Part V
, Birds. U.S. Army, Signal Corps, Washington, D.C. Pages
115-196.
Udvardy, M. D. F. 1963. Zoogeographic study of the Alcidae. Pages 85-111 _in_ J. L. Gressitt, ed. Pacific Basin biogeography, a symposium. Pac. Sci. Congr. Proc. 10.
U.S. Bureau of Sport Fisheries and Wildlife. 1973. Semidi Islands wilderness report. Semidi Islands, National Wildlife Refuge. (Unpublished report)
U.S. Department of Commerce. 1964. United States Coast Pilot, No. 9, Pacific and Arctic Coasts, Cape Spencer to the Beaufort Sea. Coast and Geodetic Survey, Washington, D.C. 330 pp.
Walker, E. P. 1923. Definite breeding record for the Aleutian tern in southern Alaska. Condor 25:113-117.
Willet, G. 1914. Birds of Sitka and vicinity, Southeastern Alaska. Condor 16:71-91.
Willet, G. 1918. Bird notes from Forrester Island, Alaska. Condor 20:85.
Williamson, F. S. L., and L. S. Peyton. 1963. Interbreeding of glaucous-winged herring gulls in the Cook Inlet Region, Alaska. Condor 65:28.
Status and Distribution of Breeding Seabirds of Southeastern Alaska, British Columbia, and Washington
by
David A. Manuwal
College of Forest Resources University of Washington Seattle, Washington 98195
and
R. Wayne Campbell
Provincial Museum Victoria, British Columbia, Canada
Abstract
Current breeding seabird population estimates, nest-site preferences, and population changes are reviewed for southeastern Alaska, British Columbia, and Washington. There are 19 species of seabirds and a minimum of 216,566 pairs breeding in British Columbia and Washington. There are limited data on breeding populations for southeastern Alaska. Species diversity ranges from 17 species in Alaska to 15 species in British Columbia and 14 species in Washington. Eighty percent of all British Columbia seabirds breed on the east coast of Queen Charlotte Islands and the northwest coast of Vancouver Island. The three most numerous species in British Columbia are the fork-tailed storm-petrel, _Oceanodroma furcata_ (31.3%); Cassin's auklet, _Ptychoramphus aleuticus_ (24.6%); and ancient murrelet, _Synthliboramphus antiquus_ (12.5%). In Washington, 74% (43,274 pairs) of the seabird population resides on the Olympic coast; the remaining 26% are in the San Juan Island area. About 54% of this population consists of the common murre _(Uria aalge)_ and rhinoceros auklet _(Cerorhinca monocerata)_. The rhinoceros auklet and glaucous-winged gull _(Larus glaucescens)_ make up 97% of the total seabird population of the San Juan Islands. About 68% of all seabirds on the northeastern Pacific coast are nocturnal, burrow or rock crevice-nesting species. Currently available population data are inadequate to determine significant changes in population density for most species. Suggested topics for future research are presented.
The purpose of this paper is to discuss the known distribution, habitat, abundance, and status of breeding seabirds of the Alexander Archipelago in southeastern Alaska, the Province of British Columbia, Canada, and the State of Washington.
Even though several studies of the breeding biology of several seabird species in this area have been published, there have been few published surveys of known breeding colonies. In British Columbia the most extensive work has been done by the British Columbia Provincial Museum and the University of British Columbia (Drent and Guiguet 1961). Gabrielson and Lincoln (1959) summarized the available literature on Alaskan birds up to about 1958. Since then, no extensive surveys have been conducted in southeastern Alaska. The U.S. Department of the Interior (1972), in its environmental impact statement for the Trans-Alaska Pipeline, presented additional information on the seabirds of other parts of Alaska. In Washington, there are no published comprehensive surveys except those of Kenyon and Scheffer (1961) and unpublished surveys by the U.S. Fish and Wildlife Service and the University of Washington.
Table 1. _Taxonomic distribution of marine birds breeding along the Pacific Coast of Washington, British Columbia, and southeastern Alaska._
------------------------------------------------------------------------ Regions --------------------------------------- British Southeastern Total Family Common name Washington Columbia Alaska forms ------------------------------------------------------------------------ Hydrobatidae Storm-petrels 2 2 2 2 Phalacrocoracidae Cormorants 3 3 1 3 Haematopodidae Oystercatchers 1 1 1 1 Laridae Gulls and terns 2 2 3 4 Alcidae Auks, murres, puffins 6 7 9 9 Total 14 15 16 19 ------------------------------------------------------------------------
Taxonomic Distribution of Marine Birds
There are 19 species of seabirds that breed along the Pacific coast of southeastern Alaska, British Columbia, and Washington (Table 1). Southeastern Alaska has the largest number (17) of species. Errors in species identification are most likely with the Larus gulls,
## particularly in southeastern Alaska where the herring gull _(L.
argentatus)_ and glaucous-winged gull _(L. glaucescens)_ breed in mixed colonies (Patten and Weisbrod 1974). A similar situation exists in Washington where the western _(L. occidentalis)_ and glaucous-winged gulls intergrade (Scott 1971). Brandt's _(Phalacrocorax penicillatus)_ and double-crested cormorants _(P. auritus)_ are often difficult to identify from the air. This would be a problem in Washington and the southwest coast of Vancouver Island, where the two species are locally sympatric.
Southeastern Alaska
The area under consideration is the 400-km-long Alexander Archipelago (Fig. 1). This complex pattern of islands, bays, and inlets is characterized by extremely high precipitation and typical cool marine temperatures. Average annual precipitation in the Sitka area is 245.4 cm (1931-60), and the average annual temperature is 6.3°C (U.S. Weather Bureau 1974). As a consequence of this cool, humid environment, most of the islands are densely covered with conifers, chiefly Sitka spruce _(Picea sitkensis)_ and hemlock _(Tsuga heterophylla)_, and an almost impenetrable shrub cover composed of salmonberry _(Rubus spectabilis)_, elderberry _(Sambucus callicaipa)_, devil's club _(Echinopanax horridus)_, and three species of _Vaccinium_ (Heath 1915).
[Illustration: Fig. 1. Map of southeastern Alaska showing major seabird breeding colonies: 1--North Marble Island; 2--Forrester Island.]
There are 16 species of marine birds breeding in the Alexander Archipelago. The major seabird breeding colonies are located at Glacier Bay and at St. Lazaria, Hazy, and Forrester islands (Fig. 1; Table 2). Published surveys of these colonies are available only for St. Lazaria (Willett 1912) and Forrester islands (Heath 1915; Willett 1915). Several authors have reported on seabirds from surrounding areas (Grinnell 1897, 1898, 1909; Swarth 1911, 1922, 1936; Patten 1974). There have been no surveys of seabirds of southeastern Alaska since before the 1940's (J. G. King, Jr., personal communication). However, since census data are available for only two colonies, we discuss them in more detail.
Table 2. _Population estimates of seabirds breeding on St. Lazaria and Forrester islands, southeastern Alaska_ (data from Willett 1912 and 1915).
St. Lazaria Island Forrester Island ---------------------------------------------------------------------- Number Percent Number Percent Bird species of pairs of total of pairs of total ---------------------------------------------------------------------- Fork-tailed storm-petrel 2,000 8.0 10,000 6.0 Leach's storm-petrel 20,000 80.0 50,000 30.0 Pelagic cormorant 150 0.6 150 0.0 Black oystercatcher 4 0.0 50 0.0 Glaucous-winged gull 300 1.2 8,000 4.8 Herring gull 220 0.0 Common murre 300 1.2 20,000 12.0 Pigeon guillemot 150 0.6 300 0.0 Ancient murrelet 20,000 12.0 Cassin's auklet 2,000 1.2 Rhinoceros auklet 75 0.0 20,000 12.0 Horned puffin 12 0.0 1,100 0.7 Tufted puffin 2,000 8.0 35,000 21.0 Total 24,991 166,820
The studies by Willett (1912, 1915) and Heath (1915) provide some base-line information on species composition and abundance with which future studies on St. Lazaria and Forrester islands can be compared (Table 2). The somewhat greater species diversity on Forrester Island is primarily due to its greater size and more suitable soil type for ancient murrelets _(Synthliboramphus antiquus)_ and Cassin's auklets _(Ptychoramphus aleutica)_, species that are absent on St. Lazaria. Storm-petrels (_Oceanodroma_ spp.) are the most numerous species on both islands, but there are proportionately more storm-petrels (88%) on St. Lazaria than on Forrester (36%). On the other hand, there are many large, burrowing alcids on Forrester Island. Nearly a third of the birds on Forrester are rhinoceros auklets _(Cerorhinca monocerata)_, tufted puffins _(Lunda cirrhata)_, and horned puffins _(Fratercula corniculata)_.
The species composition of seabirds breeding on other islands is similar to that found on Forrester and St. Lazaria islands but less abundant. In Glacier Bay, for example, the only population data available are those provided by Patten (1974) for North Marble Island: pelagic cormorants, _Phalacrocorax pelagicus_ (30 pairs); black oystercatchers, _Haematopus bachmani_ (8); herring gulls (7); glaucous-winged gulls (500); common murres, _Uria aalge_ (18); pigeon guillemots, _Cepphus columba_ (60); horned puffins (4); and tufted puffins (30).
At the present time, it is impossible to draw any conclusions about changes in population density and distribution for most of the seabirds breeding in southeastern Alaska. Adequate data are available only for St. Lazaria and Forrester islands where Willet and Heath provided the only early extensive census data for this part of Alaska.
British Columbia
The rugged British Columbia coastline is characterized by 930 km of islands and inlets (Figs. 2, 3). With the exception of the inner southern portion, this coast is mostly uninhabited. The physical characteristics of the offshore islands are similar to those found off the Washington coast. Descriptions of some of these islands and the 15 species of breeding seabirds on them have been given by Drent and Guiguet (1961), Guiguet (1971), and Summers (1974).
A detailed analysis of British Columbia seabirds is not presented here since a more thorough analysis is in preparation by R. W. Campbell and R. H. Drent (manuscript). Instead, we present seabird population estimates available for the Province up to the summer of 1975; Tables 3 and 4 summarize these estimates for the five major portions of coastal British Columbia. The coast of British Columbia contains a myriad of small islands where there may be small numbers of breeding seabirds. Many of these have not been censused and are too numerous to include in Tables 3 and 4.
[Illustration: Fig. 2. Map of northern British Columbia showing sites of major seabird breeding colonies: 1--Skedans Island; 2--Limestone Island; 3--Agglomerate Island; 4--Bischoff Island; 5--Ramsey Island; 6--Alder Island; 7--Rankins Island.]
[Illustration: Fig. 3. Map of southern British Columbia showing sites of major seabird breeding colonies: 1--Triangle Island; 2--Cleland Island.]
More than half of the breeding seabirds in British Columbia are found on the east coast of the Queen Charlotte Islands, and the fork-tailed storm-petrel _(Oceanodroma furcata)_ comprises more than half of that total. However, new unpublished data (K. Vermeer) for Triangle Island and the northwest coast of Vancouver Island indicate that the population figures in Table 3 for this area are underestimates. Nevertheless, these two regions have nearly 80% of all the breeding seabirds in the Province. This results from the very large populations of the rhinoceros auklet and tufted puffin on Triangle Island and the fork-tailed storm-petrel, ancient murrelet, and Cassin's auklet on various islands on the east coast of the Queen Charlotte Islands (Table 3).
Continuing surveys of breeding seabirds are being conducted by personnel of the British Columbia Provincial Museum and the Canadian Wildlife Service.
Washington State
_General Environment_
For this report, we have distinguished two major geographical areas in Washington where breeding seabirds are found--the western coast of the Olympic Peninsula and the San Juan Islands, including the Strait of Juan de Fuca.
On the Olympic Peninsula, seabirds breed on the offshore rocks, islands, and precipitous cliffs from Copalis Beach to Cape Flattery (Fig. 4). The offshore rocks and islands throughout this area (except Tatoosh Island) are now included in the Washington Islands National Wildlife Refuge. Most of the larger rocks and islands have dense stands of salmonberry, salal, and grasses, and a few support stands of stunted conifers (Fig. 5); most are inaccessible to man. The adjacent coast is dominated by the Olympic rain forest where the mean annual precipitation is about 337.1 cm (U.S. Weather Bureau 1956, 1965_a_, 1965_b_).
Because the San Juan Islands lie northeast of the Olympic Peninsula and east of Vancouver Island (Fig. 6) they are in a rain shadow; however, because of highly variable topography and aspect, most islands have a diverse assemblage of plant communities (Franklin and Dyrness 1973). Exposed south-facing slopes are occupied by grassland vegetation and frequently by scattered trees, usually _Pseudotsuga menziesii_ and _Arbutus menziesii_. Most of the seabird colonies are located on rather small exposed islands with short, grassy, shrubby vegetation. In general, these islands are not suitable for burrowing species.
Table 3. _Species composition, population estimates, and distribution of seabirds in British Columbia._[5][6] (+ = Present.)
Southwest Northwest West coast Straits of coast of coast of of Queen Georgia and Vancouver Vancouver Charlotte Bird species Juan de Fuca Island Island Island Fork-tailed storm-petrel + + 1,050 Leach's storm-petrel 10,000 + 1,800 Double-crested cormorant 1,058 0 0 0 Brandt's cormorant 370 0 0 Pelagic cormorant 2,174 336 3,350 1,456 Glaucous-winged gull 10,123 6,870 600 412 Common murre 16 3,000 0 Pigeon guillemot 1,029 204 250 358 Ancient murrelet 0 0 200 Cassin's auklet + 50,000 + Rhinoceros auklet 1,200 + 10,000 Tufted puffin 1 154 20,000 190 Total 14,385 19,150 77,200 15,466
East coast Prince Rupert of Queen to Queen Percent Charlotte Charlotte Total of Bird species Island Island birds total
Fork-tailed storm-petrel 97,100 + 98,160 31.3 Leach's storm-petrel 180 750 12,730 4.1 Double-crested cormorant 0 0 2,116 >1.0 Brandt's cormorant 0 0 370 >1.0 Pelagic cormorant 496 12 9,998 3.2 Glaucous-winged gull 866 540 29,534 9.4 Common murre 0 0 3,016 1.0 Pigeon guillemot 1,458 1,650 5,978 1.9 Ancient murrelet 42,150 4 42,354 13.5 Cassin's auklet 26,500 450 76,950 4.6 Rhinoceros auklet 300 200 11,700 3.7 Tufted puffin 0 42 20,388 6.5 Total 169,050 3,648 313,294 81.2
Table 4. _Breeding seabird population estimates for British Columbia_[7][8]
--------------------------------------------------------------------------- Population Percent Geographic location estimate of total --------------------------------------------------------------------------- Straits of Georgia and Juan de Fuca 14,385 9.2 Southwest Coast of Vancouver Island 9,575 6.1 Northwest Coast of Vancouver Island 38,600 24.6 West Coast of Queen Charlotte Island 7,733 4.9 East Coast of Queen Charlotte Island 84,530 54.0 Prince Rupert to Queen Charlotte Strait 1,824 1.2 Total 156,647 100.0
[Illustration: Fig. 4. Map of the Olympic Peninsula of Washington State showing sites of major seabird breeding colonies: 1--Protection Island; 2--Carroll Island; 3--Destruction Island.]
In the Strait of Juan de Fuca, the two most important sites are Smith and Protection islands. Both are composed of glacial deposits and heavy sod that has developed under dense grassy vegetation (Fig. 7). Consequently, these two islands support most of the burrowing seabirds in the region. Unfortunately, both islands have historically been subjected to much human disturbance (Richardson 1961; Manuwal 1974).
The existing information on seabird colonies in both the coastal and San Juan Island areas has been largely derived from aerial surveys by the U.S. Fish and Wildlife Service. These surveys are inherently biased toward surface-nesting species such as gulls and cormorants. Population estimates for guillemots, auklets, storm-petrels, and puffins are less accurate. Some additional information obtained by direct island visitation has been provided by Kenyon and Scheffer (1961), Richardson (1961), Thoresen and Galusha (1971), G. Eddy (unpublished data), and D. A. Manuwal (unpublished data). Although other accounts of Washington seabirds are available, the references listed above are specifically oriented toward population assessment.
_Olympic Peninsula_
Despite the large number of offshore rocks, islets, and islands along the Pacific coast of Washington, significant seabird colonies are present only on about 30 islands. Since Table 5 summarizes the population estimates for 12 species of seabirds breeding on 24 major sites, it represents only the majority and not the total number of breeding seabirds on the Pacific coast of Washington. About 74% of the entire Washington seabird population resides on the coastal rocks and islands.
Major colony sites with more than 2,500 breeding pairs are Grenville Arch, Willoughby Rock, Destruction Island, Cake Rock, Carroll Island, and Bodelteh Island. More intensive censusing, especially of nocturnal burrowing species will undoubtedly raise the population estimates for these and other islands off the coast. About 54% of the total coastal population is composed of the common murre and rhinoceros auklet.
[Illustration: Fig. 5. Photograph of Destruction Island off the coast of Washington.]
[Illustration: Fig. 6. Map of the San Juan Archipelago showing sites of major seabird breeding colonies: 1--Viti Rocks; 2--Colville Island; 3--Smith Island.]
_San Juan Islands_
There are about 86 actual or potential seabird colony sites in this area; 25 (30%) are now considered important. Eleven islands are under Federal protection as National Wildlife Refuges. Part of Protection Island is owned by the Washington State Game Department to protect the largest rhinoceros auklet colony in the State. Most colony sites are on small islands with poorly developed soil which prevents burrowing species from using them. Consequently, the dominant species are surface nesters (such as gulls and cormorants) and rock-crevice nesters (like the pigeon guillemot). In all, about 31,000 seabirds of 7 species breed in the San Juan Island area. Breeding seabird population estimates for 49 of the 86 nesting sites are given in Table 6. Even though this does not represent all the colonies, it covers the most important islands and those islands where there appears to be potential for seabird breeding.
[Illustration: Fig. 7. Photograph of Smith Island in the Strait of Juan de Fuca, Washington. The glacial deposits are evident from the composition of the cliff faces.]
Table 5. _Estimated breeding seabird populations of the outer coast of Washington_.[9] (Unpublished data from U.S. Fish and Wildlife Service and University of Washington)
----------------------------------------------------------------------- Species ----------------------------------------------------------------------- Storm-petrels Cormorants -----------------------------------------------------------------------
Fork- Uniden- Double- Breeding site tailed Leach's tified crested Brandt's Pelagic ----------------------------------------------------------------------- Copalis Rock -- -- 15 -- -- -- Point Grenville -- -- -- 60 30 80 Grenville Arch -- -- -- 30 20 -- Flat Rock -- -- 30 -- -- -- Split Rock -- -- -- 100 -- -- Willoughby Rock -- -- -- 80 40 15 South Rock -- -- -- -- -- 40 Abbey Islet -- -- -- -- -- 30 Destruction Island -- -- -- -- -- -- Middle Rock -- -- -- -- -- 25 North Rock -- -- -- -- -- -- Alexander Island -- -- -- -- -- 50 Rounded Island -- -- -- -- -- 25 Giant's Graveyard -- -- -- -- -- 10 Quillayute Needles -- -- -- 50 50 50 James Island -- 30 -- -- -- 40 Cake Rock -- 500 -- -- -- 150 Sealion Rock -- -- -- 70 -- 30 Carroll Island -- 3,100 -- -- -- 100 Ball Rock -- -- -- -- -- 50 White Rock -- -- -- -- -- 100 Ozette Island -- -- -- -- -- -- Bodelteh Island 1,900 -- -- -- -- 100 Tatoosh Island -- 25 -- -- -- 100 Total 1,900 3,655 45 390 140 995 -----------------------------------------------------------------------
----------------------------------------------------------------- Species ----------------------------------------------------------------- Gulls ----------------------------------------------------------------- Black Glaucous- oyster- winged Common Pigeon Breeding site catcher Western western murre guillemot ----------------------------------------------------------------- Copalis Rock -- 30 -- -- -- Point Grenville -- 165 40 1,100 -- Grenville Arch 1 60 -- 3,000 4 Flat Rock -- -- 60 300 -- Split Rock 1 150 -- 2,100 4 Willoughby Rock -- 150 -- 3,000 -- South Rock -- -- 50 -- -- Abbey Islet 3 -- 50 -- -- Destruction Island 12 350 -- -- 25 Middle Rock -- -- 25 -- 50 North Rock -- -- 25 -- -- Alexander Island 5 -- 225 -- -- Rounded Island -- 25 -- -- 1 Giant's Graveyard -- -- -- 150 -- Quillayute Needles -- -- 150 900 -- James Island -- -- 150 750 40 Cake Rock -- -- 600 300 12 Sealion Rock -- -- 250 -- -- Carroll Island 3 -- 550 -- -- Ball Rock 7 -- 150 -- -- White Rock -- -- 75 250 -- Ozette Island 1 -- 15 -- -- Bodelteh Island 2 -- 300 -- 5 Tatoosh Island -- -- 1,500+ 100 20 Total 35 930 4,215 11,950 161 -----------------------------------------------------------------
------------------------------------------------------- Species ------------------------------------------------------- Auklets -------------------------------------------------------
Tufted Breeding site Cassin's Rhinoceros puffin Total ------------------------------------------------------- Copalis Rock -- -- -- 45 Point Grenville -- -- -- 1,475 Grenville Arch -- -- 3 3,118 Flat Rock -- -- -- 390 Split Rock -- -- -- 2,355 Willoughby Rock -- -- 25 3,310 South Rock -- -- -- 90 Abbey Islet -- -- 10 93 Destruction Island -- 10,940 350 11,677 Middle Rock -- -- -- 100 North Rock -- -- -- 25 Alexander Island -- -- 1,550 1,830 Rounded Island -- -- -- 51 Giant's Graveyard 50 150 -- 360 Quillayute Needles -- -- 350 1,550 James Island -- -- 20 1,030 Cake Rock -- 50 1,000 2,612 Sealion Rock -- -- 5 355 Carroll Island 25 250 2,400 6,428 Ball Rock -- -- 750 957 White Rock -- -- 100 525 Ozette Island -- -- -- 16 Bodelteh Island -- -- 750 3,057 Tatoosh Island 25? 25? 30 1,825 Total 100 11,415 7,343 43,274 -------------------------------------------------------
Table 6. _Breeding seabird population estimates for the San Juan Islands and Strait of Juan de Fuca, Washington, 1973-75_.[10]
A: Double-crested B: Pelagic C: Black oystercatcher D: Glaucous-winged gull E: Pigeon guillemot F: Rhinoceros auklet G: Tufted puffin
------------------------------------------------------------------ Species ------------------------------------------------------------------ Cormorants ---------- Breeding site A B C D E F G Total ------------------------------------------------------------------ Bare Island -- 50 1 120 + -- 2 173 Barren Island -- -- -- -- -- -- -- 0 Battleship Island -- -- -- -- -- -- -- 0 Bird Rocks 30 -- + 320 -- -- -- 350 Cactus Island -- -- 1 -- -- -- -- 1 Castle Island -- -- -- -- 30 -- -- 30 Colville Island -- 40 1 1,000 -- -- -- 1,041 Danger Island -- -- -- 125 7 -- -- 132 Decatur Island -- -- -- -- -- -- -- 0 Eliza Island -- -- -- 3 1 -- -- 4 Eliza Rock -- -- -- 1 -- -- -- 1 Flat Top Island -- -- -- -- + -- -- + Flower Island -- 17 -- 90 -- -- -- 107 Goose Island -- -- -- 60 -- -- -- 60 Gull Rock -- -- + 125 7 -- -- 132 Gull Reef -- -- -- -- -- -- -- 0 Hall Island -- -- 1 275 -- -- -- 276 Harbor Rock -- -- -- -- -- -- -- 0 Iceberg Island -- -- -- -- -- -- -- 0 Johns Island -- -- 1 -- -- -- -- 1 Long Island -- -- 8 80 -- -- -- 88 Low Island -- -- 1 75 17 -- -- 93 Lummi Rocks -- -- -- 4 -- -- -- 4 Matia Island -- -- -- -- + -- -- + Mummy Rocks -- -- -- 55 -- -- -- 55 Minor Island -- -- -- 100 -- -- -- 100 O'Neal Island -- -- -- -- -- -- -- 0 Patos Island -- -- -- 20 + -- -- 20 North Peapod Island -- -- 1 220 2 -- -- 223 South Peapod Island -- -- 1 75 2 -- -- 78 Pearl Island -- -- -- -- -- -- -- 0 Pointer Island -- -- -- 58 2 -- -- 60 Protection Island 3 110 3 1,500 30 9,200 35 10,881 Puffin Island -- -- 1 350 15 -- -- 366 Ripple Island -- -- -- -- -- -- -- 0 Sentinel Island -- -- -- -- 10 -- -- 10 Sentinel Rock -- -- 1 -- -- -- -- 1 Skip Jack Island -- -- -- 75 20 -- -- 95 Smith Island -- 20 6 10 30 600 -- 666 Speiden Island -- -- -- -- -- -- -- 0 South Sister Island 2 11 1 131 -- -- -- 145 Middle Sister Island -- -- 1 22 -- -- -- 23 North Sister Island -- -- 2 412 3 -- -- 417 Viti Rocks 29 80 1 387 1 -- -- 498 Waldron Island -- -- -- -- 2 -- -- 2 Williamson Rocks -- 67 1 346 2 -- -- 416 Whale Island -- -- 1 70 -- -- -- 71 White Rock -- -- + 125 13 -- -- 138 Yellow Island -- -- -- -- -- -- -- 0 Total per species 64 395 34 6,234 194 9,800 37 16,758 Percent of total population 0.4 2.3 0.2 37.2 1.2 58.5 0.2 100.0 ------------------------------------------------------------------
The major colony sites with more than 250 breeding pairs are located at Protection and Smith islands, Bird Rocks, Colville Island, Hall Island, North and South Peapod rocks, Puffin Island, North Sisters, Viti Rocks, and Williamson Rocks (Fig. 6). Glaucous-winged gulls are the predominant species on all these islands except Protection and Smith islands, where there are large colonies of rhinoceros auklets. Rhinoceros auklets (65%) and glaucous-winged gulls (32%) make up 97% of the total San Juan Islands seabird population.
Nest-site Preferences
Food supply and availability of nest sites are two critically important factors influencing the distribution and abundance of seabirds. Whereas information on general diet composition is known for most seabird species, we know little about the availability of favored seabird prey. The dynamics of seabird food chains is reviewed elsewhere in these proceedings.
The nest-site preferences for seabirds of the northeast Pacific Ocean are given in Table 7, and Table 8 indicates the proportion of seabirds that belong to specific nest-site categories. These preferences, in conjunction with knowledge of the physical characteristics of seabird habitat, permit a partial explanation of the present distribution and abundance of seabirds. For example, if we compare the San Juan Island habitats with those of the Washington coast, it is apparent that there are more cliff-nesting species on the coast. This reflects the physical characteristics of the two habitats. There are few cliffs in the San Juan Islands, and those that exist are very unstable. Colony sites in the San Juan Islands are typically on low, flat islands. Glaucous-winged gulls are the most abundant nesting species there. Coastal islands, on the other hand, are either covered by dense vegetation or are large monolithic chunks of rock with few available flat areas. Population estimates for the Washington coast are heavily biased toward surface nesters, since most of the data have been gathered by aerial surveys. Consequently, the burrow and rock crevice categories are underestimated. The aerial survey is appropriate for only about 43% of the birds nesting on the Washington coast.
Table 7. _Nest-site preference for seabirds breeding from Cape Fairweather, Alaska, to the Columbia River, Washington._
Nest-site type Bird species
Burrow-rock crevice Diurnal Pigeon guillemot Horned puffin Tufted puffin
Nocturnal Fork-tailed storm-petrel Leach's storm-petrel Kittlitz's murrelet Ancient murrelet Cassin's auklet Rhinoceros auklet
Open nests Flat or slope Double-crested cormorant Brandt's cormorant Glaucous-winged gull Herring gull Western gull Black oystercatcher
Cliff face Pelagic cormorant Common murre Black-legged kittiwake
Tree branch Marbled murrelet
Northern and southern British Columbia provide another good example of habitat availability as revealed through seabird population estimates. The population data are more comprehensive and have largely been gathered by island visitations. The islands in the northern portion are heavily vegetated and many have well-developed soil into which storm-petrels, auklets, and murrelets can burrow. Indeed, 96% of the seabird population consists of nocturnal, burrow-nesting species. In southern British Columbia, however, there are more open-nest species,
## particularly glaucous-winged gulls and cormorants.
Overall, 68% of the breeding seabirds found along the northeastern Pacific coast are nocturnal and nest in burrows or rock crevices (Table 8). The most conspicuous nesting birds such as gulls, cormorants, and murres, comprise only 22% of the total population. Consequently, our current estimates of breeding seabirds still underestimate the more secretive, nocturnal, burrow-nesting species.
Table 8. _Proportional nest-site preferences of Pacific coast seabirds.[11]_
Estimated number of pairs
British Columbia Total San Juan Washington Site Northern Southern Islands coast Population
Burrow-rock crevice Diurnal 1,849 11,334 231 7,504 20,918 Nocturnal 90,347 30,600 9,800 17,070 147,817 Open nests Flat or slope 909 15,101 6,298 5,755 28,063 Cliff face 982 5,525 395 12,945 19,847
Total 94,087 62,560 16,724 43,274 216,645
Percent of population
British Columbia Total San Juan Washington Site Northern Southern Islands coast Percent
Burrow-rock crevice Diurnal 2.0 18.1 1.4 17.3 9.7 Nocturnal 96.0 48.9 58.6 39.4 68.1 Open nests Flat or slope 1.0 24.2 37.6 13.3 13.0 Cliff face 1.0 8.8 2.4 30.0 9.2
Population Changes
The available data are inadequate to detect changes in population distribution and density for most species (Table 9). In Washington, for instance, limited unsubstantiated information suggests an overall decline of the double-crested cormorant and tufted puffin in the San Juan Island area. Likewise, there seems to be an increase in glaucous-winged gulls there. In British Columbia, Drent and Guiguet (1961) were able to detect changes in some species. For example, they noted increases in the double-crested cormorant, pelagic cormorant, and glaucous-winged gull. No change was observed in the tufted puffin. Since then, the Brandt's cormorant has established a colony in Barkley Sound (Guiguet 1971). The data in southeastern Alaska are inadequate for all species except, perhaps, the Cassin's auklet which Gabrielson and Lincoln (1959) reported to be declining throughout Alaska. In short, no definitive statements can now be made concerning changes in seabird population numbers.
Species Accounts
Fork-tailed Storm-petrel _(Oceanodroma furcata)_
Storm-petrels are especially difficult to census because they are nocturnal, and the burrows and rock crevices where they breed are often difficult to locate, especially in mixed-species colonies. The census data are inadequate to determine whether there have been changes in population density and distribution. Indeed, the biology of this species is perhaps the least known of the North Pacific colonial seabirds. In southeastern Alaska, this species is outnumbered by at least 5 to 1 by the Leach's storm-petrel _(Oceanodroma leucorhoa)_. The reasons for this are poorly understood. There is some evidence that the numbers of breeding fork-tailed storm-petrels on Forrester Island may fluctuate drastically from one year to the next (Gabrielson and Lincoln 1959).
Leach's Storm-petrel _(Oceanodroma leucorhoa)_
Of the two subspecies of this petrel (_O. l. leucorhoa_ and _O. l. beali_), only _O. l. beali_ is found in southeastern Alaska. The _leucorhoa_ subspecies is more northerly in distribution. Where both fork-tailed and Leach's storm-petrels are sympatric, Leach's predominates; however, this relationship becomes more unpredictable in British Columbia and Washington. This species is undoubtedly widespread in the forested islands of the Alexander Archipelago.
Double-crested Cormorant _(Phalacrocorax auritus)_
The double-crested cormorant apparently does not breed in southeastern Alaska since Willett (1912), Gabrielson and Lincoln (1959), and S. Patten (personal communication) do not report breeding colonies for the area. The largest populations occur in southern British Columbia principally in the Gulf Islands, where 71% of all breeding double-crested cormorants are found (Table 10). According to Jewett et al. (1953), this species was less common in Puget Sound than was Brandt's cormorant, but is certainly not the case today (D. A. Manuwal, unpublished data). The only common cormorants in the San Juan Islands are the pelagic and double-crested species. The double-crested cormorant seems to have declined in numbers on both coastal and inland waters. On the basis of his observations, R. W. Campbell believes that this species is increasing in British Columbia.
Table 9. _Distribution and status of marine birds breeding along the Pacific coast of Washington, British Columbia, and southeastern Alaska._ (X = known to breed in the region;? = data insufficient; + = evidence indicates an overall increase in size of population; - = evidence indicates an overall decrease in size of population; 0 = no population change.)
----------------------------------------------------------------------------- British Washington Columbia ---------------- --------------- Family and species Common name Presence Status Presence Status ----------------------------------------------------------------------------- Hydrobatidae _Oceanodroma furcata_ Fork-tailed X ? X ? storm-petrel _O. leucorhoa_ Leach's storm-petrel X ? X - Phalacrocoracidae _Phalacrocorax auritus_ Double-crested X - X - cormorant _P. penicillatus_ Brandt's cormorant X ? X 0 _P. pelagicus_ Pelagic cormorant X ? X + Haematopodidae _Haematopus bachmani_ Black oystercatcher X ? X + Laridae _Larus glaucescens_ Glaucous-winged gull X + X + _L. occidentalis_ Western gull X ? X ? _L. argentatus_ Herring gull _Rissa tridactyla_ Black-legged kittiwake Alcidae _Uria aalge_ Common murre X ? X - _Cepphus columba_ Pigeon guillemot X ? X + _Brachyramphus marmoratus_ Marbled murrelet X ? X ? _B. brevirostris_ Kittlitz's murrelet _Synthliboramphus antiquus_ Ancient murrelet X ? _Ptychoramphus aleuticus_ Cassin's auklet X ? X ? _Cerorhinca monocerata_ Rhinoceros auklet X ? X + _Fratercula corniculata_ Horned puffin _Lunda cirrhata_ Tufted puffin X - X 0 Total species 14 15 -----------------------------------------------------------------------------
--------------------------------------------------------------------- Southeastern Alaska ---------------- Family and species Common name Presence Status --------------------------------------------------------------------- Hydrobatidae _Oceanodroma furcata_ Fork-tailed X ? storm-petrel _O. leucorhoa_ Leach's storm-petrel X ? Phalacrocoracidae _Phalacrocorax auritus_ Double-crested cormorant _P. penicillatus_ Brandt's cormorant ? _P. pelagicus_ Pelagic cormorant X ? Haematopodidae _Haematopus bachmani_ Black oystercatcher X ? Laridae _Larus glaucescens_ Glaucous-winged gull X ? _L. occidentalis_ Western gull _L. argentatus_ Herring gull X ? _Rissa tridactyla_ Black-legged X ? kittiwake Alcidae _Uria aalge_ Common murre X ? _Cepphus columba_ Pigeon guillemot X ? _Brachyramphus marmoratus_ Marbled murrelet X ? _B. brevirostris_ Kittlitz's murrelet X ? _Synthliboramphus antiquus_ Ancient murrelet X ? _Ptychoramphus aleuticus_ Cassin's auklet X - _Cerorhinca monocerata_ Rhinoceros auklet X ? _Fratercula corniculata_ Horned puffin X ? _Lunda cirrhata_ Tufted puffin X ? Total species 16 ---------------------------------------------------------------------
Brandt's Cormorant _(Phalacrocorax penicillatus)_
Brandt's cormorant is the least abundant of the three cormorant species that nest in the study area. Washington is at the northernmost edge of the breeding distribution of this species. Only one more northerly colony exists, on Sartine Island off Vancouver Island (Vermeer et al. 1976). Brandt's cormorant comprises about 85% of the cormorant population in Oregon (U.S. Fish and Wildlife Service, unpublished data). However, in Washington it is only about 9% and in British Columbia 3% of the total cormorant population.
Table 10. _Estimated seabird populations breeding from Cape Fairweather, Alaska, to the Columbia River, Washington._[12][13][14] (? = present in unknown numbers; - = inadequate data.)
----------------------------------------------------------------------------- Northern Southern San Juan Washington Total all British British Islands coast regions Columbia Columbia
Bird species Population Population Population Population Population ----------------------------------------------------------------------------- Fork-tailed storm-petrel 49,080 ? 0 1,900 50,980 Leach's storm-petrel 1,365 5,000 0 3,655 10,020 Double-crested cormorant 0 1,058 64 390 1,512 Brandt's cormorant 0 185 0 140 325 Pelagic cormorant 982 4,017 395 995 6,389 Glaucous-winged gull 909 13,858 6,234 4,215 25,216 Western gull 0 ? 0 930 930 Common murre 0 1,508 0 11,950 13,458 Pigeon guillemot 1,733 1,256 194 161 3,345 Ancient murrelet 21,177 0 0 0 21,177 Cassin's auklet 13,475 25,000 0 100 38,575 Rhinoceros auklet 5,250 6,000 9,800 11,415 27,065 Horned puffin 0 0 0 0 0 Tufted puffin 116 10,078 37 7,343 17,574 Total 94,087 67,960 16,724 43,194 216,566 --------------------------------------------------------------------------
----------------------------------------------------------------------------- Northern Southern San Juan Washington Total all British British Islands coast regions Columbia Columbia
Bird species Percent Percent Percent Percent Percent ----------------------------------------------------------------------------- Fork-tailed storm-petrel 52.2 - - 4.4 23.5 Leach's storm-petrel 1.5 8.0 - 8.5 4.6 Double-crested cormorant - 1.7 >0.1 >0.1 >0.1 Brandt's cormorant - >0.1 - >0.1 >0.1 Pelagic cormorant 1.0 6.4 2.4 2.3 3.0 Glaucous-winged gull 1.0 22.2 37.3 9.8 11.6 Western gull - - - 2.2 >0.1 Common murre - 2.4 - 27.7 6.2 Pigeon guillemot 1.8 2.0 1.2 >0.1 1.5 Ancient murrelet 22.5 - - - 9.8 Cassin's auklet 14.3 40.0 - >0.1 17.8 Rhinoceros auklet 5.6 >0.1 58.6 26.4 12.5 Horned puffin - - - - - Tufted puffin >0.1 16.1 >0.1 17.0 8.1 ---------------------------------------------------------------------------
Comparing information in Jewett et al. (1953) with the current situation, it is apparent that there has been a drastic change in the distribution and probably in the numbers of this species in Washington. Today, there are no Brandt's cormorant colonies in the San Juan Islands or Strait of Juan de Fuca. Yet Jewett et al. (1953) reported colonies at Bellingham Bay and on Lopez and Matia islands. We have observed juvenile Brandt's cormorants in the San Juan Islands during the summer. This species may be particularly susceptible to human disturbance, since all three areas listed above are heavily used in the summer for recreation.
Pelagic Cormorant _(Phalacrocorax pelagicus)_
The distribution of breeding colonies of the pelagic cormorant is strongly determined by the availability of the steep cliffs on which it constructs its nest. This is the only common cormorant in southeastern Alaska. Throughout its extensive range, this species is generally found breeding in small numbers. Nothing is known about fluctuations in its numbers in Alaska.
This species is common in both British Columbia and Washington; nesting sites are of the same type as those in Alaska except in the San Juan Islands, where 200-300 birds nest on cliff faces composed of glacial deposits. Here, there is frequent nest loss due to slippage off the cliff face; this loss is especially severe on Smith and Protection islands. There do not appear to be any changes in the distribution of pelagic cormorants, but an accurate assessment of abundance is impossible from the data currently available.
Glaucous-winged Gull _(Larus glaucescens)_
The glaucous-winged gull is the characteristic gull of southeastern Alaska and British Columbia. In Washington, it is the dominant gull in the San Juan Island area but interbreeds with the western gull on the Washington outer coast from Tatoosh to Copalis Beach (Scott 1971). In Alaska, it is widely distributed and locally abundant on Forrester Island, St. Lazaria, and throughout Glacier Bay (S. Patten, personal communication). The biology of this species has been extensively studied in the southern part of its range, especially by Vermeer (1963) and James-Veitch and Booth (1954). The only study of the breeding biology of this species in southeastern Alaska is by Patten (1974) for Glacier Bay. Glaucous-winged gulls are apparently increasing in British Columbia (R. W. Campbell, unpublished data) and in Washington (T. R. Wahl, personal communication). This increase is undoubtedly a result of the proximity of breeding colonies to garbage dumps and commercial fishing fleets in both Canada and the United States. Little is known about changes in populations of gulls in southeastern Alaska.
Western Gull _(Larus occidentalis)_
The western gull is the common breeding gull of the Washington outer coast; however, there is increased interbreeding with glaucous-winged gulls northward from Destruction Island to Tatoosh Island. The percentage of glaucous-winged gulls steadily increases until Vancouver Island and the Strait of Juan de Fuca, where western gulls are rare. Population estimates of gulls on the outer coast of Washington are derived primarily from aerial flights. This makes identification of gulls difficult, and in view of the amount of interbreeding, it is probably impossible to classify many of the breeding gulls as to species. Western gulls appear to be increasing in the Grays Harbor area (G. D. Alcorn, personal communication).
Herring Gull _(Larus argentatus)_
The herring gull is typically found in inland Alaska but can be found uncommonly along the coast of southeastern Alaska, where it often forms mixed colonies with glaucous-winged gulls. These two species apparently hybridize where they are sympatric (Williamson and Peyton 1963; Patten and Weisbrod 1974; Patten 1974).
Black-legged Kittiwake _(Rissa tridactyla)_
The black-legged kittiwake is found only in the northern portions of southeastern Alaska. It apparently is a common breeding bird in Glacier Bay National Monument (S. M. Patten, Jr., personal communication). No population estimates are available for this species other than that it is locally abundant.
Common Murre _(Uria aalge)_
Common murres are common in southeastern Alaska and the coast of Washington but breed only in small numbers in British Columbia and are absent in the San Juan Islands. Since this species usually prefers cliffs or the tops of inaccessible rocks, they are probably limited by island topography in British Columbia, and are most certainly so limited in the San Juan and Gulf Island groups.
In Alaska, common murres breed in unknown numbers in Glacier Bay and in large numbers on St. Lazaria, Forrester, and the Hazy islands. No data on population changes are available for any of the three regions.
Pigeon Guillemot _(Cepphus columba)_
The pigeon guillemot is common throughout the region from Cape Fairweather to Washington. Even though it is not truly colonial, it may be locally abundant where there are suitable nest sites. Since these nest sites are usually difficult to find, population estimates are seldom accurate, usually being conservative. It is evident that guillemots appear to be small in number when compared with other seabirds nesting at major colony sites in the north Pacific region (Table 10). This disparity may be exaggerated by the difficulty of censusing guillemots.
Marbled Murrelet _(Brachyramphus marmoratus)_
Since the marbled murrelet has been found to nest in coniferous forests (Binford et al. 1975), traditional census techniques are unsuitable. This species is common in southeastern Alaska (Gabrielson and Lincoln 1959), in British Columbia (Drent and Guiguet 1961), and in Washington (Jewett et al. 1953).
Kittlitz's Murrelet _(Brachyramphus brevirostris)_
The difficulties in assessing breeding populations of Kittlitz's murrelet are the same as those for the marbled murrelet. This species nests on the ground at high elevation near the coast (Bailey 1973). The largest concentrations are in the vicinity of Glacier Bay National Monument (Gabrielson and Lincoln 1959). They are not found breeding in Washington or British Columbia.
Ancient Murrelet _(Synthliboramphus antiquus)_
Ancient murrelets appear to be locally common throughout southeastern Alaska. Their presence is probably strongly dependent upon a suitable soil in which to excavate burrows. The only available population estimates are those by Willett (1915) for Forrester Island (Table 1). Censusing this species is especially difficult because its burrows are easily confused with those of Cassin's auklet. There are no studies of this species in southeastern Alaska; however, it has been well studied in the Queen Charlotte Islands to the south by Sealy (1975).
Cassin's Auklet _(Ptychoramphus aleuticus)_
A synthesis of literature and unpublished observations led Gabrielson and Lincoln (1959) to conclude that Cassin's auklet has greatly decreased in numbers and is not abundant anywhere in Alaska. They also concluded that the colony on Forrester Island (Table 1) was the only well-documented colony in southeastern Alaska. Fishermen in the southeastern Alaska area occasionally see this species (M. E. Isleib, personal communication), but it is apparently still uncommon though more widespread than just Forrester Island. The nocturnal habits and burrowing in dense vegetation makes censusing this species very difficult. Nothing is known about the ecology of this species in Alaska.
Rhinoceros Auklet _(Cerorhinca monocerata)_
Rhinoceros auklets seem to be found breeding only on islands where there is a well-developed soil in which to excavate their extensive burrows. From the limited evidence available, it appears that the largest rhinoceros auklet populations probably are to be found in southeastern Alaska. Willett (1912) found a very large population on Forrester Island (Table 2), and the species has been found in the summer in the Barren Islands east of Kodiak Island (E. P. Bailey, personal communication). More intensive surveys of the Alexander Archipelago will probably reveal other populations of this species.
This species is less common in British Columbia than either Alaska or Washington. A possible reason for this is lack of suitable nesting areas. In Washington, the two largest colonies are at Protection Island in the Strait of Juan de Fuca and Destruction Island on the outer coast. Smaller numbers exist on other coastal islands and on Smith Island in the Strait of Juan de Fuca. The Smith Island colony is an interesting one since it appears that early human disturbance in the late 19th or early 20th century eliminated the species from the island. In their discussion of Smith Island, Jewett et al. (1953) made no mention of auklets, only of puffins and guillemots. Couch (1929) did not record the species in 1925. The colony now numbers about 600 pairs.
Horned Puffin _(Fratercula corniculata)_
Although the horned puffin is one of the most abundant seabirds in other parts of Alaska, it is much less abundant in the southeastern portion. In addition to the information discussed by Sealy (1973), it now appears that this species may breed as far south as Triangle Island, British Columbia (K. Vermeer, personal communication; D. A. Manuwal, personal observation). Here, as on Forrester Island, it is greatly outnumbered by the tufted puffin. No data are available on the breeding or status of this species in the study area.
Tufted Puffin _(Lunda cirrhata)_
The tufted puffin is found breeding on scattered islands throughout the region. The largest known colonies are on Forrester Island, Alaska, Triangle Island, British Columbia, and Carroll Island, Washington. It is notably absent from most of the gulf and San Juan Islands. Even though puffins have apparently never been numerous in the San Juan Islands, their population has noticeably declined during the past 35 years. For example, Jewett et al. (1953) reported a colony of 50 pairs on Bare Island in 1937, but in 1973 only 2 pairs were counted (D. A. Manuwal, unpublished data). Likewise, in 1915 there were more than 250 pairs on Smith Island, but by 1916 there were only 75 pairs (Jewett et al. 1953). The decline is attributed to rapid erosion of the glacial-deposit cliffs. There are no puffins on Smith Island today, and the largest colony in the Puget Sound area is the 35 pairs on Protection Island (D. A. Manuwal, unpublished data).
Discussion
The total minimum estimate of the breeding seabird populations of British Columbia and Washington is 216,500 pairs (Table 10). No comprehensive estimates are available for breeding seabirds of southeastern Alaska. It is likely, however, that the number of breeding seabirds in the Alexander Archipelago may be equal to (or exceed) the populations of both British Columbia and Washington. Data are desperately needed from that area. Of the total seabird population in the study area (Table 10) 43% reside in northern British Columbia. The Washington State population represents 28% of the total. Fork-tailed storm-petrels comprise almost 25% of all the breeding seabirds in the area under consideration. The Cassin's auklet is the next most numerous species (18% of the total).
It is apparent that current data are, for the most part, inadequate for assessing anything but catastrophic changes in seabird breeding colonies. This inadequacy is due to inadequate censusing because of excessive reliance upon aerial surveys; in the past, this has often been a result of insufficient funding.
Of the several threats facing seabird populations, none may be as important as oil pollution. A general review of this subject is presented elsewhere by Vermeer and Vermeer (1975). It is apparent from this review that the most vulnerable species are those that dive beneath the sea surface, including all the alcids and cormorants breeding along the coast that are discussed in this paper. This group makes up almost 60% of all the breeding seabirds in this area. Unfortunately, our knowledge of several of these species is scanty and our current census techniques are unsuitable for most of these birds.
Studies of the changes in seabird numbers have been made in other oceans. For example, in Great Britain (Bourne 1972_a_, 1972_b_; Harris 1970), eastern Canada (Nettleship 1973), and the Atlantic coast of the United States (Kadlec and Drury 1968), two major trends seem apparent. First, there is an overall decline in alcid and tern numbers. The decline in auks may be due to their extreme vulnerability to oil pollution (Bourne 1972_a_, 1972_b_; Vermeer and Vermeer 1975). The Atlantic puffin, however, may be suffering the additional effects of gull cleptoparasitism (Nettleship 1972). Secondly, there seems to be an increase in gull populations on both sides of the Atlantic,
## particularly the herring gull and black-legged kittiwake.
Compared with the Atlantic coast of North America and northern Europe, the data base for seabird populations of the Pacific coast is poor. The fragmentary evidence now available indicates that there may be small population increases in the western and glaucous-winged gulls and range extensions of the Brandt's and double-crested cormorants and of the rhinoceros auklet (Scott et al. 1974). Whether these changes represent actual population increases or displacements remains unclear. The remote locations of most of the large Pacific seabird colonies may provide unofficial protection from human interference. Intensive surveys are needed to establish base-line inventories in these areas.
As a consequence of this first comprehensive review of the status of breeding marine birds of the northeast Pacific coast of North America, we recommend the following future research topics as necessary for the conservation of this great international resource.
• Seabird colony census techniques should be refined since almost 68% of the seabirds in this area are nocturnal and nest in burrows. The present reliance on aerial censusing, although economical, is inadequate to census most breeding seabird populations; more on-site surveys are needed. For surface-nesting species and diurnal, burrowing species, studies on species specific activity cycles are needed so that census data can be corrected for birds not observed at the colony. For nocturnal, burrowing species seasonal burrow occupancy rates must be determined so that burrow counts can be corrected for inactive burrows.
• Comprehensive surveys should be made every 3-5 years.
• In 1980 a coordinated breeding bird survey of the entire Pacific coasts of Mexico, Canada, and the United States should be conducted.
• Specific islands where key populations exist should be carefully monitored for subtle changes in population density or species composition.
• Increased study of the breeding biology of seabirds should be carried out so that base-line reproductive characteristics can be determined.
• Detailed studies of the effects of human disturbance should be made, especially for species that breed near large coastal cities or marine recreation areas.
References
Bailey, E. P. 1973. Discovery of a Kittlitz's murrelet nest. Condor 75:457.
Binford, L., B. Elliott, and S. Singer. 1975. Discovery of a nest and the downy young of the marbled murrelet. Wilson Bull. 87:303-319.
Bourne, W. 1972_a_. The decline of auks in Great Britain. Biol. Conserv. 4:144-146.
Bourne, W. 1972_b_. Threats to seabirds. Int. Counc. Bird Preserv. Bull. XI:200-218.
Couch, L. 1929. Introduced European rabbits in the San Juan Islands, Washington. J. Mammal. 10:334-336.
Drent, R. H., and C. Guiguet. 1961. A catalogue of British Columbia seabird colonies. Occas. Pap. B. C. Prov. Mus. 12. 173 pp.
Franklin, J., and C. Dyrness. 1973. Natural vegetation of Oregon and Washington. U.S. For. Serv. Gen. Tech. Rep. PNW-8. 417 pp.
Gabrielson, I., and F. Lincoln. 1959. The birds of Alaska. The Stackpole Company, Harrisburg, Penn., and Wildlife Management Institute, Washington, D.C. 922 pp.
Grinnell, J. 1897. Petrels of Sitka, Alaska. Nidologist 4:76-78.
Grinnell, J. 1898. Summer birds of Sitka, Alaska. Auk 15:122-131.
Grinnell, J. 1909. Birds and mammals of the 1907 Alexander Expedition to southeastern Alaska. Univ. Calif. Publ. Zool. 5:171-264.
Guiguet, C. 1971. A list of seabird nesting sites in Barkley Sound, British Columbia. Syesis 4:253-259.
Harris, M. P. 1970. Rates and causes of increases of some British gull populations. Bird Study 17:325-335.
Heath, H. 1915. Birds observed on Forrester Island, Alaska during the summer of 1913. Condor 17:20-41.
James-Veitch, E., and E. Booth. 1954. Behavior and life history of the glaucous-winged gull. Walla Walla Coll., Publ. Biol. 12.
Jewett, S., W. Taylor, W. Shaw, and J. Aldrich. 1953. Birds of Washington State. Univ. of Washington Press, Seattle. 767 pp.
Kadlec, J., and W. Drury. 1968. Structure of the New England herring gull population. Ecology 49:644-676.
Kenyon, K., and V. Scheffer. 1961. Wildlife surveys along the northwest coast of Washington. Murrelet 42:29-37.
Manuwal, D. A. 1974. Conservation notes (Protection Island). Pac. Seabird Group Bull. 1.
Nettleship, D. 1972. Breeding success of the common puffin (_Fratercula arctica_ L.) on different habitats at Great Island, Newfoundland. Ecol. Monogr. 42:239-268.
Nettleship, D. 1973. Tenth census of seabirds in the sanctuaries of the north shore of the Gulf of St. Lawrence. Can. Field-Nat. 87:395-402.
Patten, S. 1974. Breeding ecology of the glaucous-winged gull _(Larus glaucescens)_ in Glacier Bay, Alaska. M.S. Thesis. Univ. of Washington, Seattle. 78 pp.
Patten, S., and A. R. Weisbrod. 1974. Sympatry and interbreeding of herring and glaucous-winged gulls in southeastern Alaska. Condor 76:343.
Richardson, F. 1961. Breeding biology of the rhinoceros auklet on Protection Island, Washington. Condor 63:456-473.
Scott, J. M. 1971. Interbreeding of the glaucous-winged gull and western gull in the Pacific Northwest. Calif. Birds 2:129-133.
Scott, M., W. Hoffman, D. Ainley, and C. Zeillemaker. 1974. Range expansion and activity patterns in rhinoceros auklets. West. Birds 5:13-20.
Sealy, S. 1973. Breeding biology of the horned puffin on St. Lawrence Island, Bering Sea, with zoogeographical notes on the north Pacific puffins Pac. Sci. 27:99-199.
Sealy, S. 1975. Feeding ecology of the ancient and marbled murrelets near Langara Island, British Columbia. Can. J. Zool. 53:418-433.
Summers, K. 1974. Seabirds breeding along the east coast of Moresby Island, Queen Charlotte Islands, British Columbia. Syesis 7:1-12.
Swarth, H. 1911. Birds and mammals of the 1909 Alexander Alaska Expedition. Univ. Calif. Publ. Zool. 7:9-172.
Swarth, H. 1922. Birds and mammals of the Stikine River Region of northern British Columbia and southeastern Alaska. Univ. Calif. Publ. Zool. 24:194-314.
Swarth, H. 1936. Origins of the fauna of the Sitkan District. Alaska. Proc. Calif. Acad. Sci. Ser. 4, 15:59-78.
Thoresen, A., and J. Galusha. 1971. A nesting population study of some islands in the Puget Sound area. Murrelet 52:20-23.
U.S. Department of the Interior, Interagency Task Force. 1972. Environmental setting between Port Valdez, Alaska, and west coast ports. Final Environmental Impact Statement, Vol. 3.
U.S. Weather Bureau. 1956. Climatic summary of the United States--supplement for 1931 through 1952, Washington. Climatography of the United States 11-39. 79 pp.
U.S. Weather Bureau, Environmental Data Service. 1965_a_. Climatic summary of the United States--supplement for 1951 through 1960, Oregon. Climatography of the United States 86-31. 96 pp.
U.S. Weather Bureau, Environmental Data Service. 1965_b_. Climatic summary of the United States--supplement for 1951 through 1960, Washington. Climatography of the United States 86-39. 92 pp.
U.S. Weather Bureau, Environmental Data Service. 1974. Climatological Data, Alaska Annual Summary 1974, 60:13.
Vermeer, K. 1963. The breeding ecology of the glaucous winged gull _(Larus glaucescens)_ on Mandarte Island. B.C. Occas. Pap. B.C. Prov. Mus. 13. 104 pp.
Vermeer, K., D. A. Manuwal, and D. S. Bingham. 1976. Seabirds and pinnipeds of Sartine Island, Scott Island group, British Columbia. Murrelet 57(1):14-16.
Vermeer, K., and R. Vermeer. 1975. Oil threat to birds on the Canadian west coast. Can. Field-Nat. 89:278-298.
Willett, G. 1912. Report of George Willett, Agent and Warden stationed on St. Lazaria Bird Reservation, Alaska. Bird-lore 14:419-426.
Willett, G. 1915. Summer birds of Forrester Island, Alaska. Condor 19:15-17.
Williamson, F. S. L., and L. Peyton. 1963. Interbreeding of glaucous-winged and herring gulls in the Cook Inlet region, Alaska. Condor 65:24-28.
FOOTNOTES:
[5] Data are minimum estimates of pairs and do not include breeding sites with less than 100 birds.
[6] Does not include the black oystercatcher, marbled murrelet, and western gull.
[7] Estimates only for colonies of 100 or more birds.
[8] Estimates are in number of pairs.
[9] Estimates are number of pairs.
[10] Estimates are numbers of pairs.
[11] Data for southeastern Alaska were inadequate to enable estimates of breeding pairs.
[12] Population estimates are minimum and represent numbers of pairs.
[13] Does not include the following species for which population estimates are lacking: black oystercatcher, herring gull, black-legged kittiwake, marbled murrelet, Kittlitz's murrelet.
[14] Data for southeastern Alaska were inadequate to enable estimates of breeding pairs.
THE BIOLOGY AND ECOLOGY OF MARINE BIRDS IN THE NORTH
Trophic Relations of Seabirds in the Northeastern Pacific Ocean and Bering Sea
by
David G. Ainley
Point Reyes Bird Observatory Stinson Beach, California 94970
and
Gerald A. Sanger[15]
National Marine Fisheries Service Marine Mammal Division Seattle, Washington
Abstract
Literature on the diets of seabirds is reviewed for 70 species found in five subarctic oceanographic regions of the northeastern North Pacific Ocean and Bering Sea. Species inhabiting estuaries and sheltered bays are not included. The diets of cormorants, marine ducks, alcids, and marine raptors are best known; less information is available for loons, grebes, petrels, and gulls. Enough is known, however, to broadly characterize the diet of each species. Less than 7% of all species feed on one type of prey, about 60% feed on two or three types, and the rest feed on four or more types. Only 12% of all species feed on eight or more types of prey. Most seabirds (77%) feed as secondary and tertiary carnivores. Where overlap in diet exists, seabirds
## partition resources through use of different
feeding methods, selection of different-sized prey, and zonation of habitat. Species that have specialized diets are probably more susceptible than others to local environmental catastrophes. Species whose feeding methods are highly adapted for exploitation of resources in polar and subpolar habitats are not adapted for coping with oil pollution. Competition between birds and man for marine resources can sometimes benefit seabirds and at other times harm them. More research is needed on seabird feeding relations so that the ecological roles played by marine birds can be defined and placed in perspective. Such work should be conducted at the community level, year-round, and should be so conducted as to facilitate comparison with biological oceanographic data.
The ecology, morphology, and much of the behavior of a seabird species are definable in terms of the food resources it exploits year-round and the spatial and temporal relations between food and breeding sites. This general point unifies such important reports as those by Kuroda (1954), Bédard (1969_a_), Ashmole and Ashmole (1967), Ashmole (1971), Spring (1971), and Sealy (1972). More concretely, information on trophic relations of seabirds is useful in several ways. In conjunction with biological oceanographic data, it can provide insight into geographic location, marine habitat, depth, time of day, and general method of food capture by seabirds. Collected over several years, it can provide a basis for understanding annual differences in seabird breeding phenology and success. Finally, supplemented with data on how much seabirds eat and excrete, it is necessary for an understanding of the energetic and ecological roles played by the birds in the functioning of marine ecosystems.
Several studies that describe trophic relations within seabird communities have helped to define the principals of community organization pertaining to the exploitation of available food resources and have given clues to food-chain pathways. Trophic relations have been described for breeding communities in the Barents Sea (Uspenski 1958; Belopol'skii 1961), in the tropical Pacific Ocean (Ashmole and Ashmole 1967; Ashmole 1968), in the North Sea (Pearson 1968), and in the Chukchi Sea (Swartz 1966). The last-named study pertained most directly to the geographic region discussed in this paper, but several other studies have provided sound information on segments of communities in the northeastern North Pacific and Bering Sea. These include the work on three species of auklets (_Aethia_, _Cyclorrhynchus_) in the Bering Sea (Bédard 1969_a_); investigations on cormorants and other fish predators in British Columbia by Munro (1941), Munro and Clemens (1931), and Robertson (1974); studies of murres in Bristol Bay by Ogi and Tsujita (1973); observations on several species near the Pribilof Islands by Preble and McAtee (1923); work on diving species off Oregon by Scott (1973); and studies of murrelets by Sealy (1975).
A review of available reports reveals three obvious gaps in the emphasis placed in seabird food studies. First, few studies have ever considered in detail the trophic relations of seabird communities during the winter or nonbreeding season. Partial exceptions are the works by Cottam (1939) and others on marine diving ducks, species that are seabirds only during the winter, and by several researchers (Munro and Clemens 1931; Munro 1941; Robertson 1974) on seabirds in British Columbia. Divoky (1976) studied diets of pack-ice gulls during the nonbreeding season, but those species are not included in the present analysis because they rarely are found south of the Bering Strait. Second, no study has considered the trophic relationships of an entire seabird community, i.e., not just breeding species but also nonbreeding species. In the rather broad communities considered here, 50-70% or more of the birds breed in another part of the world. To say that these nonbreeding species have no significant impact on resource exploitation or on organization and evolution among breeding members would be naive. Finally, few investigators have attempted to fit birds into an entire ecosystem, including lower trophic level origins as well as fish, marine mammals, and man.
The reasons for these gaps in study emphasis are readily apparent: the inconvenience of marine research during the winter when weather is stormy, the need for costly study platforms (boats), and the difficulties in organizing the specialized community of biologists required for such tasks. A less obvious but important reason is that oceanographers and fishery biologists have overlooked seabirds as important members of marine ecosystems.
Diets of Seabirds in Western North America
Relatively good information exists for most pelecaniformes of the region. A notable exception is the brown pelican _(Pelecanus occidentalis)_, an endangered species. This is unfortunate because dietary information is important for understanding the species' ecology. Observations in eastern North America (Palmer 1962) and Peru (Murphy 1936) indicated that their diet consisted of fish that occur at the surface. The larger cormorants are piscivorous, particularly on schooling fishes that occur at moderate to great depths (Table 1). The smaller cormorants feed more heavily on benthic fish and decapod crustaceans. Cormorants apparently feed only during daylight and then only for short periods because their wettable plumage loses its buoyancy. Thus they remain relatively close (50 km) to nesting and loafing areas.
Table 1. _Food of cormorants in different localities_ (x = major prey, o = minor prey and * = incidental prey species)
----------------------------------------------------------------------- Key: A_Amphipod B: Isopod C: Decapod D: _Clupea_ E: _Engraulis_ F: Salmonid G: Argentinid H: _Porichthys_ I: _Otophidium_ J: _Boreogadus_ K: _Microgadus_ L: _Gasterosteus_ M: _Sebastes_ N: Hexagrammid O: Cottid P: Agonid Q: Embiotocid R: _Chromis_ S: _Oxyjulis_ T: Stichacid U: Pholid V: Gobiid W: _Ammodytes_ X: Pleuronectid Y: Bothid
CRUSTACEAN Location Diet A B C D E F G H I J K L M ----------------------------------------------------------------------- Double-crested cormorant _(Phalacrocorax auritus)_[16] Alaska Peninsula (Palmer 1962) o o o x x x SE Alaska (Bailey 1927) x Mandarte Island (Robertson 1974) * * * * * Vancouver Island (Munro and Clemens 1931) x Oregon (Palmer 1962) x * * x Farallon Island (PRBO, unpublished data) * * Brandt's cormorant _(P. penicillatus)_[17] Vancouver Island (Robertson, unpublished data) x Vancouver Island (Munro and Clemens 1931) x Washington (Jewett et al. 1953) Yaquina Head (Scott 1973) x o o Farallon Island (PRBO, unpublished data) * o * * x x x San Diego (Hubbs et al. 1970) * Pelagic cormorant _(P. pelagicus)_[18] Cape Thompson (Swartz 1966) x x Pribilof Island (Preble and McAtee 1923) x Alaska (Palmer 1962) x x x SE Alaska (Heath 1915) x x Mandarte Island (Robertson 1974) x Vancouver Island (Munro and Clemens 1921) x x x Washington (Jewett et al. 1953) x x Netarts, Oregon (Gabrielson and Jewett 1940) * * x Yaquina Head (Scott 1973) o o Farallon Island (PRBO, unpublished data) x x Red-faced cormorant _(P. urile)_ Pribilof Islands (Preble and McAtee 1923) x -----------------------------------------------------------------------
----------------------------------------------------------------------- CRUSTACEAN FISH Location Diet N O P Q R S T U V W X Y ----------------------------------------------------------------------- Double-crested cormorant _(Phalacrocorax auritus)_[16] Alaska Peninsula (Palmer 1962) o x SE Alaska (Bailey 1927) Mandarte Island (Robertson 1974) * o x x Vancouver Island (Munro and Clemens 1931) Oregon (Palmer 1962) * x * * Farallon Island (PRBO, unpublished data) * x * * * Brandt's cormorant _(P. penicillatus)_[17] Vancouver Island (Robertson, unpublished data) o x Vancouver Island (Munro and Clemens 1931) Washington (Jewett et al. 1953) x Yaquina Head (Scott 1973) * o o o Farallon Island (PRBO, unpublished data) * o * * * San Diego (Hubbs et al. 1970) * o o * x Pelagic cormorant _(P. pelagicus)_[18] Cape Thompson (Swartz 1966) x x Pribilof Island (Preble and McAtee 1923) x x Alaska (Palmer 1962) x x x x x x SE Alaska (Heath 1915) x Mandarte Island (Robertson 1974) * * x x Vancouver Island (Munro and Clemens 1921) x x x Washington (Jewett et al. 1953) x x Netarts, Oregon (Gabrielson and Jewett 1940) x Yaquina Head (Scott 1973) x Farallon Island (PRBO, unpublished data) x x Red-faced cormorant _(P. urile)_ Pribilof Islands (Preble and McAtee 1923) x x x x x -------------------------------------------------------------------------------
Table 2. _Food of marine ducks and geese (x = major prey, o = minor prey, and * = incidental prey species_).[a]
Key: A: Amphipods B: Decapods C: Barnacles D: Mussels E: Rock clams F: Razor clams G: Oysters, Scallops H: Littorinids I: Chitons
------------------------------------------------------------------------ |PLANTS | |CRUSTACEANS | | |MOLLUSCS | | | |ECHINODERMS Diet[19] | | | | |FISH Location | |A|B|C|D|E|F|G|H|I| | |FISH EGGS ------------------------------------------------------------------------ =Geese= x (_Branta_ spp.) =Emperor goose= x _(Philacte canagica)_ =Oldsquaw= o * * * * * * * o _(Clangula hyemalis)_ =Harlequin duck= * x x o * * o o * * _(Histrionicus histrionicus)_ =Steller's eider= o x * * * * o * * * * _(Polysticta stelleri)_ =Common eider= * * x * o * o o * o * _(Somateria mollissima)_ =King eider= * * o * x * o o * x * _(S. spectabilis)_ =Spectacled eider= x * x o * * * * _(S. fischeri)_ =White-winged scoter= * * * * o x * x o * * o o _(Melanitta deglandi)_ =Surf scoter= o * * * x * * x o * * * o _(M. perspicillata)_ =Black scoter= o * * o x * * x * * * * _(M. nigra)_ =Red-breasted merganser= x _(Mergus serrator)_ ------------------------------------------------------------------------
Information on diets of marine ducks (Table 2) is more nearly complete than for most other seabirds. These birds fall into four groups with some overlap: species feeding on plants (_Branta, Philacte_, _Anas_-type, and _Somateria fischeri_); those feeding on benthic crustaceans (_Clangula hyemalis_, _Histrionicus histrionicus_, _Polysticta stelleri_, _S. mollissima_); those feeding on benthic molluscs (_Somateria_ spp. and _Melanitta_ spp.); and those feeding on fish (_Mergus serrator_, _Clangula hyemalis_, and _Melanitta deglandi_). A study by Perthon (1968), one of the few on a seabird's diet during most of a year, showed a seasonal change in diet for _S. mollissima_ in Norway. In general, waterfowl seem to specialize in their diets much more than other seabirds and, for that reason, are perhaps more restricted in their distributions. Some marine ducks are known to dive to considerable depths (reviewed by Kooyman 1974), but usually they occur in shallow waters where plants and sessile invertebrates are readily available.
The summer diet of the pigeon guillemot _(Cepphus columba)_ is the best known among seabirds in the region being considered here (Table 3). Only in the extreme southern part of its range (i.e., the California Channel Islands) is there no information available on its diet. The species feeds on organisms, mostly fish, from rocky habitat and apparently can dive to considerable depths (Follett and Ainley 1976). Because so much is known about guillemot diets during summer, a study of the winter diet would be valuable.
The diets of other alcids are known well enough to at least characterize them broadly. The larger species, murres, tufted and horned puffins (_Lunda cirrhata_, _Fratercula corniculata_), and the rhinoceros auklet _(Cerorhinca monocerata)_, feed heavily on fish, mainly species that school in midwater (Table 4). To a great degree, these birds are opportunistic, feeding rather heavily at times on cephalopods and crustaceans, particularly nektonic forms. Morphological differences between the two murre species suggest that thick-billed murres _(Uria lomvia)_ feed on benthic organisms much more than do common murres _(U. aalge)_, and that the latter species is more piscivorous (Spring 1971); however, field data on diets are barely adequate to confirm this. Ogi and Tsujita (1973) analyzed the stomach contents of murres drowned in salmon gill nets but did not separate the two species. For the present paper we considered them to be mostly _U. aalge_, since this species predominates in the region of the food study (Bartonek and Gibson 1972). Adult murres sometimes eat different items than they feed to their chicks (Spring 1971; Scott 1973). The smaller alcids, ancient and marbled murrelets--_Synthliboramphus antiquus_ and _Brachyramphus marmoratus_--(Table 5) and auklets (Table 6), feed on macrozooplankton: crustaceans, and fish and squid larvae. Little is known about the food or feeding ecology of Kittlitz's murrelet _(B. brevirostris)_. Its diet is probably similar to that of the other murrelets, especially the marbled murrelet, its allopatric congener, but the diets of the other murrelets differ somewhat (Bédard 1969_b_; Sealy 1975). The Kittlitz's murrelet's shorter bill suggests that it feeds more on invertebrates. Alcids feed in deep or shallow water, depending on food distribution. Some alcid species can be found at great distances from land, particularly in winter (Hamilton 1958; Scott et al. 1971).
Information on the diets of other seabirds in the region is fragmentary and sometimes rather anecdotal. A little is known about the feeding habits of loons (_Gavia_ spp.) and grebes (_Podiceps_ spp. and _Aechmophorus occidentalis_), especially off British Columbia (Table 7). The larger of these birds feed mainly on inshore fish, but as species become progressively smaller, there is a tendency toward eating crustaceans. Work by Madsen (1957) in Denmark, indicated that loons and grebes tend to take prey near or on the bottom. Much more information is available on these birds' diets at their freshwater breeding sites but this provides only partial insight into what they might eat in marine habitats.
Information is especially poor for albatrosses and petrels (order Procellariiformes) (Table 8). Yet, based on sheer numbers alone, members of this diverse group are easily among the most ecologically dominant of the region (Sanger 1972; Ainley 1977). The Laysan albatross _(Diomedea immutabilis)_ seems to be a squid specialist; the black-footed albatross _(D. nigripes)_, northern fulmar _(Fulmarus glacialis)_, scaled petrel _(Pterodroma inexpectata)_, and the fork-tailed and Leach's storm-petrels (_Oceanodroma furcata_ and _O. leucorhoa_) appear to be large, medium, small, and tiny versions, respectively, of surface-feeding generalists that eat whatever they can find, including live and dead fish, squid, coelenterates, crustaceans, and other organisms. The shearwaters (_Puffinus_ spp.) feed to an unknown degree on schooling fish, squid, and crustaceans that occur near the surface. For these very abundant shearwaters, that, unfortunately, is close to the extent of our knowledge both for the North Pacific, where they winter, and the South Pacific, where they breed. Most petrels remain in oceanic habitats, but shearwaters,
## particularly the sooty shearwater _(Puffinus griseus)_, and sometimes
fulmars feed close to, if not within, the inshore neritic habitat. A much better understanding of the diets of this group is sorely needed.
Table 3. _Food of the pigeon guillemot_ (Cepphus columba) _in different localities (x = major prey, o = minor prey, and * = incidental prey species)_.
Key: A: Amphipod B: Isopod C: Decapod D: Petromyzontid E: Chimaerid F: Clupeid G: Osmerid H: Gadid I: Gasterosteid J: Scorpaenid K: Cottid L: Agonid M: Embiotocid N: Bathymasterid O: Clinid P: Cryptacanthodid Q: Cebidichthyid R: Stichaeid S: Pholid T: Ammondytid U: Bothid V: Pleuronectid
---------------------------------------------------------------------------- |CRUSTACEAN | |OCTOPUS Diet | | |FISH Location |A|B|C| |D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V ---------------------------------------------------------------------------- Cape Thompson o o (Swartz 1966) Pribilof Island o o o (Preble and McAttee 1923) Mandarte Island o o * o x o o * o * o o o o o o (Drent 1965; Koelink 1972) Vancouver Island o o o (Munro and Clemens 1931) Olympic Peninsula o o o o (Thoresen and Booth 1958) Yaquina Head o o o o o (Scott 1973) Farallon Island o o * x x * o o o o (Follett and Ainley 1976) ----------------------------------------------------------------------------
Knowledge on the food of gulls, shorebirds, and related species is surprisingly scanty in view of all that is known about their breeding biology and social behavior. Little is known about the marine food of phalaropes, but by inference from their association with storm-petrels, plankton-feeding whales, and convergence lines (Martin and Myers 1969), their tiny size, and their method of feeding (picking at minuscule items on the water surface), one can guess that they feed on zooplankton and detritus. Skuas _(Catharacta skua)_ and jaegers (_Stercorarius_ spp.) apparently eat what they can find at the surface, as well as whatever they can steal from gulls and terns. Almost all the literature on their feeding (Bent 1946) dwells on accounts of their stealing from other birds. That spectacular behavior would seem to be so energetically costly, though, that it is probably less important than we have been led to believe. Rather surprisingly, the question of what foods the gulls and terns eat in the eastern North Pacific is difficult to answer from the literature (Tables 9 and 10). Some information exists for five of the larger larids at isolated places, but little is known about food elsewhere in their respective ranges, and the diets of the seven smaller gulls and the terns are practically unknown. Studies on gull diets in the Atlantic region (e.g., Spaans 1971; Harris 1965) provide information on what to expect from the same species in the Pacific, but that information must be considered only in general terms because, the birds being somewhat opportunistic, their diets differ greatly from one locality to another (Ingolfsson 1967). A few observations are available for arctic terns _(Sterna paradisaea)_ in Alaska, but little information exists for other terns (Table 10). Bent (1921) noted that Aleutian terns _(S. aleutica)_ sometimes associate with arctic terns during feeding.
Finally, we must include raptors, particularly the peregrine _(Falco peregrinus)_ and bald eagle _(Haliaeetus leucocephalus)_, because they are important predators on the smaller seabirds (White et al. 1971, 1973). Peregrines have, in fact, been observed feeding on storm-petrels far at sea (Craddock and Carlson 1970).
Trophic Relations Within Seabird Communities
We have compared and summarized in general terms the food partitioning by species in five rather broad oceanographic regions and their subdivisions in the northeastern North Pacific and Bering Sea, based on the specific details on diets presented in Tables 1 through 10. The five broad regions, defined oceanographically by Dodimead et al. (1963) and Favorite et al. (1976) and modified by Sanger (1972), are shown in Fig. 1. The five oceanographic regions (domains) were divided further into inshore neritic, offshore neritic, and oceanic habitats (Sanger and King, this volume). We did not include estuarine habitats or sheltered bays in the analysis.
[Illustration: Fig. 1. Schematic oceanographic domains of the subarctic Pacific regions (defined by Dodimead et al. (1963) and Favorite et al. (1976) and modified by Sanger (1972).)]
Table 4. _Food of murres and puffins in different localities (x = major prey, o = minor prey, and * = incidental prey species)._
KEY:
CRUSTACEAN A - Euphausiid B - Amphipod C - Isopod D - Decapod
E - POLYCHAETE
F - CEPHALOPOD
CRUSTACEAN POLYCHAETE CEPHALOPOD LOCATION A B C D E F -------- =Common murre= _(Uria aalge)_[20] Cape Thompson o o o o o (Swartz 1966) Pribilof Islands x o o (Preble and McAtee 1923) E. Bering Sea x o (Ogi and Tsujita 1973) Forrester Island o o (Heath 1915) Vancouver Island o o (Robertson, unpublished data) Olympic Peninsula (Cody 1973) Yaquina Head x o (Scott 1973) Farallon Islands x o (PRBO, unpublished data)
=Thick-billed murre= _(U. lomvia)_[21] Cape Thompson o o o (Swartz 1966) Pribilof Islands x x (Preble and McAtee 1923) Hooker Island x o (Demme 1934, _in_ Dement'ev et al. 1968) NE Canada x o o o (Tuck and Squires 1937)
=Tufted puffin= _(Lunda cirrhata)_[22] Cape Thompson * (Swartz 1966) Forrester Island (Heath 1915) Langara Island (Sealy 1973_a_) Washington (Jewett et al. 1953) Olympic Peninsula (Cody 1973) Farallon Island (PRBO, unpublished data) x
=Horned puffin= _(Fratercula corniculata)_ Cape Thompson o (Swartz 1966) Alaska (Bent 1946) Forrester Island (Heath 1915)
=Rhinoceros auklet= _(Cerorhinca monocerata)_ NW Pacific (Kozlova 1961; x Komaki 1967) Forrester Island (Heath 1915) Langara Island (Sealy 1973_a_) Destruction Island (Richardson 1961) Olympic Peninsula (Cody 1973) So. California (Linton x 1908; Grinnell 1899) ---------------------------------------------------------------
KEY:
FISH G - Clupea H - Sardinops I - Engraulis J - Salmo K - Onchorhynchus L - Hypomesus M - Thaleichthys N - Mallotus O - Boreogadus P - Microgadus Q - Theragra R - Lycodes S - Gasterosteus T - Sebaste U - Triglops V - Myoxocephalus W - Cottid X - Cymatogaster Y - Embiotocid Z - Chirolophis AA - Stichaeid BB - Ammodytes CC - Pleuronectid DD - Liparid
FISH A B C D LOCATION G H I J K L M N O P Q R S T U V W X Y Z A B C D -------- =Common murre= _(Uria aalge)_[20] Cape Thompson x o o o x (Swartz 1966) Pribilof Islands o (Preble and McAtee 1923) E. Bering Sea x x x (Ogi and Tsujita 1973) Forrester Island x (Heath 1915) Vancouver Island x o (Robertson, unpublished data) x x o o Olympic Peninsula (Cody 1973) x x o x o o o Yaquina Head (Scott 1973) x o o * x o o Farallon Islands (PRBO, unpublished data)
=Thick-billed murre= _(U. lomvia)_[21] x o o o o o x o Cape Thompson (Swartz 1966) Pribilof Islands (Preble and McAtee 1923) Hooker Island (Demme 1934, _in_ Dement'ev et al. 1968) o x * x * o x o o o NE Canada (Tuck and Squires 1937)
=Tufted puffin= x _(Lunda cirrhata)_[22] * Cape Thompson (Swartz 1966) x Forrester Island (Heath 1915) x Langara Island x (Sealy 1973_a_) x x x x Washington o (Jewett et al. 1953) x o x Olympic Peninsula x (Cody 1973) x o Farallon Island (PRBO, unpublished data)
=Horned puffin= x o _(Fratercula corniculata)_ o x Cape Thompson (Swartz 1966) Alaska (Bent 1946) x Forrester Island (Heath 1915)
=Rhinoceros auklet= _(Cerorhinca monocerata)_ x o x x NW Pacific (Kozlova 1961; Komaki 1967) x Forrester Island (Heath 1915) x Langara Island (Sealy 1973_a_) o x Destruction Island o (Richardson 1961) x x o Olympic Peninsula (Cody 1973) x So. California (Linton 1908; Grinnell 1899) -----------------------------------------------------------------------------
Table 5. _Food of ancient and marbled murrelets (x = major prey, o = minor prey, and * = incidental prey species)._
Column Headings:
CRUSTACEAN A - Euphausiid B - Thysanoessa C - Euphausia D - Mysid E - Acanthomysis F - Amphipod G - Gammarid H - Carid shrimp I - Decapod J - Larvae
CRUSTACEAN
Location DIET A B C D E F G H I J ------------------------------------------------------------------------------ =Ancient murrelet= _(Synthliboramphus antiquus)_[23]
Commander Islands (Dement'ev et al. 1968) x x Amchitka Island (White et al. 1971, 1973) x x x x Langara Island (Sealy 1975) x x x * * *
=Marbled murrelet= _(Brachyramphus marmoratus)_[24]
SE Alaska (Grinnell 1897) Langara Island (Sealy 1975) x x * Vancouver Island (Munro and Clemens 1931) x Olympic Peninsula (Cody 1973)
Column Headings:
SQUID K - Larvae
FISH L - Engraulis M - Osmerid N - Scorpaenid O - Cymatogaster P - Stichaeid Q - Ammodytes R - Larvae
SQUID FISH
Location DIET K L M N O P Q R ----------------------------------------------------------------------------- =Ancient murrelet= _(Synthliboramphus antiquus)_[23]
Commander Islands (Dement'ev et al. 1968) Amchitka Island (White et al. 1971, 1973) x Langara Island (Sealy 1975) o o x
=Marbled murrelet= _(Brachyramphus marmoratus)_[24]
SE Alaska (Grinnell 1897) o Langara Island (Sealy 1975) * * * x * Vancouver Island (Munro and Clemens 1931) x x Olympic Peninsula (Cody 1973) x x
Table 6. _Diets of auklets in different localities (x = major prey, o = minor prey, and * = incidental prey species)._
Table Headings
CRUSTACEAN A - Euphausiid B - Thysanoessa C - Mysid D - Stylomysis E - Amphipod F - Parathemisto G - Phronema H - Gammarid I - Copepod J - Calanus K - Carid shrimp
L - POLYCHAETE
SQUID M - Larvae
FISH N - Cottid O - Larvae
Location Diet A B C D E F G H I J K L M N O
=Cassin's auklet= _(Ptychoramphus aleuticus)_ Forrester Island (Heath 1915) x x x Olympic Peninsula (Cody 1973) x x Farallon Islands (Manuwal 1974) x x x x x o x
=Parakeet auklet= _(Cyclorrhynchus psittaculus)_ Chukhotsk Peninsula (Portenko 1934, _in_ Dement'ev et al. 1968) x x x x x Aleutian Islands (Bent 1946) x St. Lawrence Island (Bédard 1969_a_) x x o x x o o * o o o
=Crested auklet= _(Aethia cristatella)_[25] W. Bering Sea (Portenko 1934, _in_ Dement'ev et al. 1968) x x Commander Islands (Stejneger 1885) x Amchitka (White et al. 1973) x x x x x St. Lawrence Island. (Bédard 1969_a_) x x x o o x x * Pribilof Islands (Preble and McAtee 1923) x x
=Least auklet= _(A. pusilla)_ Commander Islands (Stejneger 1885) x Aleutian Islands (Bent 1946) x St. Lawrence Island (Bédard 1969_a_) o o * o o o x x x
=Whiskered auklet= _(A. pygmaea)_ Commander Islands (Stejneger 1885) x x *
Table 7. _Diets of loons and grebes in different localities (x = major prey, o = minor prey, and * = incidental prey species)._
Table Headings:
CRUSTACEANS A - Euphausid B - Amphipod C - Mysid D - Decapod
E - POLYCHAETE
FISH F - Anguilla G - Clapea H - Sardinops I - Salmo J - Thaleichthys K - Atherinops Location A B C D E F G H I J K
=Common loon= _(Gavia immer)_ Alaska (Palmer 1962) * * o o Vancouver Island (Munro and Clemens 1931) x Denmark (Madsen 1957) *
=Yellow-billed loon= _(G. adamsii)_[26] Alaska (Cottam and Knappen 1939) * * Alaska (Bailey 1922)
=Arctic loon= _(G. arctica)_[27] Vancouver Island (Palmer 1962) x Vancouver Island (Robertson, unpublished data) x California (Palmer 1962) Denmark (Madsen 1957) * o
=Red-throated loon= _(G. stellata)_[28] Oregon (Palmer 1962) No. Atlantic (Palmer 1962) Denmark (Madsen 1957) * o
=Western grebe= _(Aechmophorus occidentalis)_ Vancouver Island (Munro 1941) o * x Vancouver Island (Robertson, unpublished data) x Puget Sound (Phillips and Carter 1957) x Washington (Chatwin 1956) * x California (Palmer 1962) o * x x
=Red-necked grebe= _(Podiceps grisegena)_ Pribilof Islands (Preble and McAtee 1923) o Vancouver Island (Wetmore 1924) Vancouver Island (Munro 1941) x o E. No. America (Wetmore 1924) o * o
=Horned grebe= _(P. auritus)_[29] Pribilof Islands (Preble and McAtee 1923) x o W. No. America (Wetmore 1924) x x * Vancouver Island (Munro 1941) x x Denmark (Madsen 1957) o o o
=Eared grebe= _(P. nigricollis)_[30] W. No. America (Wetmore 1924) * x * Vancouver Island (Munro 1941) x x o Denmark (Madsen 1957) x *
Table Headings:
FISH L - Zoarchid M - Gadid N - Fundulus O - Gasterosteus P - Sebastes Q - Cattid R - Cymatogaster S - Stichaeid T - Ammodytes U - Gobiid Location L M N O P Q R S T U
=Common loon= _(Gavia immer)_ Alaska (Palmer 1962) o o o Vancouver Island (Munro and Clemens 1931) Denmark (Madsen 1957) o x * o
=Yellow-billed loon= _(G. adamsii)_[26] Alaska (Cottam and Knappen 1939) o x Alaska (Bailey 1922) x
=Arctic loon= _(G. arctica)_[27] Vancouver Island (Palmer 1962) Vancouver Island (Robertson, unpublished data) California (Palmer 1962) x Denmark (Madsen 1957) * x x * x *
=Red-throated loon= _(G. stellata)_[28] Oregon (Palmer 1962) x No. Atlantic (Palmer 1962) x x o Denmark (Madsen 1957) * x o * * o
=Western grebe= _(Aechmophorus occidentalis)_ Vancouver Island (Munro 1941) x Vancouver Island (Robertson, unpublished data) x Puget Sound (Phillips and Carter 1957) * o o o Washington (Chatwin 1956) California (Palmer 1962) x *
=Red-necked grebe= _(Podiceps grisegena)_ Pribilof Islands (Preble and McAtee 1923) Vancouver Island (Wetmore 1924) x Vancouver Island (Munro 1941) x E. No. America (Wetmore 1924) o x
=Horned grebe= _(P. auritus)_[29] Pribilof Islands (Preble and McAtee 1923) W. No. America (Wetmore 1924) o o Vancouver Island (Munro 1941) o o * Denmark (Madsen 1957) o
=Eared grebe= _(P. nigricollis)_[30] W. No. America (Wetmore 1924) o Vancouver Island (Munro 1941) Denmark (Madsen 1957) o
Table 8. _Diets of albatrosses and petrels in different localities (x = major prey, o = minor prey, and * = incidental prey species)._
Key: CRUSTACEAN A: Euphausiid B: Amphipod C: Copepod D: Decapod E: Larvae F: Barnacle
FISH G: "Fish" H: _Engraulis_ I: Myctophid J: _Sebastes_ K: _Ammodytes_ L: Carrion, fish offal M: Fish eggs
----------------------------------------------------------------------------- |CRUSTACEAN | |COELENTERATE | | |ECHINODERM | | | |CEPHALOPOD Location Diet |A|B|C|D|E|F| | | | --------------------------------------------------------------------- =Black-footed albatross= _(Diomedea nigripes)_ No. Pacific (Palmer 1962) x Aleutian Islands (Cottam and Knappen 1939) o x o California (Miller 1936, 1940) o o x =Laysan albatross= _(D. immutabilis)_ No. Pacific (Palmer 1962; Bartsch 1922; Fisher 1904) x =Northern fulmar= _(Fulmarus glacialis)_ Pribilof Islands (Preble and McAtee 1923) o x Alaska (Gabrielson and Lincoln 1959) x x Oregon (Gabrielson and Jewett 1940) x No. Atlantic (Hartley and Fisher 1936; Einarsson 1945; Fisher 1952) x =Flesh-footed shearwater= _(Puffinus carneipes)_ Australia (Oliver 1955; Serventy et al. 1971) x x =Pink-footed shearwater= _(P. creatopus)_ California (Murphy 1936; Ainley, personal observation) x E. Pacific (Cottam and Knappen 1939) x =Buller's shearwater= _(P. bulleri)_ SW Pacific (Falla 1934; Serventy et al. 1971) x x Peru (Murphy 1936) x =Sooty shearwater= _(P. griseus)_ Aleutian Islands (Sanger, personal observation) x x British Columbia (Martin 1942; Sealy 1973_a_) x Oregon (Gabrielson and Jewett 1940) x California (Ainley, personal observation) x Peru (Murphy 1936) x x SW Pacific (Oliver 1955; Serventy et al. 1971) x x =Short-tailed shearwater= _(P. tenuirostris)_ Bristol Bay (Bartonek, personal communication) x Alaska (Cottam and Knappen 1939) x x x No. Pacific (Palmer 1962; Kuroda 1955) x x Australia (Serventy et al. 1971) x x Bass Strait (Sheard 1953) x =Mottled petrel= _(Pterodroma inexpectata)_ Pacific Ocean (Imber 1973) E. No. Pacific (Kuroda 1955) =Fork-tailed storm-petrel=_(Oceanodroma furcata)_ Pribilof Islands (Preble and McAtee 1923) SE Alaska (Heath 1915) x British Columbia (Martin 1942) California (Ainley, personal observation) =Leach's storm-petrel= _(O. leucorhoa)_ SE Alaska (Heath 1915) x California (PRBO, unpublished data) x x x So. California (Palmer 1962) x No. Atlantic[31] (Palmer 1962) x x x ---------------------------------------------------------------------
---------------------------------------------------------------- |FISH Location Diet|G|H|I|J|K|L|M ---------------------------------------------------------------- =Black-footed albatross= _(Diomedea nigripes)_ No. Pacific (Palmer 1962) x x Aleutian Islands (Cottam and Knappen 1939) x x California (Miller 1936, 1940) x x x =Laysan albatross= _(D. immutabilis)_ No. Pacific (Palmer 1962; Bartsch 1922; Fisher 1904) =Northern fulmar= _(Fulmarus glacialis)_ Pribilof Islands (Preble and McAtee 1923) Alaska (Gabrielson and Lincoln 1959) x Oregon (Gabrielson and Jewett 1940) No. Atlantic (Hartley and Fisher 1936; Einarsson 1945; Fisher 1952) x =Flesh-footed shearwater= _(Puffinus carneipes)_ Australia (Oliver 1955; Serventy et al. 1971) x =Pink-footed shearwater= _(P. creatopus)_ California (Murphy 1936; Ainley, personal observation) x E. Pacific (Cottam and Knappen 1939) x =Buller's shearwater= _(P. bulleri)_ SW Pacific (Falla 1934; Serventy et al. 1971) x Peru (Murphy 1936) =Sooty shearwater= _(P. griseus)_ Aleutian Islands (Sanger, personal observation) x British Columbia (Martin 1942; Sealy 1973_a_) x x Oregon (Gabrielson and Jewett 1940) California (Ainley, personal observation) x Peru (Murphy 1936) x SW Pacific (Oliver 1955; Serventy et al. 1971) x =Short-tailed shearwater= _(P. tenuirostris)_ Bristol Bay (Bartonek, personal communication) Alaska (Cottam and Knappen 1939) o No. Pacific (Palmer 1962; Kuroda 1955) x Australia (Serventy et al. 1971) x Bass Strait (Sheard 1953) =Mottled petrel= _(Pterodroma inexpectata)_ Pacific Ocean (Imber 1973) x E. No. Pacific (Kuroda 1955) x =Fork-tailed storm-petrel= _(Oceanodroma furcata)_ Pribilof Islands (Preble and McAtee 1923) x SE Alaska (Heath 1915) British Columbia (Martin 1942) x California (Ainley, personal observation) x =Leach's storm-petrel= _(O. leucorhoa)_ SE Alaska (Heath 1915) California (PRBO, unpublished data) x x So. California (Palmer 1962) x No. Atlantic[31] (Palmer 1962) x x ----------------------------------------------------------------
Table 9. _Diets of gulls in different localities (x = major prey, o = minor prey, and * = incidental prey species)._
Key: CRUSTACEAN A: Euphausiid B: Barnacle C: Decapod
MOLLUSC D: Shell fish E: Cephalopod
FISH F: "Fish" G: _Clupea_ H: _Engraulis_ I: _Osmerus_ J: _Porichihys_ K: _Otaphidium_ L: _Mallotus_ M: _Borrogadus_ N: _Microgadus_ O: _Gadus_ P: _Lycodes_ Q: _Sebastes_ R: _Myxocephalus_ S: _Genyonemus_ T: Embiotocid U: _Ammodytes_
BIRD V: Eggs X: Chicks Y: Adults
|CRUSTACEAN | |POLYCHAETE | | |MOLLUSC | | | |ECHINODERM | | | | |COELENTERATE | | | | | |FISH Diet | | | | | | Location |A|B|C| |D|E| | |F|G|H|I| --------------------------------------------------------------------------- =Glaucous gull= _(Larus hyperboreus)_ St. Lawrence Island (Fay and Cade 1959) Chukchi Sea (Swartz 1966) x x x Pribilof Islands (Preble and McAtee 1923) x x x x Vancouver Island (Munro and Clemens 1931) x =Glaucous-winged gull= _(L. glaucescens)_[32] Pribilof Islands (Preble and McAtee 1923) x x x Alaska (Bent 1921) No. Pacific (Sanger 1973) x * * Mandarte Island (Ward 1973) x x x Vancouver Island (Munro and Clemens 1931; x x Robertson, unpublished data) =Western gull= _(L. occidentalis)_[33] Farallon Islands (PRBO, unpublished data) x x o * x * * x =Herring gull= _(L. argentatus)_ No. Atlantic (Zelikman 1961) x E. No. America (Bent 1946; Ainley, x x x x x personal observation) Vancouver Island (Munro and Clemens 1931) x x =Mew gull= _(L. canus)_ Alaska (Bent 1921) x Vancouver Island (Munro and Clemens 1931) x x =Heermann's gull= _(L. heermanni)_ California (Bent 1921) x x x =Bonaparte's gull= _(L. philadelphia)_ E. No. America (Bent 1921) x x x =Black-legged kittiwake= _(Rissa tridactyla)_[34] Chukchi Sea (Swartz 1966) o * o Pribilof Islands (Preble and McAtee 1923) o x Alaska (Bent 1921) x Cook Inlet[35] (Snarski, personal o o o communication) No. Atlantic (Hartley and Fisher x 1936; Zelikman 1961) =Red-legged kittiwake= _(R. breuirostris)_ Pribilof Islands (Preble and McAtee 1923) x x x =Sabine's gull= _(Xenia sabini)_ Pt. Barrow (Banner 1954) x --------------------------------------------------------------------------- Location Diet |J|K|L|M|N|O|P|Q|R|S|T|U| ----------------------------------------------------------------------------- =Glaucous gull= _(Larus hyperboreus)_ St. Lawrence Island (Fay and Cade 1959) Chukchi Sea (Swartz 1966) x x Pribilof Islands (Preble and McAtee 1923) Vancouver Island (Munro and Clemens 1931) =Glaucous-winged gull= _(L. glaucescens)_[32] Pribilof Islands (Preble and McAtee 1923) Alaska (Bent 1921) No. Pacific (Sanger 1973) Mandarte Island (Ward 1973) x Vancouver Island (Munro and Clemens 1931; Robertson, unpublished data) =Western gull= _(L. occidentalis)_[33] Farallon Islands (PRBO, unpublished data) x o o o x o o =Herring gull= _(L. argentatus)_ No. Atlantic (Zelikman 1961) E. No. America (Bent 1946; Ainley, personal observation) Vancouver Island (Munro and Clemens 1931) =Mew gull= _(L. canus)_ Alaska (Bent 1921) x Vancouver Island (Munro and Clemens 1931) =Heermann's gull= _(L. heermanni)_ California (Bent 1921) =Bonaparte's gull= _(L. philadelphia)_ E. No. America (Bent 1921) =Black-legged kittiwake= _(Rissa tridactyla)_[34] Chukchi Sea (Swartz 1966) o x o o x Pribilof Islands (Preble and McAtee 1923) Alaska (Bent 1921) Cook Inlet[35] (Snarski, personal x o x communication) No. Atlantic (Hartley and Fisher 1936; Zelikman 1961) =Red-legged kittiwake= _(R. breuirostris)_ Pribilof Islands (Preble and McAtee 1923) =Sabine's gull= _(Xenia sabini)_ Pt. Barrow (Banner 1954) ----------------------------------------------------------------------------- Diet |CARRION-OFFAL | |BIRD | | |FISH EGGS Location | |V|X|Y| ---------------------------------------------------------------------- =Glaucous gull= _(Larus hyperboreus)_ St. Lawrence Island (Fay and Cade 1959) x x x Chukchi Sea (Swartz 1966) x x Pribilof Islands (Preble and McAtee 1923) x Vancouver Island (Munro and Clemens 1931) x =Glaucous-winged gull= _(L. glaucescens)_[32] Pribilof Islands (Preble and McAtee 1923) x x x x Alaska (Bent 1921) x No. Pacific (Sanger 1973) Mandarte Island (Ward 1973) x Vancouver Island (Munro and Clemens 1931; x Robertson, unpublished data) =Western gull= _(L. occidentalis)_[33] Farallon Islands (PRBO, unpublished data) x o o o =Herring gull= _(L. argentatus)_ No. Atlantic (Zelikman 1961) E. No. America (Bent 1946; Ainley, x * o x personal observation) Vancouver Island (Munro and Clemens 1931) x =Mew gull= _(L. canus)_ Alaska (Bent 1921) x x Vancouver Island (Munro and Clemens 1931) x =Heermann's gull= _(L. heermanni)_ California (Bent 1921) x =Bonaparte's gull= _(L. philadelphia)_ E. No. America (Bent 1921) =Black-legged kittiwake= _(Rissa tridactyla)_[34] Chukchi Sea (Swartz 1966) Pribilof Islands (Preble and McAtee 1923) o Alaska (Bent 1921) o Cook Inlet[35] (Snarski, personal communication) No. Atlantic (Hartley and Fisher 1936; Zelikman 1961) =Red-legged kittiwake= _(R. breuirostris)_ Pribilof Islands (Preble and McAtee 1923) =Sabine's gull= _(Xenia sabini)_ Pt. Barrow (Banner 1954) ----------------------------------------------------------------------
=Table 10=. _Diets of terns in different localities (x = major prey species)._
------------------------------------------------------------------------ CRUSTACEAN FISH ------------------------------------------------------------------------ |"Crustacean"|_Mallotus_ | |Euphausiid| |Cottid Diet | | |Amphipod| | |_Ammodytes_ Location | | | | | | larvae ------------------------------------------------------------------------ =Arctic tern= _(Sterna paradisaea)_ Pribilof Islands (Preble and McAtee 1923) x x Alaska (Bent 1921) x x x No. Atlantic (Hartley and Fisher 1936) x =Common tern= _(S. hirundo)_ E. No. America (Bent 1921) x x ------------------------------------------------------------------------
The oceanic habitat includes waters of the photic zone overlying the deep ocean and continental slopes beyond the continental or insular shelves. The Bering Sea and central subarctic domains are largely made up of oceanic habitat. The other three domains include both inshore and offshore neritic as well as some oceanic habitat. The boundary between the inshore and offshore neritic has yet to be defined in terms of bird life, but it lies at that line beyond which the bottom is too deep for a diving bird to exploit. A depth contour thus defines the boundary. In the antarctic South Pacific, emperor penguins _(Aptenodytes fosteri)_ dive to depths of 275 m, but so far as is known, no comparable bird exists in the North Pacific. Some marine ducks and loons reportedly dive to 50-60 m (Kooyman 1974). The inshore-offshore neritic boundary for seabirds may lie near the 70-m depth contour.
Food resource partitioning by seabirds in the five oceanographic domains are shown in Tables 11-15. Within each domain, the common and usual members of the seabird community are listed, and the major and minor categories in each of their diets are shown (on the basis of available literature, Tables 1-10). The categories are grouped further, and rather tenuously, according to the trophic level at which a bird is presumably feeding: I = herbivore, II = secondary carnivore, III = tertiary carnivore, IV = final carnivore, and Sc = scavengers (carnivorous) feeding at many levels. Birds at level I feed on large algae and seed plants and are not directly part of the same food webs involving other species. These food webs originate with phytoplankton (Fig. 2). So far as is known, no bird feeds on phytoplankton and few, if any, feed on microzooplankton; hence birds do not generally feed as primary carnivores. An exception at times might be the least auklet _(Aethia pusilla)_ when it feeds on small copepods (see Bédard 1969_b_).
The above groupings are "tenuous" because prey in each category may represent more than one trophic level, and a single prey species could occur at one level one day or place and at another level the next day or place, depending upon what it happened to be eating. This is shown in Fig. 2, where the parakeet auklet _(Cyclorrhynchus psittaculus)_ can occur in the food web at different levels, depending both on the prey it is eating and on what its prey is eating. Even without this complication, many seabirds feed at more than one level in the food web. For instance, murres eating euphausiids would be feeding at a different level than murres feeding on larger fish. It might be "safer" to regard prey organisms in level II as macrozooplankton, prey organisms in level III as micronekton, and prey organisms (seabirds themselves) in level IV as macronekton (after Sverdrup et al. 1942).
[Illustration: Fig. 2. Schematic food web of the parakeet auklet in the eastern Bering Sea (based on Bédard 1969_a_ and Dunbar 1946). Arrow sizes indicate relative importance of prey and Roman numerals refer to prey sizes (see text).]
Table 11. _Use of food resources by seabirds in the Bering Sea coastal domain._ Information is from Tables 1-10. (Trophic level I = plants, II = secondary carnivore, III = tertiary carnivore, IV = upper level carnivore [on birds only in this table], Sc = scavenger on carrion, offal, or detritus [II-IV]; x = major food in diet, o = minor food, * = incidental food, ? = probable food.)
----------------------------------------------------------------------------- Habitat, bird trophic levels (I-IV. Sc), and food categories ----------------------------------------------------------------------------- Oceanic and offshore neritic Inshore neritic Inshore neritic ----------------------------------------------------------------------------- Key: II II III A. Crustacean J. Crustacean, midwater R. Fish, midwater B. Polychaete K. Crustacean, benthic S. Fish, benthic C. Coelenterate L. Coelenterate T. Cephalopod D. Fish/squid eggs & larvae M. Echinoderm IV. U. Birds III N. Mollusc Sc. V. Carrion/offal/ E. Fish Q. Fish/squid eggs & larvae detritus F. Cephalopod IV G. Birds Sc H. Carrion/offal/detritus I I. Plant
Seabirds | A B C D| E F G H I| J K L |M N Q |R S T |U V | ----------------------------------------------------------------------------| _Gavia adamsii_ * o x _G. arctica_ o x _Podiceps grisegena_ o o x _Diomedea nigripes_ x o o o x x x _Fulmarus glacialis_ x o x o x x x _Puffinus griseus_ x x x o o _P. tenuirostris_ x o x o o _Oceanodroma furcata_ x o o x x x x _Phalacrocorax auritus_ o x o _P. pelagicus_ x x _P. urile_ x x _Branta bernicla_ x _Philacte canagica_ x _Clangula hyemalis_ o x o o _Histrionicus histrionicus_ o x o _Polysticta stelleri_ o x o o _Samateria mollissima_ x o x _S. spectabilis_ o o o x _S. fischeri_ x x _Melanitta deglandi_ x o _M. nigra_ o o x _Haliaeetus leucocephalus_ x x x _Falco peregrinus_ x _Phalaropus fulicarius_ x x o x x _Lobipes lobatus_ x x o x x _Stercorarius_ spp. o x x ? x x x x _Larus hyperboreus_ o o o o o o o o o o x x x _L. glaucescens_ o o o o o o o o o o x x x _L. argentatus_ o o o o o o o o o o x o x _L. canus_ x o o o x x _Rissa tridactyla_ x x x o _Xema sabini_ x x o o _Sterna paradisaea_ x x o o _Uria aalge_ x o x x o o x o _U. lomvia_ x o x x o x o x _Lunda cirrhata_ ? x x _Fratercula corniculata_ * x x _Cepphus columba_ o x o _Synthliboramphus antiquus_ x x o _Brachyramphus brevirostris_ x o _Cyclorrhynchus psittaculus_ x o * * _Aethia cristatella_ x x _A. pusilla_ x o -----------------------------------------------------------------------------
Table 12. _Use of food resources by seabirds in the oceanic and offshore neritic habitats, Bering Sea domain._ Information is from Tables 1-10. (Trophic level I = plants, II = secondary carnivore, III = tertiary carnivore, IV = upper level carnivore; Sc = scavenger on carrion, offal, or detritus [II-IV]; x = major food in diet, o = minor food, * = incidental food, ? = probable food.)
Bird trophic levels and food categories
II III IV Sc --------------------------------------------------------------------------- Fish/Squid eggs & Larvae | Fish Coelenterate | | | Cephalopod Polychaete | | | | | Birds Crustacean | | | | | | | Carrion/offal Seabirds | | | | | | | | | /detritus --------------------------------------------------------------------------- _Diomedea nigripes_ x o o o x x x _D. immutabilis_ x _Fulmarus glacialis_ x o x o x x x _Puffinus griseus_ x x x _P. tenuirostris_ x o x _Pterodroma inexpectata_ x x _Oceanodroma furcata_ x o o x x x x _Phalaropus fulicarius_ x x o _Lobipes lobatus_ x x o _Stercorarius_ spp. o x x ? x _Larus hyperboreus_ x o o o x x ? x _L. glaucescens_ x o o o x x ? x _Rissa tridactyla_ x x x o _R. brevirostris_ x x x o _Xema sabini_ x x o o _Sterna paradisaea_ x x o o _Uria aalge_ x o x x _U. lomvia_ x o x x _Lunda cirrhata_ ? x x _Fratercula corniculata_ * x x _Synthliboramphus antiquus_ x x _Cyclorrhynchus psittaculus_ x o * * _Aethia cristatella_ x x _A. pusilla_ x o _A. pygmaea_ x -----------------------------------------------------------------------------
Information contained in Tables 11-15 can be summarized to show characteristics of seabird trophic relations. One such characteristic is the range of diet breadth or diet complexity (Table 16). Few species (about 6%) feed on only one type of prey and might, therefore, be referred to as "specialists." Included are eared grebe _(Podiceps caspicus)_, Laysan albatross, brown pelican, emperor goose _(Philacte canagica)_, black brant _(Bernicia bernicla)_, peregrine falcon, and whiskered auklet _(Aethia pygmaea)_. Consideration of these species as specialists may require revision when more data become available. Except for the albatross and auklet, these species are members of the inshore neritic cohort. Food specialization does not seem to be characteristic of oceanic birds in particular or of most seabirds in general.
Table 13. _Use of food resources by seabirds in the Alaska Stream domain._ Information is from Tables 1-10. (Trophic level I = plants, II = secondary carnivore, III = tertiary carnivore, IV = upper level carnivore, Sc = scavenger on carrion, offal, or detritus [II-IV]; x = major food in diet, o = minor food, * = incidental food, ? = probable food.)
---------------------------------------------------------------------------- Habitat, bird trophic levels (I-IV. Sc), and food categories
Key: Oceanic and offshore neritic II A: Crustacean B: Polychaete C: Coelenterate D: Fish/squid eggs & larvae
III E: Fish F: Cephalopod
IV G: Birds
Sc H: Carrion/offal/detritus
I I: Plant
Inshore neritic II J: Crustacean, midwater K: Crustacean, benthic L: Coelenterate M: Echinoderm IV: N: Mollusc Sc: Q: Fish/squid eggs & larvae
III R: Fish, midwater S: Fish, benthic T: Cephalopod
IV U: Birds
Sc V: Carrion/offal/detritus
Seabirds A B C D E F G H I J K L M N Q R S T U V ---------------------------------------------------------------------------- _Gavia immer_ * x x _G. adamsii_ * o x _G. stellata_ * o x _Podiceps grisegena_ o x o _Diomedea nigripes_ x o o o x x x _Fulmarus glacialis_ x o x o x x x _Puffinus griseus_ x x x o _P. tenuirostris_ x o x o _Pterodroma inexpectata_ x x _Oceanodroma furcata_ x o o x x x x _Phalacrocorax auritus_ o x o _P. pelagicus_ x x _P. urile_ x x _Philacte canagica_ x _Clangula hyemalis_ o x o _Histrionicus histrionicus_ x x o _Polysticta stelleri_ o x o o _Somateria mollissima_ x o x _S. spectabilis_ o o x _S. fischeri_ x x _Melanitta deglandi_ x o _M. perspicillata_ o x o _M. nigra_ o o x _Mergus serrator_ o x x _Haliaeetus leucocephalus_ x x x _Falco peregrinus_ x _Phalaropus fulicarius_ x x o x x _Lobipes lobatus_ x x o x x _Stercorarius_ spp. o x x ? x x x x _Larus hyperboreus_ o o o o o o o o o o x x x _L. glaucescens_ o o o o o o o o o o x x x _L. argentatus_ o o o o o o o o o o x o x _L. canus_ x o o o x x _Rissa tridactyla_ x x x o _R. brevirostris_ x x x o _Sterna paradisaea_ x x o o x o _S. aleutica_ x o _Uria aalge_ x o x x o o x o _U. lomvia_ x o x x o x o x _Lunda cirrhata_ ? x x _Fratercula corniculata_ * x x _Cepphus columba_ o x o _Brachyramphus marmoratus_ x o x _B. brevirostris_ x o _Synthliboramphus antiquus_ x x x _Cyclorrhynchus psittaculus_ x o * * _Aethia cristatella_ x x _A. pusilla_ x o _A. pygmaea_ x
Table 14. _Use of food resources by seabirds in the oceanic habitat, central subarctic domain._ Information is from Tables 1-10. (Trophic level I = plants, II = secondary carnivore, III = tertiary carnivore, IV = upper level carnivore, Sc = scavenger on carrion, offal, or detritus [II-IV]; x = major food in diet, o = minor food, * = incidental food, ? = probable food.)
-------------------------------------------------------------------- Bird trophic levels and food categories --------------------------------------- II III IV Sc -------------- ------- --- ------------ |Crustacean | |Polychaete | | |Coelenterate | | | |Fish/squid eggs & larvae | | | | |Fish | | | | | |Cephalopod | | | | | | |Birds Seabirds | | | | | | | |Carrion/offal/ | | | | | | | | detritus -------------------------------------------------------------------- _Diomedea nigripes_ x o o o x x x _D. immutabilis_ x _Fulmarus glacialis_ x o x o x x x _Puffinus carneipes_ o x x _P. griseus_ x x x _P. tenuirostris_ x o x _Pterodroma inexpectata_ x x _Oceanodroma furcata_ x o o o x x x _O. leucorhoa_ x o o o x x x _Phalaropus fulicarius_ x x o _Lobipes lobatus_ x x o _Stercorarius_ spp. o x x ? x _Larus hyperboreus_ x o o o x x ? x _L. glaucescens_ x o o o x x ? x _L. argentatus_ x o o o x x x _Rissa tridactyla_ x x x o _Xema sabini_ x x o o _Sterna paradisaea_ x x o o _Uria aalge_ x * x x _U. lomvia_ x * x x _Lunda cirrhata_ o x x _Fratercula corniculata_ * x x _Cerorhinca monocerata_ x x _Synthliboramphus antiquus_ x x _Cyclorrhynchus psittaculus_ x o * * _Ptychoramphus aleuticus_ x o --------------------------------------------------------------------
Most species (roughly 53% in any community) include two or three prey categories in their diets--usually midwater schooling fish, squid, and crustaceans. These birds include the most numerous in the communities--the shearwaters and some alcids--which feed largely on three prey types, and also include some of the less abundant birds, the marine ducks, which feed mostly on two prey categories.
The remaining seabirds are more general in their feeding. Many have large populations, but are not as abundant as shearwaters or most alcids. The true "generalists" are the species that feed on as many as eight or more types of prey, and relatively few (12%) such species exist in each avian community. These birds, the scavengers, include black-footed albatross, fulmar, storm-petrels, and large gulls. The petrels are the scavengers of the oceanic habitat and the gulls are their counterparts in the neritic habitat (but see Sanger 1973).
Another comparison is shown in Table 17, where the species in each community are categorized according to the number feeding at each trophic level. If a species feeds at more than one level, it is tallied once in each level. Most seabirds (66-77%) feed at the second and third levels as secondary and tertiary carnivores. Few feed as terminal carnivores, and relatively few are scavengers. Actually, most scavenging occurs at levels II and III, so about 90% of the seabirds in each community feed at levels II and III. Communities including an inshore neritic feeding element are the only ones that include herbivores, and even then, few of these species exist in significant numbers in the marine environment (discounting estuaries and sheltered bays).
Table 15. _Use of food resources by seabirds in the North American coastal domain._ Information is from Tables 1-10. (Trophic level I = plants, II = secondary carnivore, III = tertiary carnivore, IV = upper level carnivore, Sc = scavenger on carrion, offal, or detritus [II-IV]; x = major food in diet, o = minor food, * = incidental food, ? = probable food.)
----------------------------------------------------------------- Habitat, bird trophic levels (I-IV, Sc), and food categories ----------------------------------------------------------------- Key: Oceanic and offshore neritic II A: Crustacean B: Polychaete C: Coelenterate D: Fish-squid eggs & larvae
III E: Fish F: Cephalopod
IV G: Birds
Sc H: Carrion/offal/detritus
I I: Plant
Inshore neritic II J: Crustacean, midwater K: Crustacean, benthic L: Coelenterate M: Echinoderm N: Mollusc O: Fish/squid eggs & larvae
III P: Fish, midwater Q: Fish, benthic R: Cephalopod
IV S: Birds
Sc T: Carrion/offal/detritus
Seabirds A B C D E F G H I J K L M N O P Q R S T ---------------------------+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- _Gavia immer_ * x x _G. adamsii_ * o x _G. arctica_ o x _G. stellata_ o x _Podiceps grisegena_ o x o _P. nigricollis_ x o _P. auritus_ x x o _Aechmophorus occidentalis_ o x x _Diomedea nigripes_ x o o o x x x _Fulmarus glacialis_ x o x o x x x _Puffinus creatopus_ o x x _P. carneipes_ o x x _P. bulleri_ x x x _P. griseus_ x x x o o o _P. tenuirostris_ x o x o o o _Oceanodroma furcata_ x o o o x x x _Pelecanus occidentalis_ x _Phalacrocorax auritus_ o x o _P. penicillatus_ o x _P. pelagicus_ x x _Branta bernicla_ x _Clangula hyemalis_ o x o o _Histrionicus histrionicus_ o x o _Melanitta deglandi_ x o o _M. perspicillata_ o x o _M. nigra_ * o o x _Mergus serrator_ * x x _Haliaeetus leucocephalus_ x x x _Falco peregrinus_ x _Phalaropus fulicarius_ x x o x x o _Lobipes lobatus_ x x o x x o _Stercorarius_ spp. o x x ? x x x o x _Larus hyperboreus_ o o o o ? o o o o o o x x x _L. glaucescens_ o o o o ? o o o o o x x x x _L. occidentalis_ x x x x o x o o o * * x x o x _L. argentatus_ o o o o o x o o o o o x o x _L. heermanni_ x x x _L. canus_ x o o o x x x _L. philadelphia_ x x o _Rissa tridactyla_ x x x o _Xema sabini_ x x o o _Sterna paradisaea_ x x o o _S. hirundo_ o x _Uria aalge_ x o x x o x o _U. lomvia_ x o x x o x o x _Lunda cirrhata_ ? x x _Fratercula corniculata_ * x x _Cerorhinca monocerata_ x x _Cepphus columba_ o x o _Brachyramphus marmoratus_ x o x _B. brevirostris_ x o _Synthliboramphus antiquus_ x x o _Ptychoramphus aleuticus_ x x ---------------------------+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Table 16. _Number of seabirds of different oceanographic regions having different numbers of categories of food in their diets._
---------------------------------------------------------------------------- Number of categories in the diets[36] ------------------------------------ Oceanographic region (domain) 1 2 3 4 5-7 7 8+ ---------------------------------------------------------------------------- Bering Sea coastal 3 11 9 6 5 4 5 Bering Sea 2 6 5 7 0 5 0 Alaskan Stream 3 14 14 5 4 4 5 Central Subarctic 1 6 8 4 0 7 0 North American Coastal 3 14 17 6 3 4 6 Total 12 51 53 28 12 24 16 Percent total species (196) 6 26 27 14 6 12 8 ----------------------------------------------------------------------------
It is readily apparent from the foregoing comparisons that much overlap exists in the prey eaten by seabirds within each community. The question whether real competition ever exists is academic. Competition perhaps exists only rarely because seabirds partition resources through use of different feeding methods, selection of different-sized prey, and habitat zonation. Table 18 lists feeding methods (after Ashmole 1971 and Ainley 1977) and the body size and bill length of each species considered in this review. Bill length is usually related directly to body size (Ashmole 1968; Bédard 1969_b_), but note, for instance, that the longer species of the two kittiwakes has the shorter bill. Body weight would be a better measure of relative size than body size, but few reliable weight data are available for seabirds.
The use of different feeding methods by species in each community grossly assigns birds to feeding at different depths. Thus, whereas shearwaters, puffins, and small gulls (_Xema_ sp., _Rissa_ spp.) overlap almost entirely in prey categories and even prey species, the gulls can capture these organisms only at the surface; the shearwaters capture them at shallow depths; and the puffins capture them at much deeper depths. Direct field observations of this phenomenon are few but Gould (1971) and Sealy (1973_a_) compared the diets of birds feeding in mixed-species flocks. An example of how even finer divergence in feeding methods helps to partition food resources has been provided by Spring (1971) in his comparison of the two murres. Both species feed by diving to great depths, but the thick-billed murre is able to hover over the bottom and thereby is better able to capture benthic organisms.
Table 17. _Number of species feeding at different trophic levels within seabird communities and habitats of the northeastern North Pacific Ocean and Bering Sea._ A single species can be represented in more than one level. (Trophic level I = vegetarian, II = secondary carnivore, III = tertiary carnivore, IV = upper level carnivore, Sc = scavenger [II-IV].)
------------------------------------------------------------------------------ Oceanic/offshore neritic Inshore neritic ------------------------- ---------------------------- Domain II III IV Sc I II III IV Sc ------------------------------------------------------------------------------ Bering Sea Coastal 11 17 1? 10 6 23 18 6 6 Bering Sea 22 21 3? 11 -- -- -- -- -- Alaska Stream 21 19 1? 12 5 28 21 6 6 Central Subarctic 23 22 3? 12 -- -- -- -- -- North American Coastal 25 24 3? 11 3 28 35 7 10 Total 102 103 11? 56 14 79 74 19 22 Proportion 0.38 0.39 0.02[37]0.21 0.07 0.38 0.28 0.09 0.10 ------------------------------------------------------------------------------
Table 18. _Size relationships and feeding methods of major species in the eastern North Pacific and Bering Sea._ (D = dive, SS = surface seize, PP = pursuit plunge, Di = dip, P = plunge, T = tip, x = eats seabirds, A = piracy, SP = shallow plunge.)
-------------------------------------------------------------------- Body length[a] Bill length[b] Feeding[c] Species (cm) (mm) method -------------------------------------------------------------------- _Gavia adamsii_ 63.5 90-91 D _G. immer_ 61.0 80-82 D _G. arctica_ 45.7 51-52 D _G. stellata_ 43.5 51-52 D _Podiceps grisegena_ 33.0 48-50 D _P. nigricollis_ 22.9 24-26 D _P. auritus_ 24.1 23-24 D _Aechmophorus occidentalis_ 45.7 65-76 D _Diomedea nigripes_ 71.1 141-144 SS _D. immutabilis_ 71.1 102-112 SS _Fulmarus glacialis_ 45.7 36-37 SS _Puffinus carneipes_ 45.7 41-46 PP _P. creatopus_ 45.7 41-46 PP _P. bulleri_ 38.1 38-45 PP _P. griseus_ 40.3 41-42 PP _P. tenuirostris_ 38.1 31-32 PP _Oceanodroma furcata_ 19.0 15 Di,SS _O. leucorhoa_ 19.0 16 Di,SS _Pterodroma inexpectata_ 29.2 26-27 SS _Phalacrocorax auritus_ 68.6 55-57 D _P. penicillatus_ 73.7 66-71 D _P. urile_ 71.1 54-55 D _P. pelagicus_ 55.9 47-50 D _Pelecanus occidentalis_ 104.0 294-319 P _Branta_ spp. _(bernicla)_ 43.5 33-36 T _Philacte canagica_ 45.7 37-42 T _Anas_ spp. 40.0 32-35 T _Clangula hyemalis_ 38.1 25-27 D _Histrionicus histrionicus_ 30.5 25-28 D _Polysticta stelleri_ 30.5 37-43 D _Somateria mollisima_ 43.5 45-55 D _S. spectabilis_ 40.3 31-33 D _S. fischeri_ 38.1 22-26 D _Melanitta deglandi_ 35.6 41-44 D _M. perspicillata_ 40.3 ca. 40 D _M. nigra_ 35.6 42-47 D _Mergus serrator_ 40.3 45-54 D _Haliaeetus leucocephalus_ 80.0 52-54 X _Falco peregrinus_ 37.5 21-25 X _Phalaropus fulicarius_ 16.5 22 SS _Lobipes lobatus_ 15.2 22 SS _Stercorarius pomarinus_ 43.5 40 SS,A _S. parasiticus_ 40.3 32 SS,A _S. longicaudus_ 38.1 29 SS,A _Larus hyperboreus_ 61.0 55-60 SS _L. glaucescens_ 55.9 54-58 SS _L. occidentalis_ 53.0 54-57 SS,Di _L. argentatus_ 50.8 48-54 SS,Di _L. californicus_ 43.5 45-50 SS,Di _L. heermanni_ 38.1 42-46 SS,Di _L. canus_ 35.6 34-36 SS,Di _L. philadelphia_ 27.9 30-31 Di _Rissa tridactyla_ 34.2 39-40 Di _R. brevirostris_ 38.1 29-30 Di _Xema sabini_ 27.9 26-27 Di _Sterna paradisaea_ 38.1 31-33 Di,SP _S. hirundo/forsteri_ 35.6 36-39 Di,SP _S. aleutica_ 33.0 33 Di,SP _Uria aalge_ 35.6 43-47 D _U. lomvia_ 35.6 39-42 D _Lunda cirrhata_ 31.8 57-60 D _Fratercula corniculata_ 29.2 49-51 D _Cerorhinca monocerata_ 29.2 34-35 D _Cepphus columba_ 26.7 32-33 D _Brachyramphus marmoratus_ 20.3 15 D _B. brevirostris_ 19.0 10 D _Synthliboramphus antiquus_ 20.3 13 D _Ptychoramphus aleuticus_ 17.8 19 D _Aethia pygmaea_ 16.5 8-9 D _A. pusilla_ 13.3 8 D _A. cristatella_ 17.8 11 D _Cyclorrhynchus psittaculus_ 18.4 15 D --------------------------------------------------------------------
The scavengers (generalists) offer a good example of how a range of bird and bill sizes is usually represented among species having similar diets and feeding methods. The progression of oceanic scavenger sizes is graded rather evenly from the black-footed albatross down to the northern fulmar, to the scaled petrel, to the storm-petrel. All these species capture prey that occur only at or near the water surface. Recently Sanger (1973) reported appreciable numbers of glaucous-winged gulls _(Larus glaucescens)_ and herring gulls _(L. argentatus)_, noted neritic scavengers, out in the oceanic realm of the petrel. He presented limited data that suggested an overlap between the diet of these gulls and that of black-footed albatrosses, as noted by Miller (1940). It would not be surprising if these gulls were as much generalists in the oceanic habitat as they are in the neritic. Interestingly, their bill and body sizes fall between those of the albatross and the fulmar, thus in theory enabling them to invade the oceanic habitat without great competition. It is likely that their invasion occurred during historical times and is related to their habit of following fishing boats from shore out to sea (Sanger 1973). If so, the gulls might be assuming from other species part of a previously uncontested resource.
Another interesting group of species that shows close similarities in diet consists of the piscivorous loons, grebes, and mergansers. All these birds, including seven or eight species, apparently feed on fish occurring on or near the bottom in the inshore neritic habitat. Again, however, an even progression in size exists: yellow-billed loon _(Gavia adamsii)_, common loon _(G. immer)_, arctic loon _(G. arctica)_, red-throated loon _(G. stellata)_, western grebe _(Aechmophorus occidentalis)_, red-necked grebe _(Podiceps grisegena)_, and common merganser _(Mergus merganser)_. Most likely then, they select different-sized fish. Another example of this phenomenon is provided by the eight neritic gulls, which are largely scavengers and show a remarkably even progression in bill and body size. Finally, as shown clearly by Bédard (1969_a_, 1969_b_) and Harris (1970), alcids of different sizes select different-sized prey, often of the same species.
A final important way in which seabirds partition available resources is by inhabiting different zones. Zonation is especially evident during the breeding season when species common to the same breeding site sort themselves out according to the distances they range for food. This phenomenon was discussed by Murphy (1936), Shuntov (1974), Sealy (1972), Cody (1973), and Scott (1973).
Trophic Relations and Seabird Conservation
The species that appear to have specialized food habits (if further research confirms that indeed they do) are probably very sensitive to vagaries in food availability or are, at least, much more sensitive than other species. Some specialists which also have very restricted distributions would, therefore, be susceptible to localized catastrophes occurring where specialists are concentrated around the food resource. This is proved in the case of the scoters, which are both specialized and rather restricted to nearshore beds of molluscs and have fallen victim to local oil slicks (Smail et al. 1972). An example of another potentially critical situation is that of the black brant, which at certain times of the year concentrate their entire population around eelgrass beds in Bristol Bay, Alaska, where much offshore oil drilling may soon occur.
Birds adapted to feed by diving, with the exception of cormorants, spend most of their time in the water. These species are therefore most susceptible to oiling (Smail et al. 1972), but pursuit plungers (the shearwaters) are also highly susceptible (Point Reyes Bird Observatory, unpublished data). A characteristic of polar and subpolar seabird communities is the high percentage of birds that feed by diving and pursuit plunging. These birds are mostly absent from tropical and subtropical communities because feeding by these methods is not adaptive there (Ainley 1977). Hence, oil pollution has all the potential of rendering maladaptive the principal feeding methods of many polar seabirds.
Another way in which seabird feeding relates to conservation problems concerns competition between birds and man for commercially valuable fishes. A related problem is the mass mortality of seabirds due to man's fishing gear. An acute situation is the drowning of seabirds caught in salmon gill nets (Bartonek et al. 1974; Pacific Seabird Group 1975; Ripley 1975; King et al., this volume). Immediate action is definitely required.
Further, competition between birds and man for the same resource has the potential for disastrous effects on bird populations if humans out-compete the birds and overfish the resource. A classic example, reviewed by Idyll (1973), is the possible collapse of the Peruvian anchovy _(Engraulis ringens)_ fishery; if overfishing and an El Niño should coincide, the Peruvian seabird populations could collapse as well. The California fisheries and apparently the double-crested cormorants that nest on the Farallon Islands have both suffered from the demise of the Pacific sardine _(Sardinops caerulea)_ in the California current (Ainley and Lewis 1974). In regulating fish harvests, fishery organizations should include in their calculations the harvest by creatures other than man (Schaefer 1970), rather than evading the issue by referring to a vague "natural mortality."
* * * * *
Finally, fishing by humans can benefit seabirds by removing fish (or whales) that compete with birds for food (Laws 1977). A potential example is that of northern California, where salmon and seabirds both feed heavily on juvenile rockfishes (Fitch and Lavenberg 1971; Point Reyes Bird Observatory, unpublished data). Harvest of salmon should theoretically leave more rockfish available for birds to eat. This sort of situation has not yet been fully documented and definitely warrants further study, especially in such areas as the Bering Sea, where some fish stocks have become depressed due to overfishing (Gulland 1970).
Recommendations for Further Research
Many people realize intuitively that seabirds are important members of marine ecosystems. Although the supporting evidence is not now available, it will be needed if seabirds are to be protected. Emotion alone will not justify the protection of seabirds in an age when the human race moves steadily toward global famine. The job at hand is, in part, to sell seabirds, not just to the public, government officials, executives of oil companies, or fish-packing concerns, but also to marine biologists and oceanographers, for the scientists have the best means to study organisms at sea. We must move away from the concept that seabirds are merely yo-yos of various sizes, shapes, and colors on strings of various lengths that venture forth to sea from the land, grab a quick lunch, and then return to the safety of terra firma. Seabirds are marine organisms and deserve at least as much research attention as that currently given marine mammals.
The information now available on seabird diets is largely presented in terms of the number and volume of various prey species taken. Whereas these data provide the relative importance of prey, fishery data on prey stocks are usually measured in terms of biomass. Thus, it is difficult to relate seabird data to the immense wealth of information on biological oceanography. If we are to recognize the importance of seabirds in the nutrient and energy cycling of marine ecosystems, rather than considering them merely as "yo-yo predators," we must relate them to the total marine community.
The goal of marine ornithologists should be to refine and broaden considerably in detail such studies as those by Sanger (1972), Shuntov (1974), and Laws (1977), who attempted to assess the relations between seabird populations and stocks of other marine organisms for the northern North Pacific, the world oceans, and the Antarctic, respectively. The trophic roles played by seabirds must be studied in detail at the community level year-round before those analyses can be properly refined. Another exemplary work is that done by Brownell (1974), who studied trophic relations of higher vertebrates off Uruguay, including dolphins, pinnipeds, seabirds, and some large fish. In a review study, Sanger (1974) considered the food-chain relations of similar vertebrates in the Bering Sea. These sorts of studies will serve to bring the role of seabirds into perspective with other upper trophic level feeders.
Acknowledgments
We much appreciate the opportunity to participate in the symposium at which this paper was presented. The encouragement and help given by J. C. Bartonek was indispensable. D. G. Ainley's participation in the symposium was supported by the Point Reyes Bird Observatory. This is contribution No. 124 of the Point Reyes Bird Observatory.
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