Somateria mollissima

This is a heavy-bodied duck with a relatively short, stout neck and distinctive long triangular (wedge-shaped) bill and head profile. From fall through early summer, adult males have a black crown, greenish rear of head, dark or yellow bill, black underparts, white upperparts and chest, black tail and area around the tail. From summer to fall, adult males are dark brown to blackish overall, with a pale brown stripe through the, brown breats with white flecking, back feathers white with black edges. Immature males are similar to females but have a white chest. Adult females are dark gray to rusty-brown, with fine black barring that forms lines on the flanks.

Nonbreeding habitat includes rocky seacoasts, bays, and estuaries. Rocks, sandbars, and ice are used as resting sites. In winter in the Gulf of St. Lawrence, eiders concentrated in areas with shallow water reefs and high prey density (Guillemette et al. 1993). Most migration is coastal. Nests are on the ground in grass or brush, usually close to salt water, often on an island or rocky headland or along the shore of a pond or lagoon. Nests often but not always are concealed by plants (forest, shrub, or herbaceous), rocks, logs, driftwood. Often nests are in the same site in successive years. See Blumton et al. (1988) for habitat suitability index model.

Predation by herring gull and great black-backed gull causes most nesting failures on islands in Maine, but eider nesting success may be enhanced in nests close to a gull colony (gulls defend area against other avian pradators). Arctic fox is sometimes an important predator on nesters in Alaska. Ravens, raccoons, and mink sometimes destroy nests. Annual survivorship of adult generally is relatively high, with sport hunting likely the major cause of mortality in the Atlantic flyway (Kehoe 1994).

Nesting in Maine occurs from late April to early July. Nesting in the Beaufort Sea region begins in mid- to late June (Johnson and Herter 1989). Clutch size averages 3-5. Incubation, by the female, lasts 24-30 days. The female relies on endogenous energy reserves during incubation. Eggs hatch mainly mid- to late July (sometimes into August) in the region arctic of Alaska and Canada. Young are led to water soon after hatching, are tended by the female, soon join young of other broods, and are independent at around 60-75 days). Female first breeds at 2-3 years, generally not until at least 3 years old. Females rarely renest if the clutch is lost, unless loss occurs during laying or early incubation.

Common eiders commonly nest in loose aggregations or colonies (usually a few dozen pairs, but up to several thousand pairs in some areas). Females commonly deposit eggs in the nests of other females.

Female common eiders that nested successfully lead their young to water and may be accompanied by nonbreeding females that participate in chick protection. Broods often join to form "crèches" of up to many dozens of young. Once formed, a crèche tends to stay together throughout the brood rearing period, although some of the adult females attending it may depart.