[order] Charadriiformes | [family] Sternidae | [latin] Sterna caspia | [UK] Caspian Tern | [FR] Sterne caspienne | [DE] Raubseeschwalbe | [ES] Gaviotín de Pico Rojo | [IT] Sterna maggiore | [NL] Reuzenstern

Reuzenstern determination

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The largest of the terns, the Caspian Tern is one of the most widespread tern species in the world, occurring on every continent except Antarctica. It is white with a light gray mantle and white undersides. The breast and face are also white. The legs and eyes are black, and the bill is large, heavy, and bright red-orange. It has a shallowly forked tail and a slight crest that gives the head a squared-off look. In breeding plumage, the Caspian Tern sports a solid black cap, which recedes in the non-breeding season, resulting in a spray of white at the face mixing with black. Juveniles appear similar to adults in non-breeding plumage but have a lighter mantle that is mottled with light tan.
Caspian Terns are less gregarious than other terns, nesting in smaller colonies, although this is changing in Washington. They can be quite aggressive. When foraging, they fly with their bills pointing downward. When they spot a fish, they hover and then plunge into the water after it, often submerging completely. Their broad wings allow them to soar, gull-like, flapping with strong, slow wing-beats.

Caspian Terns use fresh- and saltwater wetlands, especially estuaries, coastal bays, and beaches. They are not usually found on open ocean, but prefer protected waters. Nesting usually takes place on low sand or gravel islands with sparse vegetation. In Washington, the birds have shifted their preferred habitat from natural sites inland to coastal, human-altered sites (often islands made from dredged material). They have also shifted from nesting in small groups mixed with gulls to large colonies of only Caspian Terns.

Sterna caspia breeds patchily along the Baltic Sea coast and in south-east Europe, which accounts for less than a quarter of its global breeding range. Its European breeding population is small (as few as 4,700 pairs), and underwent a large decline between 1970-1990. Although the species increased substantially overall during 1990- 2000—with increasing, stable or fluctuating trends across most of its European range—its population size still renders it susceptible to the risks affecting small populations, and consequently it is evaluated as Rare.
Being absent from only Antarctica and South America, this large tern has a nearly world-wide but very fragmented distribution. In Europe it is breeding in the Baltic Sea and along the northern coasts of the Black and Caspian seas. In 1988 there was a breeding case in Spain. Baltic birds winter mainly in Mali. The total European population is estimated at 4700-7800 breeding pairs, but has strongly fluctuated in the past. Since several decades it is undergoing a decline, the causes of which are not well understood but could be linked to increasing dryness in the Sahel region.
Sterna caspia breeds patchily along the Baltic Sea coast and in south-east Europe, which accounts for less than a quarter of its global breeding range. Its European breeding population is small (as few as 4,700 pairs), and underwent a large decline between 1970-1990. Although the species increased substantially overall during 1990- 2000-with increasing, stable or fluctuating trends across most of its European range-its population size still renders it susceptible to the risks affecting small populations.

The vast majority of the diet of the Caspian Tern is fish, especially those that swim near the surface of the water. In the Columbia River estuary, where most of Washington's population breeds, salmonid smolts are a major prey item.

This species has a large range, with an estimated global Extent of Occurrence of 1,000,000-10,000,000 km˛. It has a large global population estimated to be 180,000-320,000 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]

First breeding at the age of three years, Caspian Terns nest in colonies in areas with no vegetation, often on islands. Both parents help build the nest, which is located on the ground and can range from a scrape in the sand to a depression lined with a sturdy rim of vegetation and mollusk and crustacean shells. Both parents incubate the 1 to 3 eggs for about three weeks. A few days after hatching, the young may leave the nest but stay nearby, or they may remain at the nest until ready to fly. Both parents help feed the young during the long adolescent period. The young first fly about a month after hatching, but may stay with, and be fed by, the parents for many more months.

Migratory throughout most of west Palearctic. Dispersal from Baltic breeding grounds begins soon after fledging, from mid-July to August, and continues through Europe until October, occasionally November. Prevailing movement is south along broad spreading front from Portugal to Black Sea. Minority follow North Sea and Atlantic coast, and may stray: e.g. to Britain, July-November, where more often found inland than on coast. Most birds from Baltic and Black Sea areas winter in tropical West Africa. Spring migration (March-May) through Europe apparently follows reverse of autumn routes; but passage through most countries generally lighter and less protracted than in autumn, partly because adults travel faster and roost less without accompanying offspring. Main arrival in Baltic late April to May.