distances from refuse sources and observed 

 that fledging success was greatest at the 

 near islands. Since there is little dif- 

 ference between the fledging success of 

 two and three egg clutches (Kadlec and 

 Drury 1P68), when chick mortality does 

 occur, it is generally not because of 

 insufficient food, but rather due to 

 parental neglect (Drury and Smith 1968; 

 Hunt 1972). If gull chicks are left 

 unattended for long periods of time, they 

 may wander into adjacent territories and 

 may be attacked by neighboring adults 

 (Hunt and McLoon 1975). 



Another potential control on popula- 

 tion growth is available breeding space. 

 During the last 75 years of rapid expan- 

 sion, the density of nests in herring gull 

 colonies has reipained unchanged (Kadlec 

 and Drury 1568). As the number of birds 

 in the New England gull population has 

 grown, new nesting pairs have established 

 new colonies, expanding the breeding 

 range. Most breeding colonies occur on 

 nearshore islands, the same type of 

 islands used by breeding terns. Kadlec 

 and Drury (1968) have estimated that 

 approximately 15% to 30% of adult herring 

 gulls are nonbreeders in any given year. 

 There is a tendency for gulls that find no 

 space in existing colonies to establish 

 territories on islands that support tern 

 colonies and, in time, to displace the 

 terns (Drury 1974). 



Terns are much more selective in 

 their feeding than gulls, preferring small 

 fish and crustaceans. Unlike the herring 

 gulls, their population growth is food- 

 limited. During the breeding season, adult 

 males may hunt for food up to 14.5 hours 

 per day (Nisbet 1973). There is evidence 

 that the number of chicks that survive to 

 fledging may be a function of food avail- 

 ability. LeCroy and Collins (1972) found 

 that both roseate and common tern produc- 

 tivity in Long Island Sound, as measured 

 by successful fledgings, fluctuated year- 

 ly, and the authors suggested that these 

 fluctuations were related to food avail- 

 ability. These workers also examined the 

 relationship between clutch size and chick 

 survival. Common and roseate terns may 

 lay either two or three egg clutches and, 

 unlike the herring gulls, the survival 

 from hatched egg to fledging is much 

 greater in two egg clutches than three. 



This evidence suggests that (1) dur- 

 ing this century, we have increased the 

 carrying capacity of New England for the 

 herring and great black-backed gull popu- 

 lations, (2) tern populations are limited 

 by natural controls, and (3) both groups 

 overlap considerably in their preferred 

 breeding areas. Collectively then, this 

 evidence implies that the dense coastal 

 hum.an population of the northeast is 

 threatening the continued coexistence of 

 these two groups of birds. 



5.4 HERONS AND OTHER WADING BIRDS 



For many people, the most conspicu- 

 ously beautiful and aesthetically pleasing 

 birds that frequent tidal flats are the 

 herons and egrets. These long-legged and 

 slender-necked wading birds are elegant as 

 they take off and land with broad wings 

 beating in slow motion. At other times as 

 they pursue prey with feet splashing, head 

 jerking, and wings flapping, they seem 

 clumsy. Like the gulls and terns, herons 

 and other wading birds are colonial breed- 

 ers that often nest on islands. Table 6 

 shows the relative abundance of coastal 

 breeding herons in New England. Most spe- 

 cies frequent the New England coast only 

 during the warmer months, but the great 

 blue and the black-crowned night herons 

 may remain all winter. After young are 

 fledged, there is a general dispersion 

 northward and then a southward migration 

 in the fall. In New England, herons are 

 primarily tree nesters. Until the 1950's, 

 most kinds of wading birds nested only in 

 more southern states. Since then there 

 has been a steady "invasion" into New Eng- 

 land (R. Andrews; U.S. Fish and Uildlife 

 Service, Newton Corner, Massachusetts; 

 April 1981; personal communication). In 

 the south, dense multispecies breeding 

 and feeding assemblages frequently occur. 

 Each species has a characteristic foraging 

 behavior and the collective repertoire of 

 the feeding behaviors of this group has 

 been studied extensively. 



Soon after arriving from wintering 

 areas, pairs of herons establish well- 

 defended breeding territories. At least 

 one member of the pair always occupies the 

 territory (Jenni 1969). Nest site selec- 

 tion is species-specific. Snowy egrets 

 have a tendency to nest in exposed areas 



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