auk (ôk) [key], common name for a member of the family Alcidae (alcid family), swimming and diving birds of the N Atlantic and Pacific, which includes the guillemots and puffins. Their legs are set far back on their bodies, making them clumsy on land, where they seldom venture except to nest. The extinct, flightless great auk, Pinguinus impennis, or garefowl, represents the largest species. It was about the size of a goose, black above and grayish white below, and was formerly abundant in the N Atlantic. Slaughtered in its breeding grounds for its flesh, feathers, and oil, it became extinct c.1844. The least auklet (about 61/2 in./16.3 cm), common in the Bering Sea region, is the smallest of the family, and the razor-billed auk, Alca torda (16–18 in./40–45 cm), is the largest surviving member. The Eskimos hunt the dovekie ( Plautus alle ), or little auk, for food and use its feathered skin for clothing. Auks return to the same breeding grounds every year, and each individual goes to the very same nesting site. The single egg is laid on bare rock on cliff ledges, and incubation duties are shared by both parents. Auks are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Charadriiformes, family Alcidae.