Gull-billed Tern Sterna nilotica
- IdentificationVisual tips about this species
- BehaviourHabitat, behaviour, and food
- PopulationSubspecies and numbers
- ReproductionNesting and eggs
Identification
The Gull-billed Tern gets its name from the fact that its bill is thicker and more gull-like than in other terns but it might have been more helpful to call it the 'gull-winged tern' as it is the broader wings and more leisurely gull-like flight which make it stand out from other terns. Its relatively large size and black bill separate it from all except Sandwich Tern but notice that the upperwing looks much cleaner, uniformly pearl-grey with just a vague dark border to the primaries. Also, the neat black crown and the stout black bill give the head a much tidier look. From below, the black trailing edge to the primaries is more distinct than on any other tern. In winter and juvenile plumages the head looks strikingly white apart from a finger of black leading backwards from the eye.
Ageing
Juveniles are quite variable with some having heavy markings on the upperparts and others virtually none. Usually the wings appear uniformly pale grey. The head is finely streaked with a darker streak through the eye. Winter adults are similar, but are more uniform above and have a paler crown, with a darker stripe through the eye.
Voice
Gull-billed Terns often announce their presence with a loud call ‘kay-veck’ ‘kay-veck, kay-veck’.
Sexing
Sexes similar.
Length
37cm
Migration
Winters in sub-Saharan Africa from Mauritania east to Nigeria and Chad.
Habitat
Breeds colonially at salt-pans, coastal lagoons and inland saline lakes. Often seen flying over open farmland close to the breeding sites; otherwise occurs most frequently in coastal areas.
Food
Mainly insects but also small fish, frogs and crustaceans.
Population trends
Having decreased since the end of the 19th Century this bird is now considered endangered. This decline is particularly worrying since it has occurred throughout the birds breeding strongholds of Russia, Spain and Turkey. Habitat loss and the destruction or disturbance of nesting sites are thought to be the chief causes of this trend but poisoning by pesticides in its winter quarters could also be important. In both Denmark and Germany this species is now restricted to just one breeding site.
Subspecies
Monotypic within the region.
Where in Britain and Ireland
A mostly annual vagrant to Britain. 271 British and Irish records up to the end of 2000.
Population in Europe
3,000-3,500 breeding pairs mainly in Spain, with other, smaller populations in France, Ukraine, Romania, Greece, Germany, Denmark and Italy. The last Dutch breeding population was destroyed with the building of the Rotterdam Harbour in the 1950's.
Where in Europe
A few pairs breed in the Danish part of the Waddensee but this is mostly a bird of southern Europe including coastal wetlands such as the Ebro Delta and Coto Donana (Spain) and many of the inland lakes of the central Turkish plateau (eg. Seyfe Golu and Kulu Golu). Occurs more widely as a passage migrant.
Nests
Nests closely together in large, dense colonies on small islands. It creates a shallow hollow with little or no lining.
Eggs
1-4, very pale yellow-buff or cream with blackish or dark brown spots and blotches, laid in April to June. Incubation takes 22-23 days. Young fledge after 28-35 days.1 brood per year.
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