Medium-sized pale tern with black cap and crest. Long slender bill, long pointed wings and moderately long, and forked tail. back and upperwigs pale ash grey. Rump and tail white. underparts white, sometimes tinged with pink. Primaries with white inner webs and silvery outer webs. Bill varies from black with yellow tip. Legs black, Occasionally yellow. Races differ only slightly.eurygnatha is mainly yellow-billed, but often with dark bill base, legs sometimes partly yellow, rarely all yellow. acuflavidus slightly smaller, with outer tips of outer primaries grey rather than white.
Strictly coastal and mainly a warm-water species. favoured breeding sites are low-lying and subject to inundation, wind-blown sand. Prefers open, unvegetated sandy, muddy or bare coral substrates. Late breeders forced to nest closer to high tide line. Outside breeding season frequents sandy or rocky beach fronts, mangrove flats, estuaries and harbours.
Sterna sandvicensis is a widespread but very dispersed breeder in coastal areas of
Europe, which holds >50% of its global population. Its European breeding population
is relatively small (<130,000 pairs), and underwent a moderate decline between 1970-
1990. Although there were declines in a few countries during 1990-2000, key
populations in the Netherlands, Ukraine and Russia fluctuated, and the species
declined only slightly overall. Nevertheless, its population still remains below the
level that preceded its decline, and consequently it is evaluated as Depleted.
This tern is breeding along the coasts of western Europe, from Aquitaine to Scotland and Estonia, in the western Mediterranean, in the Black and Caspian seas and along the eastern coasts of the Americas. Birds of Europe winter along the Atlantic coasts of Africa, from Senegal to South Africa. The population of the European Union is estimated at 60000 breeding pairs. After a strong decline during last century, this species has recovered but it is still subject to important fluctuations
Diet entirely on fish, mainly menhaden and anchovies, sometimes sardines (Flying-fish in Caribbean). Also swoops to pick up marine worms from mudflats, and takes shorebird chicks. Plunge-dives for small fish, from up to 10 m. Feeds over fishing nets. Scavenges over sea lions and sometimes feeds over porpoise pods. Sometimes defend feeding territories along shore.
This species has a large range, with an estimated global Extent of Occurrence of 100,000-1,000,000 km˛. It has a large global population estimated to be 460,000-500,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]
Start of breeding depend on geographical zone. May-June in Europe, May in Curacao, June in Brazil and December in Argentina. Usually nests next to other terns or gulls. Nest is a shallow scrape rimmed with excreta. 1-2 eggs are laid, incubation 21-29 days. Chicks are whitish to buff, grey or brown, with few or heavy black speckles.
Migratory throughout west Palearctic. West European and probably Estonian birds share similar winter quarters, mainly on west coast of Africa from Mauritania south to Cape of Good Hope. Birds from Black Sea winter principally in eastern Black Sea and central and south-east Mediterranean; also along coasts of Spain and Portugal, occasionally reaching West Africa. Caspian Sea population has separate winter quarters, mainly in Persian Gulf and Arabian Sea. Great majority of 1-year-olds remain in winter quarters during summer; small proportion move north, mainly to Mediterranean or Iberia, and a few further north. Some 2-year-olds remain in tropics throughout summer, but majority migrate to European waters, many reaching colonies about June when, exceptionally, they breed. At 3 years old, minority still summer in tropics, but majority migrate to breeding grounds, arriving at colonies from late April (Denmark) to May (Britain and Ireland). Most birds breeding by 4 years old, so full migration pattern shown from that age.