Table 2. Food of marine ducks and geese (x = major prey, o = minor prey, and * = incidental prey species).[19]
LocationDiet[19]
PLANTSCRUS­TA­CEANSMOL­LUSCSECHI­NO­DERMSFISHFISH EGGS
Am­phi­podsDec­a­podsBar­na­clesMus­selsRock clamsRa­zor clamsOys­ters, Scal­lopsLit­tor­i­nidsChi­tons
Geesex
(Branta spp.)
Emperor goosex
(Philacte canagica)
Oldsquawo*******o
(Clangula hyemalis)
Harlequin duck*xxo**oo**
(Histrionicus histrionicus)
Steller's eiderox****o****
(Polysticta stelleri)
Common eider**x*o*oo*o*
(Somateria mollissima)
King eider**o*x*oo*x*
(S. spectabilis)
Spectacled eiderx*xo****
(S. fischeri)
White-winged scoter****ox*xo**oo
(Melanitta deglandi)
Surf scotero***x**xo***o
(M. perspicillata)
Black scotero**ox**x****
(M. nigra)
Red-breasted merganserx
(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 1969b; 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).
Lo­ca­tionDi­et
CRUS­TA­CEANO
C
T
O
P
U
S		FISH
A
m
p
h
i
p
o
d		I
s
o
p
o
d		D
e
c
a
p
o
d		P
e
t
r
o
m
y
z
o
n
t
i
d		C
h
i
m
a
e
r
i
d		C
l
u
p
e
i
d		O
s
m
e
r
i
d		G
a
d
i
d		G
a
s
t
e
r
o
s
t
e
i
d		S
c
o
r
p
a
e
n
i
d		C
o
t
t
i
d		A
g
o
n
i
d		E
m
b
i
o
t
o
c
i
d		B
a
t
h
y
m
a
s
t
e
r
i
d		C
l
i
n
i
d		C
r
y
p
t
a
c
a
n
t
h
o
d
i
d		C
e
b
i
d
i
c
h
t
h
y
i
d		S
t
i
c
h
a
e
i
d		P
h
o
l
i
d		A
m
m
o
n
d
y
t
i
d		B
o
t
h
i
d		P
l
e
u
r
o
n
e
c
t
i
d
Cape Thompson (Swartz 1966)oo
Pribilof Island (Preble and McAttee 1923)ooo
Mandarte Island (Drent 1965; Koelink 1972)oo*oxoo*o*oooooo
Vancouver Island (Munro and Clemens 1931)ooo
Olympic Peninsula (Thoresen and Booth 1958)oooo
Yaquina Head (Scott 1973)ooooo
Farallon Island (Follett and Ainley 1976)oo*xx*oooo

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.