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Henderson Petrel Pterodroma atrata
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Justification
This species qualifies as Endangered as 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.

Taxonomic source(s)
Brooke, M. de L. 2004. Albatrosses and Petrels Across the World. Oxford University Press, Oxford.
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

Taxonomic note
Pterodroma arminjoniana (Sibley and Monroe 1990, 1993) has been split into P. arminjoniana, P. heraldica and P. atrata following Brooke (2004).

Identification
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.

Distribution and population
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 1995a). It is likely to breed on other islands in the region too (Murphy and Pennoyer 1952), such as the Gambier and Marquesas Islands (French Polynesia) (Murphy and Pennoyer 1952, Thibault and Bretagnolle 1999). In 1991-1992, the breeding population on Henderson was estimated at c.16,000 breeding pairs and it was suggested that the species could be undergoing a long-term decline (Brooke 1995a). While its non-breeding range is not well known, it has been sighted at Easter Island (A. Jaramillo in litt., 2011).

Population justification
Brooke (2004).

Trend justification
The species is presumed to be declining as a result of predation by introduced mammals.

Ecology
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 1995a, Brooke and Rowe 1996). Breeding success is low, with less than 20% of eggs yielding fledglings and failure mostly occurring at the early chick stage (Brooke 1995a). In other absence of other known colonies elsewhere, there is no source of immigrants to sustain the Henderson petrel population (Brooke 2010).

Threats
Predation by Polynesian rat Rattus exulans is believed to be the main cause of chick mortality on Henderson, although predation by crabs Coenobita spp. is also a possibility (Brooke 1995a). 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). If it ever bred on Pitcairn, it is likely to have been extirpated there because of predation by feral cats and introduced rats (Brooke 1995a). The species is potentially threatened by climate change because it has a geographically bounded distribution: it is restricted to an island with a maximum altitude of 33 m (BirdLife International unpublished data).

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 another 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 (J. Hall in litt. 2012). A follow-up monitoring expedition is planned for 2013 to assess the success of the rat eradication. 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
Periodically resurvey the species to establish and monitor any trends. Periodically check Oeno and Ducie for rats, and ensure that further alien species are not accidentally introduced to the Pitcairn Islands.

Related state of the world's birds case studies

References
Bell, B.; Bell, D. 1998. Pitcairn paradise preserved. World Birdwatch 20: 8-11.

Brooke, M. De L. 1995. The breeding biology of the gadfly petrels Pterodroma spp. of the Pitcairn Islands: characteristics, population sizes and controls. Biological Journal of the Linnean Society 56: 213-231.

Brooke, M. De L. 2004. Albatrosses and petrels across the world. Oxford University Press, Oxford.

Brooke, M. De L.; Rowe, G. 1996. Behavioural and molecular evidence for specific status of pale and dark morphs of the Herald Petrel Pterodroma heraldica. Ibis 138: 420-432.

Imber, M. J.; Jolly, J. N.; Brooke, M. De L. 1995. Food of three sympatric gadfly petrels (Pterodroma spp.) breeding on the Pitcairn Islands. Biological Journal of the Linnean Society 56: 233-240.

Murphy, R. C.; Pennoyer, J. M. 1952. Larger petrels of the genus Pterodroma. American Museum Novitates 1580.

Thibault, J.-C.; Bretagnolle, V. 1999. Breeding seabirds of Gambier Islands, Eastern Polynesia: numbers and changes during the 20th century. Emu 99: 100-107.

Further web sources of information
Alliance for Zero Extinction (AZE) species/site profile. This species has been identified as an AZE trigger due to its IUCN Red List status and limited range.

Click here for more information about the Alliance for Zero Extinction (AZE)

Explore HBW Alive for further information on this species

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Calvert, R., Mahood, S., O'Brien, A., Pople, R., Shutes, S., Stattersfield, A., Symes, A., Anderson, O.

Contributors
Brooke, M., Hall, J., Wragg, G.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2014) Species factsheet: Pterodroma atrata. Downloaded from http://www.birdlife.org on 19/09/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/09/2014.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Henderson petrel (Pterodroma atrata) 0

Key facts
Current IUCN Red List category Endangered
Family Procellariidae (Petrels, Shearwaters)
Species name author Mathews, 1912
Population size mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 7,130,000 km2
Country endemic? Yes
Links to further information
- Additional Information on this species