Tristan Albatross (Diomedea dabbenena)

Tristan Albatross

Subspecies

Genus	Species	subspecies	Region	Range
Diomedea	dabbenena		AO	Tristan da Cuhna group

Genus

Albatrosses are the ‘largest’ birds in terms of wingspan. Royal Abatrosses, for instance, may reach a wing span of almost 3.5m, which make them look like feathered sail plaines. They are also the largest members of the tubenose family. Only the smallest albatross species are equalled in size by the Giant Petrels (Macronectes). Albatrosses occur in all oceans, except the northern part of the Atlantic. In ancient times they were also present in that part of the world, but nowadays only an occasional straggler find its way to the North Atlantic. Most of the 24 species are Southern Hemisphere breeders, only three actually breed north of the Equator in the Pacific Ocean.
Albatross taxonomy is subject of discussion for a long time, and has been at times rather chaotic. Based on external characters: plumage patterns, tail shapes, bill structure (size, organization of the plates and coloration) albatrosses were, until recently, divided in 13-14 species in four ‘natural groups’: the Great Albatrosses, the Mollymawks, the North Pacific Albatrosses, grouped in the genus Diomedea and the Sooty Albatrosses Phoebastria. More recently DNA-analyses supports the division in four distinct groups but the were elevated to a generic status and has led to a splitting into 24 species: Great Albatrosses Diomedea (7 species), the Northern (Pacific) Albatrosses Phoebastria (4 species), the southern Mollymawks Thalassarche (11 species) and the Sooty Albatrosses Phoebetria (2 species). Recently this taxonomy is challenged by who proposed to lump some of the ‘species’ again based on their molecular analysis. Since then the discussion flared up and has not ended yet. Some list six species of Great Albatrosses, including two subspecies of Antipodian Albatross.

Physical charateristics

Huge albatross, very similar in plumage to Wandering Albatross D.exulans. Probably indistinguishable in field, but plumage generally darker. Separated by smaller size (e.g. bill c.25 mm shorter) and slower acquisition of white adult plumage, never attaining very white plumage of old male D. exulans.

wingspan min.:	340	cm	wingspan max.:	360	cm
size min.:	105	cm	size max.:	115	cm
incubation min.:	0	days	incubation max.:	0	days
fledging min.:	0	days	fledging max.:	0	days
broods:	1		eggs min.:	1
			eggs max.:	0

Range

Atlantic Ocean : Tristan da Cuhna group. Diomedea dabbenena breeding Pacific Oceanpulations are essentially restricted to Gough Island, Tristan da Cunha, St Helena (to UK), having become extinct on Tristan (although birds were seen prospecting in 1999).

Habitat

It nests at 400-700 m (rarely to 300 m), primarily in wet heath where it is open enough for take-off and landings.

Reproduction

These albatross have a slow reproductive rate, producing just one egg every two years. It is a colonial, biennially breeding species. Adults return in November and December, lay in January and the chicks fledge in November. Immature birds begin returning to their breeding colony at 3-7 years after fledging. Most D. dabbenena recruit in their natal colony, at a mean age of 10 years (range 4-20 years). During the breeding season the length and range of foraging trips varies considerably, depending on the stage of the breeding cycle.

Feeding habits

It catches prey by surface-seizing, and the prevalence of a bioluminescent group of cephalopods in one dietary study suggests that D. dabbenena often feed at night. It feeds on cephalopods and fish, and probably follows ships and trawlers for offal and galley refuse

Video Tristan Albatross

httpv://www.youtube.com/watch?v=uGA_C4LaVlw

Conservation

This species qualifies as Critically Endangered owing to its extremely small breeding range and a projected extremely rapid population decline over three generations (70 years). Modelled population declines are a consequence of very low adult survival owing to incidental mortality in longline fisheries, compounded by low fledging success caused by predation of chicks by introduced mice.
On Inaccessible Island, its decline was probably due to predation by feral pigs (now absent) and humans. The failure to recover is unclear, but may be because young birds become entangled in thick vegetation. On Tristan, its extirpation was probably the result of human exploitation, although predation by rats may have been a factor. On Gough, predation by the introduced house mouse Mus musculus causes very low breeding success and alone is sufficient to drive a population decline of over 50% over three generations. An additional threat on Gough is peat slips caused by storms burying and killing nestlings and adults, though this is probably a very rare event. The main threat comes from interactions with longline fisheries, with a high proportion of “Wandering” Albatross bycatch in southern Brazilian waters being of this species, including a few birds banded at Gough. Satellite tracking of breeding birds indicates considerable overlap between birds and areas of longline fishing, although due to lag times associated with albatross demography we are probably only now likely to start to pick up population trends associated with longline mortality. Together, the dual threats of mice and bycatch give a worst-case scenario of extinction in roughly 30 years, though the true situation is likely a continued and severe decline. Having a distribution on relatively low-lying islands, this species is also potentially susceptible to climate change through sea-level rise and shifts in suitable climatic conditions.

Tristan Albatross status Critically Endangered

Migration

Outside the breeding season, it disperses to South Atlantic and South African waters, with numerous recent records from Brazilian waters and one from Australia, suggesting that birds may occasionally disperse into the Indian Ocean.

Distribution map

Tristan Albatross distribution range map

Planet of Birds