Knowledge of feeding methods is important in evaluating potential 

 environmental impacts. For example, in the event of an oil spill birds that 

 spend most of their time on the water and dive for their food are more 

 susceptible to feather oiling than are birds that feed on the wing. Creation 

 of impoundments for tidal power may reduce the amount of intertidal mudflats 

 and adversely affect species that feed there. 



As a group seabirds feed primarily on fish and crustaceans but also consume 

 cephalopods, other invertebrates, offal and garbage (table 14-9). Birds that 

 feed by dipping, pattering, and surface seizing eat crustaceans, other 

 invertebrates, small fish, and cephalopods. Birds that feed by pursuit 

 diving, shallow plunging, and deep plunging eat fish and, to a lesser extent, 

 large invertebrates. Birds that feed on the bottom take benthic invertebrates 

 and some fish. 



Along the Maine coast food may be abundant overall but is usually concentrated 

 in specific habitats and may be dispersed in patches. Some species of 

 seabirds (e.g., terns) are better adapted for finding these patches of food 

 and their activity in turn attracts other species. As a result, feeding 

 associations between seabird species are common. They usually avoid competing 

 with each other by using different feeding methods and by selecting different 

 prey. 



Seabirds may also feed with pods of marine mammals (whales, dolphins, and 

 seals) and sometimes with large fish (such as tuna and mackerel) according to 

 Baltz and Morejohn (1976). Fishermen may use groups of feeding terns, gulls, 

 and shearwaters (as well as marine mammals) to locate schools of fish. 



Natural Factors Affecting Abundance 



The factors that control the abundance of seabirds along the Maine coast are 

 not entirely known. The following paragraphs summarize the ways in which 

 predation, food supply, and nesting habits might affect abundance. 



Predation. Except during the breeding season, seabirds are relatively 

 free from natural predators. Small islands afford the safest breeding 

 locations because they are relatively free of mammalian predators. Gulls 

 (herring and great black-backed), ravens, crows, and great horned owls may 

 prey heavily on the eggs and flightless young. Islands with introduced 

 mammalian predators or islands that occasionally are attached to the mainland 

 by ice make poor seabird nesting areas. 



Food supply . The effects of limited food supply are difficult to quantify 

 in offshore areas, where food supplies usually are widely scattered. In 

 Massachusetts a positive correlation exists between the annual herring harvest 

 and tern nesting success (Nisbet 1973). An increase in garbage dumps resulted 

 in higher survival of herring and great black-backed gulls and largely 

 accounted for their population explosion in Maine and elsewhere in New England 

 (Drury and Kadlec 1974). The large flocks of Bonaparte's, herring, and great 

 black-backed gulls, and northern phalaropes (see "Shorebirds" below) found in 

 Passamaquoddy Bay in late summer occur where marine upwelling areas and tidal 

 rips concentrate foods such as euphausiid shrimp. 



14-21 



10-80 



