Data Zone
Justification of Red List category
This species is listed as Near Threatened owing to its small population size. 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.
Population justification
The total population has been estimated at 3,500-6,500 individuals, roughly equivalent to 2,300-4,300 mature individuals (Jouventin et al. 1988).
Trend justification
The South African population is listed in the Regional Red Data Book as Critically Endangered (Taylor and Wanless 2015), due to the apparent loss of the population on Prince Edward Island. 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 overall stable and not undergoing any significant decline.
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, although only a single nest could be located in 2008 and no breeding was observed in 2011 [Barnes 2000, Whittington et al. 2009, Taylor and Wanless 2015]), Crozet Islands (French Southern Territories) (150-200 pairs over 1980-1982) and Kerguelen Islands (French Southern Territories) (1,000-2,000 pairs during 1982-1985).
This species is apparently sedentary, dispersing only to seas adjacent to its breeding islands outside the breeding season (Harrison 1985). 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 20 days of dependence (del Hoyo et al. 1996).
Feral cats are present on the Kerguelen Islands group, but the Kerguelen Tern inhabits only predator-free islets around the main island. It is possible that the recovery of Kerguelen Tern at Marion Island was due, in part, to successful eradication of feral cats in 1991. If cats were to colonise the islets inhabited by the Kerguelen Tern, it would likely do severe damage to the population (Ryan et al. 2003, 2009). A native predator, the Brown Skua Catharacta antarctica, is increasing in population size and thought to be exerting a considerable predation pressure on Kerguelen Terns on Prince Edward Island. Although the Kerguelen Tern is not thought to be their primary target, its low numbers on this island means that even a very low level of skua predation could damage the island’s population (Ryan et al. 2009). Strong winds prevent feeding in both the marine and terrestrial environments and impacts the time of laying season, potentially causing nest desertion. Bad weather in 1980 likely resulted in laying delays of several weeks, bringing the Kerguelen Tern into competition with Antarctic Tern populations on the same islands and reducing the fledging success of chicks (Sagar 1991, Weimerskirch and Stahl 1988).
Conservation Actions Underway
The introduction of salmonid fish into rivers on Kerguelen has provided a new source of food.
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.
Text account compilers
Stuart, A., Taylor, J., van der Merwe, N., Butchart, S., Anderson, O., Moreno, R., O'Brien, A., Martin, R., Palmer-Newton, A., Shutes, S., Stattersfield, A.
Contributors
Bretagnolle, V.
Recommended citation
BirdLife International (2024) Species factsheet: Kerguelen Tern Sterna virgata. Downloaded from
https://datazone.birdlife.org/species/factsheet/kerguelen-tern-sterna-virgata on 22/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/11/2024.