About Sterna hirundinacea R.Lesson, 1831
Adult Size
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).
Plumage Similarity to Related Species
At all times of year, they closely resemble these two species in plumage.
Adult Beak and Wing Features
Adult South American terns have a larger, red beak, and lack a dark-coloured bar on the carpus of the wing.
Adult Cap Markings
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.
Juvenile Plumage Characteristics
Juveniles have boldly barred, dusky upper parts, and retain their barred tertials into their immature plumage.
Immature Plumage Distinguishing Feature
This feature differentiates immature South American terns from immature common and Arctic terns.
General Distribution Range
This tern is found around the coasts of the southern half of South America.
Atlantic Coast Breeding Range
Its breeding range extends along the Atlantic coast from east central Brazil southwards through Argentina and the Falkland Islands to Tierra del Fuego.
Pacific Coast Breeding Range
On the Pacific coast, it breeds in southern Peru and Chile.
Winter Migration Range
In winter, birds from the southern end of the species' range migrate northwards to Ecuador, Uruguay and Southern Brazil.
