TROPHIC RELATIONS OF SE ABIRDS 



99 



(Somateria spp. and Melanitta spp.); and 

 those feeding on fish (Mergus serrator, Clan- 

 gula 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 consider- 

 able 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 Is- 

 lands) 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 Ain- 

 ley 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 cornicu- 

 lata), 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 cephalo- 

 pods and crustaceans, particularly nektonic 

 forms. Morphological differences between the 

 two murre species suggest that thick-billed 

 murres (Uria lomvia) feed on benthic or- 

 ganisms 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 predomi- 

 nates in the region of the food study (Barto- 

 nek and Gibson 1972). Adult murres some- 

 times eat different items than they feed to 

 their chicks (Spring 1971; Scott 1973). The 



smaller alcids, ancient and marbled murre- 

 lets 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 murre- 

 lets, especially the marbled murrelet, its allo- 

 patric congener, but the diets of the other 

 murrelets differ somewhat (Bedard 19696; 

 Sealy 1975). The Kittlitz's murrelet's shorter 

 bill suggests that it feeds more on inverte- 

 brates. 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 pro- 

 gressively 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 alba- 

 trosses 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 ful- 

 mar (Fulmarus glacialis), scaled petrel (Ptero- 

 droma inexpectata), and the fork-tailed and 

 Leach's storm-petrels (Oceanodroma furcata 

 and O. leucorhoa) appear to be large, 

 medium, small, and tiny versions, respec- 

 tively, 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 



