Sterna bianca

Identificazione

The white tern has a wingspan of 76–87 cm (30–34 in). It has white plumage and a long black bill. Nesting on coral islands, usually on trees with small branches but also on rocky ledges and on man-made structures, the white tern feeds on small fish which it catches by plunge diving. Giant tortoises have been observed to hunt the bird on Fregate Island in the Seychelles.

Tassonomia

The white tern was first formally described by the Swedish naturalist Anders Sparrman in 1786 under the binomial name Sterna alba. The genus Gygis was introduced by the German zoologist Johann Georg Wagler in 1832. The name Gygis is from the Ancient Greek guges for a mythical bird and the specific alba is Latin for "white".<p>Molecular phylogenetic studies have shown that the white tern is more closely related to the noddies than it is to the other terns. This implies that "white noddy" would be a more appropriate English name.<p>The white tern has the following recognized subspecies:<p>Some authors have postulated that there may be three species of Gygis: Gygis alba, in the Atlantic Ocean, and Gygis candida and Gygis microrhyncha, both in the Pacific.

Nome scientifico

Gygis alba

Autorità

(Sparrman, 1786)

Ordine

Caradriformi

Famiglia

Laridae

Genere

Gygis

Areale e habitat

The white tern ranges widely across the Pacific Ocean from the coasts of Chile and Colombia to New Zealand and along the eastern and southern coasts of Asia from China to India, South Maldives, the islands of the Indian Ocean, and the coast of South Africa. Rarely it is also found in Japan, Madagascar, Mexico, and on some islands in the Atlantic Ocean. It is a pelagic and epipelagic bird, living along the coast and moving into wooded areas during the breeding season.

Areale riproduttivo

TrO : widespread on tropical and subtropical is. (except Caribbean, n, e Indian Ocean)

Areale non riproduttivo

tropical seas

Migrazione

Resident species

Comportamento

This species is notable for laying its egg on bare thin branches in a small fork or depression without a nest. This behaviour is unusual for terns, which generally nest on the ground, and even the related tree-nesting black noddy constructs a nest. It is thought that the reason for the absence of nests is the reduction in nest parasites, which in some colonial seabirds can cause the abandonment of an entire colony. In spite of these benefits there are costs associated with tree nesting, as the eggs and chicks are vulnerable to becoming dislodged by heavy winds. For this reason the white tern is also quick to relay should it lose the egg. The newly hatched chicks have well developed feet with which to hang on to their precarious nesting site. It is a long-lived bird, having been recorded living for 42 years.

Conservazione

Tendenza della popolazione

stable