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Antarctic Tern

Sterna vittata

Number Of Mature
Individuals (Regional)

8 450

Regional
Population Trend

Decreasing

lc

2025
Regional Category

Least Concern

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CONTENTS
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    Overview

    Names

    IOC English Name:

    Antarctic Tern

    SA & IOC Scientific Name:

    Sterna vittata

    BirdLife International Taxonomy (scientific name):

    Sterna vittata

    Order:

    CHARADRIIFORMES

    Family:

    Laridae

    Species name author:

    Gmelin 1789

    Afrikaans:

    Grysborssterretjie

    Sesotho (South Africa):

    Lepheulane la sefubaputswa

    Sesotho (Lesotho):

    Siswati:

    Zulu:

    insukakudeyeqhwa

    Current Assessment Status

    2025 Regional Category [Criteria]

    Breeding: Species of Conservation Concern.

    Non-breeding: LC (Follows Global Status)

    2024 Global Category [Criteria]

    LC

    Population size (Regional)

    24 – 40 (Marion Island 2016-2023 (DFFE unpubl data); c. 8 (Prince Edward Island Whittington et al. (2009)).

    Non-breeding population: c. 8450 mature individuals (Tree and Klages 2004)

    Population size (Global)

    87 700 – 142 400 (Tree and Klages 2004, Wetlands International 2024)

    Distribution size (EOO) (Regional) km2

    720 (breeding); 36 450 (non-breeding)

    Distribution size (EOO) (Global) km2

    30 700 000 (BirdLife International 2019, breeding/resident)

    Distribution size (AOO) (Regional) km2

    334 (breeding), 4800 (non-breeding)

    Generation time

    11 years (BirdLife International 2019)

    Status change reason

    Error Correction

    Migrant (in the region)

    Breeding and visiting populations

    Regional endemic

    No

    Historic Listing Information

    2000 Regional Status

    LC

    2015 Regional Status

    EN [D]

    Status change reason (if applicable)

    Criteria application to breeding population only

    2015 Population size (Regional)

    c. 60 (breeding)

    2015 Global Status

    LC

    Reason for Inclusion

    Reason for Inclusion in the Assessment

    The Antarctic Tern Sterna vittata was previously assessed as regionally Endangered (Taylor and Wanless 2015) based on the breeding population only.

    Category Justification

    Category Justification

    Although the regional breeding population of Antarctic Tern on the Prince Edward Islands satisfies Criterion D for classification as Critically Endangered due to the small population size, it does not exceed the regional filter of 5% of global population, for which an IUCN category can be applied. According to IUCN Regional Guidelines this population is therefore considered Not Applicable. The regional non-breeding population found along the coast of South Africa satisfies the criterion for small population size with decline (Criterion C), but insufficient evidence of a population trend prevents the use of this criterion. The global status of Least Concern is therefore adopted, which applies to the majority of the South African population, represented by non-breeding visitors.

    Population Justification

    The global population has not been quantified (BirdLife International 2019). Wetlands International (2024) do provide estimates of the various populations totalling 132 900 – 144 550 individuals (c. 87 700 – 95 400 mature individuals). Tree and Klages (2004) also provide a global estimate of 44 500 breeding pairs (c. 142 400 mature individuals), based on information collated from the literature and specialist knowledge. Confidence in these estimates are low as numbers from several sites are dated.

    Regionally the species consists of a small breeding population on Marion and Prince Edward Islands and a non-breeding population that visits the coast of South Africa. Berruti and Harris (1976) estimated there to be 10 – 30 pairs on Marion Island. Between 1996/1997 and 2008/2009, the highest estimate at Marion Island was of 10 pairs (Whittington et al. 2009). Ryan and Bester (2008) estimated there to be 25 pairs on Marion Island and five pairs on Prince Edward Island. Four pairs were recorded at Prince Edward Island in 2008 (Whittington et al. 2009). Between 12 and 20 pairs were recorded at Marion Island between 2016 and 2023 (Department of Forestry, Fisheries and the Environment South Africa (DFFE), unpubl data). Confidence in the breeding population estimate is low and an urgent investigation is required. The breeding population is small and does not exceed the 5% filter adopted by the region and is therefore considered Not Applicable.

    The size of the non-breeding population of Antarctic Terns visiting the coast of South Africa is estimated to be 12 800 individuals (c. 8450 mature individuals) based on surveys carried out in 2001 (Tree and Klages 2004). Confidence in this estimate is high, but as the information is dated and the population trends are unknown it is unclear whether this estimate still holds true.

    Trend Justification

    The global population trend is currently unknown (BirdLife International 2019).

    From 1974 to 1977, the regional breeding population of Antarctic Terns at Marion Island was <50 pairs (Williams et al. 1979), decreasing in 1979 to <20 pairs (Brooke 1984) and then increasing slightly to <25 pairs in the 1980s (Cooper and Brown 1990). Numbers fluctuated between 1996/1997-2008/2009 from zero to 10 pairs without any apparent trend (Whittington et al. 2009). Between 12 and 20 pairs were recorded at Marion Island between 2016 and 2023 (DFFE unpubl data). Confidence in this regional trend estimate is low.

    The non-breeding regional population has not been consistently monitored and therefore population trends are unknown. Based on comparisons of data from their 2001 survey to earlier data set out in Brooke et al. (1988), Tree and Klages (2004) provide evidence of declines in the Western Cape as well as increases in the Eastern Cape. The authors do, however caution against using the data to determine trends due to uncertainties in the earlier surveys and indicate that the declines along the coast of the Western Cape are possibly offset by the increases along the Eastern Cape coast but were uncertain to what degree.

    Biology & Ecology

    Taxonomy

    At the subspecific-level, the taxonomy of the Antarctic Tern needs revision. Six subspecies are recognised by Gill and Donsker (2015), with the nominate form S. v. vittata being endemic to the western Indian Ocean islands (Crozet and Kerguelen archipelagos and Prince Edward Islands) and this is the most common race visiting South Africa during winter (although three other races also reportedly occur). Connan et al. (2015) did not find genetic evidence supporting more than two subspecies from a sample of 79 Antarctic Terns caught around the South African coast in winter.

    Identification

    35–40 cm, c. 140 g. Sexes alike. Crown black. Narrow, white cheek stripe separates grey throat and neck from black cap. Upperparts and wings grey, contrasting with white rump. Tail white to pale grey and forked with long outer rectrices. Underwing with white coverts and secondaries; pale grey primaries with whitish trailing edge. Underparts fairly dark grey, paling slightly on belly. Undertail coverts white. Bill and legs bright red. Eyes dark brown. Non-breeding birds have grizzled crown with white forecrown. Underparts white with outer rectrices shorter than in breeding birds (Tree 2005).

    Distribution

    The Antarctic Tern breeds on Subantarctic and Southern Ocean islands and on the Antarctic Peninsula (Higgins and Davies 1996) including the Prince Edward Islands. Birds on the Prince Edward Islands breed on the more sheltered eastern coasts (Ryan et al. 2003). Indian Ocean breeding birds, of the nominate race S. v. vittata, are moderately common winter visitors to the coastline and offshore islands of Western and Eastern Cape provinces (Tree and Klages 2004). It is probable, but not known with certainty, that these groups include wintering birds from the Prince Edward Islands. Birds in South African waters occur in loose flocks up to the continental shelf edge, sometimes up to 150 km offshore (Brooke et al. 1988). Calculating the regional Extent of Occurrence (EOO) for the visiting population is complicated given the marine environment where this species occurs. EOO was calculated as the sum of the area of Southern African Bird Atlas Project (SABAP2) Quarter Degree Grid Cells for South Africa, Lesotho and Eswatini (albeit effectively only South Africa in this case) for which the species had occurred, being 54 QDGCs, suggesting a potential EOO of 36 450 km2. Similarly, the potential Area of Occurrence calculated from 64 pentads and presuming an average pentad area of 75 km2 is 4800 km2.

    Ecology

    The Antarctic Tern is a surface-nesting, summer-breeder (Cooper and Brown 1990) with egg-laying taking place between December and February. A generation length of 11 years is provided by BirdLife International (2019). Breeding Antarctic Terns feed almost exclusively at sea (Weimerskirch and Stahl 1988) and time their breeding to coincide with the calmest period of the year (Berruti and Harris 1976). Birds forage over the kelp zone approximately 20–200 m from shore (Berruti and Harris 1976), predominantly by day and sometimes in brightly moonlit conditions (Murphy 1936). Unlike the sympatric Kerguelen Tern S. virgata, Antarctic Terns are not known to forage over land at the Prince Edward Islands (Berruti and Harris 1976), although they do forage over pastures and agricultural lands at Tristan da Cunha (RM Wanless pers obs).

    Threats & Conservation

    Threats

    Subsequent to the removal of cats at Marion Island there are no known, explicit threats to the Antarctic Terns breeding at the Prince Edward Islands. However, the population has failed to recover despite the eradication of cats, suggesting that other threats are impacting this species. The naturally small population size, especially at Prince Edward Island, is an intrinsic threat. Because this is apparently a natural circumstance, mitigating the threat from small population size is not recommended. Because this species migrates northwards for winter (including to South Africa’s coastline), it is possible that it experiences threats at wintering sites; this possibility should be investigated.

    Conservation Measures Underway

    No specific conservation measures are in place for this species, but various general conservation and management measures are in place at the Prince Edward Islands. Several of the wintering roost sites are protected areas e.g. Dassen and Dyer Island Nature Reserves, and Bird Island Algoa Bay which is incorporated into the Addo Elephant National Park.

    The species is listed under the African-Eurasian Migratory Waterbird Agreement, an intergovernmental treaty developed under the framework of the Convention on the Conservation of Migratory Species of Wild Animals. The subspecies migrating to South Africa are listed in Column A Category 1c (Populations, which number less than around 10,000 individuals) (AEWA 2022).

    Conservation Measures Proposed

    Until the fundamental aspects of the species’ ecology are better understood, no conservation measures are proposed besides attainment of the knowledge required. Regular coordinated surveys of the non-breeding population would provide better estimates of population size and trends.

    Research Priorities and Questions

    • Dispersal during winter is to unknown areas and should be investigated. Stable isotope studies of feathers (grown during winter) would provide information about broadscale wintering grounds and possibly also about foraging preferences (e.g. near-shore or pelagic).
    • Dietary studies during breeding at Marion Island may elucidate mechanisms preventing the expansion of the regional population and could also shed light on the causes for decreases in the regional population of the closely related Kerguelen Tern S. virgata.
    • Are any of reproductive success, juvenile survival, recruitment rates, adult survival or other demographic parameters preventing the population from expanding, or is food availability, inter-specific competition, nesting requirements or territory size a limiting factor?
    • Undertake research at the various roost sites to determine threats facing the species, especially on Dyer Island, where the majority of the S.v. tristanensis population occurs during the non-breeding period.

    Contributors & References

    Assessor/s

    Phil Whittington, Kevin Shaw

    Reviewer/s

    Robert Crawford, Azwianewi Makhado

    References

    AEWA. 2022. Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) – Agreement Text and Annexes. As amended at the 8th Session of the Meeting of the Parties to AEWA. 26–30 September 2022, Budapest, Hungary, UNEP/AEWA Secretariat.

    Berruti A, Harris A. 1976. Breeding schedules of Antarctic and Kerguelen terns at Marion Island. Notornis 23: 243–245.

    BirdLife International. 2019. Sterna vittata (amended version of 2018 assessment). The IUCN Red List of Threatened Species 2019: e.T22694635A155620911. Available: https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T22694635A155620911.en [Accessed on 6 August 2023].

    Brooke RK. 1984. South African Red Data Book – Birds. Pretoria, South Africa: Foundation for Research Development, CSIR.

    Brooke RK, Cooper J, Hockey PAR, Ryan PG, Sinclair JC, Suter W, Tree AJ. 1988. Distribution, population size, and conservation of the Antarctic Tern Sterna vittata in southern Africa. Cormorant 16: 107–113.

    Connan M, Teske PR, Tree AJ, Whittington PA, McQuaid CD. 2015. The subspecies of Antarctic Terns (Sterna vittata) wintering on the South African coast: evidence from morphology, genetics, and stable isotopes. Emu 115: 223–236.

    Cooper J, Brown C. 1990. Ornithological research at the Subantarctic Prince Edward Islands: a review of achievements. South African Journal of Antarctic Research 20: 40–57.

    Gill F, Donsker D. 2015. IOC World Bird List (version 5.3). Available: http://www.worldbirdnames.org.

    Higgins PJ, Davies SJJF. 1996. Handbook of Australian, New Zealand and Antarctic Birds, Vol. 3: Snipe to Pigeons. Melbourne, Australia: Oxford University Press.

    Murphy RC. 1936. Oceanic Birds of South America, Vol. 2. New York, USA: Macmillan Company.

    Ryan PG, Bester MN. 2008. Pelagic predators. In: Chown SL, Froneman PW (eds), The Prince Edward Islands: Land-Sea Interactions in a Changing Ecosystem. Stellenbosch, South Africa: Sun Media. pp 121–164.

    Ryan PG, Cooper J, Dyer BM, Underhill LG, Crawford RJM, Bester MN. 2003. Counts of surface-nesting seabirds breeding at sub-Antarctic Prince Edward Island, summer 2001/02. African Journal of Marine Science 25: 441–451.

    Taylor MR, Wanless RM. 2015. Antarctic Tern Sterna vittata. In: Taylor MR, Peacock F, Wanless RW (eds), The Eskom Red Data Book of Birds of South Africa, Lesotho and Swaziland. Johannesburg, South Africa: BirdLife South Africa pp. 164–165.

    Tree AJ, Klages NTW. 2004. Population size, distribution, and origins of Antarctic Terns Sterna vittata wintering in South Africa. Marine Ornithology 32: 55–61.

    Tree AJ. 2005. Antarctic Tern Sterna vittata. In: Hockey PAR, Dean WRJ, Ryan PG (eds), Roberts – Birds of southern Africa (7th Edn). Cape Town, South Africa: Trustees of the John Voelcker Bird Book Fund. pp 461–462.

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

    Wetlands International. 2024. Waterbird Populations Portal. Available: https://wpp.wetlands.org/ [Accessed on 12 February 2025].

    Whittington PA, Crawford RJM, Dyer BM, Ryan PG. 2009. Estimates of numbers of Kelp Gulls and Kerguelen and Antarctic Terns breeding at the Prince Edward Islands, 1996/97–2008/09. African Journal of Marine Science 31(3): 439–444.

    Williams AJ, Siegfried WR, Burger AE, Berruti A. 1979. The Prince Edward Islands: a sanctuary for seabirds in the Southern Ocean. Biological Conservation 15: 59–71.

    Citation

    Whittington PA, Shaw K 2025. Antarctic Tern. In: Lee ATK, Rose S, Banda S, Bezeng SB, Maphalala MI, Maphisa DH, Smit-Robinson H (eds), The 2025 Red Data Book of Birds of South Africa, Lesotho and Eswatini. Johannesburg, South Africa: BirdLife South Africa. Available at: https://www.birdlife.org.za/red-list/antarctic-tern/

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