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Gallirallus australis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA AVES GRUIFORMES RALLIDAE

Scientific Name: Gallirallus australis
Species Authority: (Sparrman, 1786)
Common Name(s):
English Weka

Assessment Information [top]

Red List Category & Criteria: Vulnerable A3bce+4bce ver 3.1
Year Published: 2012
Date Assessed: 2012-05-01
Assessor(s): BirdLife International
Reviewer(s): Symes, A. & Butchart, S.
Contributor(s): Bartle, S., Beauchamp, A., Bramley, G., Hitchmough, R., King, D. & Weeber, B.
Facilitator/Compiler(s): Benstead, P., Bird, J., Harding, M., Khwaja, N., Mahood, S., McClellan, R., Taylor, J.
Justification:
This species's future hold on its mainland range is precarious, with a complex array of threats causing rapid declines resulting in local extinctions. Its situation may be unique in that the species remains numerous on a very large number of islands. Whilst population declines have slowed to an extent over the last ten years, the species is projected to undergo rapid population declines over the next decade based on extrapolation from historic trends, the absence of any change in the threatening processes, and the impact of climate change. It is therefore considered Vulnerable.

Geographic Range [top]

Range Description: Gallirallus australis is endemic to New Zealand. Subspecies greyi is mostly restricted to the east coast of the North Island; it experienced significant declines and local extinctions from the 1900s, and the remnant population underwent a significant decline after the early 1980s, falling to c.4,000 birds (Beauchamp et al. 1999, D. King in litt. 1999, A. J. Beauchamp in litt. 2000, G. Bramley in litt. 2012). Several releases to former mainland habitats have been attempted, but most have been largely unsuccessful (Beauchamp et al. 1999) owing to high levels of predation. However, introduced populations at Russell and Kawakawa Bay, as well as the main remnant population on the east coast of the North Island between Motu and Opitiki, have all expanded and the total population size of this subspecies is now estimated at c.11,000 individuals (A. J. Beauchamp in litt. 2012). Nominate australis remains locally common in north and west South Island (Heather and Robertson 1997, Beauchamp et al. 1999), but numbers fluctuate dramatically, even in large populations (Beauchamp et al. 1999). In north-west Nelson, numbers plummeted by c.95% (A. J. Beauchamp in litt. 2000), in north Westland, counts indicate declines of over 90% in c.20 years (S. Bartle in litt. 2000), and declines were also noted in Fiordland. However, a number of reintroductions and predator control for the benefit of a number of threatened mainland species have led to recent increases in parts of the South Island (A. J. Beauchamp in litt. 2008), although predator control appears not be a major factor in facilitating such increases (G. Bramley in litt. 2012). Subspecies hectori is now extinct in its natural range, but was introduced to Chatham and Pitt Islands where it may number 38,000-58,000 birds (A. J. Beauchamp in litt. 2000), and survives a take of 5,000 birds annually (Beauchamp et al. 1999). Some individuals of this subspecies have been returned to islands on lakes in the South Island, with much success, and mainland releases have taken place, using predator fencing, although these have suffered heavy predation pressure even with intensive management (A. J. Beauchamp in litt. 2008, 2012, G. Bramley in litt. 2012). Subspecies scotti became extinct on Stewart Island in the 1990s (D. King in litt. 1999), but introduced populations survive on surrounding islands (Heather and Robertson 1997). Their total numbers are thought to be less than 8,000 and declining (A. J. Beauchamp in litt. 2008). Overall, the four races are present (many as introduced populations) on more than 70, mostly tiny, offshore islands (Beauchamp et al. 1999). Whilst there have been no major declines in the last ten years, future population crashes are predicted, as climate change is likely to increase the probability of such events occurring, and inbreeding depression remains a challenge (G. Bramley in litt. 2012).

Countries:
Native:
New Zealand
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The population of subspecies australis is estimated to number 50,000-100,000 individuals, although with large fluctuations; subspecies greyi c.11,000 (A. J. Beauchamp in litt. 2012); subspecies hectori 38,000-58,000 on Chatham and Pitt Islands, and subspecies scotti fewer than 8,000 on the islands surrounding Stewart Island (A. J. Beauchamp in litt. 2012). On the basis of these estimates, the total population is thought to number 107,000-177,000 individuals, probably including 71,000-118,000 mature individuals.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: It utilises most habitats, including forests, grasslands, scrub, inland and coastal wetlands and even semi-urban environments. It is omnivorous, taking mostly fruit and invertebrates, but also vertebrates (Marchant and Higgins 1993, Beauchamp et al. 1999). Birds breed in their first year and eggs are laid year-round (Bramley and Veltman 2000).

Systems: Terrestrial; Freshwater; Marine

Threats [top]

Major Threat(s): Rapid declines are due to a combination of habitat clearance and degradation, road-kills, a wide range of introduced mammalian predators and competitors, combinations of drought and flood years, poison baits used for possum and rabbit control, and possibly disease (Heather and Robertson 1997, Beauchamp et al. 1998, 1999; D. King in litt. 1999). Birds have been eradicated from several islands due to possible risks to other native biota, and removal from Pitt and other islands is a future possibility (Beauchamp et al. 1999).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
Further island translocations are planned (Beauchamp et al. 1999). Surveys of distribution and density are presently being completed in parts of the mainland range considered to be strongholds (D. King in litt. 1999, A. J. Beauchamp in litt. 2000).

Conservation Actions Proposed
Conduct research on the impacts and management of threats (Beauchamp et al. 1999). Implement monitoring programmes in appropriate sites for all subspecies. Identify the most important threats affecting sites and instigate management programmes to address these. Establish further populations to ensure each subspecies has at least one large mainland population and three island population; select island sites carefully, as populations in wetter, less variable climates will be less susceptible to fluctuation (Beauchamp et al. 2009). Carry out long-term demographic studies of healthy populations to determine why they undergo catastrophic declines (G. Bramley in litt. 2012). Conduct genetic analysis to confirm the taxonomic status of the four subspecies, the origin of some island populations, and the genetic diversity of translocated and island populations (G. Bramley in litt. 2012).


Citation: BirdLife International 2012. Gallirallus australis. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 28 August 2014.
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