About Sterna hirundinacea R.Lesson, 1831
Adult South American terns (Sterna hirundinacea) reach a length of 40 to 44 centimetres (16 to 17 in), making them larger than either common terns (Sterna hirundo) or Arctic terns (Sterna paradisaea). At all times of year, they closely resemble these two species in plumage. Adult South American terns have a larger, red beak, and lack a dark-coloured bar on the carpus of the wing. Their black cap extends below the eye, usually separated from the eye by a white crescent, and the rear edge of the cap is neatly defined. Juveniles have boldly barred, dusky upper parts, and retain their barred tertials into their immature plumage. This feature differentiates immature South American terns from immature common and Arctic terns. This tern is found around the coasts of the southern half of South America. Its breeding range extends along the Atlantic coast from east central Brazil southwards through Argentina and the Falkland Islands to Tierra del Fuego. On the Pacific coast, it breeds in southern Peru and Chile. In winter, birds from the southern end of the species' range migrate northwards to Ecuador, Uruguay and Southern Brazil.
