Species

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 stable, 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.

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.
AOU. 1998. Check-list of North American birds. American Ornithologists' Union, Washington, D.C.
Christidis, L.; Boles, W. E. 1994. The taxonomy and species of birds of Australia and its territories. Royal Australasian Ornithologists' Union, Melbourne.
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.
Dowsett, R. J.; Forbes-Watson, A. D. 1993. Checklist of birds of the Afrotropical and Malagasy regions. Tauraco Press, Li
Sibley, C. G.; Monroe, B. L. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, USA.
Turbott, E. G. 1990. Checklist of the birds of New Zealand. Ornithological Society of New Zealand, Wellington.

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.

Synonym(s)
Thalasseus bergii AOU checklist (1998 + supplements), Thalasseus bergii Christidis and Boles (2008), Thalasseus bergii , Thalasseus bergii bergii Christidis and Boles (2008)

Distribution and population
This species can be found found on islands and coastlines of the tropical and subtropical Old World, ranging from the Atlantic Coast of South Africa, south around the Cape and continuing along the coast of Africa and Asia almost without break to south-east Asia and Australia. It can also be found on Madagascar, islands of the western Indian ocean and islands of the western and central Pacific Ocean. Outside the breeding season it can be found at sea throughout this range, with the exception of the central Indian Ocean (del Hoyo et al. 1996).

Population justification
The global population is estimated to number c.150,000-1,100,000 individuals (Wetlands International 2006), while national population estimates include: c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in China; c.10,000-100,000 breeding pairs and c.1,000-10,000 individuals on migration in Taiwan and c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Japan (Brazil 2009).

Trend justification
The overall population trend is stable, although some populations have unknown trends (Wetlands International 2006).

Ecology
Behaviour Many populations of this species remain sedentary in their breeding areas or disperse locally (del Hoyo et al. 1996) although some are more migratory (Urban et al. 1986). The species breeds in large dense colonies, or in small groups of less than 10 pairs amidst colonies of other species (e.g. King Gull Larus hartlaubii or Silver Gull Larus novaehollandiae) (del Hoyo et al. 1996). It usually forages singly (Urban et al. 1986) or in small groups (del Hoyo et al. 1996) but several hundred individuals may gather at roost sites (Langrand 1990). Habitat The species inhabits tropical and subtropical coastlines, foraging in the shallow waters of lagoons (Higgins and Davies 1996, del Hoyo et al. 1996), coral reefs (del Hoyo et al. 1996), estuaries (Urban et al. 1986, del Hoyo et al. 1996), bays, harbours and inlets (Higgins and Davies 1996), along sandy, rocky, coral (del Hoyo et al. 1996) or muddy shores, on rocky outcrops in open sea, in mangrove swamps (Langrand 1990) and also far out to sea on open water (del Hoyo et al. 1996). It shows a preference for nesting on offshore islands (Urban et al. 1986, del Hoyo et al. 1996), low-lying coral reefs, sandy or rocky coastal islets, coastal spits, lagoon mudflats (del Hoyo et al. 1996), and artificial islets in saltpans and sewage works (Urban et al. 1986, del Hoyo et al. 1996) within 3 km of the coast (del Hoyo et al. 1996). Diet Its diet consists predominantly of pelagic fish 10-50 cm long (Urban et al. 1986, del Hoyo et al. 1996) although it will also take cephalopods (e.g. squid), crustaceans (del Hoyo et al. 1996) (e.g. crabs (del Hoyo et al. 1996) and prawns (Higgins and Davies 1996)), insects and hatchling turtles opportunistically (del Hoyo et al. 1996). Breeding site The nest is a shallow scrape in bare sand, rock or coral (del Hoyo et al. 1996) in flat open sites (Urban et al. 1986) on offshore islands (Urban et al. 1986, del Hoyo et al. 1996), low-lying coral reefs, sandy or rocky coastal islets, coastal spits, lagoon mudflats (del Hoyo et al. 1996) or islets in saltpans and sewage works (Urban et al. 1986, del Hoyo et al. 1996). The species nests in dense colonies (Urban et al. 1986) with neighbouring nests very close together (rims may be touching) (del Hoyo et al. 1996), and usually forages within 3 km of the breeding colony (del Hoyo et al. 1996).

Threats
The species is vulnerable to human disturbance (e.g. tourism) at breeding colonies on offshore islands (Benoit and Bretagnolle 2002) which can lead to nest desertion and increased predation of eggs and nestlings by gulls and ibises (Cooper et al. 1990). The species is also threatened by injury and mortality from entanglement with baited hooks, fishing lines, nets and human refuse (e.g. plastic bags) (Cooper et al. 1990). Utilisation Most breeding colonies of this species are subject to subsistence egg collecting (de Korte 1991, del Hoyo et al. 1996).

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

Langrand, O. 1990. Guide to the birds of Madagascar. Yale University Press, New Haven, USA.

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.

del Hoyo, J.; Elliott, A.; Sargatal, J. 1996. Handbook of the Birds of the World, vol. 3: Hoatzin to Auks. Lynx Edicions, Barcelona, Spain.

Benoit, M. P.; Bretagnolle, V. 2002. Seabirds of the southern Lagoon of New Caledonia; distribution, abundance and threats. Waterbirds 25(2): 202-213.

de Korte, K. 1991. Status and conservation of Indonesia's seabird colonies. In: Croxall. J. P. (ed.), Seabird Status and Conservation: A Supplement, pp. 225-247. International Council for Bird Preservation, Cambridge, UK.

Cooper, J.; Crawford, R. J. M.; Suter, W.; Williams, A. J. 1990. Distribution, population size and conservation of the Swift Tern Sterna bergii in Southern Africa. Ostrich 61(1-2): 56-65.

Further web sources of information
View 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.

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

Recommended citation
BirdLife International (2013) Species factsheet: Sterna bergii. Downloaded from http://www.birdlife.org on 20/05/2013. Recommended citation for factsheets for more than one species: BirdLife International (2013) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 20/05/2013.

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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Additional resources for this species