Data Zone
Justification of Red List category
This species qualifies as Endangered as it has a very small area of occupancy, it probably breeds at fewer than five locations (although currently only known from one) and its population is suspected to be declining as a consequence of predation by rats.
Population justification
In 1991-1992, the breeding population on Henderson was estimated at c.16,000 breeding pairs, though using the incorrect island area. The revised estimate is 18,668 pairs (Oppel et al. 2017), and it was suggested that the species could be undergoing a long-term decline (Brooke 1995, Brooke et al. 2010). In 2015, the population was estimated to be 19,987 pairs (Oppel et al. 2017).
Trend justification
High variability in breeding success suggests the population may be declining, but infrequent surveys (1991, 2015), which do not suggest any substantial change, make this difficult to confirm.
Pterodroma atrata is known to breed only on Henderson Island, Pitcairn Islands (to UK), but may have also bred on Pitcairn Island in the past and has apparently become extirpated from Ducie, also in the Pitcairn Islands (Brooke 1995). It is possible it also breeds on the Gambier and Marquesas Islands (French Polynesia) (Murphy and Pennoyer 1952, Thibault and Bretagnolle 1999), but there has been no conclusive evidence. While its non-breeding range is not well known, it has been sighted at Easter Island (A. Jaramillo in litt. 2011). Birds may range up to 2500 km from Henderson Island during incubation (Oppel et al. 2017).
Like P. heraldica it may feed predominantly on cephalopods, also taking fish and crustaceans (Imber et al. 1995). On Henderson, it nests exclusively on the plateau, scattered in the dense forest, though nearer to the coast than P. heraldica (Brooke 1995, Brooke and Rowe 1996, Oppel et al. 2017). Breeding success may be low, with less than 20% of eggs yielding fledglings and failure mostly occurring at the early chick stage (Brooke 1995), but was 28-50% in 2015 (Oppel et al. 2017), which is sufficient for a stable population using the demographic parameters from Brooke et al. (2010). In other absence of other known colonies elsewhere, there is no source of immigrants to sustain the Henderson petrel population (Brooke 2010).
Predation by Polynesian rat Rattus exulans is believed to be the main cause of chick mortality on Henderson (Oppel et al. 2017) and although predation by crabs Coenobita spp. also occurs, it is thought to be negligible in comparison (Oppel et al. 2017). In August 2011, a rat eradication operation was carried out on Henderson Island to eradicate R. exulans from the island (J. Hall in litt. 2012), but the project failed, with little apparent impact on the Henderson Petrel population (Oppel et al. 2016). It is thought that their breeding habitat may be significantly affected by changing sea levels, as well as damage to the coral reefs caused by an increase in sea temperature (del Hoyo et al. 2018).
Conservation Actions Underway
In 1997, feral cats were eradicated from Pitcairn, but subsequently re-introduced by residents. A programme to eradicate rats in 1997-1998 (Bell and Bell 1998) was unsuccessful, although petrels were observed prospecting the island during a period of no cats and low rat numbers (G. Wragg in litt. 1999). In the same year, rats were eradicated on Oeno and Ducie to increase the chance of a population becoming established there (Bell and Bell 1998). Several follow-up visits to Oeno and Ducie have not found any signs of rats (M. de L. Brooke in litt. 2000, 2003). Following a feasibility study (Brooke and Towns 2008), a rat eradication operation was carried out on Henderson Island in August 2011, but was unsuccessful (Amos et al. 2016). In 1988, Henderson was designated a World Heritage Site. A rudimentary monitoring protocol was established on Henderson in 2003 (M. de L. Brooke in litt. 2000, 2003).
Conservation Actions Proposed
Eradicate rats from Henderson Island. Periodically resurvey the species to establish and monitor any trends. Periodically check Oeno and Ducie for rats and nesting P. atrata, and ensure that further alien species are not accidentally introduced to the Pitcairn Islands.
36 cm. Medium-sized, slight, dark grey-brown, gadfly petrel. Fairly uniform grey-brown plumage, somewhat paler on underparts. Greyer feather tips on forehead and chin give mottled appearance around bill. Underwing shows pale leading edge between carpal joint and body, and some silvery-white at base of primaries. Black bill. Pink legs, with pink feet proximally, black distally. Similar spp. Dark phase Kermadec Petrel P. neglecta slightly bigger, with white primary shafts, and wholly black legs. Murphy's Petrel P. ultima is a greyer bird. Providence Petrel P. solandri is distinctly larger, and usually has more facial frosting.
Text account compilers
Pople, R., Shutes, S., Stattersfield, A., Stuart, A., Symes, A., Fjagesund, T., Calvert, R., Hermes, C., Anderson, O., Mahood, S., Martin, R., Moreno, R., O'Brien, A.
Contributors
Wragg, G., Hall, J., Bond, A., Brooke, M., Oppel, S.
Recommended citation
BirdLife International (2024) Species factsheet: Henderson Petrel Pterodroma atrata. Downloaded from
https://datazone.birdlife.org/species/factsheet/henderson-petrel-pterodroma-atrata on 22/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/11/2024.