The Gull-billed Tern (Sterna nilotica or Gelochelidon nilotica) is a seabird of the tern family Sternidae.
It breeds in warmer parts of the world. It can be found in southern Europe (and a very small isolated population in northern Germany and Denmark), temperate and eastern Asia, both coasts of North America, eastern South America and Australia. This bird has a number of geographical races, differing mainly in size and minor plumage details.
After breeding, these birds will disperse from their flocks and begin their winter migration. The northern breeders are the most migratory, wintering south to Africa, the Caribbean and northern South America, southern Asia and New Zealand.
This gregarious species breeds in colonies on lakes, marshes and coasts. It builds its nests in a ground scrape into which the female lays two to five eggs.
This is a somewhat uncharacteristic tern. In appearance its similar to Sterna tern, but its feeding habits are more like that of the Chlidonias marsh terns, Black Tern and White-winged Tern. It is sometimes grouped in the genus Sterna, and sometimes given its own genus Gelochelidon.
The Gull-billed Tern does not normally plunge dive for fish like the other white terns. Instead it feeds on insects taken in flight, and also often hunts over wet fields in search of frogs and small mammals (mice, voles, etc).
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 make it distinctive. During the summer the adult has grey upperparts, white underparts, a black cap, strong black bill and black legs. The call is a characteristic ker-wik.
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 lighter mask but otherwise look much like winter adults.
Juvenile Sandwich Terns have a short bill, and are frequently mistaken for Gull-billed Tern where the latter species is uncommon, such as North Sea coasts.