01-09-2019 Skerries Co.Dublin
[order] Charadriiformes | [family] Sternidae | [latin] Sterna sandvicensis | [UK] Sandwich Tern | [FR] Sterne caugek | [DE] Brandseeschwalbe | [ES] Gaviotín Brasilero | [IT] Beccapesci | [NL] Grote Stern | [IRL] Geabhróg scothdhubh
Measurements
spanwidth min.: 85 cm
spanwidth max.: 87 cm
size min.: 37 cm
size max.: 43 cm
Breeding
incubation min.: 21 days
incubation max.: 29 days
fledging min.: 28 days
fledging max.: 30 days
broods 1
eggs min.: 1
eggs max.: 2
Physical characteristics
Medium-sized pale tern with black cap and crest. Long slender bill, long pointed wings and moderately long, and forked tail. back and upper wings 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.
Habitat
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.
Other details
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
Feeding
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.
Breeding
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.
Migration
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.
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Common Tern (Sterna hirundo)
[group] Gulls and terns | [order] CHARADRIIFORMES | [family] Laridae | [latin] Sterna hirundo | [UK] Common Tern | [FR] Sterne pierregarin | [DE] Fluss-Seeschwalbe | [ES] Gaviotin Comun | [NL] Visdief | [IRL] Geabhróg
Sea Swallow
Status: Summer visitor from March to October to all Irish coasts.
Conservation Concern: Amber-listed in Ireland due to its localised breeding population. The European population has been evaluated as Secure.
Identification: Usually seen over the sea or over large inland lakes. Slender seabird with narrow, pointed wings, long forked tail and long, pointed bill. Grey above and white below, dark cap to head. Flight light and buoyant, can hover briefly over the sea before diving in. Very similar to Artic Tern (with which it breeds) and told apart by plumage and structure. Common Tern has a longer head and bill and slightly broader wings, which look central on the body. Adults have a orangey red bill, usually with a small dark tip. Underparts are whiter than Artic Tern and there is no contrast with cheek. The wing pattern is useful in separation, Common tern shows a dark wedge in the primaries which develops over the summer and a defuse bar to the trailing edge of the primaries. Common terns have shorter tail steamers, not extending beyond the wing tips. Adult winter plumage, like all terns is different from breeding plumage and can develop in the summer months. Has a white forehead, all dark bill and dark carpel bar. Also has distinctive juvenile plumage with gingery mantle, a dark secondary bar and dark carpel bar. Bill base is orange. Shows a diffuse trailing edge to the primaries. First and second summer plumages are rarely seen in Europe.
Similar Species: Arctic and Roseate Terns.
Call: A noisy bird when breeding, giving a rapid series of quarrelsome calls.
Diet: Chiefly fish.
Breeding: Nest colonially on the ground from April to October. Breeds on the coast, with larger colonies in Co. Dublin, Co. Wexford and Co. Galway. Also breeds inland on islets in freshwater lakes, notably in Co. Galway and in Co. Mayo.
Wintering: Winters in west and south Africa.