black and white seabird of the North Atlantic, bearing a sharp, heavy, compressed beak. About 40 cm (16 inches) long, it is the largest living member of the auk family, Alcidae (order Charadriiformes), and the nearest kin to the extinct great auk. Razor-billed auks are deep divers, feeding on fish (including shellfish). They breed along North Atlantic coasts; some migrate as far south as the Mediterranean Sea.