Giant petrel

Giant petrel
Southern giant petrel juvenile
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Procellariiformes
Family: Procellariidae
Genus: Macronectes
Richmond, 1905
Species

Macronectes giganteus
Southern giant petrel
Macronectes halli
Northern giant petrel

Giant petrels form a genus, Macronectes, from the family Procellariidae, which consists of two species. They are the largest birds of this family. Both species are restricted to the Southern Hemisphere, and though their distributions overlap significantly, with both species breeding on the Prince Edward Islands, Crozet Islands, Kerguelen Islands, Macquarie Island and South Georgia, many southern giant petrels nest further south, with colonies as far south as Antarctica. Giant petrels are aggressive predators and scavengers, inspiring another common name, the stinker.[1] South Sea whalers used to call them gluttons.

Taxonomy

The giant petrels are two large seabirds from the genus Macronectes. Long considered to be conspecific (they were not established as separate species until 1966),[2] the two species, the southern giant petrel, Macronectes giganteus, and northern giant petrel, Macronectes halli, are considered with the two fulmars, Fulmarus, to form a distinct subgroup within Procellariidae, and including the Antarctic petrel, Cape petrel, and the snow petrel, they form a separate group from the rest of the family.[3]

Description

The southern giant petrel is slightly larger than the northern giant petrel, at 3 to 8 kg (6.6–17.6 lb), 180 to 210 cm (71–83 in) across the wings and 86 to 100 cm (34–39 in).[1][4] The northern giant petrel is 3 to 5 kg (6.6–11.0 lb), 150 to 210 cm (59–83 in) across the wings and 80 to 95 cm (31–37 in).[5][6] They superficially resemble the albatross, and are the only procellarids who can equal them in size. They can be separated from the albatrosses by their bill; the two tube nostrils are joined together on the top of the bill, unlike on albatross where they are separated and on the side of the bill. They are also the only members of the Procellariidae family to have strong legs to walk on land.[1] They are also much darker and more mottled brown (except for the white morph southern, which are whiter than any albatross) and have a more hunch-backed look. The bills of Procellariiformes are also unique in that they are split into between seven and 9 horny plates. The petrels have a hooked bill called the maxillary unguis which can hold slippery food. They produce a stomach oil made up of wax esters and triglycerides which is stored in the proventriculus. This can be sprayed out of their mouths as a defence against predators and as an energy rich food source for chicks and for the adults during their long flights.[7] Finally, they have a salt gland situated above the nasal passage and helps desalinate their bodies, due to the high amount of ocean water they imbibe. It excretes a high saline solution from their noses.[8]

They are hard to tell from each other, possessing similar long pale orange bills and uniform mottled grey plumage (except for 15% of southern petrels, which are almost completely white). The billtip of M. halli is reddish-pink and that of M. giganteus is pale green, appearing slightly darker and lighter than the rest of the bill, respectively. The underside of older M. halli is paler and more uniform than M. giganteus, the latter showing a contrast between paler head and neck and darker belly.[9] Additionally, adult M. halli typically appear pale-eyed, while adult M. giganteus of the normal morph typically appear dark-eyed (occasionally flecked paler). Classic examples of northern giant are identifiable at some range. Unfortunately, young birds of both species are all dark and very hard to distinguish unless bill tip colour can be seen. Some relatively young northern giant petrels can appear to be paler on the head, suggesting southern giant, thus this species is harder to confirm.

Etymology

Macronectes comes from the Greek words makros meaning "long" and nēktēs meaning "swimmer". Also, petrel is derived from St. Peter and the story of his walking on water as they appear to run on the water when they take off.[10]

Giant petrel feeding on a seal carcass in South Georgia

Behaviour

Feeding

Petrels are highly opportunistic feeders. Uniquely among procellarids they will feed on land as well as at sea; in fact, they find most of their food near the coast. On land they feed on carrion,[1][9] particularly that of seals and penguins. They also display their dominance over carcasses with a "sealmaster posture":[11] the head and the wings are held outstretched, the head pointing at the opponent and the wingtips pointing slightly back; the tail is raised to a vertical position. They are also capable of killing other seabirds, even those as large as an albatross, which they kill either by battering them to death (most commonly chicks of other species during the breeding season) or drowning.[12] At sea they feed on krill, squid and fish, often following fishing fleets in the hope of picking up offal.[9]

Giant petrel with chick in Antarctica

Reproduction

The southern giant petrel is more likely to form loose colonies than the northern, both species laying a single egg in a rough nest built about 50 cm (20 in) off the ground. The egg is incubated for about 60 days, once hatched the chick is brooded for 3 weeks. Chicks fledge after about 4 months, but do not achieve sexual maturity for another 6–7 years after fledging.[1]

Conservation

While both species are listed as near threatened in the 2008 IUCN Red List,[13][14] recent evidence suggests they are less threatened than previously believed, and the populations of both actually appear to have increased, at least locally. Consequently, they will be listed as least concern on the 2009 Red List.[9][15]

The southern giant petrel is listed as endangered on the Australian Environment Protection and Biodiversity Conservation Act 1999, while the northern giant petrel is listed on the same act as vulnerable.[16] Their conservation status also varies from state to state within Australia. For example:

References

  1. 1 2 3 4 5 Maynard, B. J. (2003)
  2. ↑ Remsen Jr., J. V. (2008)
  3. ↑ Tree of Life (2008)
  4. ↑ http://www.heardisland.aq/nature/animals/fact_file_southern_giant_petrel.html
  5. ↑ http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=1061#description
  6. ↑ http://www.oiseaux.net/birds/northern.giant-petrel.html
  7. ↑ Double, M. C. (2003)
  8. ↑ Ehrlich, Paul R. (1988)
  9. 1 2 3 4 BirdLife International (2009a)
  10. ↑ Gotch, A. F. (1995)
  11. ↑ de Bruyn, P. J. N. & Cooper, Æ J. (2005). "Who's the boss? Giant petrel arrival times and interspecific interactions at a seal carcass at sub-Antarctic Marion Island" (Abstract). Polar Biology. 28 (7): 571–573. doi:10.1007/s00300-005-0724-7.
  12. ↑ Cox, J. B. (1978). "Albatross Killed by Giant-petrel" (PDF). Emu. 78 (2): 94–95. doi:10.1071/MU9780094.
  13. ↑ BirdLife International (2008a)
  14. ↑ BirdLife International (2008b)
  15. ↑ BirdLife International (2009b)
  16. ↑ "EPBC Act List of Threatened Fauna". Australian government: Department of the Environment, Water, Heritage and the Arts. Retrieved 25 July 2009.
  17. ↑ Department of Sustainability and Environment, Victoria
  18. ↑ Department of Sustainability and Environment, Victoria
  19. ↑ Victorian Department of Sustainability and Environment (2007)

Further reading

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