Sterno dalla corona innevata

Identificazione

The snowy-crowned tern is 28 to 35 cm (11 to 14 in) long with a wingspan of 76 to 78 cm (30 to 31 in) and weighs 146 to 160 g (5.1 to 5.6 oz). It has a rather blocky head, a thick neck, long wings, and a forked tail. The sexes have the same plumage. Adults in breeding plumage have a white head and neck with a black band through the eye. Their upperparts are pale gray with a whitish rump and uppertail coverts. Their underparts are grayish white. Their upperwing is pale gray with silvery primaries and the underwing is white. Their iris is brown and their bill orange with a yellow tip and a black band separating the colors. Their legs and feet are reddish orange. Non-breeding adults are similar to breeding ones, but with a grayer stripe on the face, more intense silvery on the primaries, and a black bill with a yellowish tip. Juveniles have a black and white pattern on their back, a black band near the end of the tail, a black bill, and dark legs.

Tassonomia

Some genetic data indicate that the snowy-crowned tern and several other closely related terns belong in a genus separate from Sterna. At the least, the snowy-crowned and Forster's tern (S. forsteri) are sister species. The snowy-crowned tern is monotypic.<p>The snowy-crowned tern was first described by the American ornithologist John James Audubon in 1838. He had been sent a specimen by his friend Dr. James de Berty Trudeau (1817–1887) of Louisiana, who had reportedly found several of the terns at Great Egg Harbor Bay, New Jersey. Audubon named the bird in his honor.

Nome scientifico

Sterna trudeaui

Autorità

Audubon, 1838

Ordine

Caradriformi

Famiglia

Laridae

Genere

Sterna

Areale e habitat

The snowy-crowned tern breeds from southeastern Brazil south through Uruguay to Argentina's Buenos Aires Province and also in Chile between the provinces of Aconcagua and Llanquihue. Outside the breeding season it ranges along the Atlantic coast as far north as the Rio de Janeiro area and on the Pacific coast as far north as the Department of Ica in Peru. It has appeared as a vagrant as far south as the Straits of Magellan and on the Falkland Islands. Undocumented sight records in Paraguay lead the South American Classification Committee of the American Ornithological Society to treat it as hypothetical in that country. The purported type locality of New Jersey is not supported by any documented North American records.<p>The snowy-crowned tern inhabits coastal and inland wetlands both fresh and saline, though it favors freshwater landscapes. It mostly breeds on lagoons in the Pampas and Patagonia but also on islands in coastal lagoons.

Migrazione

Complete migrants

Comportamento

The snowy-crowned tern feeds mostly on fish but also on insects. It forages over shallow water along the edges of wetlands, rivers, and lagoons and over plowed fields. It takes fish by plunge-diving.<p>The snowy-crowned tern's breeding biology is not fully understood. Its breeding season appears to include October to December. It nests in colonies, often sharing areas with brown-hooded gulls (Larus maculipennis). It builds a floating platform nest in shallow water, either free-floating or anchored to emergent vegetation. Both sexes vigorously defend the nest. The clutch size is two to four eggs, but usually three. The incubation period, time to fledging, and details of parental care are not known.<p>The snowy-crowned tern's call is "a series of rapid notes "je-je-je-je", or a short, grating "jeeer"."

Conservazione

Tendenza della popolazione

stable