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Sooty Tern Onychoprion fuscatus

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 is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds 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.

Taxonomic note
Onychoprion fuscatus (del Hoyo and Collar 2014) was previously placed in the genus Sterna as S. fuscata.

Synonym(s)
Onychoprion fuscata ssp. fuscata , Onychoprion fuscatus AOU checklist (1998 + supplements), Sterna fuscata Linnaeus, 1766

Distribution and population
The Sooty Tern breeds on tropical islands and ranges through most of the tropical oceans (del Hoyo et al. 1996).

Population justification
The global population is estimated to number c.21,000,000-22,000,000 individuals (Wetlands International 2006), while the population in Japan has been estimated at < c.100,000 breeding pairs and < c.1,000 individuals on migration (Brazil 2009).

Trend justification
The overall population trend is uncertain, as some populations are decreasing, while others are increasing or have unknown trends (Wetlands International 2006).

Ecology
Behaviour The species is dispersive and migratory (Higgins and Davies 1996). At most colonies adults leave for the open sea after breeding (del Hoyo et al. 1996) and become strongly pelagic (Higgins and Davies 1996) for 2-3 months before returning to the breeding grounds (del Hoyo et al. 1996). On returning to the breeding colonies they continue to forage pelagically by day and settle on land at night for a further 2-3 months before beginning to breed (del Hoyo et al. 1996). The timing of breeding varies throughout the species's range, with nesting occurring all year round at some colony sites but seasonally at others (del Hoyo et al. 1996). The species nests in very large colonies (del Hoyo et al. 1996) and remains gregarious throughout the year (congregating in small to large flocks to feed at sea) although it may be observed singly (Higgins and Davies 1996). Habitat Breeding It breeds on flat, open, sparsely or heavily vegetated, oceanic or barrier islands of sand, coral or rock in productive tropical and subtropical offshore waters rich in plankton, fish and squid (del Hoyo et al. 1996). It is absent from cold current areas and generally avoids islands with terrestrial predators (del Hoyo et al. 1996). Non-breeding Outside of the breeding season the species is highly pelagic but generally avoids cold current areas (del Hoyo et al. 1996). Diet Its diet consists predominantly of fish up to 18 cm long (usually 6-8 cm) and squid, but it also occasionally takes crustaceans, insects and offal (del Hoyo et al. 1996). The species is reliant upon prey driven to the surface by predatory fish (e.g. tuna, Scombidae), especially when breeding (Higgins and Davies 1996). Breeding site The nest is a slight depression (del Hoyo et al. 1996) or scrape on the ground (Higgins and Davies 1996). It shows a preference for nesting on flat, bare sand, coral grit or shell (Higgins and Davies 1996, del Hoyo et al. 1996) amongst low vegetation (Higgins and Davies 1996, del Hoyo et al. 1996) on beaches above the high-water mark (Higgins and Davies 1996) or on coral islands, atolls and sandbanks (Higgins and Davies 1996). Less often it may nest on rock stacks or other offshore islets, and on ledges or terraces of cliffs (although it avoids sheer cliff-faces) (Higgins and Davies 1996). It nests in dense colonies within which neighbouring nests may be placed c.50 cm apart (del Hoyo et al. 1996). Higher nesting densities occur in areas where bare ground predominates but which are vegetated with plants greater than or equal to 15 cm tall (Feare et al. 1997). Management information The mortality of the species was significantly reduced on Isla Isabel (a densely forested tropical island off the Pacific coast of Mexico) by the eradication of introduced domestic cats Felis catus using a combination of poisoning, trapping and hunting with firearms (Rodriguez et al. 2006). The nesting density and therefore the number of breeding pairs was increased in colonies on Bird Island by clearing areas of dense native or introduced vegetation and burning existing colony areas annually to prevent the growth of woody plants (Feare et al. 1997).

Threats
Some colonies (e.g. on Ascension Island) (del Hoyo et al. 1996) are threatened by predation from introduced rats and domestic cats Felis catus (Rodriguez et al. 2006), and the species has been displaced from nesting colonies on Bird Island by invasive ants Anoplolepis longipes (Feare 1999). Persistent large scale egg-collecting in some areas has encouraged the species to move to suboptimal nesting sites, resulting in higher mortality and reduced reproductive success (van Halewyn and Norton 1984). It may also be threatened by climatic change, as variations in sea-surface temperature have been shown to negatively influence the species's foraging success at breeding colonies (hence lowering reproductive success) (Erwin and Congdon 2007). The species is vulnerable to oil pollution from oil spills and tankers transporting fuel (del Hoyo et al. 1996) and is threatened by reductions in the global populations of tuna (a result of over-fishing) due to it's dependence on tuna to force prey to the surface (Reichel 1991). Utilisation The eggs of this species are harvested in many areas (e.g. Caribbean) (van Halewyn and Norton 1984, del Hoyo et al. 1996).

References
Brazil, M. 2009. Birds of East Asia: eastern China, Taiwan, Korea, Japan, eastern Russia. Christopher Helm, London.

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.

Erwin, C. A.; Congdon, B. C. 2007. Day-to-day variation in sea-surface temperature reduces sooty tern Sterna fuscata foraging success on the Great Barrier Reef, Australia. Marine Ecology Progress Series 331: 255-266.

Feare, C. 1999. Ants take over from rats on Bird Island, Seychelles. Bird Conservation International 9(1): 95-96.

Feare, C. J.; Gill, E. L.; Carty, P.; Carty, H. E.; Ayrton, V. J. 1997. Habitat use by Seychelles Sooty Terns Sterna fusca and implications for colony management. Biological Conservation 81: 69-76.

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.

Reichel, J. D. 1991. Status and conservation of seabirds in the Mariana Islands. In: Croxall, J.P. (ed.), Seabird status and conservation: a supplement, pp. 249-262. International Council for Bird Preservation, Cambridge, U.K.

Rodríguez, C.; Torres, R.; Drummond, H. 2006. Eradicating introduced mammals from a forested tropical island. Biological Conservation 130: 98-105.

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.

Further web sources of information
Click here to read about RSPB's work with Sooty Terns on Ascension Island

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.

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

Recommended citation
BirdLife International (2014) Species factsheet: Onychoprion fuscatus. Downloaded from http://www.birdlife.org on 31/07/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 31/07/2014.

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 - Sooty tern (Sterna fuscata) 0

Key facts
Current IUCN Red List category Least Concern
Family Laridae (Gulls, Terns, Skimmers)
Species name author Linnaeus, 1766
Population size mature individuals
Population trend Unknown
Distribution size (breeding/resident) 120,000 km2
Country endemic? No
Links to further information
- Additional Information on this species
- Projected distributions under climate change