Atlantic Petrel Pterodroma incerta Scientific name definitions

Often considered to be of doubtful affinities in the years following its description, the Atlantic Petrel is structurally similar to the Great-winged Petrel (Pterodroma macroptera) and the White-headed Petrel (Pterodroma lessonii), but in morphology this gadfly petrel most closely resembles the dark-morph Soft-plumaged Petrel (Pterodroma mollis) and the Herald Petrel (Pterodroma arminjoniana). Appropriately, Atlantic Petrel is only recorded in the Atlantic Ocean, and is restricted as a breeder to the islands of Tristan da Cunha and Gough, with the overwhelming majority of the population confined to the latter. It nests in winter, in burrows and exposed ridges, but there is still very little published breeding data. Worryingly for the species’ conservation, there is evidence of predation by House Mice on this petrel’s chicks. Considered of no conservation concern just a decade ago, the recent data from Gough of very low breeding success have led BirdLife International to currently list the species as Endangered, with a precautionary note that the Atlantic Petrel might warrant upgrading to the highest conservation priority, Critically Endangered, in the near future. Atlantic Petrel probably feeds mainly on squid, of which some may be captured underwater, although smaller percentages of fish and crustacea are also taken. In the Neotropics, this species is known solely from southern Brazil, where it has been recorded mainly in the austral spring, largely in the post-breeding season.

40–43 cm; 420–720 g (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ) (exceptionally 310 g) (2 Bugoni, L., Sander, M. and Schneider Costa, E. (2007). Effects of the first Southern Atlantic hurricane on Atlantic Petrels. Wilson J. Orn.. 119(4): 725-729. Close ); wingspan 104 cm. Only petrel of its size that is all dark with white lower breast and belly ; undertail-coverts dark. White abdomen , otherwise plumage dark brown, including hood , vent and undertail-coverts , blacker patch around eye; bases of primaries paler and greyer, but contrast is rather slight; in worn plumage looks paler and greyer, especially on hood, with paler, whitish throat, and more contrasting dark facial patch; iris very dark brown; bill black; legs pale fleshy pink with blackish-grey distal portion of toes. Sexes alike. Juvenile has greyish tips to mantle feathers in fresh plumage. Other dark petrels with white abdomen sharing similar range have either contrasting whitish markings on underwing (P. mollis) or white wing flashes in upperwing (P. neglecta (3 Flood, B. (2010). More Trindade Petrels around the Atlantic. Birding World 23(7):305–306. Close ) and pale-morph P. arminjoniana, which is also smaller, with different wing shape, more elongated tail, more dynamic flight action and can show some white on underwing) (3 Flood, B. (2010). More Trindade Petrels around the Atlantic. Birding World 23(7):305–306. Close ), preventing confusion; furthermore, P. incerta may flap its wings at top of glides, unlike most other Pterodroma (4 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ), and P. neglecta has a fuller, more rounded head and thicker, shorter neck, relatively short and stubby bill, and shorter and broader tail (3 Flood, B. (2010). More Trindade Petrels around the Atlantic. Birding World 23(7):305–306. Close ).

Marine and probably pelagic . Breeds on oceanic islands, occupying ridges at altitudes of 50–600 m, mainly below 300 m on Gough, where burrows are exclusively located in coastal tussock and fernbush habitats (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ).

Disperses throughout S Atlantic , occurring off E coast of S America and rounding South Africa into Indian Ocean (mainly in Jun–Dec) (8 Enticott, J.W. (1991). Identification of the Soft-plumaged Petrel. British Birds. 84(7): 245-264. Close ), with records spread far and wide, reaching NW to Eilat, Israel/Jordan (May 1982, Apr 1989) (9 Shirihai, H. (1999). Fifty species new to Israel, 1979–1998: their discovery and documentation, with tips on identification. Sandgrouse 21(1):45–105. Close ), E to Australia  , off W Victoria (Feb 2005) (10 Clarke, R.H. (2007). An Atlantic Petrel Pterodroma incerta at sea off Western Victoria. Australian Field Orn.. 24(1): 1-6. Close ) and perhaps also N to Indian waters, off the Chagos archipelago and between Cape Comorin and the Maldive Ridge (the latter in Jun 1985) (11 Snow, D. W., and C. M. Perrins, Editors (1998). The Birds of the Western Palearctic. Concise Edition. Volume 1. Non-passerines. Oxford University Press, Oxford, UK. Close ). In Atlantic, off E South America is generally found N to at least 20° S, and S to 56º S (being most abundant at 42–46º S) (12 Orgeira, J.L. (2001). Nuevos registros del Petrel Atlántico (Pterodroma incerta) en Océano Atlántico Sur y Antártida. Orn. Neotropical. 12(2): 165–171. Close ), while in C Atlantic most frequently occurs at 33–50º S, but in SE Atlantic is generally recorded in small numbers at latitudes of 12–48º S (8 Enticott, J.W. (1991). Identification of the Soft-plumaged Petrel. British Birds. 84(7): 245-264. Close ). Small numbers reach South Georgia (53º S) (13 Prince, P. A., and J. P. Croxall (1996). The birds of South Georgia. Bulletin of the British Ornithologists’ Club 116(2):81–104. Close ), the Drake Passage (56–59° S) and even occasionally Antarctic waters, e.g. at the South Shetland Is, with a record of five together in Weddell Sea (below 65º S) in Jan 1990 (12 Orgeira, J.L. (2001). Nuevos registros del Petrel Atlántico (Pterodroma incerta) en Océano Atlántico Sur y Antártida. Orn. Neotropical. 12(2): 165–171. Close ). A remarkable inland record from Europe—a bird found dead in what is now the Slovak Repubic in 1870 (14 Bourne, W.R.P. (1992). Atlantic Petrel in the Western Palearctic. Dutch Birding. 14(3): 100-101. Close )—is now not generally accepted (11 Snow, D. W., and C. M. Perrins, Editors (1998). The Birds of the Western Palearctic. Concise Edition. Volume 1. Non-passerines. Oxford University Press, Oxford, UK. Close ) given that its provenance is uncertain and unclear (15 Trnka, A. and Matousek, B. (1996). Occurrence of Atlantic Petrel in Western Palearctic. Dutch Birding. 18(6): 309-310. Close ); the specimen, which is no longer extant, was originally identified as P. hasitata (14 Bourne, W.R.P. (1992). Atlantic Petrel in the Western Palearctic. Dutch Birding. 14(3): 100-101. Close ). In South America, three emaciated birds were collected at a hydroelectric power dam in Pará (E Amazonian Brazil) in Sept 1984 (03º50’ S, 49º45’ W), 400 km from the nearest open sea and > 2000 km from the species’ usual range in the W Atlantic (16 Teixeira, D.M., Oren, D. and Best, R.C. (1986). Notes on Brazilian seabirds, 2. Bull. Brit. Orn. Club. 106(2): 74-77. Close ).

Mostly cephalopods (especially gonatid, onychoteuthid and histioteuthid squid) (17 Klages, N.T.W. and Cooper, J. (1997). Diet of the Atlantic Petrel Pterodroma incerta during breeding at South Atlantic Gough Island. Marine Orn.. 25(1): 13-16. Close ), with some mesopelagic fish (notably myctophids) (17 Klages, N.T.W. and Cooper, J. (1997). Diet of the Atlantic Petrel Pterodroma incerta during breeding at South Atlantic Gough Island. Marine Orn.. 25(1): 13-16. Close ) and crustaceans (e.g., Euphausiacea, Hyperiidea, Natantia) (17 Klages, N.T.W. and Cooper, J. (1997). Diet of the Atlantic Petrel Pterodroma incerta during breeding at South Atlantic Gough Island. Marine Orn.. 25(1): 13-16. Close ). Studies have revealed that squid forms 70% or 87% (by weight) of diet (species include Argonauta argo, Brachioteuthis sp., Chiroteuthis sp., Discoteuthis discus, Gonatus antarcticus, Histioteuthis sp., H. atlantica, H. meleagroteuthis, Onychoteuthis ?banksi, Taonius sp., Todarodes sp.) (17 Klages, N.T.W. and Cooper, J. (1997). Diet of the Atlantic Petrel Pterodroma incerta during breeding at South Atlantic Gough Island. Marine Orn.. 25(1): 13-16. Close ), with 11% or 17% comprising fish (species include Diaphus sp., Gymnoscopelus piabilis, Lampanyctus australis, Melamphaes simus, Melanonus sp., Borostomias ?mononema) (17 Klages, N.T.W. and Cooper, J. (1997). Diet of the Atlantic Petrel Pterodroma incerta during breeding at South Atlantic Gough Island. Marine Orn.. 25(1): 13-16. Close ) and 13% or just 1% crustacea (17 Klages, N.T.W. and Cooper, J. (1997). Diet of the Atlantic Petrel Pterodroma incerta during breeding at South Atlantic Gough Island. Marine Orn.. 25(1): 13-16. Close ). Squid prey up to 54 cm and 234 g in mass have been recorded (17 Klages, N.T.W. and Cooper, J. (1997). Diet of the Atlantic Petrel Pterodroma incerta during breeding at South Atlantic Gough Island. Marine Orn.. 25(1): 13-16. Close ). Prey taken generally by surface seizing, but it has been suggested that some may be taken underwater (4 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Generally appears to forage alone or in monospecific flocks, rather than joining mixed-species feeding frenzies (12 Orgeira, J.L. (2001). Nuevos registros del Petrel Atlántico (Pterodroma incerta) en Océano Atlántico Sur y Antártida. Orn. Neotropical. 12(2): 165–171. Close ).

Considered similar to that of P. macroptera (4 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ).

Breeds in winter, returning to colonies for courtship and burrow renovation in late Mar to late Apr (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ), then depart on pre-laying exodus for a minimum of c. 50 days (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ), with egg laying in mid Jun–Jul, hatching mid Aug to mid Sept (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ), and late fledglings may depart only in Jan (4 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Exclusively nocturnal on land (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ). Colonial; nests in burrows dug in soft soil. Clutch single white egg, mean size 68·9 mm × 49·8 mm (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ); incubation c. 55 days (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ); chicks have brown-grey down; fledging about 138 days (one of the longest periods of any Pterodroma), gaining mass at rate of just c. 4 g/day (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ). Nothing is known of age of first breeding, breeding frequency or survival. Current breeding success on Gough is very low (based on sample data from 2001 and 2004), with just 20% of eggs producing fledged young and most losses occurring during chick-rearing period (fledging success was 35% versus hatching success of 57%), and in 2007, from 58 nests sampled just one chick fledged (18 Wanless, R.M., Ratcliffe, N., Angel, A., Bowie, B.C., Cita, K., Hilton, G.M., Kritzinger, P., Ryan, P.G. and Slabber, M. (2012). Predation of Atlantic Petrel chicks by house mice on Gough Island. Animal Conservation. 15(5): 472-479. Close ); main predators of fledglings appear to be house mice (Mus musculus) (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ).

ENDANGERED. Previously considered Vulnerable. Present population numbers perhaps a few hundred breeding pairs at Tristan da Cunha (although recent evidence of breeding is unavailable) (19 Sommer, E., Cuthbert, R. and Hilton, G. (2010). Tristan and Nightingale Islands wildlife monitoring manual. RSPB Research Report No. 33. Royal Society for the Protection of Birds, Sandy, UK. Close ) and perhaps 1,790,000 pairs (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ) at Gough I; BirdLife International considers that the overall population might number five million birds. Apparently absent from Nightingale and Inaccessible Is, in Tristan group, although survey work during the winter breeding season is limited. At Tristan, suffered extreme human exploitation prior to the 1940s, especially as other food was scarce in winter, by which time P. incerta was very rare there, but is unlikely to suffer much harvesting now; several introduced predators, including rats and previously cats (which were eradicated in 1970s). On Gough I, house mouse (Mus musculus) is only introduced predator (but is extremely abundant) (1 Cuthbert, R. (2004). Breeding biology of the Atlantic Petrel, Pterodroma incerta, and a population estimate of this and other burrowing petrels on Gough Island, South Atlantic Ocean. Emu. 104(3): 221–228. Close ), and has recently been confirmed to be main predator of chicks (including healthy individuals) of this petrel and other seabirds, including albatrosses (Diomedea exulans) (20 Wanless, R.M., Angel, A., Cuthbert, R.J., Hilton, G.M. and Ryan, P.G. (2007). Can predation by invasive mice drive seabird extinctions? Biol. Lett.. 3(3): 241-244. Close ) and Ardenna gravis—data from the breeding seasons between 2003 and 2008 indicate that mean daily survival rate of eggs is 0·998, hatching success through entire incubation period 0·924 and daily chick survival rates 0·990, which gave modelled fledging success of 0·247 and mean annual breeding success (chicks fledged per breeding attempt) of 0·228 (a low figure compared to congeners, but is perhaps far too optimistic given finding that just one chick fledged from sample of 58 nests in one season) (18 Wanless, R.M., Ratcliffe, N., Angel, A., Bowie, B.C., Cita, K., Hilton, G.M., Kritzinger, P., Ryan, P.G. and Slabber, M. (2012). Predation of Atlantic Petrel chicks by house mice on Gough Island. Animal Conservation. 15(5): 472-479. Close ). Burrow occupany rates (based on chicks) are also low, averaging 26% over three seasons (2000, 2001 and 2010), with estimates of chick survival in same years varying from 36% to 69% (mean 49%) and house mice predation the apparent principal cause of mortality (21 Cuthbert, R.J., Louw, H., Lurling, J., Parker, G., Rexer-Huber, K., Sommer, E., Visser, P. and Ryan, P.G. (2013). Low burrow occupancy and breeding success of burrowing petrels at Gough Island: a consequence of mouse predation. Bird Conservation International. 23(2): 113–124. Close ). In addition, population of 6000–8000 skuas (Catharacta antarctica) on Gough feed almost entirely on seabirds, including the present species. Night strikes (the birds having been attracted to lights) have been ameliorated at Gough meteorological station, but may still pose a problem on ships. Freak events may also cause heavy mortality, e.g. by Hurricane Catarina in Mar 2004, wherein 354 birds were recorded blown up to 420 km inland (and to altitudes of 1100 m above sea level) across the S Brazilian states of Rio Grande do Sul and Santa Catarina, all in heavy moult and near starvation, with the larger numbers of females recorded thought to be due to difference in at-sea distribution or in body condition (2 Bugoni, L., Sander, M. and Schneider Costa, E. (2007). Effects of the first Southern Atlantic hurricane on Atlantic Petrels. Wilson J. Orn.. 119(4): 725-729. Close ); one analysis of occasional carcasses washed-up on S Brazilian beaches revealed no evidence of susceptibility to range of threats that affect so many other seabirds (oil pollution, ingestion of plastic materials, etc.) (22 Petry, M.V. and Fonseca, V.S.S. (2002). Effects of human activities in the marine environment on seabirds along the coast of Rio Grande do Sul, Brazil. Orn. Neotropical. 13(2): 137–142. Close ). Thorough census needed, as well as study of biology and ecology, to establish conservation requirements.