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Black Tern Chlidonias niger
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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). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to 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.

Taxonomic source(s)
AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: # _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: #

Distribution and population
The Black Tern is found in the Old and New World. It ranges from southern Scandinavia to southern Spain, east through Europe and western Asia to central Mongolia. Individuals from this area predominately winter on the Atlantic coast of Africa, from the Western Sahara to South Africa. It is also found across much of Canada to northern regions of the USA, with individuals wintering on the Pacific coast of Mexico, the Pacific and Atalantic coast of Central America and northern South America (del Hoyo et al. 1996).

Trend justification
This species has undergone a small or statistically insignificant decrease over the last 40 years in North America (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).

Behaviour This species is strongly migratory (del Hoyo et al. 1996) and travels both over land and over sea (Snow and Perrins 1998). It breeds between May and June (del Hoyo et al. 1996) in colonies, usually of less than 20 pairs (rarely more than 100 pairs) (del Hoyo et al. 1996) and often close to other species (Flint et al. 1984, Snow and Perrins 1998). After breeding it departs for its wintering grounds from July onwards (Richards 1990), returning north again from late-March (Snow and Perrins 1998). The species is gregarious throughout the year (Snow and Perrins 1998), foraging in groups of 2-20 during the breeding season and congregating in large flocks offshore on passage and in the winter over shoals of predatory fish (Richards 1990, del Hoyo et al. 1996, Snow and Perrins 1998). Habitat Breeding The species breeds on fresh or brackish wetlands (Richards 1990) such as small pools, lakes, marshes (Richards 1990, del Hoyo et al. 1996), ditches, overgrown canals, quiet reaches of rivers, swampy meadows (Richards 1990), peat bogs and rice-fields (del Hoyo et al. 1996), showing a preference for well-vegetated areas (del Hoyo et al. 1996) with sparse, open emergent vegetation (del Hoyo et al. 1996) (e.g. Typha spp., sedge or reeds) (Flint et al. 1984) and floating water-lilies (del Hoyo et al. 1996), and with water 1-2 m deep (del Hoyo et al. 1996). It generally avoids small marshland areas less than 4 ha in area (del Hoyo et al. 1996). Non-breeding On passage the species frequents inland wetlands including pools, ditches (del Hoyo et al. 1996), reservoirs, lakes and sewage farms (Snow and Perrins 1998), as well as coastal habitats and estuaries (del Hoyo et al. 1996). In winter it is predominantly coastal however, frequenting estuaries (del Hoyo et al. 1996, Snow and Perrins 1998), saltmarshes, bays (Snow and Perrins 1998), coastlines and coastal lagoons (del Hoyo et al. 1996) as well as marine waters up to 400-600 km offshore (Urban et al. 1986). Diet Breeding Its breeding diet consists predominantly of insects (e.g. chironomids, Odonata, Ephemeroptera and Coleoptera) as well as small fish (del Hoyo et al. 1996) and amphibians (Snow and Perrins 1998) (e.g. tadpoles and frogs) (del Hoyo et al. 1996). Non-breeding On passage and during the winter the species's diet consists largely of marine fish although insects and crustaceans may also be taken (Snow and Perrins 1998). Breeding site The nest may be a low compressed mound of plant matter (Flint et al. 1984, Snow and Perrins 1998) placed in very shallow water (Snow and Perrins 1998) or on a floating mat of aquatic vegetation (Flint et al. 1984) over water more than 50 cm deep (del Hoyo et al. 1996). The nest may also be a shallow scrape (Snow and Perrins 1998) on the ground amongst marsh vegetation (Snow and Perrins 1998). The species breeds in small colonies and may forage up to 2-5 km from breeding sites (del Hoyo et al. 1996). Management information In the Netherlands the provision of anchored artificial nesting rafts has been partly successful as a conservation measure (van der Winden et al. 2004, 2005), especially in habitats where unstable nest substrates (such as floating water-lilies) result in poor breeding successes (van der Winden et al. 2004). In the Netherlands there have also been successful programmes to reduce disturbance and improve habitat quality in agricultural areas, which has benefited the species (van der Winden 2005). The application of glyphosphate-based herbicides to combat and prevent the overgrowth of Typha spp. in wetlands may also benefit the species (Linz and Blixt 1997).

On its breeding grounds the species is threatened by reductions in food availability due to the eutrophication of surface waters (which reduces the diversity of large insects) (Beintema 1997), the acidification of lakes (which leads to the death of fish) (Beintema 1997), the introduction of exotic fish species (e.g. peacock bass Cichla ocellaris) (del Hoyo et al. 1996) and pesticide pollution (which may also lead to direct mortality from poisoning) (del Hoyo et al. 1996). When breeding the species is also threatened by fluctuating water levels (Snow and Perrins 1998), the loss and deterioration of freshwater nesting habitats (del Hoyo et al. 1996, van der Winden 2005) (e.g. through drainage for agriculture (del Hoyo et al. 1996, Snow and Perrins 1998) and overgrowth of Typha spp. beds [del Hoyo et al. 1996, Linz and Blixt 1997]), and human disturbance (del Hoyo et al. 1996, Snow and Perrins 1998, van der Winden 2005) (especially where this forces breeding pairs to leave the nest before the young are fully fledged) (van der winden 2002). The species is also susceptible to avian influenza so may be threatened by future outbreaks of the virus (Melville and Shortridge 2006).

Beintema, A. J. 1997. European Black Terns (Chlidonias niger) in trouble: examples of dietary problems. Colonial Waterbirds 20(3): 558-565.

del Hoyo, J.; Elliott, A.; 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.; Kuznetsov, A. A. 1984. A field guide to birds of the USSR. Princeton University Press, Princeton, New Jersey.

Linz, G. M.; Blixt, D. C. 1997. Black Terns benefit from cattail management in the Northern Great Plains. Colonial Waterbirds 20(3): 617-621.

Melville, D. S.; Shortridge, K. F. 2006. Migratory waterbirds and avian influenza in the East Asian-Australasian Flyway with particular reference to the 2003-2004 H5N1 outbreak. In: Boere, G.; Galbraith, C., Stroud, D. (ed.), Waterbirds around the world, pp. 432-438. The Stationary Office, Edinburgh, UK.

Richards, A. 1990. Seabirds of the northern hemisphere. Dragon's World Ltd, Limpsfield, U.K.

Snow, D. W.; Perrins, C. M. 1998. The Birds of the Western Palearctic vol. 1: Non-Passerines. Oxford University Press, Oxford.

Sparks, T. H.; Huber, K.; Bland, R. L.; Crick, H. Q. P.; Croxton, P. J.; Flood, J.; Loxton, R. G.; Mason, C. F.; Newnham, J.A.; Tryjanowski, P. 2007. How consistent are trends in arrival (and departure) dates of migrant birds in the UK? Journal of Ornithology 148: 503-511.

Urban, E. K.; Fry, C. H.; Keith, S. 1986. The birds of Africa vol. II. Academic Press, London.

van der Winden, J. 2002. Disturbance as a important factor in the decline of Black Tern Chlidonias niger in the Netherlands. Vogelwelt 123(1): 33-40.

van der Winden, J. 2005. Black tern Chlidonias niger conservation in the Netherlands - a review. Vogelwelt 126(3): 187-193.

van der Winden, J.; Beintema, A.. J.; Heemskerk, L. 2004. Habitat related Black Tern Chlidonias niger breeding success in The Netherlands. Ardea 92(1): 53-61.

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

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Text account compilers
Ekstrom, J., Butchart, S., Malpas, L.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2016) Species factsheet: Chlidonias niger. Downloaded from on 24/10/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from on 24/10/2016.

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

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Black tern (Chlidonias niger) 0

Key facts
Current IUCN Red List category Least Concern
Family Laridae (Gulls, Terns, Skimmers)
Species name author (Linnaeus, 1758)
Population size mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 1,430,000 km2
Country endemic? No
Links to further information
- Additional Information on this species
- 2015 European Red List assessment