Greater Crested Tern

Greater Crested Tern Thailand

Gulf of Thailand

The greater crested tern has a wide distribution across the old word in tropical and warm temperate coastal regions. It breeds in South Africa, the Indian Ocea and the Pacific as far as Australasia. I photographed this bird perched on a mooring post out in the shallow waters of the Gulf of Thailand while on a whale watching trip,

Habitat

The great crested tern inhabits coastlines and islands.

Feeding

Fish make up 90% of the greater crested terns' diet  and the remainder consists of crustaceans, cephalopods and insects although occasionally they predate on lizards and turtle hatchlings.

They feed at sea by plunge diving for up to a metre or dipping on the surface with food swallowed in flight. Shoals of anchovy and sardines are favourite prey but they will so scavenge on the discarded catch of trawlers.

Breeding

The greater crested tern breeds in large colonies often with other seabirds. They choose tropical sandy islands  for breeding and roosting.  The male aggressively defends the chosen nest site from intruders but females of the species are welcomed with displays of head raising and bowing  which are reciprocated and they also exchange fish as part of the bonding process. Greater crested terns are monogamous and may continue a relationship for more than one season.

The nest is a shallow scrape, either unlined or lined with stones or cuttlefish bones, positioned on low‑lying sandy, rocky, or coral islands, sometimes amongst stunted shrubs, often without any shelter, One or two cream coloured eggs with blackish streaks are incubated by both parents and the precocial chicks are also fed by both.

Wildfile Specials
  • The greater crested tern stalks trawlers by both day and night and during the fishing season trawl discards such as prawns, gobies and cardinal fish can make up  70% of its diet. In an area of the Great Barrier Reef numbers have increased ten-fold probably as result of trawl by-catch.
  • The largest recorded greater crested tern colony contained between 12 and 15 thousand pairs and was located in the Gulf of Carpenteria, Australia.
  •  In South Africa, 7.5% of greater crested gulls nest on the roofs of buildings.
  •  Greater crested terns have red oil droplets in the cone cells of their eyes. These droplets sharpen their distance vision and increase contrast.
  • Greater crested terns can be confused with lesser crested terns but are 25% larger with a longer bill, bigger head and bulkier body. The orange-tinted bill of the lesser crested tern is diagnostic when compared with the yellow bill of the greater crested tern.