South polar skua (Stercorarius maccormicki)

Description

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South polar skua fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
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South polar skua description

A widespread and prominent bird of the Antarctic, the south polar skua (Stercorarius maccormicki) has a rather notorious reputation as a proficient hunter and hostile scavenger ^{(3) (4)}. It is a large, heavy, barrel-chested species, with broad, round wings and a short, broad tail ⁽⁵⁾. Despite being a fairly large bird, the south polar skua generally has a smaller head, a thinner and less prominently hooked bill, shorter, less heavy legs and narrower wings than other skuas of the same genus ^{(2) (6)}. The male south polar skua is generally smaller and lighter than the female, and the female also tends to have paler plumage ⁽³⁾.

The south polar skua is the greyest of the skua species, lacking the warm brown colouration often seen in other skuas. During the breeding season, the adults may have narrow yellow streaks on the back and sides of the neck, which sometimes continue across the upper breast to form a narrow necklace ⁽⁶⁾. In general, the south polar skua occurs in two different colour morphs, with individuals being either a light or dark morph, or occasionally an intermediate between the two ^{(2) (5) (6)}.

In light morph birds, the south polar skua is pale smoky-grey to greyish-brown on the head and underparts, providing a distinctive and striking contrast between the dark bill, dark eyes, and the dark brown wings, back and tail ^{(2) (5)}. The pale hind neck sometimes extends into a pale saddle on the upper back, making the contrast between the body, wings and rear appear particularly stark. Some pale individuals also have a blaze of pale colouration on the face ⁽⁶⁾.

The dark morph south polar skua is generally uniformly blackish-brown on the shoulder feathers and back, with golden hackles on the back of the neck ⁽⁵⁾. The head, wings and rest of the back are generally dark brownish-olive, appearing less two-tone than the pale morph ⁽²⁾. Dark morph skuas may also have a pale blaze on the face, and sometimes narrow, inconspicuous mantle streaks and a paler hind collar ⁽⁶⁾. 

The juvenile south polar skua is generally dark, with dark brown to dark grey plumage ⁽⁵⁾. The upperparts may have indistinct pale scaling. The bill of young birds is pale blue on the base and blackish above, and the legs and feet are pale ⁽⁶⁾.

The south polar skua is a fairly noisy bird during the breeding season, calling in high-pitched, fast, harmonic screams and shrieks ⁽⁶⁾. This species has three main types of call, used in courtship, contact and alarm ⁽⁷⁾.

Also known as

MacCormick’s skua.

Synonyms

Catharacta maccormicki.

French

Labbe de McCormick.

Size

Length: 50 - 55 cm ⁽²⁾

Wingspan: 130 - 140 cm ⁽²⁾

Weight

900 - 1600 g ⁽²⁾

South polar skua biology

A highly territorial bird, the south polar skua usually breeds from November to January, in loose colonies or isolated pairs ^{(2) (7)}. It is monogamous ⁽⁷⁾, with most pairs tending to breed in the same location for several years ⁽³⁾. The south polar skua typically nests in an unlined scrape on flat ground, free from snow and ice ^{(2) (9)}. Like all other skua species, the south polar skua lays a clutch of 2 eggs which are incubated by both adults for around 30 days ^{(2) (10)}.

The two eggs usually hatch a few days apart, with the first chick to hatch typically being larger and heavier than the second ^{(2) (3)}. The skua chicks leave the nest 1 or 2 days after hatching, although they do not fly until they are around 36 to 45 days old ⁽²⁾. In most cases, only one of the skua chicks will survive to fledging. This low breeding success is mainly due to ‘siblicide’, where the older of the two chicks will kill the younger chick, or will aggressively drive it from the nest, leaving it to die of starvation or be predated ^{(2) (3)}. The south polar skua reaches maturity at around six years old, and will first breed at around seven to nine years of age ^{(2) (3)}.

The south polar skua feeds mainly on fish ^{(2) (6) (8)}, particularly the Antarctic silverfish (Pleuragramma antarcticum) ⁽²⁾. It is also known to feed on eggs and chicks taken from penguin colonies ^{(2) (3) (8) (10) (11)}, although the skua’s reliance on penguins varies depending on the location of the breeding colony, as well as the proximity of competitors such as the brown skua (Stercorarius lonnbergi). The south polar skua may also scavenge food ⁽²⁾, and is also known to display occasional kleptoparasitism, stealing food from other birds during flight ⁽⁶⁾.

This species is a long distance migrant, departing its Antarctic breeding grounds in March to cross the equator and winter in the northern hemisphere ⁽²⁾.

South polar skua range

The south polar skua is considered to have the most southerly breeding range of any bird in the world, with some individuals breeding as far south as the Amundsen Scott Station at the South Pole ⁽³⁾. However, most breeding colonies of the south polar skua are scattered around the Antarctic coast and on offshore islands, especially in the Ross Sea region ^{(2) (3) (8)}. Its breeding range extends northwards to the Antarctic Peninsula and some of the South Shetland Islands ^{(9) (10)}.

In general, pale morph birds are thought to be more common in the Ross Sea area, while dark morph skuas are typically found on the Antarctic Peninsula ⁽²⁾

This species is highly migratory, leaving Antarctica after the breeding season to cross the equator and winter in the North Pacific and North Atlantic, as far north as Alaska and Greenland ^{(5) (8)}.

South polar skua habitat

The south polar skua breeds on relatively snow-free areas in Antarctica ^{(2) (8)}. It is predominantly coastal, although it frequently forms small inland colonies in mountainous areas, and is often found in association with penguin rookeries and inland petrel colonies ⁽²⁾.

South polar skua status

The south polar skua is classified as Least Concern (LC) on the IUCN Red List ⁽¹⁾.

South polar skua threats

Although not currently globally threatened, the south polar skua has very low breeding success rates, and chick survival and adult foraging could be further reduced by harsh weather conditions ⁽³⁾.

In addition, threats from oil spills and other environmental pollution in the Antarctic may impact the breeding population of the south polar skua ⁽¹²⁾.

South polar skua conservation

There are no specific conservation measures in place for the south polar skua; however, it is protected under the Antarctic Treaty, which governs human activity in the Antarctic and the use of its environmental resources. The Antarctic is also protected by the Protocol on Environmental Protection to the Antarctic Treaty, which further governs the use of resources in the region and allows for conservation of flora and fauna, prevention of marine pollution and protection of sites of special scientific interest. It also prohibits commercial mineral resource exploitation, and regulates waste disposal and management ⁽¹³⁾.

The south polar skua is also listed on Australia’s Environment Protection and Biodiversity Conservation Act 1999 as a migratory species ⁽¹⁴⁾.

Find out more

Find out more about the south polar skua and the conservation of other bird species:

• BirdLife International - South polar skua:
  http://www.birdlife.org/datazone/speciesfactsheet.php?id=3199

Find out more about Antarctica:

• British Antarctic Survey:
  http://www.antarctica.ac.uk/
• Antarctic Treaty System:
  http://www.ats.aq/
• Discovering Antarctica:
  http://www.discoveringantarctica.org.uk/

Visit ARKive’s Antarctic ecoregion page:

• ARKive - Antarctic : 
  http://www.arkive.org/eco-regions/antarctic/

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Glossary

Genus

A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Incubate

To keep eggs warm so that development is possible.

Kleptoparasitism

A feeding method whereby one individual steals food from another.

Mantle

In birds, the wings, shoulder feathers and back, when coloured differently from the rest of the body.

Monogamous

Having only one mate during a breeding season, or throughout the breeding life of a pair.

Morph

One of two or more distinct types of a given species, often distinct colour forms, which occur in the same population at the same time (that is, are not geographical or seasonal variations).

Territorial

Describes an animal, a pair of animals or a colony that occupies and defends an area.

References

1. IUCN Red List (August, 2012)
   http://www.iucnredlist.org/
2. del Hoyo, J., Elliott, A. and Sargatal, J. (1996) Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona.
3. Given, A. (2009) The south polar skua (Catharacta maccormicki) - A study of past research and future opportunity. Supervised Project, Graduate Certificate in Antarctic Studies, Gateway Antarctica, University of Canterbury.
4. British Antarctic Survey - Birds (February, 2012)
   http://www.antarctica.ac.uk/about_antarctica/wildlife/birds/other_birds.php
5. Alderfer, J. and Dunn, J.L. (2011) National Geographic Field Guide to the Birds of North America, Sixth Edition. National Geographic Society, Washington.
6. Olsen, K.M. and Larsson, H. (1997) Skuas and Jaegars. Pica Press, Sussex.
7. Charrier, I., Jouventin, P., Mathevon, N. and Aubin, T. (2001) Individual identity coding depends on call type in the South Polar skua Catharacta maccormicki. Polar Biology, 24: 378-382.
8. BirdLife International (February, 2011)
   http://www.birdlife.org/
9. Polar Conservation Organisation - South polar skua (February, 2012)
   http://www.polarconservation.org/education/antarctic-animals/antarctic-birds/south-polar-skua
10. Hemmings, A.D. (1984) Aspects of the breeding biology of McCormick’s skua Catharacta maccormicki at Signy Island, South Orkney Islands. British Antarctic Survey Bulletin, 65: 65-79.
11. Baker, S.C. and Barbraud, C. (2001) Foods of the south polar skua Catharacta maccormicki at Ardery Island, Windmill Islands, Antarctica. Polar Biology, 24: 50-61.
12. ­U.S. Fish and Wildlife Service: Waterbird Conservation for the Americas Initiative - South polar skua (February, 2012)
    http://www.fws.gov/birds/waterbirds/MANEM/PDFs/SPSK_final1.pdf
13. The Antarctic Treaty (February, 2012)
    http://www.ats.aq/index_e.htm
14. Australian Government - Environment Protection and Biodiversity Conservation Act 1999 (February, 2012)
    http://www.environment.gov.au/epbc/