Pterodroma incerta 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Procellariiformes Procellariidae

Scientific Name: Pterodroma incerta (Schlegel, 1863)
Common Name(s):
English Atlantic Petrel
French Pétrel de Schlegel
Spanish Petrel de Schlegel
Taxonomic Source(s): Brooke, M. de L. 2004. Albatrosses and Petrels Across the World. Oxford University Press, Oxford.
Identification information: 43 cm. Large, stocky, dark brown-and-white petrel. Uniformly dark chocolate-brown above and on upper breast. Head can appear grey in worn plumage. Sharp demarcation from brown upper breast to white lower breast and belly. Brown vent, undertail-coverts and tail. Uniform brown underwing. Similar spp. Soft-plumaged Petrel P. mollis has patterned underwing. Trindade Petrel P. arminjoniana has white wing flashes. Hints May flap at top of glides unlike most Pterodroma spp. Concentrates around subtropical convergence.

Assessment Information [top]

Red List Category & Criteria: Endangered B2ab(v) ver 3.1
Year Published: 2016
Date Assessed: 2016-10-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Bond, A., Bourgeois, K., Bugoni, L., Cuthbert, R., Hilton, G., Ryan, P.G. & Wanless, R.
Facilitator/Compiler(s): Clay, R., Ekstrom, J., McClellan, R., Moreno, R., Shutes, S., Stattersfield, A. & Temple, H.
This species has been listed as Endangered because it has an extremely small occupied breeding range, and there is now evidence that chick predation by introduced mice is causing very low breeding success and is likely to be causing the population to decline. It has not been recorded from Tristan de Cunha for 35 years, and, were it to be confirmed as extinct there, it may qualify for uplisting to Critically Endangered.

Previously published Red List assessments:

Geographic Range [top]

Range Description:

Pterodroma incerta breeds only on Gough Island, Tristan da Cunha (St Helena to UK). It is absent from Nightingale where there is no suitable habitat, and probably also from Inaccessible, although it is possible that a small number of birds could breed there because there have been no surveys during the winter breeding season (P. G. Ryan in litt. 1999), and Tristan, where though the population was estimated to be 100-200 pairs in 1972-1974, and there may only be a few scattered pairs remaining. On Gough, the first quantitative population estimate indicates a total of around 1.8 million pairs (Cuthbert 2004), considerably larger than the earlier estimate of at least 20,000 pairs (P. G. Ryan in litt. 1999). However, a recent estimate that takes into account occupancy rates of burrows suitable for the species halves this number, indicating a population size of 860,000 pairs varying between 630,000 and 1,100,000 pairs (Rexer-Huber et al. 2014). Several studies revealed very low breeding success: less than 20% (Cuthbert and Hilton 2004, Wanless et al. 2007, Dilley et al. 2015). At sea, it is practically restricted to the South Atlantic, occurring off the east coast of South America to the west coast of Africa (Enticott 1991, P. G. Ryan in litt. 1999), occasionally rounding the Cape of Good Hope into the Indian Ocean (Hobbs in litt. 2009).

Countries occurrence:
Argentina; Brazil; Falkland Islands (Malvinas); Namibia; Saint Helena, Ascension and Tristan da Cunha (Tristan da Cunha); South Africa; Uruguay
Antarctica; Israel; Jordan; South Georgia and the South Sandwich Islands
Additional data:
Estimated area of occupancy (AOO) - km2:64Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:23300000
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:2Continuing decline in number of locations:Unknown
Extreme fluctuations in the number of locations:NoLower elevation limit (metres):50
Upper elevation limit (metres):700
Range Map:Click here to open the map viewer and explore range.

Population [top]


On Gough, Cuthbert (2004) estimated 1.8 million breeding pairs in 2001, suggesting a world population of around 5 million birds. The population size was re-estimated by Rexer-Huber et al. (2014), taking into account the occupancy rates of suitable burrows in 2010 and 2012. This new estimate indicates a population size of 860,000 pairs varying between 630,000 and 1,100,000 pairs. Because occupancy rates varied interannually, the species’ total breeding area was only estimated crudely, and burrow densities were assumed to be similar throughout the habitat, this estimate should be treated with caution. However, stochastic population models computing a modelled breeding success of 24.7% and parameters estimated for other gadfly petrels (adult survival = 93%, immature survival = 79% and recruitment age = 6 years) suggested population decline of 0.7% per annum (Wanless et al. 2012). Given that breeding success seems to be even lower (less than 20%; Cuthbert and Hilton 2004, Wanless et al. 2012, Dilley et al. 2015) and that adult and immature survival rates were probably over-estimated as they were those from gadfly species not exposed to predation by subantarctic skuas Catharacta antarctica, the population might be decreasing at a faster rate.

Trend Justification:  Stochastic population models computing a modelled breeding success of 24.7% and parameters estimated for other gadfly petrels (adult survival = 93%, immature survival = 79% and recruitment age = 6 years) suggested population decline of 0.7% per annum (Wanless et al. 2012). 

Current Population Trend:Decreasing
Additional data:
Number of mature individuals:1800000Continuing decline of mature individuals:Yes
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:2Continuing decline in subpopulations:Unknown
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No
No. of individuals in largest subpopulation:100

Habitat and Ecology [top]

Habitat and Ecology:It feeds mainly on squid with some fish and crustaceans (Klages and Cooper 1997). It nests in burrows dug in peaty soils in fern-bush vegetation from 50-300 m on Gough and formerly, at higher elevations on Tristan. Nothing is known of age of first breeding, breeding frequency or survival (P. G. Ryan in litt. 1999). Heavily affected by Hurricane Catarina in March 2004, 354 birds were recorded blown inland, all in heavy moult and near starvation (Bugoni et al. 2007). Larger numbers of females among these were thought to be due to difference in at-sea distribution or in body condition (Bugoni et al. 2007). Evidence suggests moult is completed during exodus period and before egg-laying, which occurs from 15 June to 21 July (Cuthbert 2004).

Systems:Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat:Unknown
Generation Length (years):15.6
Movement patterns:Full Migrant
Congregatory:Congregatory (and dispersive)

Threats [top]

Major Threat(s): This species was once of major economic importance to the Tristan Islanders as it was one of the few sources of food in winter but, by the 1940s, the birds had become scarce (Richardson 1984). It is very unlikely to be exploited today (P. G. Ryan in litt. 1999, A. Bond in litt. 2016). On Tristan, rats and mice are present and have probably driven it to extinction (Richardson 1984, R. Wanless et al. 2012). On Gough, the only threat is an introduced predator, the house mouse Mus musculus and recent research reveals that mice are predating chicks and causing very low breeding success which is driving the long-term decline (Cuthbert and Hilton 2004, Wanless et al. 2007, Wanless et al. 2012, Cuthbert et al. 2013, Dilley et al. 2015). The large population of native Southern Skua Stercorarius antarcticus feed on seabirds including P. incerta (Richardson 1984). Night strikes (as a result of being attracted to lights) are a further threat. This has been ameliorated at the Gough meteorological station, but may still pose a problem on ships at sea (Glass and Ryan 2013). The mortality associated with Hurricane Catarina points to a potential threat from hurricane activity in the South Atlantic, postulated to increase in frequency with global warming (Bugoni et al. 2007).

Conservation Actions [top]

Conservation Actions:

Conservation Actions Underway
On Tristan, a programme to eradicate cats was successful in the 1970s. Gough is a nature reserve and World Heritage Site (Cooper and Ryan 1994). The first ever quantitative population survey was undertaken on Gough, 2000/1, coupled to research into breeding ecology and reproductive output (Cuthbert 2004, Cuthbert and Hilton 2004). During 2003-7 then 2010-14, further research on reproductive output and mouse predation was conducted (Wanless et al. 2007, Cuthbert et al. 2013, Dexer-Ruber et al. 2014, Dilley et al. 2015). Searches on Tristan da Cunha have failed to locate any birds (Wanless et al. 2007). Burrow density and occupancy, and breeding success are monitored annually on Gough (A. Bond in litt.)

Conservation Actions Proposed
Eradicate mice from Gough. Minimise the risk of further introduced species establishing on Gough, particularly any rat Rattus species (P. G. Ryan in litt. 1999). Confirm the status of the population on Tristan da Cunha and whether birds also breed on Inaccessible. 

Citation: BirdLife International. 2016. Pterodroma incerta. The IUCN Red List of Threatened Species 2016: e.T22698084A95224555. . Downloaded on 14 August 2018.
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