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LC
Common Tern Sterna hirundo

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). 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 extremely 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: #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.

Distribution and population
The Common Tern has a circumpolar distribution and can be found breeding in most of Europe, Asia and North America except the extreme north and south. It winters further south, being found along the coast and inland of South America down to the Falkland Islands (Islas Malvinas), along the coast of Africa excluding the north, along parts of the Arabian Peninsula and the whole coast of India, and throughout much of south-east Asia and Australasia (excluding New Zealand) (del Hoyo et al. 1996).

Population justification
The global population is estimated to number c.1,600,000-4,600,000 individuals (Wetlands International 2006), while national population sizes have been estimated at c.10,000-100,000 breeding pairs, c.1,000-10,000 individuals on migration and c.50-1,000 wintering individuals in China and c.10,000-100,000 breeding pairs and c.1,000-10,000 individuals on migration in Russia (Brazil 2009).

Trend justification
The overall population trend is decreasing, although some populations may be stable and others have unknown trends (Wetlands International 2006). This species has undergone a large and statistically significant decrease over the last 40 years in North America (-70.4% decline over 40 years, equating to a -26.2% decline per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).

Ecology
Behaviour This species is a strongly migratory coastal seabird (del Hoyo et al. 1996, Snow and Perrins 1998). It breeds between April and June in solitary pairs or colonially in groups of up to several thousand pairs (inland colonies often smaller and more widely-dispersed than coastal ones) (del Hoyo et al. 1996). Palearctic breeders migrate south after breeding between August and October, returning to the breeding grounds in March or April (del Hoyo et al. 1996). The species may moult on arrival in its the wintering grounds (e.g. the Caribbean), during which it may become vulnerable to human exploitation (van Halewyn and Norton 1984). It is gregarious throughout the year (Snow and Perrins 1998) and shoals of fish may attract dense feeding flocks, although it otherwise feeds singly or in small loose groups (del Hoyo et al. 1996, Snow and Perrins 1998). In some cases, it is territorial; in Massachusetts, feeding territories usually consist of linear strips of shoreline which are occupied and defended regularly by both members of a pair. The prevalence of territoriality at feeding sites varies between colonies and is related to food species availability (Nisbet 1983). Most individuals forage 5-10 km from breeding colonies, occasionally feeding at sea 15 km offshore (del Hoyo et al. 1996). Common Terns forage over fresh water as well as marine habitats, and often follow predatory fish , waiting for panicking baitfish to surface. They sometimes forage in mixed-species flocks together with other terns (Safina 1990, Brenninkmeijer et al. 2002). Habitat Breeding The species breeds in a wide variety of habitats in coastal and inland areas from sea-level to heights of greater than 4,000 m (del Hoyo et al. 1996). Along the coast it shows a preference for nesting on flat rock surfaces on inshore islands (Snow and Perrins 1998), open shingle and sandy beaches, dunes and spits (del Hoyo et al. 1996, Snow and Perrins 1998), vegetated inter-dune areas, sandy, rocky, shell-strewn or well-vegetated islands in estuaries (del Hoyo et al. 1996)and coastal lagoons (Snow and Perrins 1998), saltmarshes (Richards 1990, Snow and Perrins 1998), mainland peninsulas (Snow and Perrins 1998) and grassy plateaus atop coastal cliffs (del Hoyo et al. 1996). Inland it may nest in similar habitats including sand or shingle lakes shores (Richards 1990), shingle banks in rivers (Snow and Perrins 1998), sandy, rocky, shell-strewn or well-vegetated islands in lakes and rivers (del Hoyo et al. 1996, Snow and Perrins 1998), sand- or gravel-pits (Richards 1990, Snow and Perrins 1998), marshes, ponds, grassy areas and patches of dredged soil (Snow and Perrins 1998). Non-breeding The species winters on sheltered coastal waters (Higgins and Davies 1996), estuaries and along large rivers, occupying harbours, jetties, piers, beaches (del Hoyo et al. 1996) and coastal wetlands including lagoons, rivers, lakes, swamps and saltworks, mangroves and saltmarshes (Higgins and Davies 1996). During this season it roosts on unvegetated sandy beaches, shores of estuaries or lagoons, sandbars and rocky shores (Higgins and Davies 1996). Diet The species is opportunistic, its diet consisting predominantly of small fish and occasionally planktonic crustaceans and insects (del Hoyo et al. 1996). Breeding site The nest is a shallow depression on open substrates with little or no vegetation placed near a vertical object (e.g. rock, shell, plant or artefact) to provide shelter for chicks and to facilitate nest identification (del Hoyo et al. 1996). Nest sites include the edges of bare sand amongst vegetation, rocks or logs, open areas on the margins of vegetation on beaches, the edges of mats of vegetation in marshes (del Hoyo et al. 1996), and grassy or rocky substrates on rocky islets (del Hoyo et al. 1996). The species will also readily nest on artificial rafts (del Hoyo et al. 1996). Foraging range Studies have observed foraging birds at up to 37 km from the nearest colony (Cramp 1985, BirdLife International 2000). However, although Common Terns tend to range further than Roseate Terns (BirdLife International 2000), most are observed within 10 km of a breeding colony (Becker et al. 1993, Wanless et al. 1998, Newton and Crowe 1999). At various sites, visual observations e.g. of direction of flight also suggest that most feeding trips are to sites within 10 km of the colony (Hopkins and Wiley 1972, Duffy 1986, Uttley et al. 1989, Burness et al. 1994, BirdLife International 2000), although birds in these studies were recorded at a maximum of 18 km from the colony (Duffy 1986). Radio-tagging at the Wadden Sea has shown that birds forage at a mean radius of at least 6.3 km (Becker et al. 1993), although the total distance travelled by individuals on these foraging trips is much greater, around 26-30 km. In Massachusetts, feeding territories tend to be located in shallow water up to 75 m from shore, and may be at least 8.5 km away from the breeding colony (Lemmetyinen 1973, Nisbet 1983, BirdLife International 2000), as well as areas where depth changes abruptly and tidal currents are strong, which presumably produces much upwelling and mixing of cold, deep water with warmer surface water (Safina 1990). Birds lower the rate at which they attempt to forage when windspeed is high (Taylor 1983).

Threats
During the breeding season the species is vulnerable to human disturbance at nesting colonies (Buckley and Buckley 1984, Blokpoel and Scharf 1991) (e.g. from off-road vehicles, recreation, motor-boats, personal watercraft and dogs) (van Halewyn and Norton 1984, del Hoyo et al. 1996, Hyde 1997, Burger 1998), and to the flooding of nest sites as a result of naturally fluctuating water levels (Buckley and Buckley 1984, del Hoyo et al. 1996, Hyde 1997). On its breeding grounds the species is also threatened by habitat loss as a result of coastal developement (Buckley and Buckley 1984, Blokpoel and Scharf 1991, del Hoyo et al. 1996, Hyde 1997), erosion (Hyde 1997), vegetation overgrowth (rapid vegetation succession encroaching upon nesting habitats) (Blokpoel and Scharf 1991, del Hoyo et al. 1996, Hyde 1997), and chemical pollution (which may also result in eggshell thinning) (Blokpoel and Scharf 1991, del Hoyo et al. 1996, Hyde 1997). It suffers predation at nesting colonies from rats (especially on islands) (Buckley and Buckley 1984, del Hoyo et al. 1996) and from expanding populations of large gull species (Brown and Nettleship 1984, del Hoyo et al. 1996) such as Herring Gulls Larus argentatus (Buckley and Buckley 1984) (gulls may also prevent the species from nesting in the area by colonising it first) (Blokpoel and Scharf 1991, del Hoyo et al. 1996). The species is susceptible to avian influenza so may be threatened by future outbreaks of the virus (Melville and Shortridge 2006). Utilisation The species is harvested semi-commercially on its wintering grounds in the Caribbean (van Halewyn and Norton 1984, del Hoyo et al. 1996).

Conservation Actions Underway
Management techniques used to increase the breeding numbers and reproductive success of the species in the Great Lakes region of North America include creating artificial nesting sites, vegetation management, enhancement of existing nesting habitat, using models and vocalisation to attract breeding pairs and predator control (e.g. mammal-exclusion, destruction of gull nests, direct predator removal, or preventative measures against gull nesting) (Blokpoel and Scharf 1991). A conservation scheme for the protection of gull and tern breeding colonies in coastal lagoons and deltas (e.g. Po Delta, Italy) involves protection from human disturbance, prevention of erosion of islet complexes, habitat maintenance and the creation of new islets for nest sites (Fasola and Canova 1996). The scheme particularly specifies that bare islets with 30-100 % cover of low vegetation (sward heights less than 20 cm) should be maintained or created as nesting sites (Fasola and Canova 1996). Artificial nesting rafts have proved effective in promoting breeding success in areas where there is a lack of suitable nesting habitat or where human disturbance is a particular threat (1996) (del Hoyo et al. 1996). Using fire to expose the ground surface in areas where vegetation succession is proceeding too far towards closed vegetation stages has been successful in some areas (Hyde 1997). Culling predatory gulls can be an effective management tool to enhance breeding productivity (Guillemette and Brousseau 2001), although some management plans recommend non-lethal harassment techniques that target gulls (e.g. egg and nest destruction, conspicuous human observers, gull displacement walks, and pyrotechnics) to reduce predation on nesting colonies rather than culling (Donehower et al. 2007).

References
Becker, P.H., Schuhmann, S. and Koepff, C. 1993. Hatching failure in common terns (Sterna-hirundo) in relation to environmental chemicals. Environmental Pollution 79(3): 207-213.

BirdLife International. 2000. The Development of Boundary Selection Criteria for the Extension of Breeding Seabird Special Protection Areas into the Marine Environment. OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic. Vlissingen (Flushing).

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.

Brenninkmeijer, A., Stienen, E.W.M., Klaassen, M. and Kersten, M. 2002. Feeding ecology of wintering terns in Guinea-Bissau. Ibis 144(4): 602-613.

Brown, R. B. G.; Nettleship, D. N. 1984. The seabirds of north-eastern North America: their present status and conservation requirements. In: Croxall, J.P.; Evans, P.G.H.; Schreiber, R.W. (ed.), Status and conservation of the world's seabirds, pp. 85-100. International Council for Bird Preservation, Cambridge, U.K.

Buckley, P. A.; Buckley, F. G. 1984. Seabirds of the north and middle Atlantic coasts of the United States: their status and conservation. In: Croxall, J.P.; Evans, P.G.H.; Schreiber, R.W. (ed.), Status and conservation of the world's seabirds, pp. 101-133. International Council for Bird Preservation, Cambridge, U.K.

Burger, J. 1998. Effects of motorboats and personal watercraft on flight behaviour over a colony of Common Terns. Condor 100: 528-534.

Burness, G.P., Morris, R.D. and Bruce, J.P. 1994. Seasonal and annual variation in brood attendance, prey type delivered to chicks, and foraging patterns of male common terns (Sterna-hirundo). Canadian Journal of Zoology 72(7): 1243-1251.

Butler, C. J. 2003. The disproportionate effect of global warming on the arrival dates of short-distance migratory birds in North America. Ibis 145: 484-495.

Cramp, S.; Simmons, K. E. L. 1983. Handbook of the birds of Europe, the Middle East and Africa. The birds of the western Palearctic vol. III: waders to gulls. Oxford University Press, Oxford.

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.

Donehower, C. E.; Bird, D. M.; Hall, C. S.; Kress, S. W. 2007. Effects of Gull Predation and Predator Control on Tern Nesting Success at Eastern Egg Rock, Maine. Waterbirds 30(1): 29-39.

Duffy, D.C. 1986. Foraging at patches: interactions between common and roseate terns. Ornis Scandinavica 17: 47-52.

Fasola, M.; Canova, L. 1996. Conservation of gull and tern colony sites in north-eastern Italy, an internationally important bird area. Colonial Waterbirds 19: 59-67.

Guillemette, M.; Brousseau, P. 2001. Does culling predatory gulls enhance the productivity of breeding common terns? Journal of Applied Ecology 38: 1-8.

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.

Hopkins, C.D. and Wiley, R.H. 1972. Food parasitism and competition in two terns. Auk 89: 583-594.

Hyde, D. A. 1997. Special animal abstract for Sterna hirundo (common tern). Michigan Natural Features Inventory, Lansing, MI.

Lemmetyinen, R. 1973. Feeding ecology of Sterna paradisea Pontopp. and S. hirundo L. in the Archipelago of Southwest Finland. Annales Zoologici Fennici 10: 507-525.

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.

Newton, S. F.; Crowe, O. 2000. Roseate Terns - The Natural Connection. IWC-BirdWatch Ireland, Monkstown, County Dublin.

Nisbet, I.C.T. 1983. Paralytic shellfish poisoning: effects on breeding terns. Condor 85: 338-345.

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

Safina, C. 1990. Bluefish mediation of foraging competition between roseate and common terns. Ecology 71: 1804-1809.

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

Taylor, I. R. 1983. Effect of Wind on the Foraging Behaviour of Common and Sandwich Terns. Ornis Scandinavica 14(2): 90-96.

Uttley, J; Monaghan, P; White, S. 1989. Differential-effects of reduced Sandeel availability on 2 sympatrically breeding species of tern. Ornis Scandinavica 20(4): 273-277.

van Halewyn, R.; Norton, R. L. 1984. The status and conservation of seabirds in the Caribbean. In: Croxall. J. P. (ed.), Seabird Status and Conservation: A Supplement, pp. 169-222. International Council for Bird Preservation, Cambridge, U.K.

Wanless, S., Harris, M.P. and Greenstreet, S.P.R. 1998. Summer sandeel consumption by seabirds breeding in the Firth of Forth, south-east Scotland. ICES Journal of Marine Science 55(6): 1141-1151.

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
Ekstrom, J., Butchart, S., Malpas, L., Calvert, R., Hatchett, J.

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

Recommended citation
BirdLife International (2014) Species factsheet: Sterna hirundo. Downloaded from http://www.birdlife.org on 28/12/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 28/12/2014.

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 - Common tern (Sterna hirundo) 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) 16,000,000 km2
Country endemic? No
Links to further information
- Additional Information on this species
- Projected distributions under climate change