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.
AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: #http://www.aerc.eu/DOCS/Bird_taxa_of _the_WP15.xls#.
Christidis, L.; Boles, W. E. 2008. Systematics and taxonomy of Australian birds. CSIRO Publishing, Collingwood, Australia.
Cramp, S.; Perrins, C. M. 1977-1994. Handbook of the birds of Europe, the Middle East and Africa. The birds of the western Palearctic. Oxford University Press, Oxford.
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.
SACC. 2006. A classification of the bird species of South America. Available at: #http://www.museum.lsu.edu/~Remsen/SACCBaseline.html#.
Turbott, E. G. 1990. Checklist of the birds of New Zealand. Ornithological Society of New Zealand, Wellington.
Hydroprogne caspia (del Hoyo and Collar 2014) was previously placed in the genus Sterna.
Distribution and population
Hydroprogne caspia Christidis and Boles (2008), Hydroprogne caspia AOU checklist (1998 + supplements), Hydroprogne caspia Stotz et al. (1996), Sterna caspia Pallas, 1770
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 distances (del Hoyo et al.
The global population is estimated to number c.240,000-420,000 individuals (Wetlands International 2006), while national population estimates include: c.50-1,000 individuals on migration and c.50-1,000 wintering individuals in China; c.50-1,000 individuals on migration and c.50-1,000 wintering individuals in Taiwan; < c.50 individuals on migration and < c.50 wintering individuals in Japan and c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Russia (Brazil 2009).Trend justification
The overall population trend is increasing, although some populations are decreasing, stable, or have unknown trends (Wetlands International 2006). This species has undergone a large and statistically significant increase over the last 40 years in North America (266% increase over 40 years, equating to a 38.3% increase per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007)EcologyBehaviour
Although populations breeding near the equator are largely sedentary (Richards 1990), northern populations are strongly migratory and disperse after breeding before migrating southwards (del Hoyo et al.
1996). The species breeds between April and June (northern Hemisphere) or between September and December (southern Hemisphere) (del Hoyo et al.
1996) in large dense monospecific colonies or as single pairs or small groups (2-3 pairs) amidst large colonies of other species (Flint et al.
1984, del Hoyo et al.
1996, Snow and Perrins 1998). It is not a highly gregarious species outside of the breeding season (Snow and Perrins 1998) but may aggregate into flocks on passage (Urban et al.
1986), and during the winter it may feed in loose congregations (del Hoyo et al.
1996) in rich fishing areas or at nightly roost sites (Snow and Perrins 1998). Habitat
The breeding, passage and wintering habitats of this species are similar, although during the winter it is largely confined to the coast (Shuford and Craig 2002). It frequents sheltered sea coasts (del Hoyo et al.
1996, Snow and Perrins 1998), estuaries (Richards 1990, Higgins and Davies 1996, del Hoyo et al.
1996), inlets, bays, harbours (Higgins and Davies 1996), coastal lagoons (Higgins and Davies 1996, Snow and Perrins 1998), saltmarshes (del Hoyo et al.
1996) and saltpans (Martin and Randall 1987, Higgins and Davies 1996), also occurring inland on fresh or saline wetlands including large lakes, inland seas (Richards 1990, del Hoyo et al.
1996), large rivers (Flint et al.
1984, Higgins and Davies 1996), creeks (Higgins and Davies 1996), floodlands (Snow and Perrins 1998), reservoirs (Richards 1990, Higgins and Davies 1996, del Hoyo et al.
1996) and sewage ponds (Higgins and Davies 1996). When breeding the species shows a preference for nesting on sandy, shell-strewn or shingle beaches (Flint et al.
1984, Snow and Perrins 1998), sand-dunes, flat rock-surfaces (Snow and Perrins 1998), sheltered reefs (Higgins and Davies 1996) or islands (Flint et al.
1984, del Hoyo et al.
1996, Snow and Perrins 1998) with sparse vegetation and flat or gently sloping margins surrounded by clear, shallow, undisturbed waters (Snow and Perrins 1998). It also forms winter roosts on sandbars, mudflats and banks of shell (del Hoyo et al.
Its diet consists predominantly of fish 5-25 cm in length (Shuford and Craig 2002) as well as the eggs and young of other birds, carrion (del Hoyo et al.
1996), aquatic invertebrates (Flint et al.
1984) (e.g. crayfish) (Shuford and Craig 2002), flying insects (Urban et al.
1986, Shuford and Craig 2002) and earthworms (Shuford and Craig 2002). Breeding site
The nest is a shallow depression in the sand, gravel, shells, sparse vegetation (del Hoyo et al.
1996) or dried mud (Richards 1990) of ridges, beaches (Flint et al.
1984, Higgins and Davies 1996, Snow and Perrins 1998), dunes (Snow and Perrins 1998), flat rocky or stony islets, banks (Higgins and Davies 1996), islands or reefs in seas, lakes and large rivers (Flint et al.
1984), dredge spoil piles and islands in reservoirs (Higgins and Davies 1996). 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 part (del Hoyo et al.
1996). The species may forage up to 60 km from the site of the breeding colony (del Hoyo et al.
1996). 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 disturbance (Shuford and Craig 2002). 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) (Shuford and Craig 2002).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) (Shuford and Craig 2002) and may be threatened in the future by habitat loss through inundation as a result of sea-level rise (Shuford and Craig 2002). The species is vulnerable to human disturbance at nesting colonies (Blokpoel and Scharf 1991) especially during the early-courtship and incubation periods (Shuford and Craig 2002), and exposure to bioaccumulated contaminants (e.g. organochlorines or methylmercury) in fish could be lowering the species's reproductive success (del Hoyo et al.
1996). Newcastle disease (Shuford and Craig 2002, Kuiken et al.
2006) and avian botulism may also threaten concentrated local populations (although these diseases are unlikely to threaten the global population as a whole) (Shuford and Craig 2002).
Related state of the world's birds case studies
Blokpoel, H.; Scharf, W. C. 1991. Status and conservation of seabirds nesting in the Great Lakes of North America. In: Croxall. J. P. (ed.), Seabird Status and Conservation: A Supplement, pp. 17-41. International Council for Bird Preservation.
Brazil, M. 2009. Birds of East Asia: eastern China, Taiwan, Korea, Japan, eastern Russia. Christopher Helm, London.
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Lynx Edicions BirdLife International.
del Hoyo, J., Elliott, A., and Sargatal, J. 1996. Handbook of the Birds of the World, vol. 3: Hoatzin to Auks. Lynx Edicions, Barcelona, Spain.
Delany, S.; Scott, D. 2006. Waterbird population estimates. Wetlands International, Wageningen, The Netherlands.
Flint, V.E., Boehme, R.L., Kostin, Y.V. and Kuznetsov, A.A. 1984. A field guide to birds of the USSR. Princeton University Press, Princeton, New Jersey.
Higgins, P. J.; Davies, S. J. J. F. 1996. Handbook of Australian, New Zealand and Antarctic birds vol 3: snipe to pigeons. Oxford University Press, Oxford.
IUCN. 2015. The IUCN Red List of Threatened Species. Version 2015-4. Available at: www.iucnredlist.org. (Accessed: 19 November 2015).
Kuiken, T.; Fouchier, R. A. M.; Rimmelzwaan, G. F.; Osterhaus, A. D. M. E. 2006. Emerging viral diseases in waterbirds. In: Boere, G.; Galbraith, C., Stroud, D. (ed.), Waterbirds around the world, pp. 418-421. The Stationary Office, Edinburgh, UK.
Martin, A. P.; Randall, R. M. 1987. Numbers of waterbirds at a commercial saltpan and suggestions for management. South African Journal of Wildlife Research 17(3): 75-81.
Richards, A. 1990. Seabirds of the northern hemisphere. Dragon's World Ltd, Limpsfield, U.K.
Shuford, W. D.; Craig, D. P. 2002. Status Assessment and Conservation Recommendations for the Caspian Tern (Sterna caspia) in North America. U.S. Department of the Interior, Fish and Wildlife Service, Portland, OR.
Snow, D.W. and Perrins, C.M. 1998. The Birds of the Western Palearctic, Volume 1: Non-Passerines. Oxford University Press, Oxford.
Urban, E.K., Fry, C.H. and Keith, S. 1986. The Birds of Africa, Volume II. Academic Press, London.
Further web sources of information
Detailed species account from Birds in Europe: population estimates trends and conservation status (BirdLife International 2004)
Detailed species account from Birds in Europe: population estimates, trends and conservation status (BirdLife International 2004)
Explore HBW Alive for further information on this species
Search for photos and videos, and hear sounds of this species from the Internet Bird Collection
Text account compilers
Butchart, S., Calvert, R., Ekstrom, J., Malpas, L. & Ashpole, J
IUCN Red List evaluators
Butchart, S. & Symes, A.
BirdLife International (2016) Species factsheet: Hydroprogne caspia. Downloaded from
http://www.birdlife.org on 01/07/2016.
Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from
http://www.birdlife.org on 01/07/2016.
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.
To provide new information to update this factsheet or to correct any errors, please email BirdLife
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