Caspian Tern
by J McCombie
Title
Caspian Tern
Artist
J McCombie
Medium
Painting - Photographic
Description
The Caspian tern (Hydroprogne caspia, formerly Sterna caspia) is a species of tern, with a subcosmopolitan but scattered distribution. Despite its extensive range, it is monotypic of its genus, and has no accepted subspecies. The genus name is from Ancient Greek hudros, "water", and Latin progne, "swallow". The specific caspia is from Latin and, like the English name, refers to the Caspian Sea.
As large as a big gull, the Caspian Tern is the largest tern in the world and one of the most easily identified terns throughout its worldwide range. It is the world's largest tern with a length of 4860 cm (1924 in), a wingspan of 127145 cm (5057 in) and a weight of 530782 g (18.727.6 oz). Adult birds have black legs, and a long thick red-orange or coral bill with a small black tip. They have a white head with a black cap and white neck, belly and tail. The upper wings and back are pale grey; the underwings are pale with dark primary feathers. In flight, the tail is less forked than other terns and wing tips black on the underside. In winter, the black cap is still present (unlike many other terns), but with some white streaking on the forehead. The call is a loud heron-like croak.
Their breeding habitat is large lakes and ocean coasts in North America (including the Great Lakes), and locally in Europe (mainly around the Baltic Sea and Black Sea), Asia, Africa, and Australasia (Australia and New Zealand). North American birds migrate to southern coasts, the West Indies and northernmost South America. European and Asian birds spend the non-breeding season in the Old World tropics. African and Australasian birds are resident or disperse over short distances. The global population is about 50,000 pairs.
They feed mainly on fish, which they dive for, while flying over water with bill pointing down and hovering high over the water and then plunging into the water in an aerial dive. They also occasionally eat crayfish, large insects, the young and eggs of other birds and rodents. They may fly up to 60 km (37 mi) from the breeding colony to catch fish; they often fish on freshwater lakes as well as at sea.
Breeding is in wide variety of habitats along water, such as salt marshes, barrier islands, dredge spoil islands, freshwater lake islands, and river islands in spring and summer, with one to three pale blue green eggs, with heavy brown spotting, being laid. They nest either together in colonies, or singly in mixed colonies of other tern and gull species. The nest is a scrape on the ground among gravel and sand which may have elaborate rim of sticks, or it is sometimes on vegetation; incubation lasts for 2628 days. The chicks are variable in plumage pattern, from pale creamy to darker grey-brown; this variation assists adults in recognizing their own chicks when returning to the colony from feeding trips. Fledging occurs after 3545 days.
The Caspian Tern aggressively defends its breeding colony. It will pursue, attack, and chase potential predatory birds, and can cause bloody wounds on the heads of people who invade the colony. The entire colony will take flight, however, when a Bald Eagle flies overhead, exposing the chicks to predation from gulls. The world's largest breeding colony is on a small, artificial island in the Columbia River between Oregon and Washington, home to more than 6,000 breeding pairs each year. Young Caspian Terns appear to have a difficult time learning to catch fish efficiently. They stay with their parents for long periods of time, and are fed by them even on the wintering grounds. Many young terns do not return to the nesting grounds for several years, remaining instead on the wintering areas. During migration and winter found along coastlines, large rivers and lakes. Roosts on islands and isolated spits. The oldest recorded wild Caspian Tern was at least 29 years, 7 months old when it was found in Louisiana in 1989. It had been banded in Michigan in 1959. The average life span of Great Lakes Caspian Terns is estimated to be 12 years.
There is little information on Caspian Tern populations trends, but the species appears to be stable overall, according to the North American Breeding Bird Survey. In some areas, numbers may be increasing, where birds use man-made dredge spoil islands and dikes for breeding. In other areas, the species is listed as rare or vulnerable because of the scattered nature of breeding colonies. Caspian Tern are declining in Europe. The North American Waterbird Conservation Plan estimates a continental population of between 66,000-70,000 breeders, and lists it a Species of Low Concern. It rates a 10 out of 20 on the Continental Concern Score. Caspian Tern is not on the 2016 State of North America's Birds Watch List. Beach nesting areas vulnerable to disturbance and predation.
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October 3rd, 2016
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