Sooty albatross

Taxobox
name = Sooty albatross


image_width = 250px
image_caption = Light-mantled Sooty Albatross
regnum = Animalia
phylum = Chordata
classis = Aves
ordo = Procellariiformes
familia = Diomedeidae
genus = "Phoebetria"
genus_authority = Reichenbach, 1853
subdivision_ranks = Species
subdivision = "P. fusca" (Hilsenberg, 1822)
"P. palpebrata" (Forster, 1785)

The sooty albatrosses are small albatrosses from the genus "Phoebetria". There are two species, the Dark-mantled Sooty Albatross ( or Sooty Albatross, "P. fusca") and the Light-mantled Sooty Albatross ("P. palpebrata"). The sooties have long been considered distinct from the rest of the other albatrosses, and have retained their generic status through the many revisions of the family over the last 150 years. They have traditionally been thought of as primitive, sharing some morphological features with the other petrel families. However, molecular work examining the mitochondrial DNA has shown that the taxon is related to the mollymawks (genus "Thalassarche"), and that the two taxa are distinct from the great albatrosses and the North Pacific albatrosses (Nunn "et al.", 1996).

Both of the sooties have distinctive black plumage over the head, wings and bellies. The Dark-mantled Sooty has a dark back and mantle as well, whereas the Light-mantled Sooty has an ashy-grey mantle, back and rump. The two species can also be told apart by the narrow yellow line on the Dark-mantled's bill. Despite the differences between the two species they can be hard to tell apart at sea, especially in poor light. Both species have a white incomplete eye-ring, dark bills and grey feet. They are among the smallest albatrosses, with wingspans of 200 cm (83 in) and are very narrow as well. The Light-mantled, at 2.5-3.7 kg (5.5-8.2 lbs) and sometimes to 4.6 kg (10.1 lbs), is larger than the Dark-mantled, at 2.4-2.7 kg (5.4-6 lbs). Unique amongst the albatrosses they have long stiff wedge shaped tails, the purpose of which is unclear but seems to be related to their ability to dive for food.

The sooties, like most seabirds, are colonial, although sooties are less colonial than the other species of albatross. In fact, on some breeding islands (like Tristan da Cunha) sooties nest in very small groups or clusters of two to five nests, and the Light-mantled Sooties will even nest singly. This is in part due to the influence of humans, and in part due to their tendency to nest on cliffs, unlike the flatter ground preferred by other albatrosses. Sooties build cone shaped nests and lay a single egg. Eggs are incubated for 70 days, by both parents, the male taking the first stint after laying (lasting 11 days) thereafter both parents taking it in turns of 7 days. After hatching the chick is brooded for 20 days until it is able to thermoregulate on its own, after which both parents undertake the task of feeding it, on average bringing food to the chick every three days. The chick is fed for about 160 days, until it is able to fledge. There is no parental care after fledging. Sooties are able to complete a breeding cycle in under a year, but do not breed in consecutive years, instead taking a year off and returning to breed every two years. Around 22% of Dark-mantled Sooties survive until adulthood (there are no figures for Light-mantled). Both species return to the breeding colony after 7-10 years of fledging, and begin to breed a few years later.

Dark-mantled Sooty Albatrosses nest on islands in the South Atlantic (Tristan da Cunha and Gough Island) and islands in the South Indian Ocean (the Crozet Islands to Kerguelen Island). At sea they forage from South America to Australia, with a few records of birds reaching New Zealand. The Light-mantled Sooty Albatross has a wider distribution, nesting on South Georgia in the Atlantic, many of the same islands in the Indian Ocean, Macquarie Island and New Zealand's sub-Antarctic islands. At sea it forages further south than the Dark-mantled to Antarctica, and around the Southern Ocean as far north as Chile, Tasmania and South Africa. At sea they often eat more fish as opposed to squid than other albatross species, and the sooties also readily take carrion and particularly other seabirds. They also are the deepest diving of the albatross, often diving to 5m and once being recorded as deep as 12m.

The two species face similar threats, introduced species that attack chicks and eggs, and falling victim to long-line fisheries. These threats, combined with some historic harvesting of the birds and chicks, has led to an estimated 75% population decline in the Dark-mantled Sooty Albatross over the last 90 years (to around 40,000 birds), which has led to it being listed as an endangered species by the IUCN. The Light-mantled Sooty Albatross has not been as badly affected, and is considered near-threatened.

References

* Brooke, Michael (2004): "Albatrosses and Petrels across the World". Oxford University Press, Oxford, New York. ISBN 0-19-850125-0

* Nunn, Gary B.; Cooper, John; Jouventin, Pierre; Robertson, Chris J. R. & Robertson Graham G. (1996): Evolutionary relationships among extant albatrosses (Procellariiformes: Diomedeidae) established from complete cytochrome-"b" gene sequences. "Auk" 113(4): 784-801. [http://elibrary.unm.edu/sora/Auk/v113n04/p0784-p0801.pdf PDF fulltext]

* Tickell, W. L. N. (2000): "Albatrosses". Pica Press, Sussex. ISBN 1-873403-94-1