Breeding (Alternate) Plumage: Head purplish-black. Bright crescent-shaped white patch on side of face at base of bill, thin at top, rounded at bottom. Sides, breast, belly, and secondaries bright white. Back, wings, and tail black. Black of back reaching onto shoulder. Series of white squares along sides above wings. Short, triangular black bill. Eyes golden yellow.
Nonbreeding (Basic) Plumage: like female, but with some black tinge at sides.