The greater crested tern (Thalasseus bergii) is a seabird in the tern family, which 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. The greater crested tern has grey upperparts, white underparts, a yellow bill, and a shaggy black crest which recedes in winter. Like all members of the genus Thalasseus, it 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 which has learned to follow fishing boats for jettisoned bycatch, and to utilise 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. This greater crested tern in flight was photographed at Mortimer Bay in Tasmania, Australia.Photograph credit: John Harrison