Caspian Tern
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| Caspian Tern | ||||||||||||||
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 Adult in summer plumage
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| Sterna caspia (Pallas, 1770) |
The Caspian Tern (Hydroprogne caspia, formerly Sterna caspia;[1] syn. Hydroprogne tschegrava) is a species of tern, with a subcosmopolitan but scattered distribution. Despite its extensive range, it is monotypic, with no subspecies accepted.[2] In New Zealand it is also known by the Maori name Taranui.
It is the world's largest tern 48–56 cm long, with a wingspan of 127–140 cm and a weight of 574–782g.[2] Adult birds have black legs, and a long thick red-orange 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.[2] 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.[3]
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 winter in the Old World tropics. African and Australasian birds are resident or disperse over short distances.[2]
The global population is about 50,000 pairs; numbers in most regions are stable, but the Baltic Sea population (1,400–1,475 pairs in the early 1990s) is declining and of conservation concern.[2][4]
They feed mainly on fish, which they dive for, hovering high over the water and then plunging. They also occasionally eat large insects and the young and eggs of other birds. 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.[2][3]
Breeding is in spring and summer, with one to three pale blue green eggs heavily spotted brown laid. They nest either together in colonies, or singly in mixed colonies of other tern and gull species. The nest is on the ground among gravel and sand, or sometimes on vegetation; incubation lasts for 26–28 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 35–45 days.[2]
The Caspian Tern is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.
[edit] References
- ^ Bridge, E. S., Jones, A. W., & Baker, A. J. (2005). A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution. Molecular Phylogenetics and Evolution 35: 459–469. PDF pdf file
- ^ a b c d e f g del Hoyo J., Elliott, A., & Sargatal, J., eds. (1996). Handbook of the Birds of the World 3: 645. Lynx Edicions ISBN 84-87334-20-2.
- ^ a b Mullarney, K., Svensson, L., Zetterström, D., & Grant, P. J. (1999). Collins Bird Guide. Collins ISBN 0-00-219728-6.
- ^ Snow, D. W., & Perrins, C. M. (1998). The Birds of the Western Palearctic Concise Edition OUP ISBN 0-19-854099-X.
- BirdLife International (2004). Sterna caspia. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006. Database entry includes justification for why this species is of least concern
- Burnie, David & Wilson, Don E. (editors) (2001): [Caspian Tern]. In: Smithsonian Institution Animal: The Definitive Visual Guide to the World's Wildlife: 307. Washington DC & New York, Smithsonian Institution & Dorling Kindersley Publishing. ISBN 0-7894-7764-5
- Collinson, M. (2006). Splitting headaches? Recent taxonomic changes affecting the British and Western Palaearctic lists. British Birds 99(6): 306-323.
- Falla RA, Sibson RB & Turbot EG (1966) A Field guide to the birds of New Zealand. Collins, London (ISBN 0-00-212022-4)
- Harrison, Peter (1988): Seabirds (2nd edition). Christopher Helm, London ISBN 0-7470-1410-8
- National Geographic Society (2002): Field Guide to the Birds of North America. National Geographic, Washington DC. ISBN 0-7922-6877-6
- Sibley, David Allen (2000): The Sibley Guide to Birds. Alfred A. Knopf, New York. ISBN 0-679-45122-6
