Large, dark-backed gull with a broad black band on a white tail. Breeding adults have mostly clean white bodies with black backs and wings. In the nonbreeding season, adults have a black hood and a broken white eye-ring. Immatures are very distinctive, with mottled gray-brown backs and brown breasts and heads with a white patch around the bill. Usually seen on the immediate coast, where it mostly eats crabs. During the austral winter, some migrate farther north.