Justification of Red List Category
This species is listed as Endangered because it has a very small, albeit increasing, wild population. Although the total number of mature individuals in New Zealand is now considerably larger than 250, large numbers of these are in intensively managed subpopulations and/or are located on small islands or 'mainland islands' that are too small to support self-sustaining populations, so they are not treated as wild individuals in this assessment. A re-introduced population at Kahurangi National Park has not yet been established for five years and so it is also excluded from this assessment. If the wild population continues to increase, the species will warrant downlisting to Vulnerable in due course.
The species's total population is currently estimated to number 418 individuals with approximately 130 breeding pairs (Department of Conservation 2019). However, these numbers include those in 'sanctuaries', advocacy populations, sites subject to intensive management and a recently reintroduced subpopulation.
The population in the Murchison Mountains has grown to 180 individuals by 2019 (A. Digby in litt. 2019), following supplementation of at least 60 individuals since 2016 (Department of Conservation n.d.). Although breeding populations exist at Burwood Takahē Centre and at ten 'santuaries', these populations are subject to intensive management and are not considered to be self-sustaining (Department of Conservation n.d.). Therefore, they are not considered as wild individuals in this assessment. The new reintroduced subpopulation at Kahurangi National Park has not yet been established for five years and so it is also excluded from this assessment.
The population size is therefore placed here in the band 50-250 mature individuals.
The total population is thought to have been increasing by about 10% per year since 2015 (Department of Conservation 2019). However, this estimate includes individuals in 'sanctuaries', advocacy populations, sites subject to intensive management and a recently reintroduced subpopulation.
In 1948, the Murchison Mountains population numbered 250-300 birds (Heather and Robertson 1997). It declined to its lowest point in the 1970s and 1980s, with 120 individuals in 1981. A captive-rearing programme was initiated in 1985. Numbers initially increased slowly, then fluctuated between 100 and 160 birds for 20 years (Maxwell 2001). In 2007-2008, a mast-driven stoat "plague" event reduced this population by over 40% and it reached a low of 80 individuals by 2014 (Hegg et al., 2012). Since 2015, the population has been supplemented with around 60 released individuals (Department of Conservation, n.d.), and the population grew to 110 by 2016 (A. Digby in litt. 2016) and 180 by 2019 (A. Digby in litt. 2019).
Porphyrio hochstetteri is endemic to New Zealand. Subfossils indicate that it was once widespread in the South Island, but when "rediscovered" in 1948, it was confined to the Murchison Mountains in Fiordland (c.650 km2) (Bunin et al. 1997).
A captive-rearing programme was initiated in 1985, and since the late 1980s individuals have been released in a number of predator-free islands and fenced 'mainland islands'. Ten breeding populations now exist at Mana and Kapiti Islands (near Wellington), Cape Sanctuary (Cape Kidnappers Peninsula, North Island), Tawharanui (Auckland), Maungatautari Ecological Island (Waikato, North Island), three islands in the Hauraki Gulf near Auckland (Rotoroa, Tiritiri Matangi and Motutapu) and two undisclosed privately-owned islands (Department of Conservation n.d.). However, these populations are all subject to intensive management and the sites (known as 'sanctuaries') are not considered to be large enough for the populations to be self-sustaining (Department of Conservation n.d.). An intensively managed population is held at the Burwood Takahē Centre (near Te Anau). Small numbers of mostly non-breeding individuals are held at further eight sites for advocacy purposes. These sites include Willowbank Wildlife Reserve (Christchurch), Zealandia (Wellington), Wairakei Golf + Sanctuary (Taupō), Pūkaha National Wildlife Centre (Wairarapa), Punanga Manu O Te Anau / Te Anau Bird Sanctuary (Fiordland), Auckland Zoo and Orokonui Ecosanctuary (near Dunedin).
In 2018 a new population of 30 individuals was established at Gouland Downs in Kahurangi National Park in the north-west of the South Island (A. Digby in litt. 2019).
It originally occurred throughout forest and grass ecosystems. Today on the mainland it is restricted to alpine tussock grasslands and feeds primarily on juices from the bases of snow tussock and a species of fern rhizome. It eats introduced grasses on the islands. It usually lays two eggs. Chicks can begin breeding at the end of their first year, but usually start in their second. It is long-lived, probably 14-20 years (Heather and Robertson 1997).
Historically, hunting by humans, deforestation and the introduction of predatory mammals such as Stoats (Mustela erminea) are likely to have contributed to the species's disappearance from much of its range over the past thousand years (Beauchamp and Worthy 1988, Bunin and Jamieson 1995, Wickes et al. 2009). Introduced Red Deer Cervus elaphus competing for tussock were a major factor in the post-1940s decline (Mills and Mark 1977), while a series of unusually harsh winters appeared important in the population fluctuations of the 1990s (Bunin and Jamieson 1995, Bunin et al. 1997). More recent research has confirmed predation by introduced Stoats Mustela erminea to be a key threat (Crouchley 1994, Bunin and Jamieson 1996, Bunin et al. 1997, Wickes et al. 2009, Hegg et al. 2012). In 2007-2008, a mast-driven Stoat "plague" event reduced this population by over 40% (Hegg et al. 2012). The level of inbreeding in females appears to be related to the low hatching and fledging success exhibited by small island populations (Jamieson et al. 2003). Radio-tags have been shown to increase daily energy expenditure, which may influence mortality, particularly in hard winters (Godfrey et al. 2003). On Tiritiri Matangi at least there is probably some predation by Swamp Harrier Circus approximans (Baber and Craig 2003). The small island populations have also been shown to be threatened by inbreeding depression (Grueber et al. 2010). Habitat quality on some of the islands including Kapiti is probably in decline as reforestation reduces the area of foraging habitat (Baber and Craig 2003).
Conservation Actions Underway
The range of the Murchison Mountains population has been protected by a 500 km2 protected area known as the Murchison Mountains Special (Takahe) Area since soon after the species was 'rediscovered' in 1948. Public access is strictly limited. Since the 1960s, deer have been controlled at the site. Stoat trapping has also undertaken in the mountains since 2002, with an extensive trap network (Wickes et al. 2009).
A captive-rearing programme was initiated at the purpose-built Burwood Takahē Breeding Centre in 1985, with the aim of raising populations for translocation to predator-free islands. Initially, the centre was used to incubate eggs taken from the wild and hand-rear chicks (Department of Conservation n.d.). Captive-breeding efforts have increased the rate of survival to one year of age (when birds are released into the wild) by 50-60% to 90% (Maxwell and Jamieson 1997). In around 2010, captive rearing was stopped and captive breeding began, with chicks being reared by adults rather than by humans (Anon. 2016). The site now has an enclosure housing a population that is managed through supplementary feeding and nest manipulation (Department of Conservation n.d.).
The population in the Murchison Mountains population was supplemented with released individuals until 2010, then again from 2015, after a 5-year hiatus during which it was established that the population is unlikely to be self-sustaining (A. Digby in litt. 2016). Over 60 individuals have been released there since 2015, with ongoing releases of several individuals per year (Department of Conservation, n.d.). This has resulted in that population nearing capacity, with 180 individuals in December 2019 (A. Digby in litt. 2019).
Individuals have been released at Mana Island in 1987, Kapiti Island in 1989, Tiritiri Matangi Island in 1991, Maungatautari Ecological Island in 2006 and 2017, Motutapu Island in 2011-2012, Cape Sanctuary in 2012, Tawharanui in 2014, Rotoroa Island in 2015- 2018, Wairakei Golf + Sanctuary in 2015 and 2019, Orokonui Ecosanctuary, Zealandia in 2017, Pūkaha National Wildlife Centre in 2017-2019, Punanga Manu O Te Anau / Te Anau Bird Sanctuary and two undisclosed sites (A. Digby in litt, 2019). In 2018, a new population of 30 individuals was established at Gouland Downs in Kahurangi National Park in the north-west of the South Island, and there are plans to release more individuals (Department of Conservation 2019). Attempts to establish a new mainland population in the Stuart Mountains failed (Greaves 2007).
Populations at Willowbank Wildlife Reserve, Te Anau Bird Sanctuary and Rotoroa Island are provided with supplementary food (Fraser et al. 2017, Department of Conservation n.d.). Island and 'mainland island' populations of the species are managed by inter-island transfers to minimise inbreeding, and egg manipulation (primarily removal of infertile eggs to promote re-nesting) (Bunin et al. 1997). Many individuals are radio-tracked and receive health-checks and veterinary treatment In Kahurangi National Park, the toxin sodium fluoroacetate (1080) is applied aerially to control rodents and mustelids (A. Digby in litt. 2019). On Tiritiri Matangi Island, habitat is managed to maintain open habitats for the species (Supporters of Tiritiri Matangi (Inc.) 2013).
The status of island and 'mainland island' sites is reviewed annually, and improvements made where possible, and potential new sites are reviewed regularly (A. Digby in litt. 2019). Optimal site metapopulation size is modelled every five years to ensure genetic diversity is maximised (A. Digby in litt. 2019). Takahē genome sequencing is due to be completed in 2020, providing certainty on relatedness and enabling targeted management at gene level (A. Digby in litt. 2019).
Educational actives have been carried out to raise awareness of the species, including at Rotoroa Island (Fraser et. al. 2017). The species is taught about in New Zealand schools.
A population viability analysis indicated that stoat trapping, cross-fostering of eggs/chicks in wild pairs and, especially, captive rearing of eggs and chicks, were responsible for reversing the decline of the Murchison Mountains population (Hegg et al. 2013).
Conservation and Research Actions Proposed
Continue to monitor population and productivity trends of all subpopulations, including the reintroduced population at Kahurangi National Park. Continue to carry out research on captive populations to maximise productivity. Continue genetic research to enable targeted management to maximise genetic diversity. Continue to manage the small islands as a metapopulation, maximising genetic diversity by transferring individuals between subpopulations (Jamieson et al. 2003). Continue to supplement existing mainland populations as necessary, and establish further large wild sites (A. Digby in litt. 2019). On islands, manage habitat to prevent succession of open/edge habitats. Promote public awareness through the media and by providing guided visits of sites with populations (Crouchley 1994). Continue and expand stoat trapping within the Murchison Mountains (Hegg et al. 2013). Continue to control deer. Continue captive rearing programme.
63 cm. Very large, bulky, flightless, blue-and-green rail. Deep to peacock-blue head, breast, neck, shoulders. Olive-green and blue back, wings. Huge, red bill and shield. Large, powerful red legs, feet. Juvenile, duller. Dark grey bill and shield. Similar spp. Purple Swamphen P. porphyrio is much smaller and flies. Voice Slow and deep coo-eet, alarm call deep oomf. Hints Leaves behind chewed remains of tussocks, grasses, and very long, fibrous droppings.
Text account compilers
Benstead, P., Digby, A., Khwaja, N., Mahood, S., McClellan, R., Pilgrim, J. & Taylor, J.
BirdLife International (2021) Species factsheet: Porphyrio hochstetteri. Downloaded from http://www.birdlife.org on 21/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 21/10/2021.