This counterpart of the Arctic Tern does not undertake long migrations like its northern cousin, but usually stays close to breeding areas. It is similar to Arctic Tern, but has longer legs and bill and less black in it wings. Also wintering Arctic Terns lack the full black cap of breeding Antarctic Terns. Separation from the similar South American Tern (S. hirundinacea) even more difficult but that species not known from Tristan da Cunha. Five or six subspecies usually recognized, but differences slight with much overlap and the validity of some are questionable. Tristan da Cunha birds are ascribed to S. v.tristanensisi which is in the larger nominate group. It differs from nominate vittata by its larger size (longest tail and tarsus; second longest wing after subspecies gaini); plumage slightly paler gray; and narrower gray band on inner web of primaries next to shaft.
Bottom bird is a recently fledged juvenile showing dark lesser and median wing coverts which help distinguish it from juvenile Arctic and South American Terns. Neither of those species breed on or near Tristan da Cunah. Canon PowerShot SX50 HS.
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