0 the caspian tern (hydroprogne caspia , formerly sterna caspia) is a species of tern , with a subcosmopolitan but scattered distribution .
1  despite its extensive range , it is monotypic of its genus , and has no accepted subspecies .
2  the genus name is from ancient greek hudros , "water", and latin progne , "swallow" .
3  the specific caspia is from latin and , like the english name , refers to the caspian sea .
4 it is the world's largest tern with a length of 4856 cm , a wingspan of 127140 cm and a weight of 574782g .
5  adult birds have black legs , and a long thick red-orange bill with a small black tip .
6  they have a white head with a black cap and white neck , belly and tail .
7  the upper wings and back are pale grey; the underwings are pale with dark primary feathers .
8  in flight , the tail is less forked than other terns and wing tips black on the underside .
9  in winter , the black cap is still present (unlike many other terns), but with some white streaking on the forehead .
10  the call is a loud heron-like croak .
11 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) .
12  north american birds migrate to southern coasts , the west indies and northernmost south america .
13  european and asian birds spend the non-breeding season in the old world tropics .
14  african and australasian birds are resident or disperse over short distances .
15 the global population is about 50,000 pairs; numbers in most regions are stable , but the baltic sea population (1,4001,475 pairs in the early 1990s) is declining and of conservation concern .
16 the caspian tern is one of the species to which the agreement on the conservation of african-eurasian migratory waterbirds (aewa) applies .
17 they feed mainly on fish , which they dive for , hovering high over the water and then plunging .
18  they also occasionally eat large insects , the young and eggs of other birds and rodents .
19  they may fly up to 60 km from the breeding colony to catch fish; it often fishes on freshwater lakes as well as at sea .
20 breeding is in spring and summer , with one to three pale blue green eggs , with heavy brown spotting , being laid .
21  they nest either together in colonies , or singly in mixed colonies of other tern and gull species .
22  the nest is on the ground among gravel and sand , or sometimes on vegetation; incubation lasts for 2628 days .
23  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 .
24  fledging occurs after 3545 days .
25  image:caspian tern takeoff rwd .
26 jpg|preparing for takeoff image:hydroprogne caspia - gould's lagoon .
