Pterodroma externa — Details

White-necked Petrel learn more about names for this taxon

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Overview

Brief Summary

Biology

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Juan Fernández petrels spend most of their life out over the oceans, where they search for fish and squid on which to feed (2). They are often found in areas of upwelling, where cool, nutrient-rich water rises to the surface, resulting in an abundance of prey. They can be seen feeding alongside other seabirds (2), or occasionally around fishing boats (2). The Juan Fernández petrel often depends on sub-surface predators, such as cetaceans and yellowfin tuna, to drive prey to the surface (3). Juan Fernández petrels return to their isolated island to breed in October to November (2), where they form large breeding colonies. Females lay a single egg in a burrow and the grey, downy chicks hatch in February and March. The chicks are brooded for typically three weeks before being left unattended during the day while their parents go off to feed (2) (5). The adults return by dusk to their burrows and waiting offspring. Most of the petrel chicks fledge in May and June (2).
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Comprehensive Description

Description

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Petrels are oceanic birds, with broad webbed feet suited to their aquatic lifestyle, and long wings that enable them to fly great distances over the ocean and endure mighty storms. The plumage of the Juan Fernández petrel is brownish-grey on the back, with a black M-shaped marking across the extended wings. The underparts are white, with the underside of the wing edged in black. The face is white, with a black 'cap' extending to below the eyes (2) (3). The black bill has a hooked tip and houses the tubular nostrils that are a unique feature of the Procellariiformes, also known as the 'tubenoses' (4).
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Distribution

Range Description

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Pterodroma externa breeds on Alejandro Selkirk Island in the Juan Fernández Islands, Chile. It is very numerous, but could be declining7, although there is no firm evidence of this10. 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 in New Zealand and east Australia4,6.Further information may indicate declines that would warrant uplisting the species.
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Range

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The Juan Fernández petrel breeds only on Alejandro Selkirk Island, part of the Juan Fernández Islands, Chile (2). When not breeding it can be found over the tropical and subtropical waters of the east Pacific; north to Hawaii, and as far east as New Zealand and eastern Australia (2)
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Ecology

Habitat

Habitat and Ecology

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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 and adjacent grasslands at elevations of 600-1,000 m 9. One egg is laid in October-November4 and chicks hatch in Feb-March12. It is dependent on subsurface predators, especially yellowfin tuna, to drive prey to the surface1,2.

Systems
  • Terrestrial
  • Marine
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Depth range based on 5 specimens in 1 taxon.
Water temperature and chemistry ranges based on 5 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 16.430 - 27.278
  Nitrate (umol/L): 0.204 - 2.875
  Salinity (PPS): 33.374 - 35.575
  Oxygen (ml/l): 4.727 - 5.646
  Phosphate (umol/l): 0.261 - 0.394
  Silicate (umol/l): 2.153 - 5.719

Graphical representation

Temperature range (°C): 16.430 - 27.278

Nitrate (umol/L): 0.204 - 2.875

Salinity (PPS): 33.374 - 35.575

Oxygen (ml/l): 4.727 - 5.646

Phosphate (umol/l): 0.261 - 0.394

Silicate (umol/l): 2.153 - 5.719
 
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Source: Ocean Biogeographic Information System

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Habitat

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The Juan Fernández petrel is a marine and highly pelagic species that is often found in areas of upwelling, and rarely approaches land except to breed. It breeds on slopes and ridges in fern, forest or grassland, on high ground, between 600 and 1,000 meters, (2).
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Pterodroma externa

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Barcode of Life Data Systems (BOLDS) Stats
Public Records: 2
Species: 2
Species With Barcodes: 1

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Conservation

Conservation Status

IUCN Red List Assessment

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Red List Category
VU
Vulnerable

Red List Criteria
D2

Version
3.1

Year Assessed
2010

Assessor/s
BirdLife International

Reviewer/s
Calvert, R., Butchart, S., Bird, J.

Contributor/s
Brooke, M., Torres-Mura, J.

Justification
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.

History
  • 2008
    Vulnerable
  • 2006
    Vulnerable
  • 2004
    Vulnerable
  • 2000
    Vulnerable
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Status

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Classified as Vulnerable (VU) on the IUCN Red List 2007 (1)
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Population

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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 (Brooke 2004).

Population Trend
Unknown
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Threats

Threats

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Major Threats
The goat population was reduced by a Dutch hunting control programme in the late 1990s through to 2003 (6,000 down to 2,000), but remains a problem in all breeding colonies. Given that the control programme is no longer active, the population will presumably rebound within the next few years. Goat impacts include habitat alteration through plant consumption and also, at times, direct collapses of burrows5,9,11,13. Feral cat predation is thought to be causing a population decline, with a preliminary estimate of 2-3% annual mortality from cat predation. Brown rats Rattus norvegicus also prey on chicks although the incidence appears low and restricted to certain habitat types9,13. Dogs may also be causing a population decline9. Flash flooding in 2002 caused severe localised habitat loss with an estimated 30,000 burrows destroyed12. In 1995, a fire destroyed habitat at the edge of the principal colony and directly killed thousands of birds9,13. Decreased lobster catches near Isla Robinson Crusoe are displacing fishers to Alejandro Selkirk (where the species lives between September and May), resulting in an increase in human disturbance on the breeding grounds9. Fisheries may be indirectly impacting upon the species by depleting stocks of subsurface predators. During the night there are some collisions of birds with the lights of the village on Alexander Selkirk (especially on misty nights). The village is inhabited from September to May, during the period of lobster exploitation13. The species is potentially threatened by climate change because it has a geographically bounded distribution: its altitudinal distribution falls entirely within 2,000 m of the highest mountain top within its range (1,649 m).
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Threats

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The Juan Fernández petrel appears to face its greatest threats on its tiny breeding island, where numerous introduced species are causing extensive damage to the natural ecosystem, and potentially impacting petrel numbers. Introduced rats, feral cats and coatis pose a significant threat to the Juan Fernández petrel through predation; rabbits compete for burrows; and cattle trample burrows and may degrade suitable breeding habitat through grazing (2) (3) (5). The Juan Fernández petrel may also be affected by human disturbance on their breeding grounds, and fisheries may be indirectly affecting the petrel by reducing numbers of sub-surface predators, such as the yellowfin tuna (3).
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Management

Conservation Actions

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Conservation Actions
Conservation Actions Underway
The Juan Fernández Islands were designated as a National Park in 1935 (protected from 1967) and a Biosphere Reserve in 19778,9. The Chilean government began a habitat restoration programme in 19979, and the islands have been nominated for World Heritage listing5. Reserve rangers have been trained in fighting fires, but there is only one ranger on Alejandro Selkirk9. Sheep were removed from Alejandro Selkirk in 19834. A Dutch funded goat eradication programme was unsuccessful.

Conservation Actions Proposed
Establish population monitoring plots3. Improve sustainable management of yellowfin tuna stocks. Eradicate introduced fauna (goats, cows, rats etc) from Alejandro Selkirk. Monitor effects of flash floods on colonies.

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Conservation

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Since 1935, the Juan Fernández Islands have been designated a national park and in 1977 they were declared a biosphere reserve (3). However, these measures have offered no protection against the abundant introduced predators that are impacting the island's native inhabitants. There have been attempts to control these invasive species; in 1983 sheep were successfully removed from Alejandro Selkirk Island (3), and the Juan Fernández-Dutch Cooperative Project implemented control programs for several exotic plant species, goats, and rabbits (5). The Juan Fernández Islands Conservancy (JFIC) aims to protect the long term health of archipelago through a combination of basic research, applied conservation and environmental education in collaboration with local residents (5). In 2001, JFIC began a research program focused on four pelagic seabirds, including the petrel, investigating their basic ecology and factors potentially important for future conservation measures (5). However, without eliminating the threats posed by invasive species, any other conservation measure is likely to be fruitless, and thus JFIC believes that complete eradication efforts, (as opposed to control programs), are necessary (5). Improving management of yellowfin tuna fisheries to ensure their sustainability is also likely to benefit the Juan Fernández petrel (3).
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Wikipedia

Juan Fernández Petrel

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The Juan Fernández Petrel (Pterodroma externa) is a species of seabird in the Procellariidae family.

The Juan Fernández Petrel breeds only on one island in Chile, Isla Alejandro Selkirk. The breeding population was estimated at 1,000,000 pairs in 1985–86, and there may be up to 3–5 million birds globally. It is threatened by predation from introduced species (cats and rats) and, to a lesser extent, habitat loss from introduced herbivores (goats). The IUCN Red List lists this species as Vulnerable due to its endemic status and threats from introduced predators.

The Juan Fernández Petrel is a large species of gadfly petrel, 43 cm (17 in) long with a wingspan of 95–97 cm (37–38 in) and a mass of 500 g (1.1 lb). The upperparts are dark brownish-grey and there is a black M-shaped marking across the extended wings. The underparts are white, with the underside of the wing edged is black. The face is white, with a black "cap" extending to below the eyes. The bill is black with a hooked tip and houses the tubular nostrils that are unique to Procellariiformes.

Its breeding habitat is high elevation (above 750 metres (2,460 ft)) ridges, where it digs a 2–3 metres (6.6–9.8 ft) tunnel to raise one chick per year. Females lay a single, white egg in mid-November and both birds in a pair will take turns incubating the egg for approximately 60 days. The chick hatches in mid-February and is fed by both parents for approximately 90–100 days before fledging in May. The chick remains underground in the burrow until it has reached fledgling mass and is fully feathered. Chicks are fed a diet consisting mainly of fish and squid that are brought up to the nest from sea level by the parents.

During the breeding season, the Juan Fernández Petrel is found foraging in waters surrounding Isla Alejandro Selkirk and Isla Robinson Crusoe, as well as coastal Chile. The birds can be found in flocks with pink-footed shearwaters and other seabirds. During the non-breeding season, Juan Fernández Petrels forage in the equatorial currents and counter currents, north to the Hawaiian Islands.

Previously, the Juan Fernández Petrel was classified as a sub-species of the White-necked Petrel (Pterodroma cervicalis), which is found in the Tropical Pacific Ocean and Indian Ocean.

References

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