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Nesting habitat use by Common Eiders on Stratton Island, Maine.

Article Excerpt
Non-random distribution of animals among available habitats is often cited as evidence of habitat choice, a product of natural selection (Burger 1987, Clark and Shutler 1999). The choice of where to breed can have important consequences for reproductive success (Misenhelter and Rotenberry 2000). Animals are expected to select those habitats that maximize reproductive performance and, ultimately, fitness if reproductive success varies by habitat type. There is considerable evidence for birds that nest-site selection is adaptive and driven, in part, by avoidance of predators (Martin 1993, Burger and Gochfeld 1994, Clark and Shutler 1999).

American Common Eiders (Somateria mollissima dresseri) are large, colonial sea ducks that often nest on marine islands. Island-nesting and coloniality may have evolved to reduce the threat of mammalian predators (e.g., Wittenburger and Hunt 1985), but eiders and other seabirds often contend with avian predators in breeding areas (Burger and Gochfeld 1994, Goudie et al. 2000). Large gulls (Larus spp.) can be important predators of eider eggs and young (Choate 1967, Bourget 1973, Milne and Reed 1974, Mawhinney and Diamond 1999) and seemingly could exert strong selective pressures on nest placement within a colony. However, the literature on the gull-eider relationship is far from conclusive. Some studies suggest that waterfowl benefit from nesting in association with aggressive gulls (e.g., Young and Titman 1986, Gotmark and Ahlund 1988, Swennen 1989), but others document severe predation rates on ducklings (e.g., Dwernychuk and Boag 1972, Mawhinney and Diamond 1999, Donehower and Bird 2008).

We examined Common Eider nesting habitat use on Stratton Island, Maine. Our objectives were to compare nest densities and success in different habitat types. We were particularly interested in use of Asiatic bittersweet (Celastrus orbiculata) as eider nesting habitat since this invasive vine provides dense cover but is being eradicated in parts of the island to benefit wading birds. The weight and spread of bittersweet vines can topple trees and prevent foliage growth, destroying nesting trees used by Snowy (Egretta thula) and Great (Ardea alba) egrets, Glossy Ibis (Plegadis falcinellus), and Black-crowned Night (Nycticorax nycticorax) and Little Blue (E. caerulea) herons (National Audubon Society Seabird Restoration Program, unpubl, data).

METHODS

Study Area.--The study was conducted in 2004 and 2005 on Stratton Island (43[degrees] 31' N, 70[degrees] 19' W), a 12-ha National Audubon Society

waterbird sanctuary 2.4 km south of Prouts Neck, Saco Bay, Maine (Chase 1994, Kress 1998). There are no mammalian predators but hundreds of Herring (Larus argentatus) and Great Black-backed (L. marinus) gulls use the island for resting, foraging, and attempted nesting; National Audubon Society gull control measures...

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