reduction in the levels of DUE, PCBs, or 

 mercury during this period. It is diffi- 

 cult to assess recent trends in bald eagle 

 numbers in Maine, but the current levels 

 of recruitment per nest remain below that 

 necessary to sustain a stable population 

 (Famous et al . 1980). 



Several other raptors dre included in 

 Appendix III because they may consume 

 shorebirds. Of these, the peregrine fal- 

 con preys most heavily on shorebirds and 

 often follows migratory shorebird flocks 

 (E.L. Mills; Dalhousie University, Hali- 

 fax, Nova Scotia; April 1981; personal 

 communication). In a study conducted on 

 the west coast of the United States, Page 

 and Whitacre (1975) found that raptors 

 consume a large portion of wintering 

 shorebirds. At the study site, a variety 

 of hawks and owls removed 20.7% of the 

 dunlins, 11.9% of the least sandpipers, 

 and 13.5% of the sanderlings. New England 

 tidal flats are migratory stopover areas 

 for most shorebirds and such large remov- 

 als do not occur. Most of the raptors 

 studied on the west coast occur in New 

 England also and occasionally consume 

 shorebirds. 



5.7 DEPENDENCE ON TIDAL FLATS 



The major groups of coastal birds 

 differ in their dependence on tidal flats. 

 For the shorebirds that feed extensively 

 on exposed flats and the wading birds that 

 feed in shallow waters, tidal flats are 

 essential sources of food. The migratory 

 and winter habitat and feeding behavior 

 among shorebirds and the feeding behavior 

 of wading birds suggests a dependence 

 relationship that has persisted on an 

 evolutionary time-scale. Tidal flats 

 differ in their importance as feeding 

 sites, with those areas having dense popu- 

 lations of infaunal invertebrates being 

 more attractive. Also, migration routes 



differ among species of shorebirds and a 

 relatively few coastal areas support large 

 numbers of shorebirds (Morrison and Har- 

 rington 1979). The wading birds are more 

 evenly distributed, especially in southern 

 New England. Since many nest there, the 

 ability to successfully fledge young is a 

 function of how well tidal flats can pro- 

 vide energy for their metabolic demands. 



The terns and particularly the gulls 

 are the most persistent and common birds 

 of New England tidal flats, but this habi- 

 tat is only one of many used by this 

 group. Deeper waters are suitable for 

 hunting pelagic fishes and gulls feed as 

 well in rocky intertidal areas and terres- 

 trial refuse sites. Gulls make greater 

 use of the exposed tidal flats than the 

 fish-eating terns. This is true especially 

 in winter when the terns migrate south and 

 many fish leave the coastal area. Exposed 

 flats become particularly important to 

 wintering gulls that feed on sedentary 

 invertebrates and organic materials left 

 by the tides. 



Although waterfowl and diving birds 

 often forage over tidal flats at high 

 tide, they are not restricted to these 

 areas. Many species prefer rocky sub- 

 strates and those that forage in or over 

 soft substrates often do so in deeper 

 water. Exceptions are the omnivores that 

 do not dive, such as several species of 

 dabbling ducks, geese, and the mute swan. 

 For these species, foraging occurs in 

 shallow water where they can reach benthic 

 vegetation by "tipping up" without diving. 



Raptors, other than the osprey and 

 the eagle generally feed over terrestrial 

 areas and, except for peregrines and mer- 

 lins, only occasionally hunt shorebirds on 

 tidal flats. Ospreys are especially de- 

 pendent on the flats in the spring when 

 pelagic schooling species of fish are 

 rare. 



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