Common Loons are large water birds with thick necks and sharp bills. In breeding plumage, both sexes have striking black heads with white collars, white breasts, and black backs with white checkering. Adults in non-breeding plumage are brownish gray with white throats and breasts, partial white collars, and white around the eyes. Under-parts are white in all plumages. Juvenile plumage is similar to non-breeding.