Gull-billed Tern
Encyclopedia
The Gull-billed Tern formerly Sterna nilotica (Bridge et al., 2005), is a seabird
of the tern
family Sternidae. It is now considered to be in its own
genus.
It breeds in warmer parts of the world 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.
All forms show a post-breeding dispersal, but the northern breeders are most migratory
, wintering south to Africa
, the Caribbean
and northern South America, southern Asia and New Zealand
.
This species breeds in colonies on lakes, marshes and coasts. It nests in a ground scrape and lays two to five eggs. While widely distributed in freshwater areas in Eurasia, it is associated almost solely with saltwater, coastal areas in North America.
This is a somewhat atypical tern, in appearance like a Sterna tern, but with feeding habits more like the Chlidonias marsh terns, Black Tern
and White-winged Tern
. It used to be grouped in the genus Sterna
but is now placed on its own in the genus Gelochelidon.
The Gull-billed Tern does not normally plunge dive for fish
like the other white terns, and has a broader diet than most other terns. It largely feeds on insects taken in flight, and also often hunts over wet fields and even in brushy areas, to take amphibians and small mammals, as well as small birds and the chicks and eggs of other terns.
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. The call is a characteristic ker-wik. It is 33–42 cm (13–16.5 in) in length and 76–91 cm (29.9–35.8 in) in wingspan. Body mass ranges from 150–292 g (5.3–10.3 oz).
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.
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.
The Gull-billed Tern is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA
) applies.
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
of the tern
Tern
Terns are seabirds in the family Sternidae, previously considered a subfamily of the gull family Laridae . They form a lineage with the gulls and skimmers which in turn is related to skuas and auks...
family Sternidae. It is now considered to be in its own
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
genus.
It breeds in warmer parts of the world in southern Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
(and a very small isolated population in northern Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
), temperate and eastern Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, both coasts of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, eastern South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. This bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
has a number of geographical races, differing mainly in size and minor plumage details.
All forms show a post-breeding dispersal, but the northern breeders are most migratory
Bird migration
Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...
, wintering south to Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
and northern South America, southern Asia and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
.
This is a somewhat atypical tern, in appearance like a Sterna tern, but with feeding habits more like the Chlidonias marsh terns, Black Tern
Black Tern
The Black Tern, Chlidonias niger, is a small tern generally found in or near inland water in Europe and North America. As its name suggests, it has predominantly dark plumage.- Description :...
and White-winged Tern
White-winged Tern
The White-winged Tern, or White-winged Black Tern, Chlidonias leucopterus, is a small tern generally found in or near bodies of fresh water across from Southeastern Europe east to Australia....
. It used to be grouped in the genus Sterna
Sterna
Sterna is a genus of terns in the bird family Sternidae. It used to encompass most "white" terns indiscriminately, but mtDNA sequence comparisons have recently determined that this arrangement is paraphyletic...
but is now placed on its own in the genus Gelochelidon.
The Gull-billed Tern does not normally plunge dive for fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
like the other white terns, and has a broader diet than most other terns. It largely feeds on insects taken in flight, and also often hunts over wet fields and even in brushy areas, to take amphibians and small mammals, as well as small birds and the chicks and eggs of other terns.
This is a fairly large and powerful tern, similar in size and general appearance to a Sandwich Tern, but the short thick gull-like
Gull
Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...
bill
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
, 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. The call is a characteristic ker-wik. It is 33–42 cm (13–16.5 in) in length and 76–91 cm (29.9–35.8 in) in wingspan. Body mass ranges from 150–292 g (5.3–10.3 oz).
In winter, the cap is lost, and there is a dark patch through the eye like a Forster's Tern
Forster's Tern
The Forster's Tern, Sterna forsteri, is a member of the tern family Sternidae. It breeds inland in North America and winters south to the Caribbean and northern South America....
or a Mediterranean Gull
Mediterranean Gull
The Mediterranean Gull, Ichthyaetus melanocephalus, is a small gull which breeds almost entirely in Europe, mainly in the south east, especially around the Black Sea, and in central Turkey. There are colonies elsewhere in southern Europe, and this species has undergone a dramatic range expansion in...
. Juvenile Gull-billed Terns have a fainter 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
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
coasts.
The Gull-billed Tern is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA
AEWA
The Agreement on the Conservation of African-Eurasian Migratory Waterbirds is the largest of its kind developed so far under the Bonn Convention. It was concluded on 16 June 1995 at The Hague, the Netherlands and entered into force on 1 November 1999 after the required number of at least fourteen...
) applies.