South American Tern

Identification

The South American tern is a medium-to-large tern, measuring 40 to 44 centimetres in length, making it noticeably larger than the closely related common tern and Arctic tern. While it shares similar plumage patterns with these species year-round, several key features distinguish it. Most notably, adults display a bright red beak—significantly larger than that of its relatives—and lack the dark bar on the carpus (bend of the wing) seen in other terns. The black cap extends below the eye, usually separated from it by a distinctive white crescent, with a sharply defined rear edge. Juveniles are particularly distinctive, showing boldly barred and dusky upper parts and retaining barred tertials into their immature plumage, a feature that sets them apart from juvenile common and Arctic terns.

Range & Habitat

The South American tern inhabits the coasts of southern South America and is generally the most common tern throughout its range. On the Atlantic coast, its breeding range extends from east central Brazil southwards through Argentina and the Falkland Islands to Tierra del Fuego, while on the Pacific coast it breeds in southern Peru and Chile. During winter months, birds from the southern populations migrate northwards to Ecuador, Uruguay, and southern Brazil, demonstrating significant seasonal movement.

This species favours diverse coastal settings, nesting on islands, beaches, and cliff tops. Outside the breeding season, it frequents offshore waters, estuaries, and harbours, making it relatively accessible to observers across multiple habitat types.

Behaviour & Diet

The South American tern is an active forager, feeding primarily on fish along with crustaceans and other small invertebrates, typical of tern hunting behaviour. During breeding season, this species forms impressive colonies, sometimes of extraordinary density. A historic 1877 account documented a breeding colony in Chubut Province, Argentina, where an estimated 135,000 birds occupied just 130 square metres, with approximately 67,500 nests containing 112,500 eggs. Nests consist of mere scrapes in gravel and shingle, each typically holding one to three eggs that vary considerably in their individual markings.

Best Time & Places to See It

The South American tern is best observed in its breeding range during the breeding season, particularly in coastal Argentina, Chile, Peru, and the Falkland Islands. The Falkland Islands offer particularly reliable viewing opportunities, as this region supports significant populations. Winter visitors to Ecuador, Uruguay, and southern Brazil may also encounter migrant birds in estuaries and coastal waters. Year-round, coastal regions throughout southern South America provide opportunities to observe this generally common species in its preferred habitats.

Photography Tips

Photographers should target breeding colonies during nesting season for the most dramatic and accessible opportunities. The bird's larger size compared to common and Arctic terns, combined with its distinctive red beak and white-crescent eye marking, makes it highly photogenic. The striking black cap and neat demarcation of plumage provide excellent contrast in photographs. Coastal and estuarine settings offer natural backdrops, while the bird's habit of frequenting harbours and offshore waters means that patient observers may capture feeding or diving sequences. Early morning light is ideal for highlighting the red beak coloration and the crisp plumage patterns that characterize this elegant species.