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Kerguelen Tern Sterna virgata

Justification
This species is listed as Near Threatened owing to its small population. It is not thought to be undergoing a decline at present, but any indication of a decline would result in the species being reclassified as threatened.

Taxonomic source(s)
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.

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

Identification
31 cm. Very dark, small tern. Adult overall very dark grey with black cap and narrow white cheek stripe separating black cap from grey neck. Non breeding adult has grizzled forehead and paler underparts. Immature heavily barred buff on mantle and has all brown cap. Similar spp. Sympatric with Antarctic Tern S. vittata from which it differs by being darker, smaller with shirt wings and tail and with much shorter, weaker and spikey shaped bill. Voice Harsh chittick and long drawn out keeeaaar.

Distribution and population
Sterna virgata breeds in the southern Indian Ocean on the Prince Edward Islands (South Africa) (10-40 pairs on Marion Island during 1996-1999, 12-56 pairs during 1998-2009 without any apparent trend [Whittington et al. 2009], 20 pairs on Prince Edward Island [Barnes 2000] although only a single nest located in 2008 survey [Whittington et al. 2009]), Crozet Islands (French Southern Territories) (150-200 pairs over 1980-1982) and Kerguelen Islands (also French Southern Territories) (1,000-2,000 pairs during 1982-1985). The total population is estimated at 3,500-6,500 individuals (Jouventin et al. 1988, Thibault and Guyst 1993). There are no recent counts from the main breeding area on Kerguelen (V. Bretagnolle in litt. 1999) and thus population trends are unknown, but it is assumed that the species is not undergoing any significant decline.

Population justification
The total population has been estimated at 3,500-6,500 individuals, roughly equivalent to 2,300-4,300 mature individuals.

Trend justification
The population is suspected to be stable in the absence of any significant threats.

Ecology
This species is apparently sedentary, dispersing only to seas adjacent to its breeding islands outside the breeding season (Harrison 1983). It inhabits rocky, volcanic islands (del Hoyo et al. 1996). The species feeds on fish and crustaceans in seaweed Macrocystis beds, the surf zone, and in shallow water close to shore, also foraging in terrestrial vegetation for invertebrates (Sagar 1991). It breeds in scree and sparse vegetation on cliff-tops and river flats (Weimerskirch and Stahl 1988). Nests are assembled on moss from stones and twigs and are often lined with plant material (del Hoyo et al. 1996). Egg-laying commences in mid-October, and continues until January, with a peak in breeding from early November to mid-December. One or two eggs are laid. The incubation period is 24 days, followed by a fledging period of 31-39 days and then 20 days of dependence (del Hoyo et al. 1996).

Threats
Adverse weather conditions are probably the dominant threat, with gale-force winds preventing all feeding in marine and terrestrial habitats; the timing and length of the laying season are also dependent on the weather with birds known to desert breeding colonies during storms (Weimerskirch and Stahl 1988, Sagar 1991). Although there are feral cats on Kerguelen, S. virgata inhabits predator-free islets around the main island and therefore predation is not considered a major threat (T. Micol in litt. 1999). The decline in the small population of Prince Edward Island since 1984, runs contrary to the stable population of Marion Island, and is in stark contrast to trends in sub-Antarctic skuas, which have increased at Prince Edward Island but decreased at Marion Island, in spite of the eradication of feral cats (Whittington et al. 2009). Although the principal prey species of sub-Antarctic skuas at Prince Edward Island are burrowing petrels, given the small population, the loss of only a few birds to predation by skuas could pose a significant threat (Whittington et al. 2009).

Conservation Actions Underway
The introduction of salmonid fish into rivers on Kerguelen has provided a new source of food. Conservation Actions Proposed
Reassess the population size on Kerguelen (V. Bretagnolle in litt. 1999). Study the species on Kerguelen during a breeding season (V. Bretagnolle in litt. 1999). Prevent the introduction of feral cats and other predators to breeding colonies.

References
Barnes, K. N. 2000. The Eskom Red Data Book of birds of South Africa, Lesotho and Swaziland. BirdLife South Africa, Johannesburg.

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

Harrison, P. 1985. Seabirds: an identification guide. Christopher Helm, London.

Jouventin, P.; Stahl, J. -C.; Weimerskirch, H. 1988. La conservation des oiseaux des Terres Australes et Antarctiques Françaises. In: Thibault, J.-C.; Guyot, I. (ed.), Livre rouge des oiseaux menacés des régions françaises d'Outre-Mer, pp. 225-251. Conseil International pour la Protection des Oiseaux, Saint-Cloud, France.

Sagar, P. M. 1991. Aspects of the breeding and feeding of the Kerguelean and Antarctic Terns at the Kerguelean Islands. Notornis 38: 191-198.

Weimerskirch, H.; Stahl, J. -C. 1988. The breeding and feeding ecology of the Kerguelen Tern Sterna virgata. Ornis Scandinavica 19: 199-204.

Whittington, P. A.; Crawford, R. J. M.; Dyer, B. M.; Ryan, P. G. 2009. Estimates of numbers of Kelp Gulls and Kerguelen and Antarctic Terms breeding at the Prince Edward Islands, 1996/1997 - 2008/2009. African Journal of Marine Science 31(3): 439-444.

Further web sources of information
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
Anderson, O., Butchart, S., O'Brien, A., Shutes, S., Stattersfield, A., Taylor, J.

Contributors
Bretagnolle, V., Micol, T.

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

Recommended citation
BirdLife International (2014) Species factsheet: Sterna virgata. Downloaded from http://www.birdlife.org on 16/09/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/09/2014.

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.

Key facts
Current IUCN Red List category Near Threatened
Family Laridae (Gulls, Terns, Skimmers)
Species name author Cabanis, 1875
Population size 2300-4300 mature individuals
Population trend Stable
Distribution size (breeding/resident) 7,800 km2
Country endemic? No
Links to further information
- Additional Information on this species