Gelochelidon nilotica (J.F.Gmelin, 1789)

Scientific Nomenclature

This is the description of the gull-billed tern, with the scientific name Gelochelidon nilotica (J.F.Gmelin, 1789).

General Morphology

This is a fairly large, powerful tern that is similar in size and general appearance to a Sandwich tern, but can be distinguished by its distinctive short thick gull-like bill, broad wings, long legs and robust body.

Summer Adult Plumage

Summer adult individuals have grey upperparts, white underparts, a black cap, a strong black bill and black legs.

Vocalization

Their characteristic call is described as ker-wik.

Standard Measurements

This species measures 33–42 cm (13–17 in) in length, has a wingspan of 76–91 cm (30–36 in), and a body mass ranging from 150–292 g (5.3–10.3 oz).

Winter Adult Plumage

In winter, adults lose their black cap and develop a dark patch through the eye, similar to that seen on a Forster's tern or a Mediterranean gull.

Juvenile Plumage

Juvenile gull-billed terns have a fainter mask than winter adults, but otherwise closely resemble winter adults.

Identification Confusion Risk

Juvenile Sandwich terns have short bills, and are frequently mistaken for gull-billed terns in areas where gull-billed terns are uncommon, such as North Sea coasts.

Breeding Range

This species breeds in warmer regions across the globe: southern Europe, temperate and eastern Asia, both coasts of North America, and eastern South America.

Geographical Races

There are a number of geographical races of this bird, that differ mainly in size and minor plumage details.

Post-Breeding Dispersal

All forms of this tern undergo post-breeding dispersal.

Migratory Patterns

Northern breeding populations are the most migratory, migrating south to winter in Africa, the Caribbean, northern South America, southern Asia, and New Zealand.

Conservation Agreement Coverage

The gull-billed tern is one of the species covered by the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA).

Taxonomic Distinctiveness

This is a somewhat atypical tern.

Feeding Habit Comparison

While it resembles Sterna terns in appearance, its feeding habits are more similar to those of Chlidonias marsh terns, including the black tern and white-winged tern.

Diet Breadth

Unlike most other white terns, it does not normally plunge dive to catch fish, and has a broader diet than most other terns.

Typical Prey Items

It feeds largely on insects captured in flight, and also often hunts over wet fields and even brushy areas to catch amphibians and small mammals.

Opportunistic Feeding Behavior

It is an opportunistic feeder, and has been observed picking up and eating dead dragonflies from road surfaces.