Sterna virgata 


Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Charadriiformes Laridae

Scientific Name: Sterna virgata
Species Authority: Cabanis, 1875
Common Name(s):
English Kerguelen Tern
Taxonomic Source(s): del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Lynx Edicions BirdLife International.
Taxonomic Notes: 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.

Identification information: 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.

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2012
Date Assessed: 2012-05-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Bretagnolle, V. & Micol, T.
Facilitator/Compiler(s): Anderson, O., Butchart, S., O'Brien, A., Shutes, S., Stattersfield, A., Taylor, J.
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.

Previously published Red List assessments:
2010 Near Threatened (NT)
2008 Near Threatened (NT)
2006 Near Threatened (NT)
2004 Near Threatened (NT)
2000 Lower Risk/near threatened (LR/nt)
1996 Vulnerable (VU)
1994 Vulnerable (VU)
1988 Threatened (T)

Geographic Range [top]

Range Description: 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.

Countries occurrence:
French Southern Territories; South Africa
Present - origin uncertain:
Heard Island and McDonald Islands
Estimated area of occupancy (AOO) - km2: 7700
Continuing decline in area of occupancy (AOO): Unknown
Extreme fluctuations in area of occupancy (AOO): No
Estimated extent of occurrence (EOO) - km2: 7800
Continuing decline in extent of occurrence (EOO): Unknown
Extreme fluctuations in extent of occurrence (EOO): No
Continuing decline in number of locations: Unknown
Extreme fluctuations in the number of locations: No
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: 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.

Current Population Trend: Stable
Additional data:
Number of mature individuals: 2300-4300 Continuing decline of mature individuals: Unknown
Extreme fluctuations: No Population severely fragmented: No
Continuing decline in subpopulations: Unknown
Extreme fluctuations in subpopulations: No All individuals in one subpopulation: No

Habitat and Ecology [top]

Habitat and 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).

Systems: Terrestrial; Freshwater; Marine
Continuing decline in area, extent and/or quality of habitat: Unknown
Generation Length (years): 11
Movement patterns: Not a Migrant
Congregatory: Congregatory (and dispersive)

Threats [top]

Major Threat(s): 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 [top]

Conservation Actions: 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.

Citation: BirdLife International. 2012. Sterna virgata. The IUCN Red List of Threatened Species 2012: e.T22694641A38873298. . Downloaded on 25 November 2015.
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