Justification of Red List Category
This species is listed as Endangered because it has an extremely small, albeit slowly increasing, population. The recovery programme in place aims to establish a self-sustaining population of over 500 individuals. If the population continues to increase, the species will warrant downlisting to Vulnerable in due course.
The total population is currently estimated to number 280 mature birds with approximately 87 breeding pairs (A. Digby in litt. 2016). Th
The mainland population has fluctuated, including a decline of 40% due to predation in 2007/08 (Hegg et al. 2012). Translocated populations have increased slowly (Bunin et al. 1997), but may now be stabilising.
Porphyrio hochstetteri is endemic to New Zealand. Subfossils indicate that it was once widespread in the North and South Islands, but when rediscovered in 1948, it was confined to the Murchison Mountains in Fiordland (c.650 km2) (Bunin et al. 1997), and numbered just 250-300 birds (Heather and Robertson 1997). The population declined to its lowest point in the 1970s and 1980s and then fluctuated between 100 and 160 birds for 20 years (Maxwell 2001) and it is thought that this represents carrying capacity (Greaves 2007). However, a mast-driven stoat plague event reduced this population by over 40% in 2007-2008, and it had reached a low of 80 individuals by 2014 (Hegg et al, 2012). Supplementation with birds from other areas increased this population to 110 by 2016 (A. Digby, in litt. 2016). A captive-rearing programme was initiated in 1985, with the aim of raising populations for translocation to predator-free islands. In around 2010, captive rearing was stopped and captive breeding began, with chicks being reared by adults rather than by humans (Anon 2016).
Translocated populations (1984-2016) now exist on nine offshore and mainland islands – Mana Island, Tiritiri Matangi, Cape Sanctuary, Maungatautari, Motutapu Island, Tawharanui, Rotoroa Island, Burwood Takah? Centre and 1 undisclosed site - but numbers increased only slowly, with 55 adults in 1998 (Eason and Willans 2001), due to low hatching and fledging rates related to the level of inbreeding of the female of a given pair (Bunin et al. 1997, Jamieson et al 2003). The population on some small islands may now be close to carrying capacity (Baber and Craig 2003). However, successful work at the captive breeding centre at the Burwood Takah? Centre near Te Anau has increased the population at predator-free sites to 200 birds in 2016 (A. Digby, in litt. 2016).
It originally occurred throughout forest and grass ecosystems. Today it is restricted to alpine tussock grasslands on the mainland 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).
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). Other potential competitors or predators include the introduced brush-tailed possum Trichosurus vulpecula and the threatened Weka Gallirallus australis (Department of Conservation 1997). 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 may be close to carrying capacity (Baber and Craig 2003): on Tiritiri Matangi the 2000-2001 breeding season was largely unsuccessful, primarily due to the increase in territorial disputes among proximal family groups (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 is probably in decline as reforestation reduces the area of foraging habitat (Baber and Craig 2003). Hunting by humans is likely to have contributed historically to its decline (Wickes et al. 2009).
Conservation Actions UnderwaySince the 1960s, deer have been controlled in the Murchison Mountains. Attempts to establish a new mainland population in the Stuart Mountains with surplus birds from the Burwood Bush Captive Rearing facility failed (Greaves 2007). Stoat trapping is also undertaken in the mountains, with an extensive trap network (Wickes et al. 2009). Island populations of the species are managed intensively, optimising breeding success by supplementary feeding, inter-island transfers (also minimising inbreeding), and egg manipulation (primarily removal of infertile eggs to promote re-nesting) (Bunin et al. 1997). 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). A major review of management was completed in 1996-1997 (Department of Conservation 1997). Supplementation of the Murchison Mountains population was resumed in 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). Productivity of secure island sites and potential new sites are reviewed regularly. In 2015 research was started to find a new large, mainland site in the South Island, suitable for reintroduction of takahe.
Conservation Actions ProposedContinue to monitor population and productivity trends, as well as carrying out research on captive populations. Establish a second mainland population, perhaps by fencing around the captive breeding centre at Burwood, and/or introducing the species to another area of Fiordland (Wickes et al. 2009). Promote public awareness by holding captive birds for public display and visits to islands, and through the media (Crouchley 1994). Manage the small islands as a metapopulation, with regular transfers of females between islands and periodic introductions of new breeders from the Fiordland population (Jamieson et al. 2003). Remove individuals with high mean kinship values from island population, and replace them with individuals from the Fiordland population to avert inbreeding depression (Grueber et al. 2010). Consider the introduction of birds to other islands which could support a larger population. On small islands, plant clumps of native shrubs such as Coprosma spp. at 20-30 metre intervals in open grassy areas to provide cover from C. approximans.
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., Khwaja, N., Mahood, S., McClellan, R., Pilgrim, J. & Taylor, J.
BirdLife International (2020) Species factsheet: Porphyrio hochstetteri. Downloaded from http://www.birdlife.org on 29/10/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 29/10/2020.