A large sea-duck (family Anatidae) that occurs throughout the cooler regions of the northern hemisphere, feeding on crustaceans and molluscs. It comes ashore to nest on the ground, lining its nest with down feathers it plucks from its breast; the down is traditionally collected, and replaced with a substitute, to fill eiderdowns. There are three species in the genus Somateria and a fourth, Steller’s eider, is Polysticta stelleri.