Gavión cabecinegro Ichthyaetus ichthyaetus

Large powerful gull of saline, brackish, and fresh water bodies. Breeding adult has a black head with a thin incomplete crescent around the eye and a red-and-black-tipped bill. Nonbreeding adults retain a partial “hood” of patchy black on the back of the head. Young birds also have this dark patch, though it is much smaller in size. The eye crescents and a flashing white rump help to distinguish first-winter birds from Herring-type gulls. Can be readily separated by size in any plumage from the smaller dark-headed gulls.