Justification This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Family/Sub-family Laridae

Species name author Pallas, 1770

Taxonomic source(s) AERC TAC (2003), AOU checklist (1998 + supplements), Christidis and Boles (1994), Christidis and Boles (2008), Cramp and Simmons (1977-1994), Dowsett and Forbes-Watson (1993), SACC (2005 + updates), Sibley and Monroe (1990, 1993), Stotz et al. (1996), Turbott (1990)

Synonyms Hydroprogne caspia Stotz et al. (1996), Hydroprogne caspia AOU checklist (1998 + supplements), Hydroprogne caspia Christidis and Boles (2008)

Taxonomic note The BirdLife Taxonomic Working Group is aware that phylogenetic analyses have been published which have proposed generic rearrangements which may affect this species, but prefers to wait until work by other taxonomists reveals how these changes affect the entire groups involved.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

240,000 - 420,000

unset

6,290,000 km²

No

Range & population The Caspian Tern has a cosmopolitan but scattered distribution. 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 distances¹.

Important Bird Areas Click here to view map showing IBAs where species is recorded and triggers any of the IBA criteria.

Ecology: Behaviour Although populations breeding near the equator are largely sedentary², northern populations are strongly migratory and disperse after breeding before migrating southwards¹. The species breeds between April and June (northern Hemisphere) or between September and December (southern Hemisphere)¹ in large dense monospecific colonies or as single pairs or small groups (2-3 pairs) amidst large colonies of other species^{1, 3, 4}. It is not a highly gregarious species outside of the breeding season⁴ but may aggregate into flocks on passage⁶, and during the winter it may feed in loose congregations¹ in rich fishing areas or at nightly roost sites⁴. Habitat The breeding, passage and wintering habitats of this species are similar, although during the winter it is largely confined to the coast¹⁰. It frequents sheltered sea coasts^{1, 4}, estuaries^{1, 2, 5}, inlets, bays, harbours⁵, coastal lagoons^{4, 5}, saltmarshes¹ and saltpans^{5, 9}, also occurring inland on fresh or saline wetlands including large lakes, inland seas^{1, 2}, large rivers^{3, 5}, creeks⁵, floodlands⁴, reservoirs^{1, 2, 5} and sewage ponds⁵. When breeding the species shows a preference for nesting on sandy, shell-strewn or shingle beaches^{3, 4}, sand-dunes, flat rock-surfaces⁴, sheltered reefs⁵ or islands^{1, 3, 4} with sparse vegetation and flat or gently sloping margins surrounded by clear, shallow, undisturbed waters⁴. It also forms winter roosts on sandbars, mudflats and banks of shell¹. Diet Its diet consists predominantly of fish 5-25 cm in length¹⁰ as well as the eggs and young of other birds, carrion¹, aquatic invertebrates³ (e.g. crayfish)¹⁰, flying insects^{6, 10} and earthworms¹⁰. Breeding site The nest is a shallow depression in the sand, gravel, shells, sparse vegetation¹ or dried mud² of ridges, beaches^{3, 4, 5}, dunes⁴, flat rocky or stony islets, banks⁵, islands or reefs in seas, lakes and large rivers³, dredge spoil piles and islands in reservoirs⁵. The species nests in large colonies or as single pairs or small groups amidst colonies of other species, neighbouring nests placed between 0.7 and 4 m part¹. The species may forage up to 60 km from the site of the breeding colony¹. Management information Management for this species should include a number of measures such as habitat and vegetation management, the use of artificial nest substrates, predator management (e.g. control of gull populations) and the minimisation of disturbance¹⁰. Habitat and vegetation management may include the creation of artificial islands with calm water on their leeward side to allow the growth of submerged vegetation and fish spawning habitats, or alternatively the creation of floating artificial nesting-rafts (e.g. barges covered with sand)¹⁰.

Threats The species is currently threatened by the loss and deterioration of breeding habitat through accelerated vegetation succession (possibly through the introduction of exotic plant species)¹⁰ and may be threatened in the future by habitat loss through inundation as a result of sea-level rise¹⁰. The species is vulnerable to human disturbance at nesting colonies⁸ especially during the early-courtship and incubation periods¹⁰, and exposure to bioaccumulated contaminants (e.g. organochlorines or methylmercury) in fish could be lowering the species's reproductive success¹. Newcastle disease^{7, 10} and avian botulism may also threaten concentrated local populations (although these diseases are unlikely to threaten the global population as a whole)¹⁰.

References 1. del Hoyo et al. (1996). 2. Richards (1990). 3. Flint et al. (1984). 4. Snow and Perrins (1998). 5. Higgins and Davies (1996). 6. Urban et al. (1986). 7. Kuiken et al. (2006). 8. Blokpoel and Scharf (1991). 9. Martin and Randall (1987). 10. Shuford and Craig (2002).

Further web sources of information

Detailed species account from Birds in Europe: population estimates, trends and conservation status (BirdLife International 2004)

Text account compilers Stuart Butchart (BirdLife International), Rob Calvert (BirdLife International), Jonathan Ekstrom (BirdLife International), Lucy Malpas (BirdLife International)

IUCN Red List evaluators Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International)

Recommended citation BirdLife International (2010) Species factsheet: Sterna caspia. Downloaded from http://www.birdlife.org on 30/7/2010

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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