Justification of Red List Category
The last confirmed records of the species were in 2007, and it is considered by some to be extinct. If it is still extant, it is thought to have an extremely small population. Therefore, it is listed as Critically Endangered (Possibly Extinct).
Based on analysis of known threats and the lack of reliable records of this species, the species is considered to be Possibly Extinct (Bain 2009, Evans 2016, Butchart et al. 2018). If it remains extant, its population is likely to number fewer than 50 individuals and mature individuals.
If it remains extant, the species is suspected to be declining as a result of the ongoing threat from introduced predators.
This species is endemic to New Zealand. It formerly occurred along the west coast of the South Island, Banks Peninsula, Stewart Island and offshore islets (Gill et al. 2010). Despite it being highly vocal, the last confirmed records of the species were in 2007 (Miskelly et al. 2013), and before that in 1967 (Clout and Hay 1981), with several unconfirmed sightings between 1990 and 2016 (Milne and Stocker 2014, Evans 2016, Redmond 2016). In 2017 a reward was announced for information confirming the persistence of the species and over a hundred reports of possible sightings and calls were made by 2018, with the most convincing reports in the area south of Reefton and Stewart Island, but no reports have so far been confirmed (Birds New Zealand 2018). The species is likely to have been driven extinct as a result of invasive species and habitat loss across its range (Butchart et al. 2018). The probability of the species being extant has been estimated at 0.898 based on records and surveys and 0.220 based on threats (Butchart et al. 2018). Despite this high probability based on records and surveys, recent reports are not deemed to be credible and so the species is considered Possibly Extinct (Bain 2009, Evans 2016, Butchart et al. 2018).
The species is assumed to have a similar ecology to the formerly conspecific North Island Kokako Callaeas wilsoni which prefers lowland, tall podocarp/hardwood forests with a high diversity of plant species, and is rarely found in modified forests, including selectively logged forests (Heather and Robertson 1997).
The historical decline was due to large-scale habitat destruction, fragmentation and the introduction of predators and competitors. Predation of eggs and chicks by black rats Rattus rattus and brush-tailed possums Trichosurus vulpecula is the main cause of nest failure, whereas deaths to nesting adult females were caused by stoats Mustela erminea (Flux et al. 2006). These introduced predators are currently the primary threat to the species. Trichosurus vulpecula also competes for many preferred food items, and introduced goats and deer destroy favoured understorey food-plants (Innes et al. 1999). Historical forest destruction for logging has also been important, especially as the species is thought to require fairly large tracts of forest. These two threats were largely contemporaneous and so their relative importance is not completely clear (Rasch 1991).
Conservation Actions Underway
Most of the remaining habitat is protected and almost all key subpopulations are managed for the control of R. rattus and T. vulpecula. Recent research shows that "pulsing" poison bait delivery (at least three managed years every 10) may be the most effective way of dealing with the predator threat (Bassé et al. 2003). Efforts are continuing to be made to locate individuals of this species (see, e.g. Evans 2016), and sightings continue to be claimed (e.g. Redmond 2016). The South Island Kokako Charitable Trust has carried out an advocacy programme to raise awareness of the species, offered a reward for reports leading to the confirmation of the species's persistence and set up a website to encourage people to log reports (South Island Kokako Charitable Trust 2014). It has also planned research on the species's detection and biology and a systematic search across sites where the species is thought likely to persist (South Island Kokako Charitable Trust 2014).
Text account compilers
Khwaja, N., McClellan, R., Westrip, J., Stringer, C., Calvert, R., Bird, J., Hermes, C., Benstead, P., Temple, H., Wheatley, H., Taylor, J.
Flux, I.A. & Innes, J.
BirdLife International (2019) Species factsheet: Callaeas cinereus. Downloaded from http://www.birdlife.org on 14/12/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 14/12/2019.