Table 7. Diets of loons and grebes in different localities (x = major prey, o = minor prey, and * = incidental prey species).
LocationDiet
CRUSTACEANSPO­LY­CHAE­TEFISH
Eu­pha­us­idAm­phi­podMy­sidDe­ca­podAn­gu­il­laCla­peaSar­di­nopsSal­moTha­le­ich­thysA­the­ri­nopsZo­ar­chidGa­didFun­du­lusGa­ste­ro­ste­usSe­ba­stesCat­tidCy­ma­to­ga­sterSti­chae­idAm­mo­dy­tesGo­bi­id
Common loon (Gavia immer)
Alaska (Palmer 1962) * * o o o o o
Vancouver Island (Munro and Clemens 1931) x
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) x
Vancouver Island (Robertson, unpublished data) x
California (Palmer 1962) x
Denmark (Madsen 1957) * o * x x * x *
Red-throated loon (G. stellata)[28]
Oregon (Palmer 1962) x
No. Atlantic (Palmer 1962) x x o
Denmark (Madsen 1957) * o * x o * * o
Western grebe (Aechmophorus occidentalis)
Vancouver Island (Munro 1941) o * x x
Vancouver Island (Robertson, unpublished data) x x
Puget Sound (Phillips and Carter 1957) x * o o o
Washington (Chatwin 1956) * x
California (Palmer 1962) o * x x x *
Red-necked grebe (Podiceps grisegena)
Pribilof Islands (Preble and McAtee 1923) o
Vancouver Island (Wetmore 1924) x
Vancouver Island (Munro 1941) x o x
E. No. America (Wetmore 1924) o * o o x
Horned grebe (P. auritus)[29]
Pribilof Islands (Preble and McAtee 1923) x o
W. No. America (Wetmore 1924) x x * o o
Vancouver Island (Munro 1941) x x o o *
Denmark (Madsen 1957) o o o o
Eared grebe (P. nigricollis)[30]
W. No. America (Wetmore 1924) * x * o
Vancouver Island (Munro 1941) x x o
Denmark (Madsen 1957) x * o
Table 8. Diets of albatrosses and petrels in different localities (x = major prey, o = minor prey, and * = incidental prey species).
LocationDiet
CRUSTACEANCOE­LEN­TE­RA­TEE­CHI­NO­DERMCE­PHA­LO­PODFISH
Eu­pha­u­si­idAm­phi­podCo­pe­podDe­ca­podLar­vaeBar­na­cle"Fish"En­grau­lisMy­cto­phidSe­ba­stesAm­mo­dy­tesCar­ri­on, fish of­falFish eggs
Black-footed albatross (Diomedea nigripes)
No. Pacific (Palmer 1962)xxx
Aleutian Islands (Cottam and Knappen 1939)oxoxx
California (Miller 1936, 1940)ooxxxx
Laysan albatross (D. immutabilis)
No. Pacific (Palmer 1962; Bartsch 1922; Fisher 1904)x
Northern fulmar (Fulmarus glacialis)
Pribilof Islands (Preble and McAtee 1923)ox
Alaska (Gabrielson and Lincoln 1959)xxx
Oregon (Gabrielson and Jewett 1940)x
No. Atlantic (Hartley and Fisher 1936; Einarsson 1945; Fisher 1952)xx
Flesh-footed shearwater (Puffinus carneipes)
Australia (Oliver 1955; Serventy et al. 1971)xxx
Pink-footed shearwater (P. creatopus)
California (Murphy 1936; Ainley, personal observation)xx
E. Pacific (Cottam and Knappen 1939)xx
Buller's shearwater (P. bulleri)
SW Pacific (Falla 1934; Serventy et al. 1971)xxx
Peru (Murphy 1936)x
Sooty shearwater (P. griseus)
Aleutian Islands (Sanger, personal observation)xxx
British Columbia (Martin 1942; Sealy 1973a)xxx
Oregon (Gabrielson and Jewett 1940)x
California (Ainley, personal observation)xx
Peru (Murphy 1936)xxx
SW Pacific (Oliver 1955; Serventy et al. 1971)xxx
Short-tailed shearwater (P. tenuirostris)
Bristol Bay (Bartonek, personal communication)x
Alaska (Cottam and Knappen 1939)xxxo
No. Pacific (Palmer 1962; Kuroda 1955)xxx
Australia (Serventy et al. 1971)xxx
Bass Strait (Sheard 1953)x
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)x
British Columbia (Martin 1942)x
California (Ainley, personal observation)x
Leach's storm-petrel (O. leucorhoa)
SE Alaska (Heath 1915)x
California (PRBO, unpublished data)xxxxx
So. California (Palmer 1962)xx
No. Atlantic[31] (Palmer 1962)xxxxx
Table 9. Diets of gulls in different localities (x = major prey, o = minor prey, and * = incidental prey species).
LocationDiet
CRUSTACEANP
O
L
Y
C
H
A
E
T
E		MOLLUSCE
C
H
I
N
O
D
E
R
M		C
O
E
L
E
N
T
E
R
A
T
E		FISHC
A
R
R
I
O
N
-
O
F
F
A
L		BIRDF
I
S
H

E
G
G
S
E
u
p
h
a
u
s
i
i
d
B
a
r
n
a
c
l
e
D
e
c
a
p
o
d
S
h
e
l
l
f
i
s
h
C
e
p
h
a
l
o
p
o
d
"
F
i
s
h
"		C
l
u
p
e
a
E
n
g
r
a
u
l
i
s
O
s
m
e
r
u
s
P
o
r
i
c
h
i
h
y
s
O
t
a
p
h
i
d
i
u
m
M
a
l
l
o
t
u
s
B
o
r
r
o
g
a
d
u
s
M
i
c
r
o
g
a
d
u
s
G
a
d
u
s
L
y
c
o
d
e
s
S
e
b
a
s
t
e
s
M
y
x
o
c
e
p
h
a
l
u
s
G
e
n
y
o
n
e
m
u
s
E
m
b
i
o
t
o
c
i
d
A
m
m
o
d
y
t
e
s
E
g
g
s
C
h
i
c
k
s
A
d
u
l
t
s
Glaucous gull (Larus hyperboreus)
St. Lawrence Island (Fay and Cade 1959)xxx
Chukchi Sea (Swartz 1966)xxxxxxx
Pribilof Islands (Preble and McAtee 1923)xxxxx
Vancouver Island (Munro and Clemens 1931)xx
Glaucous-winged gull (L. glaucescens)[32]
Pribilof Islands (Preble and McAtee 1923)xxxxxxx
Alaska (Bent 1921)x
No. Pacific (Sanger 1973)x**
Mandarte Island (Ward 1973)xxxxx
Vancouver Island (Munro and Clemens 1931; Robertson, unpublished data)xxx
Western gull (L. occidentalis)[33]
Farallon Islands (PRBO, unpublished data)xxo*x**xxoooxooxooo
Herring gull (L. argentatus)
No. Atlantic (Zelikman 1961)x
E. No. America (Bent 1946; Ainley, personal observation)xxxxxx*ox
Vancouver Island (Munro and Clemens 1931)xxx
Mew gull (L. canus)
Alaska (Bent 1921)xxxx
Vancouver Island (Munro and Clemens 1931)xxx
Heermann's gull (L. heermanni)
California (Bent 1921)xxxx
Bonaparte's gull (L. philadelphia)
E. No. America (Bent 1921)xxx
Black-legged kittiwake (Rissa tridactyla)[34]
Chukchi Sea (Swartz 1966)o*ooxoox
Pribilof Islands (Preble and McAtee 1923)oxo
Alaska (Bent 1921)xo
Cook Inlet[35] (Snarski, personal communication)oooxox
No. Atlantic (Hartley and Fisher 1936; Zelikman 1961)x
Red-legged kittiwake (R. breuirostris)
Pribilof Islands (Preble and McAtee 1923)xxx
Sabine's gull (Xenia sabini)
Pt. Barrow (Banner 1954)x

Table 10. Diets of terns in different localities (x = major prey species).
LocationDiet
CRUSTACEANFISH
"Crustacean"MallotusEuphausiidCottidAmphipodAmmodytes
larvae
Arctic tern (Sterna paradisaea)
Pribilof Islands (Preble and McAtee 1923)xx
Alaska (Bent 1921)xxx
No. Atlantic (Hartley and Fisher 1936)x
Common tern (S. hirundo)
E. No. America (Bent 1921)xx

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 1969b).

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).

Fig. 2. Schematic food web of the parakeet auklet in the eastern Bering Sea (based on Bédard 1969a and Dunbar 1946). Arrow sizes indicate relative importance of prey and Roman numerals refer to prey sizes (see text).