definitely undergoing a peak in nesting with an
estimated 1000 adults on the island. Bulwer's Petrel
at that time was for all practical purposes absent
from the island (one adult calling from an empty
nest cavity). During the extensive October survey
only about 30 adult White-throated Storm Petrels
were present on the island with nine nests (3 with
young, 1 with egg, and 5 occupied, but as yet with-
out eggs). Bulwer's Petrel at this time was approach-
ing a peak nesting situation with a very conserva-
Date
Number Population
banded estimate Nest contents
26-28 Jan 67 - 150 1 fresh egg found
23-26 Feb 64 - 100 no evidence of nesting
14-16 Apr 66 - 300+ nesting
26-30 May 65 35 500 nesting, young present
18-20 Jul 64 56 200-300 eggs and nestlings present
29-30 Sep 65 - 2 no evidence
10-11 Oct 66 - 400(15% 20 eggs, 5 small downy
nesting) young, 5 large downy
young
3-7Nov64 15 100 no data
2-5 Dec 66 - 300(40% 50 eggs, 10 small chicks
nesting)
tive estimate of 1000 birds on the island. The ma-
jority of these were calling from empty nest cavities
or from nests with fresh eggs; an estimated five per-
cent had small downy young. Both species tend to
utilize the same nest sites to a high degree, and this
complementary seasonal nesting arrangement ap-
parently affords both populations minimum com-
petitive activity during their respective breeding
periods. Food availability in the nearby ocean may
also be a factor in creating alternating nesting sea-
sons for these similar species.
On the breeding islands, White-throated Storm
Petrels are usually absent during most of the day-
light hours (except for those attending to incuba-
tion or brooding duties). On several occasions, how-
ever, I have seen adults come to nests in full day-
light to feed young. This type of behavior is never
performed by any of the small hydrobatids in the
eastern Pacific, since any individual showing itself
during the day would be immediately set upon and
devoured by Western Gulls. The rapidity with
which the gulls attack storm petrels appears to be
the sole reason why storm petrels never appear
overland in daylight hours. In the central Pacific,
however, Nesofregetta appears to be without preda-
tors. The frigatebirds (Fregata ariel and F. minor)
were never noted harassing storm petrels, but
seemed to restrict their parasitism to larger birds
such as boobies, shearwaters, and terns.
Adult storm petrels normally come in over the
breeding islands from the ocean from about one-
half to three-quarters of an hour before dusk. This
seems to be the period of greatest activity, during
NUMBER 158 199
FIGURE 125.—Young of Nesofregetta albigularis on McKean Island.
(Photo by C. Douglas Hackman.)
which many individuals may be noted flying back
and forth over potential or actual nest sites. Birds
with active nests seem to circle repeatedly over the
general area of the nest site for some time before
landing, as do individuals obviously searching for
nest sites. When the birds land, they usually do so
ungracefully, falling softly and then awkwardly
crawling over the terrain toward the nest site or
into the nest cavity.
As with other hydrobatids and procellariiforms
in general, Nesofregetta lays only a single egg. Oc-
casionally a bird is found incubating two eggs, but
one is invariably an infertile or abandoned egg
from an earlier nesting. Relative to other storm
petrels, the eggs are large for the size of the bird.
A series of 20 eggs from- Phoenix, McKean, and
Christmas islands show the following measure-
ments: length (mean with standard error) 37.95 i t
0.41 mm (SD = 1.85); breadth 27.45 ± 0.18 mm
(SD = 0.82). The eggs have a creamy-white back-
ground color, with reddish and lavender dots which
usually form a prominent wreath about the large
end, but are scattered less finely over the entire sur-
face.
The few observations available on marked nests
show that both birds are present in the nest cavity
for some time (days?) before the egg is laid. Copu-
lation probably takes place at the nest site. During
these times and at least during early incubation,
adults utter a soft guttural "grrrrr-grrrrr-grrrrr"
call from the nest cavity. Both sexes incubate, but
the rate of changeover, as well as the length of the
incubation period, is unknown. After the chicks are
a few days old the parents only come to the nest to
feed them. The young hatch blind, but are pro-
fusely covered with medium-gray down which is
quite short on the underparts and long on the
dorsum. A chick estimated to be five days old had
down to 20 mm long on the back. I doubt if the
young can use vision in the nest until they are in
the large, fully-feathered stage, since the entire or-
bital region is completely covered by shaggy down.
When the chicks are approximately two-thirds
grown, they have a definite bi-colored aspect. The
dark and light colors correspond roughly to the
black and white areas of the adults. This bicolored
effect is brought about by the growth of new
feathers beneath the down. As the feather coat pro-
gresses, more and more down is shed until only
patches remain about the head, dorsum and flanks
(Figure 125). It is not known how soon the young
leave the island after attaining their juvenal plum-
200 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
age, but apparently it is rather soon, as birds with
traces of down still clinging to the feathers were
noted attempting to fly at night; they were at least
many yards away from any possible nest site (see
comparative data on Oceanodroma leucorhoa so-
corroensis young).
The White-throated Storm Petrel exhibits a pe-
culiar flight at sea which has not been noted in any
other species of hydrobatid. On many occasions
these birds were seen kicking off waves with con-
siderable force, using their extremely long legs and
spatulate feet. The moment their feet hit the water
surface, the birds instantly change direction and
sharply increase their speed, attesting to the force
applied to the water's surface. The usual procedure
was for the individual to "kick off" a wave, glide
for approximately 20 to 30 seconds and again "kick
off." I have on occasion noted a bird parallel a ship
for a mile or more in this manner. Both Gallagher
(1960) and Schreiber and Ashmole (1970) have
noted birds performing this behavior in the quiet
lagoon on Christmas Island. Wilson's Storm Petrels
often dabble their feet in the water, but this ap-
pears to be more of a balancing maneuver than an
actual thrust motion as in Nesofregetta. This mode
of travel might be a means of expending less energy
in equatorial regions where wind is often at a mini-
mum. At any rate, the extremely long tarsi and
spatulate feet of Nesofregetta make possible its
unique locomotory behavior.
Discussion
The hydrobatids form a rather homogeneous
group widely distributed over the Pacific regions.
In many cases their breeding distribution and pe-
lagic movements appear to be random, but un-
doubtedly reflect patterns that have been dictated
by seasonal abundance and distribution of food
items, interspecific competition, and the need to
occupy the limited breeding areas during favorable
periods. These patterns have undoubtedly under-
gone considerable fluctuation over time; the pres-
ent view of the family shows a few exceedingly
abundant forms and many uncommon to rare spe-
cies. In the Pacific region, individuals of the com-
bined subspecies of Oceanodroma leucorhoa by far
outnumber all other species combined.
The northern breeding forms of O. leucorhoa
show south-north migration patterns and practically
inundate the central and eastern equatorial Pacific
during the nonbreeding season (September-March).
Wilson's Storm Petrel, a strictly southern hemi-
sphere breeder, shows the inverse north-south move-
ments in the western Pacific and along the South
American coast during migration and nonbreeding
season from the Antarctic. Another southern hemi-
sphere breeder (White-faced Storm Petrel) demon-
strates an east-west pattern, moving east from its
Australian breeding grounds to the South Ameri-
can coast, thence north along the Peru Current and
west through the Galapagos area with a subsequent
return to the Australian region. Possibly Wilson's
performs more of a circular route in its north-south
movements. A number of forms such as Oceano-
droma leucorhoa chapmani, O. I. socorroensis, and
O. homochroa apparently do not move any great
distance from the breeding islands during the non-
breeding season. For many Pacific hydrobatids the
nonbreeding distribution is imprecisely known; for
others the stated breeding grounds are merely con-
jecture.
At sea most storm petrels are either solitary or
join with members of their own species. In certain
cases two or more species will congregate, often in
response to a temporarily plentiful food supply.
They normally do not mix with other seabird spe-
cies, even with their nearest relatives, the procel-
lariids. I believe the presence of storm petrels in
mixed feeding flocks of procellariids, terns, boobies,
etc., is usually a random occurrence. On many occa-
sions when I have observed storm petrels in the vi-
cinity of mixed feeding flocks, the hydrobatids ap-
peared to lack the intense feeding interest of the
other species and usually moved out of the immedi-
ate area of intense feeding. It should be stressed
that in most cases POBSP observers did not distin-
guish, in a recorded species association, those mem-
bers that were actually feeding or traveling to-
gether. If members of two or more species were
together at the time of initial sighting, they were
usually recorded as such. The imprecision of these
observations was the result, usually, of the impos-
sibility of detailed notations of individuals in large
mixed feeding or traveling flocks where often hun-
dreds or even thousands of birds were concerned.
In such cases a gross account of numbers was about
the best that could be acquired. Thus the presence
of one or more hydrobatids in the immediate vi-
cinity of a flock would be recorded as positive, al-
NUMBER 158 201
TABLE 32.—Intraspecific sociability (number of
individuals/number of sightings) in species of
Pacific hydrobatids
Species
Oceanodroma castro
O. leucorhoa . . . .
O. furcata
O. markhami or
O. tristrami
O. melania
O. homochroa
O hoTnbyi
O. tethys
Halocyptenu microsoma. .
Ocsanites oceanicus
O. gracilis
Pelagodroma marina
Fregetta grallaria
Nesofregetta albigularis . .
Total
Individuals
269
14,355
936
167
465
36
12
1,723
63
443
22
79
10
111
27,140
Sightings
203
9,071
235
121
214
10
7
443
48
66
6
67
8
97
12,574
Ratio of
sociability
1.3
1.6
4.0
1.4
2.2
3.6
1.7
3.9
1.3
6.7
3.7
1.2
1.3
1.1
2.2
though, as I have often stated from personal ob-
servations, this is usually not the case.
The amount of intraspecific sociability can be
calculated in a gross manner quite easily from our
data. From Table 32 it is immediately apparent
that individuals of some species are far more prone
to associate intraspecifically than others. Fork-
tailed and Wilson's Storm Petrels commonly asso-
ciate with other members of their respective species.
On the wintering grounds Leach's Storm Petrels
disperse singly or in very low densities unless a lo-
cal food source happens to bring large numbers to-
gether temporarily. During migration they com-
monly group and are noted resting on the water in
large rafts. Even with our sightings of migratory
and feeding flocks included, the low sociability ra-
tio of 1.6 for nearly 10,000 sightings (involving over
14,000 individuals) demonstrates their usual soli-
tary nature. Other species, such as the White-
throated Storm Petrel, show this solitary nature to
a greater degree and are almost invariably noted
singly. For most of the less abundant species, al-
though the available evidence suggests solitary oc-
currence, we do not have enough observations to
demonstrate their overall social behavior at sea.
The solitary nature of most hydrobatid species
away from the breeding grounds is perhaps neces-
sary because of the foraging behavior (flight low
over the water with a limited area view) to distrib-
ute themselves as widely as possible over their
range to take utmost advantage of the widely dis-
tributed small organisms which make up their diet.
Members of a species, or of several species, will
gather readily at an unusual, abundant food source
such as an oil slick. At such gatherings I have never
noted either inter- or intraspecific hostile behavior
between individuals, behavior that certainly some
(if not all) species are capable of demonstrating as
witnessed by intraspecific battles over nest sites on
the breeding grounds (Leach's, Least, Black, and
White-throated Storm Petrels).
To my knowledge all members of the Hydro-
batidae are strictly surface feeders, that is, they do
not submerge the body beneath the surface of the
water to obtain food. All Pacific species were ob-
served to glean the surface of the water for floating
objects, often with wings held aloft for balance. The
foot dabbling behavior with wings held aloft for
balance in the Wilson's Storm Petrel is well known
and documented. Leach's, Harcourt's, and most es-
pecially Least Storm Petrels will hold the wings
aloft in a V formation when feeding over an oil
slick or other concentrated food source. In this re-
spect they appear as so many butterflies on a wet
sand bar. Least Storm Petrels were never noted
dabbling their feet the way Wilson's do. They
usually feed while resting on the water with wings
up until wanting to move. Then with a few quick
wingbeats the bird moves to a new position, usu-
ally still holding the wings aloft.
The preceding species accounts provide a basis
for understanding the distribution and abundance
of Pacific hydrobatids and indicate the vast amount
of data yet to be gathered concerning these forms.
While it is unlikely that a program devoted to
pelagic ornithology in the Pacific of the magnitude
of the POBSP will occur again in the near future,
important contributions can be made to existing
knowledge by participation in cruises devoted to
any type of pelagic investigation. The great amount
of information on hydrobatids gathered during the
EASTROPAC cruises is a good example of this.
While it is understandable that we know little or
nothing about the breeding biology of many of the
southern hemispere hydrobatids, it is less explicable
why information of this sort is lacking for most of
the species and subspecies inhabiting the coastal
islands of the western United States and Mexico.
202 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
There is a decided need in these areas for long
range studies with banded birds similar to the in-
vestigation of the nominate race of Leach's Storm
Petrel on Kent Island, New Brunswick, Canada,
which was begun by Gross (1935) and continued by
Huntington (1963) and his co-workers.
A fascinating problem awaiting study is the elu-
cidation of the relationships and interactions of
winter and summer breeding populations of Leach's
Storm Petrel on Guadalupe Island. A second prob-
lem is to account for the clumping of completely
dark hydrobatids along the California and Baja
California coasts. In the Hydrobatidae, where
white patterning is widespread, the lack of this
color in so many forms (four species and three
subspecies) common to this area can hardly be co-
incidental. The factor of predation by the various
gull species (especially the Western Gull) is prob-
ably only part of the reason. The dark rump color
predominates in all forms of hydrobatids along the
coast of Japan also, possibly for the same reasons.
Appendix
Measurements of POBSP-collected specimens of Pacific hydrobatids
(number of specimens in parentheses, linear characters in millimeters, weights in grams)
TABLE A.—Various Pacific hydrobatids
Characters
and
measurements
WlNC
Range
Mean w/SE
SD
TAIL
Range
Mean w/SE
SD
CULMF.N
Range
Mean w/SE
SD
TARSUS
Range
Mean w/SE
SD
WEIGHT
Range
Mean w/SE
SD
Oceanodroma
liomochroa
(20)
133-145
138.40 ±.65
2.91
(20)
79-89
83.10 ±0.67
3.01
(20)
13.10-15.10
14.10±0.11
0.50
(20)
21.50-23.70
22.46 ±0.14
0.63
(20)
33.3-42.4
36.90 ±0.51
2.27
O.castro
(6)
148-159
O.t.kelsalli
(36)
127-141
O.t.kelsalli
(4)
119-128
i:>2.00±1.73 133.39±0.49 124.50±2.02
4.24
(6)
71-75
72.33 ±0.61
1.51
(6)
14.40-15.80
14.85 ±0.22
0.55
(6)
21.50-22.50
22.00±0.15
0.36
(6)
40.5-45.0
42.67 ±0.68
1.66
2.92
(42)
58-67
62.26 + 0.30
1.91
(41)
10.60-14.00
12.40 ±0.09
0.60
(42)
20.00-23.60
22.02 ±0.13
0.86
(26)
21.0-33.0
25.48 ±0.61
3.12
4.04
(4)
56-61
59.25 ±1.11
2.22
(4)
10.90-12.00
11.73 ±0.28
0.55
(2)
20.25-21.00
20.75 ±0.25
0.35
O.melania
(47)
163-180
O.tristrami
(13)
175-195
Halocyptena
microsoma
(11)
114-123
171.96±0.55 183.15 ±1.70 118.45 ±0.98
3.75
(44)
82-94
88.41 ±0.47
3.10
(45)
14.00-16.10
15.22 ±0.07
0.48
(46)
29.00-33.30
31.48±0.14
0.96
(44)
50.0-67.0
58.95 ±0.56
3.69
6.14
(13)
109-118
3.24
(11)
52-60
113.54 ±0.83 57.00 ±0.80
2.99
(13)
16.30-18.30
17.36±0.18
0.65
(13)
25.10-28.60
27.38 ±0.28
1.02
(10)
58.4-94.0
82.53 ±3.04
9.62
2.65
(11)
9.60-11.60
10.72±0.17
0.57
(11)
19.10-22.10
21.00 ±0.26
0.85
(11)
18.2-21.7
20.47 ±0.34
1.11
Oceanites
oceanicus
(8)
148-156
Nesofregetta
albigularis
(21)
175-193
152.50±1.07 186.38±1.16
3.02
(8)
70-76
72.00 ±0.73
2.07
(7)
11.90-13.00
12.50±0.17
0.44
(8)
33.40-35.60
34.24 ±0.26
0.72
(7)
35.0-39.0
36.71 ±0.47
1.25
5.30
(21)
89-107
97.48 ±1.11
5.10
(20)
15.70-18.00
16.63±0.13
0.57
(21)
40.00-46.60
43.07 ±0.42
1.91
(19)
57.0-70.0
62.84 ±0.%
4.17
203
204 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE B.—Oceanodroma leucorhoa leucorhoa
Characters
and
measurements
WlNC
Range
Mean w/SE
SD
TAIL
Range
Mean w/SE
SD
CULMEN
Range
Mean w/SE
SD
TARSUS
Range
Mean w/SE
SD
WEICHT
Range
Mean w/SE
SD
Central Pacific (at sea)
males
(43)
144-161
153.60 ±.57
3.72
(52)
76-92
83.35 ±.42
3.05
(54)
15.10-17.50
16.01 ±.07
.52
(54)
22.00-25.10
23.48 ±.10
.75
(48)
29.0-49.0
38.73 ±.63
4.34
females
(31)
148-166
155.19 ±.82
4.56
(42)
77-93
84.33 ±.50
3.24
(41)
15.00-16.90
16.02 ±.07
.46
(41)
22.10-25.10
23.58 ±.10
.63
(37)
31.0-54.0
40.86 ±.78
4.74
Eastern Pacific (at sea)
males
(23)
140-162
151.57 ±1.22
5.86
(37)
67-87
81.84 ±.66
4.00
(35)
13.70-17.10
16.00±.ll
.63
(35)
20.00-25.00
23.61 ±.17
1.00
(30)
25.2-55.1
44.03 ±1.25
6.85
females
(12)
144-162
152.08 ±1.73
5.99
(36)
73-95
84.00 ±.72
4.34
(36)
13.30-17.00
15.89±.12
.74
(36)
21.40-25.10
23.74 ±.16
.98
(35)
24.0-57.5
43.17±l.O2
6.03
North Pacific (breeding)
males
(4)
149-158
153.75±1.89
3.77
(4)
82-89
86.00 ±1.47
2.94
(4)
15.00-16.50
15.78 ±.32
.63
(4)
21.70-24.10
23.20 ±.56
1.12
fe vi ales
(6)
153-167
157.67 ±2.03
4.97
(4)
78-89
82.25 ±2.36
4.72
(6)
15.00-16.50
15.62 ±.23
.56
(4)
23.80-25.00
24.20 ±.28
.57
Total
(119)
140-167
153.68 ±.45
4.89
(175)
67-95
83.43 ±.28
3.72
(176)
13.30-17.50
15.97 ±.04
.598
(174)
20.00-25.10
23.59 ±.06
.84
(150)
24.0-57.5
41.35 ±.47
5.77
TABLE C.—Oceanodroma leucorhoa beali
Characters
and
measurements
WING
Range
Mean w/SE
SD
TAIL
Range
Mean w/SE
SD
CULMEN
Range
Mean w/SE
SD
TARSUS
Range
Mean w/SE
SD
WEIGHT
Range
Mean w/SE
SD
Eastern Pacific (at sea)
males
(33)
136-155
145.61 ±.78
4.48
(60)
71-86
79.17 ±.45
3.51
(56)
14.20-16.70
15.43 ±.08
.59
(61)
20.00-25.00
22.81 ±.13
1.03
(53)
32.00-52.00
40.93 ±.65
4.91
females
(34)
139-159
146.09 ±.75
4.36
(66)
71-89
79.95 ±31
4.15
(59)
14.00-16.60
15.44 ±.08
.65
(64)
20.00-25.10
22.70 ±.16
1.26
(56)
29.00-53.00
40.13 ±.67
5.03
California &
males
(30)
142-155
147.40 ±.71
3.87
(20)
73-85
79.00 ±.71
3.17
(24)
14.00-16.10
15.03 ±.11
.52
(21)
21.50-24.40
22.69 ±.16
.75
Alaska (breeding)
females
(26)
143-155
148.81 ±.65
3.31
(18)
74.5-85.9
78.57 ±.68
2.90
(23)
14.20-15.50
14.87 ±.08
.40
(18)
22.00-24.00
22.94 ±.12
.53
Coronados
males
(15)
144-154
148.80 ±.78
3.03
(6)
77-78
77.67 ±.21
.52
(14)
14.40-16.20
15.21 ±.14
.54
(6)
21.50-22.70
22.07 ±.20
.50
(6)
34.00-38.00
36.33 ±.76
1.86
(breeding)
females
(17)
139-155
148.65 ±1.01
4.18
(9)
81-84
82.44 ±.34
1.01
(17)
13.50-16.00
14.99±.14
.58
(9)
21.00-22.80
22.28 ±.19
.58
(9)
32.00-37.00
34.11 ±.51
1.54
Totd\
(155)
136-156
147.24 ±.33
4.15
(179)
71-89
79.45 ± .27
3.63
(193)
13.50-16.70
15.26 ±.04
.61
(179)
20.00-25.10
22.72 ±.08
1.03
(124)
29.00-53.00
39.85 ±.45
5.04
NUMBER 158 205
TABLE D.—Oceanodroma leucorhoa chapmani
Characters and
measurements
WING
Range
Mean w/SE
SD
TAIL
Range
Mean w/SE
SD
CULMEN
Range
Mean w/SE
SD
TARSUS
Range
Mean w/SE
SD
WEIGHT
Range
Mean w/SE
SD
San Benitos (breeding)
males females
(45)
140-150
145.44 ±.37
2.48
(39)
74-82
77.33 ±.37
2.29
(45)
14.00-16.00
15.16±.08
.57
(40)
20.00-23.50
21.73±.ll
.72
(39)
29.00-39.00
33.97 ±.35
2.18
(40)
144-153
148.28 ±.39
2.44
(39)
74-85
78.62 ±.38
2.36
(41)
14.50-16.50
15.47 ±.07
.48
(39)
20.00-24.00
22.23 ±.13
.80
(39)
30.00-42.00
35.59 ±.46
2.90
Total
(85)
140-153
146.78 ±.31
2.83
(78)
74-85
77.97 ±.27
2.40
(86)
14.00-16.50
15.31 ±.06
.55
(79)
20.00-24.00
21.97 ±.09
.80
(78)
29.00-42.00
34.78 ±.30
2.68
TABLE E.—Oceanodroma leucorhoa socorroensis
Characters
and
m easu vements
WING
Range
Mean w/SE
SD
TAIL
Range
Mean wySE
SD
CULMEN
Range
Mean w/SE
SD
TARSUS
Range
Mean w/SE
SD
WEIGHT
Range
Mean w/SE
SD
Eastern Pacific (at sea)
males
(20)
131-150
142.05 ±.92
4.12
(20)
67-81
73.05 ±.92
4.14
(21)
13.00-15.20
14.02 ±.12
.54
(22)
18.30-22.10
20.52 ±.19
.90
(14)
25.20-40.00
32.71 ±1.13
4.23
females
(26)
134-153
142.46 ±.77
3.90
(28)
68-81
74.43 ±.58
3.05
(26)
12.90-15.00
13.88±.ll
.54
(28)
18.80-21.90
20.40 ±.15
.77
(16)
28.0-42.0
33.32 ±.97
3.89
Guadalupe
males
(68)
134-146
141.07 ±.33
2.73
(44)
68-79
73.73 ±.42
2.81
(45)
13.00-15.50
14.20 ±.11
.74
(45)
19.00-22.80
20.52 ±.13
.89
(66)
24.00-44.00
31.41 ±.43
3.46
/. (summer breeding)
females
(49)
136-150
142.71 ±.46
3.22
(38)
68-80
74.29 ±.48
2.98
(39)
13.30-1550
14.08 ±.09
.56
(38)
19.00-22.30
20.23 ±.13
.81
(45)
22.40-42.10
32.29 ±.56
3.76
Guadalupe I. (winter breeding)
" kaedingi"
males
(22)
140-150
144.68 ±.59
2.75
(18)
70-82
77.72 ±.75
3.20
(18)
13.50-15.90
14.82±.13
.56
(18)
21.00-23.00
22.09 ±.15
.62
(7)
22.80-43.80
32.70 ±3.52
9.32
females
(20)
140-147
143.70 ±.72
2.34
(17)
73-84
78.24 ±.67
2.77
(17)
14.00-15.60
14.82 ±.11
.43
(17)
20.90-23.50
22.02±.15
.60
(4)
22.40-37.50
29.80 ±3.56
7.12
Total
(205)
131-153
142.38 ±.23
3.31
(165)
67-84
74.79 ±.27
3.51
(166)
12.90-15.90
14.23 ±.05
.67
(168)
18.30-23.50
20.75 ±.08
1.04
(152)
22.40-44.00
31.71 ±.34
4.16
Red-tailed Tropicbird {Phaethon rubricauda)*
Patrick J. Gould, Warren B. King, and Gerald A. Sanger
Introduction
The material contained in this report is a sum-
mary of all at-sea observations of Red-tailed Trop-
icbirds (Phaethon rubricauda) gathered by the
Pacific Ocean Biological Survey Program (POBSP)
in the central and eastern Pacific Ocean. Hum-
phrey (1965) has given a general summary of the
objectives of this program, while Gould (pp. 1-5,
herein) has summarized the areas surveyed, the
methods and materials used in obtaining and an-
alyzing the data, and has acknowledged all person-
nel who have taken part in the gathering of the
data. The reader is referred to the latter paper for
a more complete account of these activities. Litera-
ture records and data obtained from POBSP island
surveys are included as general background infor-
mation.
Pelagic observations began in August 1963
and continued through November 1968. During this
time over 2200 Red-tailed Tropicbirds were re-
corded during 2968 days (over 21,500 hours) and
more than 208,000 miles of diurnal observations.
SUMMARY OF PUBLISHED PELAGIC DISTRIBUTION.—
Red-tailed Tropicbirds are typically wide ranging,
solitary, and highly pelagic seabirds. Individuals
have been recorded from 39°N to almost 38°S, and
from about 300 miles off the western American
coasts (extreme southern California to Chile) to
southeastern Australia, Formosa, and Honshu, Ja-
pan. Population estimates for the central Pacific
Patrick J. Gould, Department of Zoology, University of Ari-
zona, Tucson, Arizona 85721. Warren B. King, International
Council for Bird Preservation, Smithsonian Institution, Wash-
ington, D. C. 20560. Gerald A. Sanger, National Marine
Fisheries Service, Northwest Fisheries Center, 2725 Mont lake
Blvd. East, Seattle, Washington, 98112.
• Paper Number 84, Pacific Ocean Biological Survey Pro-
gram, Smithsonian Institution, Washington, D. C. 20560.
islands visited by the POBSP indicate total numbers
in that area to be in excess of 31,000 birds (Table
33).
The appendix table summarizes significant pub-
lished pelagic observations. Only birds specifically
noted as Phaethon rubricauda are included in this
list. A number of sightings of "tropicbirds" or
"Phaethon sp." are omitted, as are those suggesting
any uncertainty in identification. Despite these pre-
cautions, it is possible that some of the included
sight records were in error since immature Red-
tailed Tropicbirds resemble Red-billed Tropic-
birds (Phaethon aethereus).
In general, Red-tailed Tropicbird sightings are
widely scattered across the tropical and subtropical
Pacific. Birds have been seen in higher latitudes
in the far western Pacific than in the far eastern
Pacific. Austin and Kuroda (1953:315) list six
specimen records for Honshu, Japan, the northern-
most from 39°N, 142°E. In the southern hemi-
sphere, Hindwood (1955) lists several records from
New South Wales (ca. 28°S to 30°S), and the adja-
cent ocean. Falla, et al. (1967:59-60) speculate that
this species may penetrate the Tasman Sea. Peter
Harper (pers. comm.) confirms this with a sighting
of two birds at 42°S. In contrast, the highest eastern
Pacific latitude sightings recorded are at Guadalupe
Island, ca. 29°N (Kaeding, 1905) and 12°S
(Bourne and Radford, 1961:22). The POBSP records
extend the known range of the species in the eastern
Pacific to 31 °N and to 24°S.
BREEDING PHENOLOGY.—The breeding cycle of in-
dividual Red-tailed Tropicbirds in the central Pa-
cific is annual, but the cycles for any given popula-
tion may be extended or irregular. On most islands,
birds have been recorded at some stage of breeding
activity during all months. In the northwestern
Hawaiian Islands breeding activity begins in late
206
NUMBER 158 207
TABLE 33.—Recent maximum population esti-
mates1 of Red-tailed Tropicbirds for central
Pacific islands visited by the POBSP
Location
HAWAIIAN ISLANDS
Kure
Midway
Pearl and Hermes Reef
Lisianski
Laysan
Gardner Pinnacles
French Frigate Shoals *
Necker
Nihoa
Kaula
Lehua
WAKE ATOIX
JOHNSTON ATOLL
MARSHALL ISLANDS
Taongi
Bikar
Eniwetok
Taka
Jemo
Erikub
LINE ISLANDS
Palmyra
Christmas
Jarvis
Maiden
Starbuck
PHOENIX ISLANDS
Canton
Enderbury
McKean
Birnie
Phoenix
Hull
Sidney
Gardner
HOWLAND
BAKER
Number
2,500
7,500
165
3,000
4,000
50
225
200
500
common
500
20
110
525
125
150
25
3
1
20
8,000
2,000
40
10
10
1,000
500
50
175
3
4
4
130
20
1
 High count for one day of breeding and displaying adults.
1
 Includes breeding and displaying adults and chicks.
March when a few eggs are laid, but May and June
appear to be the principal months of egg-laying.
Chicks have been recorded in all months but are
most common in July and August. Maximum num-
bers of adults have been recorded between April
and September; numbers then diminish rapidly to
a low in December and January.
On Johnston Atoll, the population follows the
same breeding pattern except that it is about one
or two months ahead of the Northwest Chain. The
egg-laying peak is in late March, and chicks are
present from late April through August. The maxi-
mum population occurs in May, and numbers di-
minish after July.
In the Phoenix and Line groups the breeding cy-
cle is similar to that of the Leewards but may be
somewhat later. On some islands egg-laying peaks
are decidedly variable. The breeding cycle of birds
in the Marshall and Gilbert islands has not been
documented. On Wake Island breeding occurs
mainly from March through July or August.
Behavior
Definitions of special terms used in this section
are as follows: a "sighting" refers to one or more
birds observed together and acting as a unit; a
"flock" is considered to be the association of five or
more individuals; a "mixed" flock or sighting is
one that contains more than one species; a "pure"
flock or sighting is one that contains only one spe-
cies, "BPS (birds per sighting)" is a good index of
the gregariousness or flocking tendency of a species.
In this section all data, except when specifically
stated otherwise, were collected under the follow-
ing conditions: (1) at sea (including areas imme-
diately offshore), (2) within about one mile of the
ship, (3) in the central Pacific, (4) from 1964
through 1966. Within these parameters 1574 Red-
tailed Tropicbirds and 1323 Red-tailed Tropicbird
sightings were recorded (Table 34).
Red-tailed Tropicbirds are among the most soli-
tary of seabirds. Of all individuals seen, 73.2 percent
(87.2 percent of all sightings) were alone. The BPS
ratio was 1.19 (Table 34) as compared with Sooty
Terns (Sterna fuscata) and Wedge-tailed Shearwa-
ters (Puffinus pacificus) which had BPS ratios of
12.79 and 4.56, respectively (derived from Tables 2
and 17). Further, only 4.5 percent of all individuals
(4.4 percent of all sightings) were associated with
other seabirds. Table 35 gives the frequency with
which Red-tailed Tropicbirds were associated with
other species of seabirds. The infrequency of such
associations can best be explained by tropicbird
208 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE 34.—Frequency of Red-tailed Tropicbirds in the central Pacific Ocean,
1964-1966
Birds per sighting
1
2
3
4
5
6
7
Total
Sightings
(No.)
1153
118
37
7
4
2
2
1323
Total sightings Birds
<%) (No.)
87.2
8.9
2.8
0.5
0.3
0.15
0.15
(mean number ol
1153
236
HI
28
20
12
14
1574
birds per sighting:
Total birds
(%)
73.2
15.0
7.0
1.8
1.3
0.8
0.9
1.19)
behavioral patterns, particularly those connected
with feeding.
Red-tailed Tropicbirds are regularly attracted to
ships, which they often follow for ten or fifteen
minutes and occasionally for an hour or more.
This, in itself, would decrease the chances of ob-
serving them in association with other species, since
most other species are not ship followers. The ma-
jor attraction of the ship is apparently the flying
fish scattered by its approach. Tropicbirds circle
above or behind the ship at estimated heights aver-
TABLE 35.—Frequency of Red-tailed Tropicbird
sightings associated with other seabirds, 1964-1966
Seabird species
Sterna fuscata
Puffinus pacificus
Phaethon Upturns
Pterodroma externa ..
Pterodroma nigripennis
Fregata species
Anous stolidus
Bulweria bulwerii . . . .
Gygis alba
Sula dactylatra
Sula sula
Oceanodroma leucorhoa
Puffinus griseus
Puffinus puffinus
Puffinus nativitatis . . .
Pterodroma alba
Peterodroma neglecta
Sterna lunata
Catharacta skim
Stercorarius pomarinus
Sightings
(No.)
Sightings
32
24
14
11
10
9
5
5
4
4
3
3
2
2
2
1
1
1
1
1
2.4
1.8
1.1
0.8
0.8
0.7
0.4
0.4
0.3
0.3
0.2
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0.1
aging 40 meters (n = 307 sightings, range 3 to ca.
250 m). While circling, their heads are held down-
ward, bill pointing toward the water. When a fish
is spotted they half-fold their wings and drop to the
water in a controlled dive, often changing direction
to compensate for movement of the fish. In 17 re-
corded instances diving heights ranged from 10 to
50 meters (average of 25 m).
Unlike the feeding behavior of most seabirds in
our study area, all Red-tailed feeding was accom-
plished only by the "plunge to surface" and "direct
to prey air dive" methods described by Ashmole
and Ashmole (1967:70-71). We have one record of
possible "contact dipping" (see below), but in this
instance the bird may have lost sight of the fish and
pulled out of the dive before hitting the water since
it was not noted to have captured a fish. The fol-
lowing examples are taken directly from POBSP field
notes:
CONTACT DIPPING?
15 August, 1964. 1818 Hours. Anonymous. ". . . another dive
from 100 feet just skimmed surface of water."
PLUNGE TO SURFACE
09 January 1965. 0715 Hours. Warren King. "2 birds. Birds
were feeding, dropping into water from 40 feet or so,
breaking their fall slightly with their wings and steering
as well. Did not appear to go below surface. Wings
somewhat extended a split second after impact keeping
birds on surface."
DIRECT TO PREY AIR DIVE
07 February 1964. 0844 Hours. Patrick Gould. "1 bird made
at least 6-10 dives, 2 from at least 100 feet up. Bird
half closed its wings, steering with wings, did not break
fall, completely submerged in water with great splash,
NUMBER 158 209
•
HIGH |
3 YEAR I
LOW |
| I  I3YEAR
3 YEAR I AVERAGE
SUNRISE SUNSET
FU.URE 126.—Hourly densities of Red-tailed Tropicbirds in the central Pacific, 1964-1966. Num-
ber of hours of observation per time period ranged from 183.7 at 0400 to 1151.6 at 1500. Total
hours of observation equal 15,962.0.
but did not remain in water for longer than 2 seconds.
A series of shorter dives were also made. One bird, after
starting its dive, altered its direction to more of an
incline and spiraled down, evidently keeping the fish in
sight at all times. It was noted to check itself in mid-
dive several times but this appeared to be due to move-
ment of prey rather than trying to reduce speed."
The above feeding habits are probably incompati-
ble with the feeding habits of other species in
mixed flocks where the birds are concentrated and
swirling in circles over the food. A diving bird
would not be able to keep a fish in sight or avoid
swirling birds. Although boobies (Sula) use the
"direct to prey air dive" when by themselves, they
apparently always switch to "dipping" or "surface
dive" when in mixed flocks. Tropicbirds are ap-
parently not as versatile as boobies, and, even when
attracted to mixed feeding flocks, generally remain
on the periphery.
Red-tailed Tropicbirds have been recorded at all
hours of the day but are most commonly observed
in the morning. Peak numbers occurred around
1000 hours (Figure 126). Nocturnal density figures
are low due to the difficulty in seeing and identify-
ing single birds at night. Most birds were active,
but 14.2 percent of all individuals recorded were
sitting on the water. Many of the birds were appar-
ently roosting on the water and were flushed by the
approaching ship.
210 SMITHSONIAN CONTRIBUTIONS TO ZOOLOCY
TABLE 36.—Measurements (in mm) of Red-tailed Tropicbirds from the central
Pacific
Area and source Sample size Range Mean Standard error
Laysan (Stager, 1964)
Northwestern Hawaiian Islands and
Johnston Atoll (POBSP)
At sea, N of 10°N (POBSI>)
At sea, 4°N-10°N (POBSP)
At sea, S of 4°N (POBSP)
Line and Phoenix (POBSP)
Marquesas, Tuamotus, Society, etc. (Stager,
1964)
Laysan (Stager, 1964)
Northwestern Hawaiian Islands and
Johnston Atoll (POBSP)
At sea, N of 10°N (POBSP)
At sea, 4°N-10°N (POBSP)
At sea, S of 4°N (POBSP)
Line and Phoenix (POBSP)
Marquesas, Tuamotus, Society, etc. (Stager
1964)
7
22
79
12
18
21
7
7
21
77
12
17
21
Wing
307-322
301-329
287-343
307-344
315-350
310-345
320-344
Exposed
58-63
50-66
57-69
59-65
61-67
59-68
length
313
316
316
320
329
334
330
culmen
61
61
62
62
63
63
_
1.5
1.4
3.4
2.5
2.1
-
_
0.6
1.0
0.6
0.4
0.6
62-70 66
Specimen Records
Two races have been recognized in the central
Pacific. Phaethon rubricauda rothschildi (Mathews)
breeds on the northern islands, including Johnston
Atoll, Wake, and the northwestern Hawaiian Is-
lands. A larger form, P. r. melanorhynchos Gmelin
breeds on islands farther south, including the Mar-
quesas, Line, Phoenix, Tuamotu, and Society is-
lands. Wing length and exposed culmen are the
major distinguishing criteria. These races appear
to represent parts of a broken cline of increasing
size from north to south. Our measurements (Table
36) show that birds from northern islands (Johnston
Atoll and the northwestern Hawaiians) have shorter
average wing and exposed culmen lengths than
birds from Line and Phoenix islands. These in
turn apparently have shorter average exposed cul-
mens (Stager, 1964) than birds from farther south
and east (Marquesas, Tuamotus, and Society is-
lands).
Specimens have been taken at sea in every month
of the year and along all commonly used POBSP
cruise tracks. Greatest numbers were collected from
June through November, the period, also, when
the greatest number of sightings was recorded.
Specimens collected at sea in the central Pacific
were divided into three groups for analysis: (1)
those collected north of 10°N, (2) those collected
between 10°N and 4°N, and (3) those collected
south of 4°N (Table 37). Birds collected north of
10° N agree in mensural characteristics with those
of the northwestern Hawaiian population. Birds
collected south of 4°N are larger than those from
the northwestern Hawaiian population areas but
slightly smaller than birds from the southern is-
lands. Birds collected in the intermediate zone are
intermediate in their measurements, but fall closer
to the northern population.
Eighteen specimens (all but three either imma-
ture or subadult) were collected at sea in the east-
ern Pacific (Table 37). These show the same tend-
ency for larger birds to be found in southern lati-
tudes, and smaller birds to be found in northern
latitudes. Two specimens in the United States Na-
tional Museum (USNM 212164, 212165), collected
at 10°N, 130°W, conform in size, as expected, to the
population from the northwestern Hawaiian Is-
lands.
Exceptions to the above pattern do occur. Seven
NUMBER 158 211
TABLE 37.—Measurements (in mm) of POBSP specimens from the eastern Pacific,
latitudes south to north (SA = subadult, IM = immature, AD=adult)
Area
24°14'S, 75°27'W
24°14'S, 75°27'W
24°14'S. 75°27'W .
23°45'S, 75°45'W
23°45'S, 75°45'W .
23°45'S, 75°45'W .
17°02'S. 106°46'W
16°34'S. 107o01'W
14°08'S, I08°26'W
14°00'S, 104°58'W
13°2rS, 108°53'W
9°57'S, 112°23'W
2OS1'S, 118°50'W
l°05'N, 11
8c08'N, 1
8°08'N, l
13O41'N, 112°20'W
31°39'N, 123°22'W
Date Age Sex Wing length Exposed oilmen
22
22
22
22
22
22
15
15
16
4
16
23
27
21
3
3
11
13
Apr
Apr
Apr
Apr
Apr
Apr
Mar
Mar
Mar
Mar
Mar
Aug
Feb
Mar
Nov
Nov
Feb
Feb
65
65
65
65
65
65
68
68
68
67
68
67
68
68
67
67
67
67
SA
SA
SA
SA
SA
SA
IM
AD
IM
SA
IM
SA
AD
IM
SA
SA
SA
AD
9
9
S
S
9
$
9
9
9
9
9
9
9
9
9
9
9
330
320 (worn)
314
332
329
312
321
334
332
344
339
323
321
334
318
322
328
310
68
66
69
68
64
68
68
68
66
63
70
65
63
64
63
61
62
59'
* Banded on Kure Atoll.
TABLE 38.—At-sea recoveries of banded Red-tailed Tropicbirds (AD=adult,
SA=subadult, L=local, N = nestling)
Location
Kure
Kure
Kure
Midway
Midway
Laysan
Christmas
Jarvis
Jarvis
Jarvis
Enderbury
Banding
Date
14 Oct 64
1 Apr 64
15 Oct 64
14 Feb 64
27 Jul 65
10 Sep 67
21 Nov 64
15 Nov 64
16 Nov 64
15 Nov 64
2 Oct 65
Age
L
AD
N
AD
AD
AD
N
N
N
N
N
Location
31°39'N, 123°22'W
4°40'N,154°20'W
38°30'N, 178°30'W
125 mi SW Midway
33°O2'N, 154°34'W
15°00'N, ln'SCW
1°57'N,177°26'W
0°22'S, 178°38'W
1°17'N,177°44'W
0°38'N,176°35'W
7°3O'S, 170°49'W
Recovery
Date
13 Feb 67
30 Nov 67
28 Apr 70
10 Jul 64
15 Nov 66
27 Feb 68
17 Sep 66
15 Oct 66
10 Dec 66
7 Feb 66
1 Dec 66
Age
AD
?
?
AD
AD
?
AD
AD
AD
SA
SA
Sex
9
?
?
?
?
?
9
9
$
S
Elapsed
Months
28.0
8.0
66.4
6.9
15.6
5.6
21.9
23.0
25.1
14.7
14.0
Miles
3300
2,000
600
125
1 3 0
3,100
1.200
1,060
1,060
975
270
exceptionally large birds (wing=335-342 mm, ex-
posed culmen = 64-69 mm) were collected north of
10°N and are referable to P. r. melanorhynchos.
The northernmost location was at 17°52'N, 166°
2 0 ^ . Two each were taken in April and Septem-
ber and three in November. Conversely, two excep-
tionally small birds (wing=315-319 mm, exposed
culmen = 62-62 mm) have been taken south of 4°N
and are referable to P. r. rothschildi. The southern-
most location was at 00°21'S, 178°38/W. One each
was collected in April and October.
There is no way of proving the island of origin
of a bird collected at sea unless it was banded as a
nestling. It is reasonable, however, to assume that
most birds collected north of 10°N originated on
northern islands because of the agreement in meas-
urements between island and at-sea specimens. On
the same basis we can assume that the birds col-
lected south of 4°N most likely originated on the
southern islands. It thus appears that Red-tailed
Tropicbirds, especially young, disperse widely at
sea, but tend to remain within the latitudinal range
of their respective populations.
Six specimens, assigned by us to P. r. melano-
212 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
rhynchos and collected off northern Chile (three at
23°45'S, and three at 24°15'S), represent a consid-
erable extended range to the southeast for this spe-
cies. One bird, originally banded as a local on
Green Island, Kure Atoll, and collected off north-
ern Baja California (31°39'N, 123°22'W), repre-
sents a northeast range extension. Its measurements
conform to the P. r. rothschildi population.
Eleven banded birds have been recovered at sea
(Table 38). Although the sample size is small, these
recoveries support the preceding arguments that
birds disperse widely but tend to remain within
the latitudinal boundaries of their respective popu-
lations. The Kure bird recovered at 04°40'N ap-
pears to be an exception; however, this latitude is
approximately at the southern border of the Equa-
torial Countercurrent, which is the dividing line
between several northern and southern seabird dis-
tribution patterns.
Molt
Molt in Red-tailed Tropicbirds appears to take
place nearly continuously except when individuals
are within a breeding cycle. Not one individual of
57 adult birds collected on many islands of the
central Pacific, including the Hawaiian, Line, Phoe-
nix, and Marshall groups and Johnston and How-
land islands, was molting remiges or rectrices, al-
though several birds showed light body contour
feather molt.
The juvenal appearance, characterized by heavy
black vermiculations over the entire dorsal surface,
a black suffusion spreading into the vanes, both dor-
sally and ventrally, from the black dorsal shafts of
the larger primaries, excluding the outermost,
short, white central rectrices and a blackish bill,
changes within 15 months, probably starting with a
complete annual molt, to a distinctive subadult
form which probably persists (on the basis of two
specimens, 15 and 16 months, respectively) well
into the second year, when it is gradually replaced
by the typical adult form. Subadults have white
backs and rumps, flecked with black, but the ver-
miculations on head and nape remain. The pri-
mary vanes become entirely white, the shafts re-
maining black dorsally. The central rectrices elon-
gate, although not to the extent of adults, and get
the first hint of reddish pigment. The bill becomes
increasingly yellow, excluding the base which re-
mains dark. Between 15 or 16 months and 23
months all black spots have disappeared from the
dorsal surface except the central portion of the
vanes of the longest secondaries which remain black
in all age classes. The black vermiculations of head
and nape remain only at the bases of feathers of
this area and are masked by white, which condition
persists in adult birds. The central rectrices are red
but possibly not as long as those of breeding birds.
It may be possible to distinguish some third year
birds from older birds by their orange rather than
red bills (the nares remain dark even in breeding
birds) and by the retention of black spots in a few
dorsal secondary coverts, often well hidden. Other-
wise, they are indistinguishable from breeding
birds. Our sample in this age class is four birds, 23,
24, 26, and 29 months. Most do not breed until at
least four years, possibly older. Thus, there is a
period of at least one year when birds have adult
appearance but do not breed.
Because the breeding cycles of populations are
not precisely synchronized, but extend in some
cases nearly year-round, and because there is evi-
dently some mixing at sea of populations from the
southern and northern hemispheres, some of the
birds collected in any given month at sea are un-
dergoing flight feather molt. In only 4 months
(June, August, September, and December) were
more than one-half of adults taken at sea not molt-
ing remiges and rectrices. Subadult and immature
birds (those with at least some black vermiculations
on their backs) molt almost continuously. Only 5
of 54 immature or subadult birds (9.3 percent) were
molting neither remiges nor rectrices, whereas 27
of 81 adults (32.5 percent) had no rectrix or remex
molt. All 18 birds collected in the eastern Pacific
(Table 37), 3 adults and 15 subadults or immatures,
were undergoing molt of flight feathers.
The pink flush that appears in the plumage of
some adult birds is evidently not tied directly to
breeding. Eight of 81 (9.9 percent) adult birds
taken at sea had a pink flush; only 2 of these were
not molting flight feathers.
REMEX MOLT.—Remex molt proceeds outward
from the carpal joint toward the outermost pri-
mary, and inward along the secondaries toward the
body. Secondary molt will not be considered fur-
ther here. Primary molt can occur at one locus, or
at 2 or 3 loci simultaneously.
NUMBER 158
number of loci
0 (no molt)
1
2
3
number of specimens
34
52
41
8
percent of
total specimens
25.2
38.5
30.4
5.9
135 100.0
Because the innermost primaries were often diffi-
cult to identify on the specimens, and, therefore,
molt of Remiges 1 or 2 might have been over-
looked, some specimens recorded molting at 1 or 2
loci might have been molting actually at 2 or 3
loci. Of those birds molting at 2 or 3 loci, the mean
number of feathers between loci was 3.3 (range 0-
6). Remex molt is usually symmetrical.
number of feathers
between loci
0
1
2
3
4
5
6
number of
occurrences
6
2
8
13
13
13
2
RECTRIX MOLT.—Red-tailed Tropicbirds usually
have 14 rectrices, including the two red elongate
central feathers, although 9 of 135 specimens taken
at sea (6.7 percent) had 16 rectrices, one apparently
had only 12 and 2 seemed to have 15.
Growth and replacement of the two central rec-
trices is apparently continuous. Even among breed-
ing birds, otherwise not molting, one of the central
rectrices is usually shorter than the other and is
growing. Because molt of the central rectrices is
evidently not part of the normal molt cycle, it will
not be considered further here.
Rectrix molt is usually completed before remex
molt. Of 40 adults and 26 subadults or immatures
number of loci
0 (no molt)
1
2
S
4
number of
specimens"
150
83
34
1
1
percent of
total specimens
56.1
30.9
12.6
.2
.2
269b 100.0
* Each side is considered independently because rectrix molt
is frequently asymmetrical.
b
 The rectrices on one side of one specimen had been dam-
aged to the extent that molt determination was impossible.
213
that were not molting rectrices, 13 adults and 21
subadults or immatures had not yet finished remex
molt. Only one adult and one immature of 135
specimens had completed remex molt but not rec-
trix molt. Rectrix molt usually proceeds from one
or two loci (see bottom of column 1).
Of those birds molting at two or more loci, the
mean number of feathers between loci was 2.1
(range 0-4).
number of feathers
between loci
0
1
2
3
number of
occurrences
S
9
14
8
5
It was not possible to determine the sequence of
rectrix molt, nor was there any obvious correlation
between the stages of remex and rectrix molt.
Distribution and Abundance
Figures 130-141 summarize the observations of
Red-tailed Tropicbirds made by POBSP in the cen-
tral and eastern Pacific between 1963 and 1968.
Data from January (Figure 130), for example, are
taken from all years in which observations were
made that month. Each day's observations are ex-
pressed in terms of birds per mile of observation,
and are located on the maps at the position of the
ship at noon (open circles). Areas of equal density
were contoured to show relative abundance in dif-
ferent parts of the ocean and in different months.
Where single line oceanic transects prevented accu-
rate contouring, contours were extended an arbi-
trary distance on either side of the cruise track,
just enough to indicate the densities encountered
along the track.
An annual pattern of pelagic occurrence is evi-
dent in the monthly distribution maps. In order to
examine this pattern more closely, the absolute den-
sity of Red-tailed Tropicbirds (birds per 100 mi2)
was determined for each month, for each of four
broad latitudinal bands between 30°N and 20°S
(20°-30°N, 10°-20°N, 0°-10°N, 0°-20°S).
CENTRAL PACIFIC.—The Red-tailed Tropicbird
was present throughout the pelagic central Pacific
during all months. Abundance in the region was
generally low in late winter and spring and high in
summer and fall (Figure 127a). As is the case with
214 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
J A N FEB MAR APR MAY JUN JUL AUG SEP O C T NOV DEC
MAXIMUM ISLAND POPULATION
o
o
oc 3.
Q.
a
ac
CQ
2 .5
1.5
. 5
«- Sfi o - - - - .
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
FIGURE 127.—Absolute density of Red-tailed Tropicbirds (birds per 100 square miles) in 10°
wide latitudinal zones: A,B, in the central Pacific; c, in the eastern Pacific.
most other seabirds, the pelagic distribution of
Red-tailed Tropicbirds is greatly affected by the
breeding cycle. Adults tend to remain near breed-
ing islands while breeding, particularly in the early
stages (i.e., egg-laying and incubation). This was
reflected in the differences in abundance observed
between the latitudinal bands of 20°N to 30°N
and 10°N to 20°N (Figure 127a). The former area
encompasses the major breeding islands, and most
cruises within this area remained relatively close to
land. In contrast, the latter area includes only one
small breeding location (Johnston Atoll), and most
cruises within the area were far from land. The
only months when densities in the 20°N to 30°N
area were greater than those of 10°N to 20°N were
in June through August, when peak numbers oc-
curred on the breeding islands. In the 10°N to
20° N zone, densities were relatively high from
September through November; the July peak can
be explained by one day of observation near Johns-
ton Atoll, when density was high (.18 birds per
mile). Figure 1276 shows a typical annual cycle
NUMBER 158 215
BREEDING
i ^ i . . i ~ i nS O N D J F M A M J J A S ' O ' N ' D ' J ' F
FIGURE 128.—Diurnal abundance of Red-tailed Tropicbirds in a pelagic area near Howland
Island.
110° 120° 130° 140° 150° 160° 170°t 180° I7O°W 160° 150° 140° 130° 120° 110° 100° 90° 80° 70°
110° 120° 130° 140° 150° 160° 170°E 180° 170°W 160° 150° 140° 130° 120° 110° 100° 90° 80° 70°
FIGURE 129.—Range of the Red-tailed Tropicbird (Phaethon rubricauda) in the Pacific Ocean.
Dark lines indicate the location of the 22°C isotherm in summer (after Muromtzev, 1958).
216 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
for a relatively small pelagic study area, 50 miles
off Johnston Atoll.
The absolute density (birds per 100 mi2) of the
species was calculated for a pelagic area near How-
land Island for the period September 1965 through
February 1967 (Figure 128). Peak numbers (1.9
birds/100 mi2) occurred in October 1966, immedi-
ately following the Howland Island breeding sea-
son. Relatively high numbers (1.2 birds/100 mi2)
also occurred in August 1966, during the breeding
season.
EASTERN PACIFIC.—Although our data are incom-
plete for the eastern Pacific, the species was present
each month observations were made. Observations
were made in all months except April, May, and
December (Figure 127c).
WESTERN PACIFIC.—The Red-tailed Tropicbird
apparently occurs in the southwestern Pacific more
commonly during the southern summer than dur-
ing other seasons. Of the 24 records from the
southwestern Pacific in the appendix for which
there are definite dates, 18 were from October
through March. Sorensen (1964) states that this
species occurs year-round in the Kermadec Islands,
but most abundantly from October through May.
Environmental Factors
It was noted that this species ranges to higher
latitudes in the western Pacific than in the eastern
Pacific (see Appendix). This is probably explained
by the fact that the Kuroshio and East Australian
Currents carry relatively warm water to relatively
high latitudes in the western Pacific.
The range of this species, as indicated in Figure
129, generally parallels the summer surface water
isotherms of ca. 22°C in both the north and south
Pacific (Muromtzev, 1958, figs. I l l , 112). Similarly,
the distribution of surface salinity in the Pacific
Ocean (Muromtzev, 1958, fig. 134) suggests that the
species does not range into waters with salinities
less than 33.5-34.0%o in the northern hemisphere
and less than 35.O2U in the southern hemisphere.
Its range appears limited to the waters between
the bounds of the north and south subtropical
convergences.
It is apparent from the preceding documentation
of the northern and southern subspecies that trans-
equatorial movements are minimal. It seems
possible that the rich equatorial current region,
especially the countercurrent, acts as a restraint to
bihemispheric movement of the subspecies, i.e.,
because of the increased abundance of food in the
equatorial region, birds flying north from the
south Pacific would have no reason to continue
northward beyond the equatorial current region,
and the same would apply to northern birds flying
south. The pattern of distribution noted in the
February map (Figure 131) may possibly be ex-
plained by this.
Discussion
The Red-tailed Tropicbird has an extremely
wide pelagic range, which includes virtually all of
the tropical and subtropical Pacific. It generally
ranges to higher latitudes in the western Pacific
(30°-35°N) than in the eastern Pacific (20°-25°N).
Although there is little direct supporting evidence,
it seems probable that most of the population stays
within latitudes of less than ca. 30° in both hemi-
spheres, but that individual birds occasionally
wander to higher latitudes, or are carried there by
storms.
It is apparent from our specimen data that a
strong tendency exists for birds breeding on south-
ern islands to remain in more southern latitudes,
although they may disperse widely within these
areas. Racial mixing in pelagic areas, however, does
occur and individuals may be found far north or
south of the usual range of their respective popu-
lations.
The distribution and abundance of Red-tailed
Tropicbirds in the central Pacific appears to be
generally correlated with the breeding season. The
period (June through August) of maximum abun-
dance and closest proximity to land in the northern
part of their range corresponds to the breeding
season in the Hawaiian Islands. Minimum abun-
dance is found immediately following the dispersal
of fledged young from the breeding grounds, and
birds are absent from the vicinity of the islands
the rest of the year. Peak abundance occurred at
sea near Howland Island immediately following
the breeding season.
Although our data from the eastern tropical
Pacific do not cover all months, there appear to be
peaks in abundance in both winter (February) and
summer (August). The winter peak possibly con-
tains some central Pacific breeders; the pelagic oc-
NUMBER 158 217
turrence of the species in the central Pacific is at a month that POBSP cruises were conducted, these
low ebb at this time. Our data suggest that pre- being all months except April, May, and December,
breeders are more likely to visit the eastern Pacific Thus, it seems quite probable that the species oc-
than breeding age birds. Birds were seen each curs in the eastern tropical Pacific year-round.
218 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
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Appendix
Summary of published data on Red-tailed Tropicbird distribution
Location
EAST-CENTRAL PACIFIC
30° N, 132°W
Guadalupe I., Mexico
Clipperton I., Mexico
8°N, 119°W to Manzanilla,
Mexico
Manzanilla, Mexico to9°S,
120°Wtoca.5°N, 139°W
6°N,82°W
0°26'N, 98°36'W
0°07'N( 87°50'W
l°10'S, 100°S7'W
3°58'S,91°15'W
4°02'S, 110°31'W
5°15'S, 113°W
8°03'S, 133°36'W
SOUTHEAST PACIFIC
12°S, 100°W
Easter I.
CENTRAL PACIFIC
30°N, 150°W
27°19'N,172°25'W
22°N, 165°W
17°44'N, 159°56'W
7°N,166°W
7°46'S, 167°16'W
8°40'S, 136°54'W
Nuku Hiva, Marquesas
Near Marquesas
SOUTH-CENTRAL PACIFIC
13°37'S, 177°18'W
Near Suva, Fiji
27°06'S, 177°41'E
28°18'S, 177°01'E
29°12'S, 178°28'E
Kermadec I.
NORTHWEST PACIFIC
Honshu, Japan
Date
no date
23 Jul 1897
19 Aug 1958
1-19 Oct 1955
24 Oct-20 Nov 1955
2 Jan 1963
22 Nov 1957
2 Apr 1950
28 Feb 1947
1 Apr 1950
22 Nov 1957
10 Nov 1960
30 Sep 1928
25 Apr 1960
Dec 1968
26 Jul 1959
24 Aug 1960
28 Apr 1945
20 Jul 1959
4 Nov 1960
31 Oct 1928
1 Oct 1928
2 Oct 1928
Dec 1955
24 Jul 1959
31 May 1959
13 Dec 1928
9 Dec 1928
11 Dec 1928
all year
May 1907; 1885;
20 Nov 1934:
Remarks
seen continuously around ship
1 specimen
1 specimen (adult $)
infrequent
singles and pairs frequently seen
1
1
1
1
1
3
1, possibly 4 others
6 in 3 sightings
1 on board ship
fair numbers, breeding
1 seen close for 1 \/z hrs.
6
3
1
1
1
1
a few
none
1
1
1
3 in 2 sightings
1
most from Oct to May
4 records are for spent, "probably
storm-driven birds"
Source
Mdrzer Bruyns, 1965:63
Kaeding, 1905:109
Stager, 1964:360
King and Pyle, 1957:36
• • • • • •
Morris in Bourne, 1965:29
Gibson, 1960:16
Laird, 1951:177
Fleming, 1950:172
Laird, 1951:177
Gibson, 1960:16
Semple in Bourne and Radford,
1962:21
Jespersen, 1933:216
Harrison in Bourne and Radford,
1961:21
Johnson, et al., 1970:535-536
Agnew in Bourne and Radford,
1961:22
Wilhoft, 1961:261
Cogswell, 1946a:48
Wilhoft, 1961:261
Morzer Bruyns, 1965:63
Jespersen, 1933:216
„ „
„ „
King and Pyle, 1957:36
Wilhoft, 1961:261
Peakall, 1960:201
Jespersen, 1933:216
.. ..
„ „
Sorensen, 1964:73
Austin and Kuroda, 1953:315
230
NUMBER 158 231
Summary of published data on Red-tailed Tropicbird distribution—Continued
Location
Linschoten I.
WEST-CENTRAL PACIFIC
West Pacific
Western tropical Pacific
Taiwan
25°26'N,124°18'E
19°09'N,120°05'E
15°N, 160°W-l°S, 148°W
10°N, 150°-120°W
Mariana and Caroline I.
Palau I.
SOUTHWEST PACIFIC
Thursday I.
15°30'S, 159°45'E
17°57'S, 169°52'E
23°28'S, 127°31'W
24°40'S, 164°W
25°13'S> 130°28'W
26°16'S, 161°24'E
26°15'S, 176°56'W
28°20'S, 140°45'W
3O°55'S, 155°17'E
32°H'S, 155°07'E
33°25'S, 162°45'E
33°27'S, 157°1O'E
33°3O'S, 165°53'E
New Zealand
Northern New South Wales,
Australia
Port Kembla, N.S.W., Australia
coastal N.S.W.
Tasman Sea
18°16'S, 151°21'W
9°53'S, 161°28'W
2O°57'S, 158°58'W
Date
1917; 30 Mar
1951; no date
14 Aug 1906
no date
Aug 1945-Mar 1946
21 May 1937
30 May 1929
22 May 1929
4-5 Dec 1955
1-19 Oct 1955
no date
28 Oct 1960
18 Mar 1929
Jun 1951
10 Dec 1957
9 Jul 1948
11 Mar 1947
2 Dec 1948
19 Dec 1957
14 Mar 1947
29 May 1955
20 Dec 1957
24 Feb 1929
27 Jan 1929
29 Jan 1929
26 Jan 1929
1877, 1936, 1942
17 Jun 1945
13 Nov 1955
12 Jan 1955
no date
18 Oct 1928
24 Oct 1928
21 Oct 1928
Remarks
1 observed, may be more common
than supposed
4 widely scattered sightings
6 sightings from 66 to 195 mi from
land
1 offshore
1
1
singles and pairs frequently seen
infrequently seen
uncommon throughout most of Mi-
cronesia, may be a resident only
in the northern Marianas
1
1
1
2 approached from direction of New
Hebrides
3 birds in 2 sightings
1
several off Pitcairn I.
1
1
no details
1
1
2
3
1
only 3 records
hurricane-driven bird, 120 mi from
coast, at altitude of over 1000 ft
1
bird found dead
may penetrate area as far as 38°S
1
2 in 2 sightings
a few
Source
Clark, 1910:42
MacDonald and Lawford, 1954:22
Dixon and Starrett, 1952:270
Hachisuka and Udagawa, 1951b: 124
Jespersen, 1933:216
" "
King and Pyle, 1957:36
Baker, 1951:71
Morzer Bruyns, 1965:63
Jespersen, 1933:216
MacDonald and Lawford, 1954:22
Gibson, 1960:18
Fleming, 1950:175
Fleming, 1950:172
Fleming, 1950:181
Gibson, 1960:18
Fleming, 1950:172
King in Bourne, 1964:28
» . . . . i,
Jespersen, 1933:216
.. ..
Oliver, 1955:195
Hindwood, 1947:57
Gibson and Sefton, 1956:198
Hindwood, 1955:160
Falla.etal., 1967:59-60
Jespersen, 1933:216
Recoveries of Banded Laysan Albatrosses (Diomedea immutabilis)
and Black-footed Albatrosses (D. nigripes)*
Chandler S. Robbins and Dale W. Rice
Introduction
This paper summarizes the distribution of at-sea
recovery records of banded Laysan Albatrosses
{Diomedea immutabilis) and Black-footed Alba-
trosses (D. nigripes). Both species now nest pri-
marily in the leeward Hawaiian Islands, and both
roam over the north Pacific Ocean, covering essen-
tially the entire area from Japan to the continental
United States and from the vicinity of the Aleutian
Islands south to about 20° N. Maps showing the
breeding sites and the total marine range for both
species (prepared by E. M. Reilly, Jr.) have been
published in Volume 1 of (he Handbook of North
American Birds (Palmer, 1962). Although these
maps indicate the known limits of occurrence, they
do not attempt to show concentration areas, sea-
sonal changes in distribution or abundance, or
differences in distribution of the various age classes.
More than two dozen papers have been pub-
lished summarizing observations at sea of one or
both species of albatross in various parts of the
north Pacific Ocean—primarily along the American
and Japanese coasts and along the main trans-
Pacific shipping lines. Unfortunately, these publi-
cations have been limited both geographically and
seasonally and only two papers (Shuntov, 1968;
Fisher and Fisher, 1972) have come close to brack-
eting the entire range of either species.
Chandler S. Robbins, Migratory Bird and Habitat Research
Laboratory, United States Bureau of Sport Fisheries and
Wildlife, Laurel, Maryland 20810. Dale W. Rice, Northwest
Fisheries Center, Marine Mammal Division, Sand Point
\'SA, Building 192, Seattle, Washington 98115.
•Paper Number 101, Pacific Ocean Biological Survey Pro-
gram, Smithsonian Institution, Washington, D.C. 20560.
Shuntov (1968) gave summer and winter maps
for each species, showing concentration areas, nor-
mal range, and the area within which each species
is rare. Fisher and Fisher (1972) summarized the
geographic occurrence at sea of Laysan Albatrosses
based on a combination of 109 recoveries of birds
they had banded, 53 published records of birds
banded by others, and 113 sight records. They
pointed out four regions in which Laysan Alba-
trosses tend to congregate. They described seasonal
shifts in concentrations, and they attempted to ex-
plain distribution and movements in relation to
turbulences, eddies and currents, water tempera-
tures, and food supply. Our findings, based on a
much larger sample of banded birds, both Laysan
and Black-footed Albatrosses, show a more orderly
distribution pattern, both for adults and for the
various age classes of subadult birds.
ADVANTAGES OF USING BANDING RECOVERIES.—The
use of recoveries of banded birds as a means of
showing geographic range at various seasons and
for various age groups has several distinct advan-
tages over compiling published data from sight
observations. The age of the great majority of
banded birds is known, permitting mapping of
distribution and relative abundance by age group.
Except for a very short period in the first season
at sea, there is no way to distinguish birds of the
year from older birds by means of sight observa-
tions. Recovery records are accumulated over many
years, thanks to the long life span and the long
period over which both species have been banded
in good numbers. This prevents abnormalities of
weather, human activities, or bird distribution
from unduly affecting the total picture. All por-
tions of the oceanic range are included in the re-
232
NUMBER 158 233
covery reports, even though there is geographic
and probably seasonal variation in intensity of
recapture effort. For a comparative study of the
distribution of these two species, the use of band-
ing recoveries offers a fairly uniform means of
sampling populations throughout the area in which
both species range.
LIMITATIONS OF BANDING RECOVERIES.—The prin-
cipal biases involved in using banding recovery
data relate to geographical differences in human
contact with the birds and in reporting rate. Since
most of the at-sea recoveries of banded albatrosses
have come from fishing vessels, the recoveries are
concentrated in those locations that are most heav-
ily used for fishing—especially longline tuna sets.
Variation from month to month and from year to
year in fishing activity also greatly influences hu-
man contact with albatrosses. Unfortunately, accu-
rate figures on relative fishing effort throughout
the north Pacific are not available on a monthly
basis, year by year. If they were, this would permit
mapping recoveries per unit of fishing effort and
result in a more meaningful analysis of albatross
distribution than is presently possible. Neverthe-
less, Japanese longline fishing effort is well distrib-
uted over most of the north Pacific as shown by
Rothschild and Uchida (1968:21), and as reflected
in the recovery records that have been obtained.
Changes in geographic concentrations of albatrosses
may very well be related to similar changes in dis-
tribution and abundance of the commercial fishery
resource, so the centers of concentration of the
birds may actually be localized in the areas where
the greatest fishing activity takes place. Shuntov
(1968:1064) concluded that "albatrosses are most
numerous in waters with an increased biological
productivity."
Banding recoveries generally cannot be used to
describe the extreme geographical limits of a bird's
range, because only a small percentage of the birds
banded are recovered. Thus the areas where a spe-
cies is common are much better represented by re-
covery records than are the marginal portions of
the range. This paper, therefore, deals primarily
with seasonal changes in the centers of populations
of the various age groups rather than with records
of individual birds.
The Black-footed Albatross has a more varied
diet than the Laysan, is more readily attracted to
fishing vessels (and other boats) and so is much
more likely to be captured at sea. Thus, recovery
rates cannot be used to compare abundance of one
species with the other in any region of interest.
Differences in the ratio of Laysan to Black-foot
recoveries from one part of the range to another,
however, can be used to show geographic differ-
ences in relative abundance. Furthermore, differ-
ences in the distribution of the various age classes
can readily be detected, since it is unlikely that
there are any geographical biases that would favor
selective capture of one age class over another.
Birds in their first three or four years, especially
Laysan Albatrosses, appear to be more susceptible
to capture than fully adult birds, but this holds
true in all parts of their range. The recovery rate
for Laysan Albatrosses reached a strong peak in
their second summer, while the highest recovery
rate for Black-footed Albatrosses occurred in their
third summer.
BANDING HISTORY.—The first Laysan Albatrosses
were banded by F. C. Hadden at Midway Atoll in
1937, and the first Black-footed Albatrosses, by
George C. Munro at the same location in 1940.
Banding continued on a small scale through 1952,
largely under the auspices of George Munro and
the Hawaii Audubon Society, with several hundred
albatrosses banded at Midway in most years. Some
335 adults were banded by Johnson Neff and
Philip A. DuMont of the U.S. Bureau of Sport
Fisheries and Wildlife in 1954.
The great majority of the banding of both spe-
cies was done during the period 1956-1969. During
1956-1967, the U.S. Bureau of Sport Fisheries and
Wildlife, at the request of the U.S. Navy, con-
ducted studies on albatrosses on Midway and some
of the other leeward Hawaiian Islands to obtain
information on albatross biology and habits that
could be used in reducing the hazard of birds to
aircraft at Midway. And during the period 1963-
1969, the Pacific Ocean Biological Survey Program
of the Smithsonian Institution included an exten-
sive banding program on all the major nesting
islands of the Laysan and Black-footed Albatrosses.
Nearly all of the banded birds were tagged in
their nesting colonies in the leeward Hawaiian
Islands, but four of them were captured and banded
at sea, and one was banded on Torishima Island,
Japan. The great majority were banded on the
Midway Islands (28°13'N, 177°20'W), but there
are also a few recoveries from albatrosses banded at
234 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE 39.—Manner of recovery of Laysan and Black-footed Albatrosses
Action
Shot
Caught on fish hook
or net
Caught and released
with band
Caught by hand . . . .
No information
Found dead
Miscellaneous . . . .
Total
Young
11
121
6
6
22
22
2
190
Laysan
Adult
17
22
2
3
12
2
1
59
Albatross
Total
28
143
8
9
34
24
3
249
Percent
11.2
57.4
3.2
3.6
13.7
9.6
1.2
99.9
Black-footed Albatross
Young
19
68
3
9
7
19
6
131
Adult
18
72
17
4
16
19
6
152
Total
37
140
20
13
23
38
12
283
Percent
13.1
49.5
7.1
4.6
8.1
13.4
4.2
100.0
Kure Atoll, about 90 miles west of Midway, and
68 from birds banded on islands in the Hawaiian
Islands National Wildlife Refuge (French Frigate
Shoals, Laysan, Lisianski, and Pearl and Hermes
Reef), between Midway and the main Hawaiian
Islands. The nesting islands on which the recov-
ered albatrosses were banded extend in nearly a
straight line from 23°40'N, 166° lOW to 28°20'N,
178°10'W, a distance of about 1000 nautical miles.
SOURCE OF DATA.—The recovery records on
which this paper is based are from the files of the
Bird Banding Laboratory of the U. S. Bureau of
Sport Fisheries and Wildlife at the Office of Mi-
gratory Bird Management in Laurel, Maryland.
Although the great majority (73%) of the birds
discussed in this paper were banded by the authors
(54%), and by POBSP personnel (19%), 76 of the
recoveries are from birds banded by H. I. Fisher
and assistants (Fisher and Fisher, 1972), 37 were
banded by R. R. Sheehan, 28 by E. Kridler, 21 are
from bandings by George Munro and his collab-
orators of the Hawaii Audubon Society, and from
1 to 8 each are from bandings by 13 other individ-
uals. This analysis includes recovery records proc-
essed through August 1972.
Summarized herein are 324 recoveries of Laysan
Albatrosses from 165,890 birds banded from 1937
through 1969, and 399 recoveries of Black-footed
Albatrosses from 48,727 birds banded from 1940
through 1969. Since tens of thousands of birds from
these banded samples are still alive, including some
individuals from nearly all years of banding, the
figures given here cannot be used to compute final
recovery rates.
Although most of the banding recovery records
specified the date and the latitude and longitude
of recapture, some oceanic records had to be omit-
ted because of insufficient data. Also omitted were
all recaptures on the various nesting islands.
MANNER OF RECAPTURE.—The principal means
of recovery of banded albatrosses at sea is by fish-
ermen who capture the birds on baited hooks or
in nets. The large majority are taken on longline
tuna gear; a typical set (Rothschild and Uchida,
1968) contains 2000 hooks on 120 kilometers of
line. As shown in Table 39, more than 50 percent
of a sample of more than 500 recoveries received
for each species were reportedly obtained by this
means. Many of the birds listed in other categories,
e.g., found dead, caught by hand, caught and
released with band, and no information, probably
also were taken on fish hooks or in nets. It is ap-
parent from Table 39 that both species are equally
susceptible to being recovered in the various man-
ners listed. Thus, although the Black-footed Alba-
tross more frequently comes in contact with man
through its habit of following ships, there is no
apparent bias in favor of one species or the other
being taken by fishing gear rather than by other
means.
Both adult and young Black-footed Albatrosses
appear to be equally susceptible to being recovered
by each of the listed categories, with the possible
exception of the first. The manner of recovery of
young Laysan Albatrosses is very similar to that of
Black-footed Albatrosses. Adult Laysans, however,
are much less frequently reported as captured in
NUMBER 158 235
nets or on hooks, and a higher proportion of these
birds were obtained by shooting.
Figure 142 shows the monthly distribution of
recoveries at sea of the Laysan and Black-footed
Albatrosses combined, according to manner of re-
covery. The top line shows all birds caught on fish
hooks or in nets. The bottom solid line shows the
recoveries of birds that were shot, and the dashed
line shows birds recovered by all other means.
It is apparent from Figure 142 that fishermen
encounter albatrosses most frequently in the months
of May, June, July, and August, and least fre-
quently in September, October, and November.
The largest numbers obtained through shooting
were in May, June, September, and October; and
almost none were shot in December, January, and
February. The seasonal distribution of birds ob-
tained by other methods so closely parallels the
graph for birds that were caught on fish hooks
that the fishing industry probably accounts for most
of the birds reported by "other" means.
ACKNOWLEDGMENTS.—We wish to thank Eugene
Kridler of the U.S. Bureau of Sport Fisheries and
Wildlife for his cooperation not only on the Mid-
way studies, but also for making available his band-
ing recoveries from the Hawaiian Islands National
Wildlife Refuge (French Frigate Shoals, Lisianski,
and Pearl and Hermes Reef). Other Bureau col-
laborators who contributed materially to the band-
ing of these albatrosses were Karl W. Kenyon, Dr.
John W. Aldrich, Cdr. E. P. Wilson, Edward J.
O'Neill, Dr. Paul A. Stewart, Norman E. Holger-
sen, John Waters, Willis C. Royall, Jr., Johnson
Neff, and Philip A. DuMont.
Navy and Coast Guard personnel not only pro-
vided the necessary logistical support, but also
assisted in many other ways. Cdr. Glenn Wilson,
Lt. Ralph Stockstad, James L. Priest, Lt. Kenneth
C. Balcomb, and Marvin L. Cunningham banded
albatross chicks in our study plots in years when
we were not present at the proper season.
Mrs. Blanche A. Pedley of the Hawaii Audubon
Society went to considerable effort to supply band-
ing data from the Society's files in order to com-
plete the official records of birds banded by George
Munro and Miss Grenville Hatch.
Personnel from the Pacific Ocean Biological Sur-
vey Program of the Smithsonian Institution under
the direction of Dr. Philip S. Humphrey conducted
intensive banding during the period 1963-1969 and
FISH HOOKS
AND NETS
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
FIGURE 142.—Manner of recovery of banded Laysan and
Black-footed Albatrosses at sea.
also cooperated closely with us in many ways. One
hundred thirty-nine recoveries used in this report
were from birds banded by them.
We are indebted to Harvey I. Fisher for checking
nesting albatrosses on our study plots at times
when we could not be on Midway, and for the use
of recoveries of birds banded by him and included
in his publication (Fisher and Fisher, 1972).
We also acknowledge with thanks the following
banders, each of whom contributed one or more
recovery records to this study: Fred C. Hadden,
Richard C. Harlow, J. H. Scarlett, R. Sheehan,
Eric E. Smith, Yamashina Institute for Ornithology,
and Dr. C. F. Yocom.
We appreciate the fine international cooperation
of Dr. Y. Yamashina of the Yamashina Institute for
Ornithology and Dr. Tatsuo Udagawa, both of
Tokyo and of A. Vinokurov and T. Shevareva of
the Centre of Ringing in Moscow. Through their
efficient processing and reporting recovery informa-
tion, actual dates and exact positions of nearly all
western Pacific recaptures were made available.
We thank Brian Sharp and Jay M. Sheppard
of the Bird Banding Laboratory for providing
copies of banding recovery records, and Rosemary
O'Loughlin and Nancy Mullis for assistance in
236 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
locating some original recovery letters for confirma-
tion of locations and dates. Danny Bystrak pre-
pared the final maps.
We also thank Mr. Warren King, Mrs. Herbert
Church, and Mr. Gerald Sanger of the Smithsonian
Institution's POBSP for their many helpful sugges-
tions regarding this manuscript.
General Patterns of Distribution
The following summary of the nesting cycle of
both species is condensed from Rice and Kenyon
(1962b:564-566). The nesting birds arrive on the
islands in the latter half of October (Black-footed
Albatross) and first half of November (Laysan Alba-
tross). Egg-laying occurs primarily in the latter
half of November (Black-footed) and from Novem-
ber 20 to January 5 (Laysan), and incubation re-
quires about 65 days. Early in the incubation
period the female, and then the male, is away at
sea for about three weeks at a time. As incubation
progresses, each mate's turn on the egg becomes
progressively shorter as does the distance they can
travel from the island. For the first 12 to 24 days
after hatching, the chick of each species is attended
by a parent, the male and female changing place
at intervals of about two days. Both parents then
leave the chick and forage independently; a parent
returns to feed the chick at an average interval of
one and one-half days to two days. Departure from
the island of both young and adults of both species
takes place primarily in June but departure of the
Laysan continues into July.
Our studies with both species, and those by
Fisher and Fisher (1969) on the Laysan Albatross,
have shown that one-year-old birds do not return
to the nesting islands, but remain continuously at
sea. By the end of their second winter at sea, a
very few individuals of each species return to their
natal islands in April. With increasing age these
nonnesting birds return to their islands in larger
numbers, and earlier and earlier in the season
(largely in March for the 3- and 4-year-olds and as
early as February or January for the older birds).
In order to determine the distribution patterns
of the albatrosses during the periods they are away
from the nesting islands, recoveries for each species
were plotted on a monthly basis for birds in their
first, second, third, and fourth years at sea and for
adults. First-year recoveries were of birds from time
of fledging until the following May.
Recoveries of Laysan Albatrosses occurred largely
during the period December through July, with a
peak of adult birds (40%) in May and June and a
peak of young birds (31% of the year's recoveries)
in June of the year after fledging.
Recovery records of the Black-footed Albatross
at sea are strongly clustered around the months of
March through August. Half (50%) the recoveries
of birds in their second, third, and fourth years
of life were reported in June and July, and the
peak of reporting of adult recoveries (45%) was in
the months of March, June, and July. The fewest
recoveries for both young and adults were obtained
in the months of November and December.
LAYSAN ALBATROSS.—Banding recoveries (Figure
143) indicate that young Laysan Albatrosses spend
their first summer primarily between 40° N and
45° N and that they range all the way from Japan
east to at least 172°W. More than half of the recov-
eries of Laysan Albatrosses during their first sum-
mer (summer of fledging) came from within 300
miles of the east coast of northern Japan. One bird
(band number 767-77884, banded as a chick by
Robbins on 30 March 1965, at Sand Island, Mid-
way) was found dead on 11 September 1965, on San
Cristobal Island (10°15'S, 161°16'E), furnishing the
first record for the British Solomon Islands. This is
the only Laysan Albatross recovery from south of
the equator. Comparison of Figures 143 and 147
shows that the distribution of young Laysan Alba-
trosses during their first summer is quite different
from the distribution of adults during the same
months. Half of the recoveries of adults came from
north of 45°N, while only two birds in their first
summer were recovered north of 45 °N.
Laysan Albatrosses tend to be more widely scat-
tered in their first four or five winters (December
through March), than at a later age. Four of the 43
first-winter recoveries (Figure 143) were from east
of the 180th meridian, as were 6 of the 17 third-
winter recoveries (Figure 145). In contrast, there
was only one winter recovery east of the 180th
meridian for birds in their sixth winter or older,
even though the entire chain of nesting islands is
situated east of the 180th meridian. As was true in
the summer months, the records for the first winter
were concentrated off the coast of Japan, with half
of the recoveries coming from within 600 miles of
Japanese shores.
NUMBER 158 237
Recoveries during the second summer (Figure
144) were concentrated off the east coast of north-
ern Japan, and it appears that birds of this age
stay much closer to shore than either first-year birds
or birds older than three years. All of the 55 re-
coveries of birds in their second summer occurred
west of 160°E.
Recoveries for the second winter at sea (Figure
144) were few in number (13), but they also were
all from west of 160°E. There was more overlap
between the summer and winter range of birds in
their second calendar year of life than in other
years.
Third-year recoveries (Figure 145) were similar
to second-year recoveries except that the birds ap-
peared to scatter farther out to sea and were not
so concentrated near the Japanese coast. This was
especially true of birds in their third winter at sea,
because they ranged all the way east to 134°W.
Fourth- and fifth-year birds (Figure 146) tended
to range farther northeast in summer than did
younger birds during the same months. The sum-
mer season distribution of adults was still farther
to the northeast, with half of the birds north of
48°N and with the heaviest concentration off the
western Aleutian Islands.
As shown in Figure 147, at-sea recoveries of adult
Laysan Albatrosses lay almost entirely (90%) west
of the 180th meridian. The recoveries indicate
very little overlap between summer and winter
range. During the summer (May through 5 Octo-
ber), all but five of the recoveries came from north
of 40°N; while during the winter months (Decem-
ber through March), all except two recoveries
were from south of 40°N. The summer recoveries
were fairly uniformly distributed between northern
Japan and the Aleutian Islands, except for a con-
centration of records from the immediate vicinity of
the Aleutians. The winter recoveries of adults were
all from the area between Japan and their breed-
ing islands in the leeward Hawaiian chain. In addi-
tion to the summer and winter recoveries, there
were widely scattered recoveries for the intervening
months of April, October, and November.
BLACK-FOOTED ALBATROSS.—After leaving their
nesting islands in June and early July, young Black-
footed Albatrosses scatter both eastward and west-
ward to within a few hundred miles of the coasts
of North America and Japan. All of the nine first-
summer recoveries fell between 35°N and 45°N
(Figure 143).
In the first winter, the birds shift southward.
Nine of the 14 recoveries were between 30°N and
35°N, and the recoveries appeared to be slightly
more clustered than they were during the summer
season. One concentration was half way between
Japan and Midway; the other was close to the
shores of California and Baja California. There
was only one first-winter recovery in the vicinity of
the Hawaiian chain. The banding recoveries indi-
cate a strong eastward shift in the population by
the second summer (Figure 144). All but 5 of the
31 recoveries came from the eastern half of the
north Pacific and half of these came from within
about 200 miles of Canada and the United States
(exclusive of Alaska). The principal concentration
of coastal recoveries of birds in their second sum-
mer extends from 30° N to 47 °N (13 out of 15 re-
coveries from south of Alaska).
Recoveries of birds taken in their second and
third winters (Figures 144, 145) suggest a shift to-
ward the central Pacific. The total numbers in-
volved, however, are admittedly very small (14
birds in their first winter, 6 in their second, and 8
in their third).
A decided northward trend in summer distribu-
tion with increasing age is indicated. The heaviest
single concentration in the third summer (Figure
145) was along the United States coast between
40°N and 51 °N; 24 recoveries were reported from
here as compared with 4 farther south and 1 far-
ther north along the coast.
By the fourth summer (Figure 146), only 7 of
the 15 coastal recoveries were in the 40°N to 48°N
range; one was farther south, and 8 farther north
off Canadian and Alaskan shores.
The Black-footed Albatross has a greater distri-
butional range than the Laysan both in latitude
and in longitude. It tends to winter farther south
than the Laysan and to be concentrated in winter
in the central portion of the north Pacific Ocean.
Recoveries of adults (Figure 148) within 1000 miles
of the Japanese coast in winter were just about
equal to the number within the same distance of
the North American coast at this season.
Summer recovery records of banded adults also
were quite uniformly distributed throughout the
north Pacific Ocean, except for concentrations
within 200 miles of the coasts of Japan, Alaska,
238 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
British Columbia, Washington, and Oregon. The
numbers of recoveries of adult birds east and west
of the 180th meridian were similar.
The separation of summer and winter records is
nearly as clear cut as for the Laysan Albatross.
There were only three summer recoveries of adult
Black-footed Albatrosses south of 30° N, and except
for five recoveries close to the California coast,
there were only two winter recoveries north of
35°N. The "winter" bird recovered at 50°N was
taken on 25 March 1966 and was actually an early
spring migrant. The other "winter" bird, at 37°N,
was taken on 9 December 1950 and could well have
been a late migrant.
A similar comparison may be drawn for birds in
their first four years. There was only one summer
recovery (out of 20) south of 35°N in the western
Pacific, and only six (out of 86) in the eastern Pa-
cific. There was only one winter record north of
40°N.
Concentration Areas
LAYSAN ALBATROSS.—Shuntov (1968) showed two
concentration areas for the Laysan Albatross in
summer, as depicted in our Figure 149, and three in
winter (Figure 150). The banding recoveries show
the same summer concentration area extending east
from northern Japan; this is occupied primarily by
young birds near shore and older ones farther to
the northeast. The concentration that Shuntov pic-
tures in his winter map along the south edge of the
western Aleutian Islands is a major feeding area for
adult Laysan Albatrosses in summer. There are no
winter banding recoveries from the vicinity of the
Aleutians. There are relatively few recoveries for
Shuntov's concentration zone between Kamchatka
and the western Aleutians, but several from a small
concentration of adult birds off the south tip of
Kamchatka. Figures 87, 88, 89 show the principal
concentration area of Laysan Albatrosses in July,
August, and September, a period in which sampling
effort is low and only 16 banding recoveries of
adults are available. First- and second-year birds
summer to the south of this concentration area.
The winter banding recoveries are strongly clus-
tered between Japan and the nesting islands. This
zone includes Shuntov's western concentration and
the southern half of the large one south of Kam-
chatka. A large concentration of wintering first-
year birds occurs southeast of Japan as a southward
extension of his westernmost concentration.
Fisher and Fisher (1972) reported the concentra-
tion areas off Japan and the western Aleutians as
well as two others which neither Shuntov (1968,
figs. 4, 6), Sanger (p. 134 ff, herein), nor we consider
important: one off the west coast of British Colum-
bia and the United States (from which there are
only four banding recoveries), and one around the
eastern end of the Hawaiian Islands (two recover-
ies). These surely must be of minor importance as
compared with the concentrations reported by
Shuntov (1968).
BLACK-FOOTED ALBATROSS.—The summer band-
ing recoveries may exaggerate the importance of
the coastal waters as concentration areas for Black-
footed Albatrosses, but these recoveries are in close
agreement with Figures 73, 74, and 75. Shuntov's
(1968) summer distribution map (Figure 151)
shows major concentrations along the 40th parallel
west of Midway and through much of the eastern
Pacific. The banding records do not detect these
areas as being of any special significance, but show
heavy concentration zones only in the offshore area
from the Aleutians to northern California as
mapped by Shuntov. Banded birds also were con-
centrated off the coast of northern Japan in an
area not considered especially important by Shun-
tov. Quite possibly the large concentrations along
and to the south of the 40th parallel are under-
sampled by banding recoveries, because no more
birds have been reported from there than from
farther north.
The winter banding recoveries match well with
that part of Shuntov's map (Figure 152) that lies
south of 40°N. By including November records in
his winter map, Shuntov included a considerable
area north of 40° N that we do not consider as win-
ter range. Otherwise, the principal differences are
a greater spread of banding recoveries to the west
of Midway, extending fully halfway to Japan, fewer
recoveries northeast of the Hawaiian chain, and
fewer along the south side of the chain.
Statistical Analysis of Geographic Range
The recovery records of each species were
grouped by months and by age of the birds, and
the mean, standard deviation, and standard error
were computed to determine which of the apparent
NUMBER 158
TABLE 40.-
239
-Mean position, standard deviation, and sample size of Lay&an Albatross band recoveries by
age and month (positions based on fewer than five records are in parentheses)
Month
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
1
-
-
(42.3°N-172.3°W)
-
1
42.18°N-151.91°E
2.95 7.86
15
44.60° N-l 47.54 °E
5.34 6.35
5
43.95°N-170.89°E
7.13 33.60
8
(39.83°N-143.87°E)
4.54 3.65
3
36.64°N-144.97°E
2.58 5.95
10
32.23°N-149.91°E
2.30 7.53
13
32.38°N-159.94°E
3.96 23.51
13
29.29°N-150.83°E
3.12 15.07
7
(48.45°N-156.38°W)
1.59 27.50
4
38.54°
3.95
41.05°
3.17
39.88°
2.59
(39.55°
5.30
(45.35°
1.20
41.32°
1.21
(40.05°
1.06
35.94°
1.65
(32.90°
5.52
(33.5°
-
(30.0°
_
(49.0°
-
2
N-148.03
5.04
11
N-147.16
5.72
24
N-l 47.67
4.41
17
N-147.00
4.67
2
N-l 49.25
3.61
2
N-l 44.78
3.33
6
N-146.50
4.95
2
N-l 46.43
6.57
9
N-l 42.50
2.12
2
N-l 35.7°
_
1
N-16O.O0
_
1
N-145.O0
-
1
°E
°E
°E
°E)
°E)
°E
°E)
°E
°E)
E )
E )
E)
Year at sea
42.36°
6.45
(39.43°
0.78
(43.17°
1.26
(46.45°
5.30
(33.0°
-
(36.82°
1.35
33.18°
3.33
(32.30°
1.73
(32.40°
2.52
(24.7°
-
3
N-156.56°E
17.13
5
N-144.80°E)
2.13
3
N-151.40°E)
7.29
3
-
N-165.10°E)
17.11
2
-
N-l 39.4 °E)
-
1
N-147.02°E)
3.10
4
N-158.17°E
23.34
6
N-l 70.35 °W)
30.71
4
N-147.20°W)
13.37
3
N-171.0°W)
-
1
4 and 5
44.64°N-166.10°E
6.52 9.57
5
43.39°N-164.31°E
3.42 30.72
8
-
(42.7°N-144.0°E)
-
1
(46.0°N-151.8°E)
-
1
(34.17°N-151.00°E)
11.26 6.38
3
(42.60°N-152.13°E)
4.68 1.40
3
(35.85° N-147.25°E)
0.21 8.41
2
-
(3O.17°N-159.7O°E)
2.52 26.34
3
(30.10°N-158.20°E)
5.37 19.09
4
(32.10° N-l 54.02° E)
6.62 26.54
4
6+
45.93° N-l 71.68°
6.24 19.36
22
47.89° N-168.43°
5.01 8.11
18
45.90° N-174.700
4.29 35.92
5
45.39° N-150.490
4.99 11.42
8
(47.10°N-176.33°
10.67 33.90
3
(47.55° N-l 72.80°
7.36 29.18
4
(37.52°N-160.30°
5.05 15.51
4
36.76°N-160.18°
4.45 13.31
5
35.36°N-145.12°
2.33 9.67
8
29.82°N-157.10°
1.00 12.14
6
33.46° N-157.660
5.82 21.68
10
40.00°N-176.60°
10.98 24.06
8
E
E
E
E
E)
E)
E)
E
E
E
E
E
differences in distribution were merely the result of
small sample size and which differences were statis-
tically significant. Although the sampling tech-
nique (recoveries of banded birds) was far from
ideal from the statistical point of view, it was con-
ducted the same way for all age groups of both
species, and should provide a valid means of por-
traying differences in distribution as a function of
age and season.
When broken down by years of age, many sample
sizes for a given month are of ten or fewer individ-
uals (Tables 40, 41). Starting with these small sam-
ples for each age and each month, comparisons
were made with adjacent months and adjacent
years. Whenever the distribution was found to be
similar, other months or other years were included
to provide larger samples. These larger samples in
turn gave more critical comparisons between other
years and other seasons.
The largest sample for each species (with the ex-
ception of a few individual months) was the birds
of breeding age. This sample of adults, therefore,
was used for comparison with birds of the younger
age groups.
LAYSAN ALBATROSS.—Adult Laysan Albatrosses
were significantly farther north (p < .05) during
240 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
TABLE 41.—Mean position, standard deviation, and sample size of Black-footed Albatross band recoveries
by age and month (positions based on fewer than five records are in parentheses)
Month
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
1
_
_
(39.5°N-177.7°W)
_ _
1
40.40°N-157.90°E
1.56 11.10
5
(40.77°N-165.53°W)
2.35 31.12
3
(39.40°N-167.25°E)
2.26 15.20
2
(35.2°N-171.7°E)
1
(33.3O°N-157.43°E)
130 16.90
3
(31.73°N-176.73°W)
135 4753
S
(36.8°N-124.0°W)
-
1
29.46°N-158.60°W
4.96 37.82
7
(40.20°N-135.77°W)
6.93 20.07
3
Year at sea
2
(365°N-141.0°E)
_
1
40.08°N-127.92°W
6.58 9.77
8
38.09°N-135.51°W
4.89 22.04
10
47.01 °N-172.19°W
12.18 34.95
8
(48.68°N-138.85°W)
6.92 20.18
4
(40.2°N-150.8°E)
-
1
(35.2°N-171.7°E)
-
1
(32.30° N-l 74.40° W)
0.71 22.06
2
-
(31.75°N-150.00°W)
2.47 0.71
2
(27.75°N-170.80°E)
6.01 2.83
2
(31.3°N-166.0°E)
-
1
3, 4, and 5
46.51 °N-147.95°W
8.87 30.07
15
45.15°N-1S2.34°W
7.18 20.83
21
45.05°N-134.06°W
5.87 22.96
31
46.89°N-160.80°W
6.38 43.11
8
48.94°N-147.32°W
4.89 3252
8
4S.42°N-169.28°E
8.93 32.36
5
(48.4°N-125.0°W)
-
1
-
31.30°N-159.08°W
7.71 22.87
5
(29.4°N-156.4°W)
-
1
33.14°N-176.00°W
3.98 42.14
5
(26.5°N-1753°W)
-
1
6 +
41.07°N-157.11°W
9.51 33.13
26
43.15°N-164.79°W
6.31 40.14
34
44.67°N-153.S7°W
5.51 37.05
42
46.66°N-162.46°W
5.63 34.58
25
48.97°N-166.32°W
7.62 31.80
9
41.16°N-149.94°W
10.56 28.67
12
(29.18°N-172.70°W)
8.95 17.71
4
32.62°N-179.77°E
4.18 13.28
6
30.63°N-173.31°E
2.66 15.76
14
29.91 °N-178.84°W
5.08 23.65
13
30.31°N-174.90°W
638 29.65
28
36.08°N-152.40°W
7.92 35.30
16
the months of May through August than from De-
cember through March. The 3- to 5-year-old birds
were significantly farther north from May through
November than from December through April.
Birds in their second year were significantly farther
north from June through November than from De-
cember through March.
The only statistically significant latitudinal dif-
ference among age classes of the Laysan Albatrosses
occurred in the month of May when adults were
farther north than birds in their second year of life.
There was a consistent trend, however, for birds in
their second year to be farther south than birds in
their third to fifth years, and for these in turn to be
farther south than the adults. This trend was noted
in the months of January, February, March, May,
June, and December. Sample sizes for one or more
of the age groups were insufficient to show any
trend for July, August, and November. Only in the
principal migration months of April, September,
and October did one of the three age classes not
conform to this general observation. This is in
marked contrast to the Black-footed Albatross, in
which there was not a single month when the mean
position in latitude increased progressively within
these three age categories.
NUMBER 158 241
BLACK-FOOTED ALBATROSS.—Adult Black-footed
Albatrosses were significantly farther north (p <
.05) from May through October than they were in
January through March, and significantly farther
north from June through September than from No-
vember through April. Birds in their third and
fourth years were significantly farther north from
May through July and September and October
than they were in February and March, and birds
in their second year were found significantly farther
north from June through October than in January
and March. There were too few records for many
of the other months. All age classes showed a high
degree of variability in latitude during the north-
ward migration in the month of April, and to a
lesser extent during the southward migration in
October and November (when the small sample
size also made it difficult to draw conclusions).
The only significant differences in latitude for
different age classes in the Black-footed Albatrosses
were between first-year and adult birds in the
months of July, August, and September and be-
tween second-year and adult birds in the month of
July. In each of these cases the younger birds were
distributed significantly farther south (p < .05)
than adults.
The small number of significant differences
found does not mean that there are not differences
in distribution, but only that with the present
small sample sizes no other differences could be
confirmed as statistically significant.
Black-footed Albatrosses in their first year at sea
stayed significantly farther toward the western Pa-
cific in July and August than did birds in any older
age group.
No significant differences in longitude were
found between the 2-year-old and the 3- and 4-year-
old birds.
Significant differences in longitude were found
between adults (6 years and more) and 3- and 4-
year birds for the months of February, June, and
July. In each case, the adult birds were found far-
ther west than the 3- and 4-year-olds.
In the Black-footed Albatross, birds in their third
to fourth year occur, on the average, farther north
than the adults in the months of January, February,
April, May, June, July, September, October, and
November. Only in March and August were the
adults farther north (insufficient data for Decem-
ber).
Comparison of Distribution of Laysan and
Black-footed Albatrosses
Despite the geographical and temporal biases in-
herent in the way in which albatrosses are recov-
ered and reported, there are certain comparisons
that can be drawn between the ranges of the two
species (as long as both species are recovered in the
same general fashion). The most striking difference
between the recovery patterns of the Laysan and
Black-footed Albatrosses is the very heavy concen-
tration of Laysan Albatross records within 1000
miles of the Japanese coast as compared with the
more uniform distribution of Black-footed Alba-
tross records throughout the north Pacific Ocean.
Botli species demonstrate a strong tendency to wan-
der both to the east and the west in their first eight
to ten months at sea. By the end of the first winter,
the two species begin to separate into distinct pat-
terns. The Laysan Albatross moves strongly toward
the Japanese coast and the Black-footed Albatross
shows a less pronounced tendency in the opposite
direction.
Using the 180th meridian as the dividing line,
90 percent of the Laysans recovered spent their first
winter in the west and 50 percent of the Black-
footed Albatrosses spent their first winter in the
east. From the second year on, more than 90 percent
of the Laysan recoveries (all seasons) came from
the western half of the Pacific Ocean, and a similar
percentage of the Black-foots in their second, third,
and fourth summers came from the eastern half.
By the time the albatrosses reach breeding age
(generally 7 or more years of age for the Laysan
and 5 or more for the Black-footed), the geographic
separation during the summer months dissolves,
but the pelagic distribution patterns during the
winter (the breeding season) remain fairly distinct.
Although both species nest on the same islands, and
in about the same relative abundance even at both
ends of their breeding range, the great majority of
winter recoveries of Laysans were from west of
160°E, while most recoveries of Black-foots were
from east of this line. Nearly all winter recoveries
of Laysans were from north of 30°N, whereas more
than half of the winter recaptures of Black-foots
were south of 30°N. Both species are well distrib-
uted west of the 180th meridian in the summer
months, but nearly all of the summer recoveries
242 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY
from east of the 180th meridian were of Black-
footed Albatrosses.
Comparative distribution of the two species at
sea throughout the year is summarized in Figures
153 through 164 where the hatching covers the
area represented by one standard deviation from the
mean latitude and longitude of all banding recov-
eries for the month. This is the range within which
two-thirds of the population is to be expected. On
each map, the range of the Laysan Albatross is cen-
tered to the left of that of the Black-footed Alba-
tross. The maps show dramatically those months in
which one or both species is confined to a relatively
small area as compared with those months when
records are scattered over a large portion of the
north Pacific Ocean.
Maps for birds in their first summer and autumn
at sea were prepared by combining two months in
order to increase the sample size. Thus, Figure 165
shows combined records for the months of July and
August, and Figure 166 shows September and Octo-
ber. The November (Figure 167) and December
(Figure 168) maps are based on Laysan Albatrosses
in their first, second, third, and fourth years, and
Black-footed Albatrosses in their first and second
years, because there was no apparent difference be-
tween years and because the samples were very
small.
Mean recovery positions of adults of each species
are summarized by two-month periods (each month
weighted equally) in Figure 169. The large dots in-
dicate positions based on 10 or more recoveries for
each month; the small dots are based on fewer than
ten in one or both months. Note the similarity be-
tween the patterns for the two species, even though
separated by 30° of longitude. A similar chart for
Laysan Albatrosses published by Fisher and Fisher
(1972), apparently was based on a mixture of band-
ing recoveries (birds of all ages) and sight observa-
tions. Their sample would seem too small to be
representative.
Recovery positions of adults of the two species
were compared statistically on both a monthly and
seasonal basis by means of the "t" test. The winter
(December through March) distribution of adult
Laysan Albatrosses was significantly different (p <
.05 for latitude, p < .01 for longitude) from that
of adult Black-footed Albatrosses for the same
period; mean positions were 34.3°N, 153.3°E for
the Laysan (n = 29) and 30.3°N, 178.5°W for the
Black-footed (n = 53). Recovery positions in early
summer (May through July) also differed signifi-
cantly (p < .05 for latitude, p < .01 for longi-
tude) ; mean positions were 47.3°N, 167.5°E for
the Laysan (n = 45) and 43.5°N, 164.9°W for the
Black-footed (n = 84).
No difference could be detected between the dis-
tribution of recoveries from birds banded at Mid-
way and Kure, at the west end of the leeward Ha-
waiian chain, and birds banded farther east at
Pearl and Hermes Reef, Lisianski, Laysan, and
French Frigate Shoals.
Discussion
The Laysan and Black-footed Albatrosses to-
gether utilize almost the entire Pacific Ocean north
of the tropics. Their distribution is limited by the
land masses of Japan, and the Asian and North
American continents, and by a line that follows
the continental shelf in the Bering Sea. Cone (1964:
83) has shown that albatrosses are incapable of sus-
tained flight in calm air, so they could not survive
long in equatorial waters of the central Pacific.
Although Laysan and Black-footed Albatrosses
nest on the same islands, and although there is al-
most complete overlap in their total oceanic ranges,
each species has its own distinctive distribution pat-
tern within its range, with significantly different
centers of population, month by month.
The pelagic ranges of the adults of both species
most closely coincide in February, when they are
making the shortest and most frequent foraging
trips to provide food for the newly hatched young.
Ranges expand in March as trips become longer
and as chick mortality relieves some of the adults
from "domestic" duties. Northward migration of
the nonbreeding adults in April and May gives a
wide distribution pattern, which contracts on the
summer feeding areas in June. The northward mi-
gration in June and July of the adults at the close
of the breeding season is hardly sampled by the
banding recoveries; it probably takes place rapidly
and through waters that are not being heavily used
by the fishing fleets.
The greatest northward penetration occurs in
September. The southward movement takes place
gradually during October and November, and by
December both species are within commuting
range of their nesting islands.
NUMBER 158 243
Young birds of both species during their first
summer and fall remain largely south of the range
of the adults at those seasons. In the first winter,
young Laysans remain closer to Japan than do the
adults. In their next four summers (Table 40, Fig-
ure 170), the average population center shifts grad-
ually east-northeast from Japanese waters to the
adult summering area in waters south of the Aleu-
tian Islands. There is also a tendency to move
slightly northward as each summer progresses.
It is not until January, February, and March of
the third winter at sea that there is a strong move-
ment away from Japanese waters. This coincides
with the first return of many of these birds to their
natal islands in the month of March.
We have no explanation for the tendency of
young Black-footed Albatrosses to fly toward Japan
when they first leave their natal islands. Most of
these young birds seem to favor waters west of the
180th meridian through their first summer and fall,
though they spend subsequent summers and win-
ters in the eastern half of the Pacific. The central
Pacific, which is the major wintering area of adult
Black-footed Albatrosses, is relatively clear of first-
winter birds.
In their second through fifth summers, Black-
footed Albatrosses remain closer to the Pacific
coast of the United States and Canada than do the
adults; and as each summer progresses they shift
gradually northward (Table 41).
In October and November, the majority of the
band recoveries of subadult Black-footed Alba-
trosses of all ages come from the western Pacific
(west of the 180th meridian). Recovery records are
too few to permit comparison of winter ranges of
the various age groups.
244 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

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