The highest densities of waterbirds occur in late summer after the young have 

 fledged and during the "fall" migration (which begins in early July). 

 Waterfowl are most abundant during the fall and spring migrations, shorebirds 

 during the fall migration, wading birds during the breeding season and fall 

 migration, and seabirds during the summer and fall migrations. Peak numbers 

 of shorebirds and seabirds correspond with the peak periods of invertebrate 

 production. Bald eagles are present throughout the year. Peak abundance 

 occurs during spring and summer. 



The role of waterbirds in energy flow, nutrient cycling, and community 

 structure in the estuarine system is little known. Studies in Massachusetts 

 and in Europe have shown that shorebirds [ oystercatcher , red knot, red shank 

 (Goss-Custard 1977), black-bellied plover (Schneider 1978), and purple 

 sandpiper (Feare 1966)] are important predators on selected prey items (i.e., 

 amphipods , Baltic clams, mud shrimps, bamboo worms, sandworms , and other 

 polychaetes) . Studies on wading birds in Florida have shown that they remove 

 most prey from temporary pools of water (Kushlan 1976) . Eiders and other 

 seaducks may influence benthic community structure (as yet not studied in 

 Maine) while geese can affect plant community structure and composition in 

 salt marshes (Jefferies et al. 1979). Changes in eelgrass populations were 

 significantly reduced during the 1930s due to a "wasting disease" (the actual 

 cause of which is questionable), which in turn reduced east coast populations 

 of brant to very low numbers. They are now making a recovery. Their diet has 

 changed from eelgrass to sea lettuce. 



The amount of energy passing through estuarine food webs that involve birds is 

 unknown. Because of their numerical abundance and large biomass, gulls, 

 eiders, and cormorants probably process the greatest prey biomass. Shorebirds 

 and waterfowl are the next group in importance. The remaining waterbird 

 groups process lesser amounts. In general, waterbirds in Maine are most 

 abundant at the same time that Maine invertebrates and fish (primary prey 

 items) are at peak densities (August to September) and less abundant when prey 

 are either at lower densities or physically unavailable (December to April). 

 For example, peak densities of shorebirds correspond to peak densities of the 

 amphipod Corophium (personal communication from P. Hicklin, Canadian Wildlife 

 Service, Sackville, New Brunswick, Canada; March, 1979). The Baltic clam is 

 the prey of medium- and longer-billed shorebirds (e.g., red knot, willet, 

 sanderling, and black-bellied plovers) in summer, when it has burrowed below 

 the reach of most shorebirds (reach is determined by bill length; Reading and 

 McGrorty 1978). In New Jersey, sanderlings have been reported to spend more 

 time feeding at midtide levels of sand beaches than on lower and upper 

 portions of the beach (Burger et al. 1977). Amphipods are also most abundant 

 in this same zone on Maine sand beaches. Research is needed to determine if 

 sanderling use of these midlevel beach areas in Maine is similar to that of 

 New Jersey. 



Migratory waterbirds (especially those that remain in coastal waters for 

 extended periods of time) represent an important energy loss from the 

 estuarine system. Shorebirds, for example, arrive in Maine with minimal fat 

 reserves. They remain for 2 to 4 weeks, during which time their weight 

 increases about 50% to 1007o. Without these added fat reserves (the energy for 

 their long transatlantic migrations), they could not successfully complete the 

 2500-mile flight from coastal Maine to the Lesser Antillies and northern South 

 America. 



5-46 



