Justification of Red List Category
This species qualifies as Critically Endangered owing to 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.
Breeding populations are essentially restricted to Gough Island, with 2-3 pairs nesting intermittently on Inaccessible Island (McClelland et al. 2016). The annual breeding population is currently estimated to be 1,250-1,750 pairs annually (RSPB and UCT unpubl. data), equivalent to a total population of 5200-7300 individuals for this biennially breeding species (RSPB and UCT unpubl. data). This roughly equates to 3,400-4,800 mature individuals.
Recent counts suggest that the population on Gough has decreased by 28% over 46 years, and at 3-5% annually between 2000 and 2016 (Cuthbert et al. 2014, RSPB and UCT unpubl. data), which is in line with population modelling predicting annual rates of decline of 2.9-5.3% (Ryan et al. 2001, Wanless et al. 2009). More recent population modelling, conducted over three generations since 1980, suggests a decline equivalent to a 96% reduction in population size over three generations, since declines began (BirdLife International unpubl. data). The rate of on-going decline is therefore placed here in the band 80-100% over three generations (86 years).
Diomedea dabbenena breeding populations 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; Ryan et al. 2001), and 2-3 pairs breed annually on Inaccessible Island (McClelland et al. 2016). Using consecutive annual accounts of incubating adults and a population model the population has been estimated at c. 1,700 breeding pairs, giving a total global population of 7,100 individuals (ACAP 2010). Recent counts suggest that the population on Gough has decreased by 28% over 46 years, and at 3% annually between 2000 and 2011 (Cuthbert et al. 2014), and by nearly 50% between 2001-2016 (0-8% decline per year; RSPB and UCT unpubl. data) in line with population modelling predictions of annual decline rates of 2.9-5.3% (Ryan et al. 2001, Wanless et al. 2009), equivalent to declines of >96% in three generations. Predation of chicks by mice has led to very low breeding success; between 2000 and 2015 this averaged only 27%, less than half that of other studied Diomedea colonies (Cuthbert et al. 2003, Cuthbert and Hilton 2004, Wanless et al. 2007, Cuthbert et al. 2014, Davies et al. 2015). Breeding success in 2014 was just 9.6%, the lowest recorded since counts started in 2001 (Davies et al. 2015). Outside the breeding season, it disperses to the western South Atlantic in summer, moves eastwards to South African waters and, northwards along the African Atlantic coast as far as southern Angola (Reid et al. 2013). Up to 15% migrate across the Indian Ocean to southern Australian waters (Reid et al. 2013).
Behaviour 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. The vast majority of D. dabbenena recruit in their natal colony, at a mean age of 10 years (range 4-20 years) (ACAP 2009). The oldest recorded bird was at least 38 years old (Ryan 2009). 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 (ACAP 2009). During the breeding season the length and range of foraging trips varies considerably, depending on the stage of the breeding cycle (BirdLife International 2004, Cuthbert et al. 2005).
Habitat Breeding It nests at 400-700 m (rarely to 300 m) (Ryan and Glass 2001, Davies et al. 2015), primarily in wet heath where it is open enough for take-off and landings.
Diet It feeds on cephalopods and fish (J. Cooper in litt. 1999), and probably follows ships and trawlers for offal and galley refuse.
Interaction with longline fisheries represents a major threat, with a high proportion of bycatch in southern Brazilian water being of this species (Neves et al. 2000, Olmos et al. 2000), including birds banded at Gough (Croxall and Gales 1998, J. Cooper in litt. 1999). It has been estimated that c. 500 individuals of this species are killed every year by longliners (Goren and Ryan 2010). Satellite tracking of breeding birds indicates considerable overlap between bird distribution and areas of longline fishing (Cuthbert et al. 2005). A study of great albatross bycatch from Uruguayan and Japanese longline fisheries in the south-west Atlantic off Uruguay found most Tristan Albatross bycatch occurred between September and November in pelagic waters where many other fleets operate (Jiménez et al. 2014).On-land threats include predation by introduced species. On Inaccessible Island, population decline was probably due to predation by rats, feral pigs (now absent) and humans (Fraser et al. 1988, Ryan et al. 1990). The failure to recover is unclear, but may be because young birds become entangled in thick vegetation (Ryan et al. 1990, P. G. Ryan in litt. 1999), or there is a high mortality in long-line fisheries. On Tristan, its extirpation was probably the result of human exploitation (Hagen 1952), although predation by rats (and possibly mice) may have been a factor (Fraser et al. 1988). At present, the greatest risk is posed by house mice Mus musculus, which causes very low breeding success on Gough and alone is sufficient to drive a population decline of over 50% over three generations (Cuthbert et al. 2003, Cuthbert and Hilton 2004, Wanless et al. 2007, Davies et al. 2015). Mouse attacks on chicks peaked in May-June at the start of the austral winter and all predation took place at night, normally 1-2 mice were recorded attacking the chick, with death occurring 3.9 ±1.2 days after the first attack (Davies et al. 2015). An additional threat on Gough is peat slips caused by storms burying and killing nestlings and adults, although this is probably a very rare event (Ryan 1993).
Conservation Actions Underway
ACAP Annex 1. On Tristan, a programme to eradicate cats was successful in the 1970s. Gough and Inaccessible are nature reserves and a World Heritage Site. Both islands are uninhabited, apart from a meteorological station on Gough (Tristan da Cunha Government and RSPB 2016). Satellite tracking to determine foraging areas during the breeding season was undertaken in 2000-2001 (Cuthbert et al. 2003). Censuses of large chicks and/or incubating adults were carried out during 1999-2016, and a monitoring protocol was devised (Cuthbert and Sommer 2004). Satellite tracking of non-breeders, further monitoring and demographic work, and an investigation of mouse predation on chicks was initiated in 2003. It is technically feasible to eradicate mice from Gough Island (Parkes 2008, Cuthbert et al. 2011a, b, RSPB unpubl. data). In September 2013 a trial drop of non-toxic bait over the vegetated cliffs of Gough showed that around 80% of the bait was retained on the cliffs and would be accessible to mice living there (Cuthbert et al. 2011a). Since 2007, birds have been marked with field-readable plastic leg rings, and by 2016, >1,000 individuals had been ringed (RSPB and UCT unpubl. data).
Conservation Actions Proposed
Eradicate mice on Gough Island as soon as possible. Annually survey numbers and assess breeding success on Gough. Continue research of at-sea distribution and foraging behaviour, particularly of non-breeding birds. Promote adoption of best-practice mitigation measures in all fisheries within the species' range, particularly via intergovernmental mechanisms such as ACAP, FAO and Regional Fisheries Management Organisations.
110 cm. 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) (Neves et al. 2000) and slower acquisition of white adult plumage, never attaining very white plumage of old male D. exulans.
Text account compilers
Moreno, R., Anderson, O., Calvert, R., Nel, D., Shutes, S., Stattersfield, A., Stuart, A., Sullivan, B., Symes, A., Taylor, J., Ashpole, J, Fjagesund, T., Hermes, C., Mahood, S., Martin, R., McClellan, R.
Hilton, G., Croxall, J., Wanless, R., Bond, A., Ryan, P.G., Cooper, J., Cuthbert, R.
BirdLife International (2020) Species factsheet: Diomedea dabbenena. Downloaded from http://www.birdlife.org on 30/10/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 30/10/2020.