Adult birds are black on their upperparts and white on the breast and belly. The thick black bill has a blunt end. The tail is pointed and longer than that of a Murre. In winter, the black face becomes white.
Their breeding habitat is islands, rocky shores and cliffs on northern Atlantic coasts in eastern North America as far south as Maine and western Europe from northern France to northwestern Russia. They usually nest in colonies and lay their eggs on bare rock or ground.
North American birds migrate offshore and south, ranging from the Grand Banks of Newfoundland to New England. Eurasian birds also winter at sea, with some moving south as far as the western Mediterranean.
These birds forage for food by swimming underwater. They mainly eat fish, also some crustaceans and marine worms.