gulls may follow each other to foraging 

 sites. Among different species of terns, 

 Erwin (1978) suggests that those species 

 which feed closer to the breeding colonies 

 are more gregarious while feeding and have 

 larger colony sizes. While feeding on 

 exposed tidal flats where food is patchy, 

 herring gulls may establish territories 

 that are defended by calls and posturing. 

 These territories may be maintained by the 

 same birds for many years (Drury and Smith 

 1968). 



The displacement of nesting terns by 

 gulls can be explained in part by review- 

 ing some aspects of the biology of these 

 species. Herring gulls 

 opportunistic foragers, 

 almost any large piece 

 rial, living or dead, 

 capitalized on a subsidy 



are general and 

 They will eat 



of organic mate- 

 and have thus 

 in the form of 



tons of organic wastes produced each year 

 by the northeastern coastal human popula- 

 tion which has increased spectacularly 

 during this century. The effect has been 

 to tremendously increase the carrying 

 capacity of their environment which has 

 released the population growth rate of the 

 gulls from dependence on food resources; 

 the New England herring gull population is 

 now dependent on human refuse. Perhaps 

 the greatest impact on the species has 

 been to increase the survival of wintering 

 yearlings that feed on refuse. Harris 

 (1965) estimated that in England as much 

 as two-thirds of the food remains of her- 

 ring gulls were attributable to human 

 waste and Kadlec and Drury (1968) sug- 

 gested that only 12% of New England gulls 

 make an "honest" living by consuming food 

 other than that generated by man. Hunt 

 (1972) studied Maine islands of varying 



The least tern is one of four species of terns that feed on small fish of the New 

 England tidal flats and nest on nearby beaches and islands. (Photo by L.C. Goldman; 

 courtesy U.S. Fish and Wildlife Service) 



58 



