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).