This is a fairly large and powerful tern, similar in size and general appearance to a Sandwich tern, but the short thick gull-like bill, broad wings, long legs and robust body are distinctive. The summer adult has grey upperparts, white underparts, a black cap, strong black bill and black legs. In winter, the cap is lost, and there is a dark patch through the eye like a Forster’s tern or a Mediterranean gull. Juvenile Gull-Billed Terns have a fainter mask, but otherwise look much like winter adults.
It is 33–43 cm in length and 85–103 cm in wingspan. Body mass ranges from 200–300 g. Life expectancy: 16 years.
The Gull-Billed Tern produces a screaming sound ker-wik, similar to the sound made by a grasshopper. The elderly have a deeper, throat cry, and the young birds issue a light and fast pi-eype. The alert sound is nasal. The bird is mostly quiet in winter.
Distribution and Habitat
A cosmopolitan species with spotted nesting range. The noun subspecies S. n. nilotica inhabits Europe, Northwest Africa and the Middle East, Kazakhstan, Iran, Pakistan, India, Manchuria. Northern breeding populations of this species are migratory. Winning in Africa. Spring migration is in April-May, and autumn – in August-September.
The Gull-Billed Tern lives in super-salted water basins; during migrations – freshwater, brackish and super-salted wetlands in the lower parts. She likes sandy beaches and coastal swamps.
It is also found in Bulgaria (a nesting-migratory, in the past only a rare migrant) mostly in Atanasovsko and Pomorie Lake. During migration, it can be seen in the other wetlands around Burgas, the Shabla and Durankulak lakes and other places along the Black Sea coast.
Gull-Billed Tern feeds on various species of terrestrial insects, lizards, amphibians, small rodents, small of gulls, shorebirds and songbirds; less often – small fish and water invertebrates. Unlike other terns, she searches for her food above the ground, lands in a high place, and flies trapping insects in flight, and can also pursue her prey on the ground.
It breeds in colonies close to coastal lagoons and inland salt marshes. The Gull-Billed Tern lays two or three eggs in a small depression, lined with shells. Sometimes the nest can be a well made cup of dry grass on a sandy island in the salt marshes. The incubation period lasts from 22 to 23 days and the young fishes fly after 28 to 35 days.
The species is in a sharp decline in Europe, currently classified as rare. Bulgaria’s Red Book – critically endangered.