Any of several species of large diving ducks (in tribes Mergini and Somateriini) that are heavy and round-bodied, with a humped bill that produces a characteristic sloping profile. Eiders are the source of eiderdown, feathers that the hen plucks from her breast to line the nest and insulate her eggs. Eiderdown is used as a warm filling for jackets, pillows, quilts, and sleeping bags. Hens are mottled brown, but drakes (males) are boldly patterned, with a green pigment on the head. Eiders live in the cold far north.