Greater crested tern

There are no global conservation concerns for this bird, which has a stable total population of more than 500,000 individuals. The breeding adult of the nominate subspecies T. bergii is 46–49 cm long, with a 125–130 cm wing-span. In winter, the upperparts plumage wears to a paler grey, and the crown of the head becomes white, merging the rear into a black crest and mask.

About Greater crested tern in brief

The greater crested tern is a large tern with a long yellow bill, black legs, and a glossy black crest that is noticeably shaggy at its rear. There are no global conservation concerns for this bird, which has a stable total population of more than 500,000 individuals. The breeding adult of the nominate subspecies T. bergii is 46–49 cm long, with a 125–130 cm wing-span; this subspecies weighs 325–397 g. The forehead and the underparts are white, the back and inner wings are dusky-grey. In winter, the upperparts plumage wears to a paler grey, and the crown of the head becomes white, merging the rear into a black crest and mask. The adults of both sexes are identical in appearance but are distinctive in winter adult, and strongly patterned in grey, brown, white and moulting bars. After moult, the young resemble the adult, but still have a variegated wing pattern. For the southern African races, the breeding period is from December to April, whereas the birds are moult on Australia and Oceania from May to October. The northern subspecies b. velox and thalassina are in breeding plumage from September to May, while the breeding birds are in plumage in August to September or October for the northern African races. The species epithet bergius commemorates Carl Heinrich Bergius, a Prussian pharmacist and botanist who collected the first specimens of this tern near Cape Town.

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, a deeply forked tail and short legs. They are distinctive with a black cap that is reduced or flecked with white in the winter, and have a dark bar on the inner flight feathers with dark bars on the inside of the wings. 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. It is thought that the critically endangered Chinese crested Tern is also very closely related, as that bird was formerly considered to be conspecific with the greater crested tern as a synonym of the subspecies t. b. cristatus. A similar number of other potential subspecies have been proposed, but are not considered valid. The greater crested tern has about five geographical races, differing mainly in the colour of the upper parts and bill.

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