Cabot's tern

Cabot's tern (Thalasseus acuflavidus) is a species of bird in subfamily Sterninae of the family Laridae, the gulls, terns, and skimmers. It is found in the eastern United States and Middle America, the Caribbean, Trinidad and Tobago, and in every mainland South American country except Bolivia and Paraguay, though rare in Chile. It is also a vagrant in eastern Canada and western Europe.

Cabot's tern is a member of the "crested tern" group. It is 34 to 45 cm (13 to 18 in) long with a wingspan of about 1.0 m (3 ft). The nominate subspecies T. a. acuflavidus weighs 175 to 202 g (6.2 to 7.1 oz). The Caribbean population of T. a. eurygnathus weighs 170 to 210 g (6.0 to 7.4 oz) and the far southern population 250 to 300 g (8.8 to 11 oz). The sexes have the same plumage and there is little difference in plumage between the subspecies. Adults in breeding plumage have a black cap and a mostly white body with a pale gray back and sometimes a rosy flush on the underparts. Their tail is forked and white. The upper side of their wing is mostly pale gray with darker primaries. Their legs and feet are all black or black with yellow soles and their iris is dark brown to black. Non-breeding adults have a white forehead and mid-crown; their crest is black. The subspecies differ mainly in bill color: The nominate's is black with a yellow tip of somewhat variable extent; that of T. a. eurygnathus is mostly to completely yellow.

Cabot's tern is very similar to Sandwich tern, sharing the black bill with a yellow tip, but differs in the bill being obviously stouter, and also differs in molt timing, losing its black forehead earlier in the summer. Its juveniles also lack the scaly pattern of juvenile Sandwich terns, being a plainer gray (though they can be confused with first-winter plumage of Sandwich tern).