Overview

Distribution

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.

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Range

Marion, Crozet, and Kerguelen islands.

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Ecology

Habitat

Habitat and Ecology

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
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Depth range based on 3 specimens in 1 taxon.
Water temperature and chemistry ranges based on 3 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 14.915 - 15.471
  Nitrate (umol/L): 3.046 - 3.863
  Salinity (PPS): 35.217 - 35.265
  Oxygen (ml/l): 5.787 - 5.868
  Phosphate (umol/l): 0.445 - 0.511
  Silicate (umol/l): 3.083 - 3.240

Graphical representation

Temperature range (°C): 14.915 - 15.471

Nitrate (umol/L): 3.046 - 3.863

Salinity (PPS): 35.217 - 35.265

Oxygen (ml/l): 5.787 - 5.868

Phosphate (umol/l): 0.445 - 0.511

Silicate (umol/l): 3.083 - 3.240
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
NT
Near Threatened

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
BirdLife International

Reviewer/s
Butchart, S. & Symes, A.

Contributor/s
Bretagnolle, V. & Micol, T.

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.

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Population

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

Population Trend
Stable
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Threats

Major 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).

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Management

Conservation Actions

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.

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Wikipedia

Kerguelen Tern

The Kerguelen tern (Sterna virgata) is a tern of the southern hemisphere.

This seabird mainly breeds colonially in the Kerguelen Islands, as its common name implies. However, smaller colonies are also found in the Prince Edward Islands (i.e. Prince Edward and Marion) and Crozet Islands. The total number of individuals is from 3,500–6,500 birds, although there is no recent data from the main colony at Kerguelen. These birds do not inhabit Kerguelen proper, instead nesting on islets free of feral cats. During bad weather, they are known to abandon their colonies.

Kerguelen terns are among the least-ranging of all typical terns. They generally do not reach far into the seas near their breeding grounds.

These birds eat fish and marine invertebrates, especially those found in beds of the seaweed Macrocystis spp. They sometimes also hunt insects on land and catch fish from rivers on Kerguelen.

References[edit]


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