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The greater crested tern〔 Retrieved 28 February 2012〕 (''Thalasseus bergii''), also called crested tern or swift tern, is a seabird in the tern family that nests in dense colonies on coastlines and islands in the tropical and subtropical Old World. Its five subspecies breed in the area from South Africa around the Indian Ocean to the central Pacific and Australia, all populations dispersing widely from the breeding range after nesting. This large tern is closely related to the royal and lesser crested terns, but can be distinguished by its size and bill colour. The greater crested tern has grey upperparts, white underparts, a yellow bill, and a shaggy black crest that recedes in winter. Its young have a distinctive appearance, with strongly patterned grey, brown and white plumage, and rely on their parents for food for several months after they have fledged. Like all members of the genus ''Thalasseus'', the greater crested tern feeds by plunge diving for fish, usually in marine environments; the male offers fish to the female as part of the courtship ritual. This is an adaptable species that has learned to follow fishing boats for jettisoned bycatch, and to use unusual nest sites such as the roofs of buildings and artificial islands in salt pans and sewage works. Its eggs and young are taken by gulls and ibises, and human activities such as fishing, shooting and egg harvesting have caused local population declines. There are no global conservation concerns for this bird, which has a stable total population of more than 500,000 individuals. == Taxonomy == The terns, family Sternidae, are small to medium-sized seabirds closely related to the gulls, skimmers and skuas. They are gull-like in appearance, but typically have a lighter build, long pointed wings (which give them a fast, buoyant flight), a deeply forked tail and short legs. Most species are grey above and white below, and have a black cap that is reduced or flecked with white in the winter.〔Snow & Perrin (1998) 764〕 |2= }} }} The greater crested tern was originally described as ''Sterna bergii'' by German naturalist Martin Lichtenstein in 1823, but was moved to its current genus, ''Thalasseus'',〔This genus had originally been created by Heinrich Boie in 1822, but had been abandoned until the Bridge (2005) study confirmed the need for a separate genus for the crested terns.〕 after mitochondrial DNA studies confirmed that the three main head patterns shown by terns (no black cap, black cap, black cap with a white forehead) corresponded to distinct clades. The greater crested tern's closest relatives within its genus appear to be the lesser crested tern (''T. bengalensis''), and the royal tern (''T. maximus'').〔 The DNA study did not include the critically endangered Chinese crested tern (''T. bernsteini'') but, as that bird was formerly considered to be conspecific with the greater crested tern as a synonym of the subspecies ''T. b. cristatus'', it is presumably also very closely related. The generic name of the greater crested tern is derived from Greek ''Thalassa'', "sea", and the species epithet ''bergii'' commemorates Carl Heinrich Bergius, a Prussian pharmacist and botanist who collected the first specimens of this tern near Cape Town.〔Higgins & Davies (1996) 605–609〕 The greater crested tern has about five geographical races, differing mainly in the colour of the upperparts and bill. These are listed below in taxonomic sequence. A similar number of other potential subspecies have been proposed, but are not considered valid.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「greater crested tern」の詳細全文を読む スポンサード リンク
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