|Scientific Name:||Pterodroma externa (Salvin, 1875)|
|Taxonomic Source(s):||Turbott, E.G. 1990. Checklist of the Birds of New Zealand. Ornithological Society of New Zealand, Wellington.|
|Identification information:||43 cm. Large, grey-and-white petrel. Black cap extends to below eyes while white of throat may extend up behind eyes, enhancing capped appearance. Grey upperparts and upperwing, with black "M" across wings. Base of grey tail can show whitish horseshoe. White underparts. White underwing with narrow black trailing edge, black tip, narrow black edge to leading edge distal to carpal joint and then short, bolder, black bar extending from joint towards centre of wing. Similar spp. Larger than overlapping Stejneger's Petrel P. longirostris, and has different underwing pattern. Hawaiian Petrel P. sandwichensis has darker cap and more extensive black on underwing.|
|Red List Category & Criteria:||Vulnerable D2 ver 3.1|
|Reviewer(s):||Butchart, S. & Symes, A.|
|Contributor(s):||Brooke, M., Hodum, P., Morgan, K. & Torres-Mura, J.|
|Facilitator/Compiler(s):||Calvert, R., Clay, R., Lascelles, B., Moreno, R. & Temple, H.|
This species is classified as Vulnerable owing to its very small breeding range, in which it is susceptible to to human impacts and stochastic events. Confirmation that introduced predators are causing a decline would result in an uplisting to Critically Endangered.
|Previously published Red List assessments:|
|Range Description:||Pterodroma externa breeds on Alejandro Selkirk Island in the Juan Fernández Islands, Chile. It is very numerous, but could be declining (Schlatter 1984), although there is no firm evidence of this (Brooke 2004). It is a transequatorial migrant, dispersing over the tropical and subtropical waters of the east Pacific, north to Hawaii, USA, and is regularly seen off west Mexico, with vagrants recorded to 42°N in the central Pacific (Howell 2012) and in New Zealand and east Australia (Carboneras 1992d, Patterson 1996). Further information may indicate declines that would warrant uplisting the species.|
Native:Chile; French Polynesia; Guam; Mexico; United States (Hawaiian Is.)
Vagrant:Australia; Japan; New Zealand
Present - origin uncertain:Costa Rica; Ecuador; French Southern Territories; Kiribati; Peru; Pitcairn
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||In 1986 the population was estimated at 1,000,000 pairs, which extrapolates to a world population of at least 3,000,000 individuals. There is no firm evidence of decline.|
Trend Justification: Breeding subpopulations have remained unchanged between the 1980s (Brooke 1987) and 2009 (Hodum 2009).
|Current Population Trend:||Stable|
|Habitat and Ecology:||It is highly pelagic, rarely approaching land except at breeding colonies. It nests in burrows on slopes in Dicksonia externa fern-forest, stands of low fern and adjacent grasslands and along open ridges at elevations of 600-1,1150 m (J. C. Torres-Mura in litt. 1999, Hodum 2009, Reyes-Arriagada et al. 2012). One egg is laid in mid-December to early January (Hodum 2009) and chicks hatch in Feb-March (Hodum and Wainstein 2003). It is dependent on subsurface predators, especially yellowfin tuna Thunnus albacares, to drive prey to the surface (Au and Pitman 1986, Ballance et al. 1997).|
|Continuing decline in area, extent and/or quality of habitat:||Unknown|
|Generation Length (years):||15.6|
|Movement patterns:||Full Migrant|
|Congregatory:||Congregatory (and dispersive)|
|Major Threat(s):||The population of feral goats Capra aegagrus hireus was reduced by a Dutch-funded hunting control programme in the late 1990s through to 2003 (6,000 down to 2,000), but remains a problem in all breeding colonies. Since the control programme ended in 2003, the goat population has rebounded, although no current population estimates exist (Hodum pers. obs.). Goat impacts include habitat alteration through native plant consumption and also, at times, direct collapses of burrows (Hulm 1995, J. C. Torres-Mura in litt. 1999, Torres in litt. 2007, Hodum in litt. 2007, Hodum 2009). Feral cat predation has been documented and is thought to be causing a population decline, with a preliminary estimate of 2-3% annual adult mortality from cat predation (Hodum 2009). Additionally, feral cats prey on near-fledging chicks when they are on the surface exercising their flight muscles, although predation rates have not been quantified (Hodum 2009). Brown rats Rattus norvegicus also prey on chicks although the incidence appears low and restricted to certain habitat types (J. C. Torres-Mura in litt. 1999, Hodum in litt. 2007). There is also limited evidence of predation on chicks by house mice (Mus musculus), although it does not appear to be widespread (Hodum 2009). Flash flooding in 2002 caused severe localised habitat loss with an estimated 30,000 burrows destroyed (Hodum and Wainstein 2003). In 1995, a fire destroyed habitat at the edge of the principal colony and directly killed thousands of birds (J. C. Torres-Mura in litt. 1999, Hodum in litt. 2007). Fisheries may be indirectly impacting upon the species by depleting stocks of subsurface predators, although the local artisanal fisheries operate on a small, largely subsistence scale (Hodum pers. obs.). Interactions with fisheries operating in international waters have not been assessed. On overcast nights, especially those with poor visibility to rain and/or drizzle, lights in the village attract birds, occasionally causing collisions with structures in the village (Hodum 2009). The village is inhabited from September to May, during the period of lobster harvesting (Hodum in litt. 2007). The species is potentially threatened by climate change because it has a geographically bounded distribution: its altitudinal distribution, currently a range of approximately 500 m, falls entirely within 2,000 m of the highest mountain top within its range (1,649 m). Invasive plant species, principally maqui (Aristotelia chilensis) and elm-leaf blackberry (Ulmus rubifolia) are present on Alejandro Selkirk and, although presently absent from breeding habitat, have the potential to become established in breeding colonies (Hodum 2009).|
Conservation Actions Underway
The Juan Fernández Islands were designated as a Chilean National Park in 1935 (protected from 1967) and a Biosphere Reserve in 1977 (Stattersfield et al. 1998, J. C. Torres-Mura in litt. 1999). The Chilean government began a habitat restoration programme in 1997 (J. C. Torres-Mura in litt. 1999), and the islands have been nominated for World Heritage listing (Hulm 1995). Reserve rangers have been trained in fighting fires, but there is only one ranger on Alejandro Selkirk (J. C. Torres-Mura in litt. 1999). Sheep were removed from Alejandro Selkirk in 1983 (Carboneras 1992). A Dutch-funded goat eradication programme was unsuccessful. Population monitoring plots were established between 2003-2006 by Oikonos Ecosystem Knowledge (Hodum 2009). Oikonos also maintains an ongoing small-scale community conservation education programme in the islands, including on Alejandro Selkirk. Incipient invasive plant species are also being systematically eliminated from the island by Oikonos in collaboration with the Corporación Nacional Forestal (CONAF), the Chilean agency that administers the park.
Conservation Actions Proposed
Establish population monitoring plots (M. de L. Brooke in litt. 1999). Improve sustainable management of yellowfin tuna stocks. Eradicate introduced fauna (goats, feral cats, rats, house mice, etc) from Alejandro Selkirk. Eradicate invasive and incipient invasive plant species from the island. Monitor effects of flash floods on colonies. Improve community awareness of the status of the species and the need for eradication programs. Improve management of cattle herd to ensure that it is excluded from potential breeding habitat.
|Citation:||BirdLife International. 2016. Pterodroma externa. The IUCN Red List of Threatened Species 2016: e.T22698030A93656296.Downloaded on 26 September 2018.|
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