This medium-sized gull changes its head pattern between breeding and non-breeding plumage. It uses Andean lakes and rivers; in Chile, some move down to the coast in winter.
In breeding plumage the head is black with a white eye-ring. The neck, chest, belly, and tail are white, while the back and upper wings are grey. Outside the breeding season the head turns white with black ear-spot marks. Juveniles have brown markings that fade with age.
In Chile it occurs singly, in pairs, or in small groups around Andean lakes and highland wetlands. It eats earthworms, insects, amphibians, and small fish, and occasionally waterbird eggs or chicks and carrion. In Chile it may descend to the coast in winter.
An extinction-risk assessment has not been added yet.