33-41 cm (13-16") Common. Lakes, rivers, bays, beaches, islands, coasts. Graceful, pigeon-sized bird with a deeply forked tail. White head with a black cap; red bill usually has black tip; white underparts; pale gray mantle, darkest at wing tips: red legs. Similar Arctic Tern has an all red bill; grayish underneath with translucent primaries.
Winter adult similar, but black cap is incomplete; bill and feet blackish.
A dark phase, a Siberian subspecies, has black feet and bill can be seen in western Alaska.
Song: "KEEarr", also "kik-kik-kik".