Juan Fernandez Petrel Pterodroma externa Scientific name definitions

The Juan Fernandez Petrel is named for the Juan Fernandez Archipelago, its only breeding site. Specifically this petrel breeds on the outer island, Alejandro Selkirk but it is highly migratory during the non-breeding season, ranging north to the Eastern Tropical Pacific. This is a large and long-winged Pterodroma petrel with grayish brown upperparts, extensively white underparts and a contrasting dark cap. At sea it overlaps broadly with the Galapagos Petrel (Pterodroma phaeopygia), which is similar in shape and size, although the Galapagos is darker above, more extensively black on the head and with a bolder dark stripe on the underwing. The IUCN lists this petrel as Vulnerable, the population is estimated at a sizeable 3 million birds, but there are various threats to the single nesting island such as feral goats, cats, dogs, and it is thought the population has declined in recent years, although a thorough study is needed to confirm this.

42·5–45 cm (1 Imber, M.J., Merton, D.V., West, J.A. and Tennyson, A.J.D. (1991). Juan Fernandez Petrels prospecting at the Chatham Islands. Notornis. 38(1): 60-62. Close , 2 Howell, S. N. G. (2012). Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA. Close ); 310–555 g (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ); wingspan 95–114 cm (2 Howell, S. N. G. (2012). Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA. Close ). Large grey-and-white , long-billed and dark-capped gadfly petrel with mostly clean white underwing. Feathers of forehead white with blackish bases appearing as dark spots, which pattern extends to fore superciliary, plainer white on foreface, blackish-grey to dark brown-grey cap extending over most of ear-coverts and around eye, where can be black, rest of upperparts  grey or brownish grey, often with paler scaling visible at close range  , darker on most of upperwing  and tail, and darkest over transversal M typical of genus, especially contrasting on innermost greater and median coverts, tertials and rump, may show some spots or even complete narrow and rather irregular whitish horseshoe between rump and uppertail-coverts, in worn plumage hindneck paler; underwing white with dark grey tips to remiges forming narrow trailing edge, rather narrow and short blackish-grey crescent starting on carpal angle but not reaching central wing, rest of carpal white, often with some blackish dots on primary-coverts; exposed undertail dark grey, but has white bases and outer pair has dark restricted to distal third or less; underparts white with large grey patch on neck-sides joining mantle and forming partial collar; iris dark brown; bill black; legs and basal part of feet pale pink, rest including outer toes blackish. Sexes alike. Juvenile similar to adult, but in fresh plumage (May–Aug) has unmoulted body- and flight-feathers, as well as indistinct paler fringes to upperwing-coverts and mantle during first year (4 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close , 2 Howell, S. N. G. (2012). Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA. Close ). Very like P. cervicalis, but lacks bold white hindcollar, tends to be slightly darker on uppertail-coverts and tail, and has less blackish on anterior underwing, especially on carpal. Similar in size to P. phaeopygia, but paler, greyer and more contrastingly patterned above, and lacks large blackish patch on carpal; upperparts more like allopatric P. cahow, P. baraui and P. hasitata, but readily separated by much whiter underwing and from last-named also by lack of broad, clear-cut white horseshoe on rear upperparts; similar plumage to other congeners (see P. defilippiana and P. longirostris), but mostly white underwing and clearly larger size should prevent confusion.

C Pacific Ocean, breeding on Alejandro Selkirk I (formerly Más Afuera I), in Juan Fernández Is (off EC Chile).

Marine and highly pelagic, rarely approaching land except at colonies. Breeds on high ground at 600–1000 m, occupying slopes  and ridges, in fern (Dicksonia externa) forest or grassland.

Mainly found around breeding islands (34º S) while nesting, although some penetrate as far S as 50º S at this season (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Transequatorial migrant, ranging over tropical and subtropical waters of E Pacific, N to Hawaii, mostly at 0–20º N (especially 0–10º N) and 90–170º W (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close , 5 Ballance, L.T. (2007). Understanding seabirds at sea: why and how? Marine Orn.. 35(2): 127–135. Close ), but also reported off NE Japan at 36º N, 148º E (6 Mochizuki, H. (1996). [Procellariiforms observed off N. E. Japan in July-August.] Jap. J. Orn.. 45(3): 191–193. (In Japanese.). Close ); occurs regularly off W Mexico, where speculated to be commonest Pterodroma and to be present year-round (7 Santaella, L. and Sada, A.M. (1991). The avifauna of the Revillagigedo Islands, Mexico: additional data and observations. Wilson Bulletin 103(4):668–675. Close ), occasionally even close to the mainland (8 Howell, S.N.G. (2004). Further observations of birds from Colima and adjacent Jalisco, Mexico. Cotinga. 21: 38–43. Close ). In equatorial waters N Pacific, mainly recorded Apr–Oct with smaller numbers in Nov–Mar, while furthest N part of range is mainly reached late May–Aug (2 Howell, S. N. G. (2012). Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA. Close ). Vagrant to New Zealand (1971), E Australia (New South Wales) and S Atlantic (at Tristan da Cunha) (4 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close ), with four records in SW Indian Ocean (Jan 2003, Feb 2004) (9 Veit, R.R., Hyrenbach, K.D. and Martin, M.-C. (2007). Records of rare birds in the Indian Ocean during the austral summers of 2003–05. Bull. Brit. Orn. Club. 127(1):27–34. Close ), and observed several times prospecting nest-sites ashore on Chatham Is (South East and Mangere) in Dec–Feb between 1984 and 1990 (1 Imber, M.J., Merton, D.V., West, J.A. and Tennyson, A.J.D. (1991). Juan Fernandez Petrels prospecting at the Chatham Islands. Notornis. 38(1): 60-62. Close ).

Probably takes mostly ommastrephid squid and flying-fish, but also recorded taking Vinciguerria (Gonostomatidae, bristlemouths) (10 Pitman, R.L. and Ballance, L.T. (1990). Daytime feeding by Leach’s Storm-Petrel on a midwater fish in the Eastern Tropical Pacific. Condor. 92(2): 527–530. Close ) and sea skaters (Halobates), the latter perhaps only taken incidentally (11 Cheng, L., L. B. Spear, and D. G. Ainley (2010). Importance of marine insects (Heteroptera: Gerridae, Halobates spp.) as prey of eastern tropical Pacific seabirds. Marine Ornithology 38(2):91–95. Close ). Catches prey by surface-seizing, dipping, aerial pursuit and pattering. Often feeds alongside other seabirds in small groups of 5–20 individuals (2 Howell, S. N. G. (2012). Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA. Close ), especially other Pterodroma, but also Ardenna pacifica, boobies (Sula), terns and sometimes Leach’s Storm-petrels (Hydrobates leucorhous) (12 Pitman, R. L., and L. T. Ballance (1992). Parkinson’s Petrel distribution and foraging ecology in the eastern Pacific: aspects of an exclusive feeding relationship with dolphins. Condor 94(4):825–835. Close , 13 Ribic, C. A., D. G. Ainley, and L. B. Spear (1997). Seabird associations in Pacific equatorial waters. Ibis 139:482–487. Close ); associates with cetaceans, especially spotted and spinner dolphins (12 Pitman, R. L., and L. T. Ballance (1992). Parkinson’s Petrel distribution and foraging ecology in the eastern Pacific: aspects of an exclusive feeding relationship with dolphins. Condor 94(4):825–835. Close ), and also with yellowfin tuna (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Occasionally seen around fishing boats.

Vocal only at colonies (4 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close ), in flight giving prolonged sighing whistles, especially during male/female chases, sometimes followed by harsh bark or “wowk” sound, while a booming “boo-booo-boo” is given both from ground and aerially, and chattering calls may also be uttered when on the ground, including sometimes from within burrows (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ).

Poorly known. Starts Oct/Nov on return to colony, with egg-laying probably between 20 Dec and 10 Jan (based on single season) and fledging between late May and early Jun (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Colonial, often shares breeding areas with P. longirostris (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ); nests in burrows, but also apparently on surface. Single white egg, mean size 67·2 mm × 48 mm (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ) (smaller in surface breeders) (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ); incubation period unknown, but shifts said to last 19–22 days (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ); chick has dusty brown-grey down, slightly darker brownish on head, whiter on abdomen; fledging period unknown (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ).

VULNERABLE. Total population was estimated to number > 1,000,000 pairs and 3,000,000 birds in 1986, with no firm evidence of decline since then (3 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Fossil material pertaining to this species is available from Easter I, but whether this indicates historical presence of breeding population or merely visitors to the archipelago is unknown (14 Marín, M., and P. Cáceres (2010). Sobre las aves de Isla de Pascua. Boletín del Museo Nacional de Historia Natural (Chile) 59:75–95. Close ). Juan Fernández Is legally protected as national park since 1935, but abundant introduced predators, e.g. rats, cats and coatis (Nasua nasua); numbers apparently decreasing due to predation. Other alien fauna include cattle, rabbits and goats; sheep removed in 1983, but population of rabbits estimated at c. 52,000, and trapping has little effect. BirdLife International summary reports that goats were reduced by control programme in late 1990s until 2003 (from 6000 to 2000 animals), but remain problem at all breeding colonies and their population will presumably rebound; impacts include habitat alteration through plant consumption and also, at times, direct collapses of burrows, while feral cat predation is thought to cause 2–3% annual mortality among petrels, and brown rats (Rattus norvegicus) also take small numbers of chicks and only in certain habitats. Flash flood in 2002 caused severe but local habitat loss, with c. 30,000 burrows destroyed, while a fire in 1995 destroyed habitat at edge of main colony and killed thousands of birds. Decreasing lobster catches Robinson Crusoe I have displaced fishers to Alejandro Selkirk, resulting in increased human disturbance at breeding grounds, while fisheries may be indirectly impacting the species by depleting stocks of subsurface predators. The species is potentially threatened by climate change because it has a geographically bounded distribution: its altitudinal distribution falls entirely within 2000 m of highest mountaintop within its range (1649 m).