• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Justification of Red List category

This species has a large range and hence does not approach the thresholds for Vulnerable under the range size criterion (extent of occurrence <20,000 km² combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is increasing, and hence does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). Although the population size numbers less than 10,000 mature individuals, without a continuing decline it does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). The species is considered to be heavily dependent on conservation, but for the reasons above it is evaluated as Least Concern.

Population justification
In 2020 the population was estimated at 2,079 pairs and is placed here in the band 3,000-6,000 mature individuals, with a best estimate of 5,000 (J. Innes in litt. 2022). The largest population on Little Barrier Island/Hauturu was estimated at 422 pairs in 2013. Other large populations numbering more than 100 pairs are in Te Urewera National Park and Waipapa Ecological Area of Pureora Forest Park; populations of more than 50 pairs are found at Kaharoa-Onaia (near Rotorua), Mangatutu (Pureora) and Mapara (King Country), and 19 other smaller populations are known (Scofield et al. 2020).

Trend justification
The population has significantly increased primarily owing to pest control and translocation, numbering just 330 pairs in 1999 but increasing to approximately 2,000 pairs in 2020 (J. Innes in litt. 2022). Populations continue to increase in areas of intensive conservation work (Robertson et al. 2021), and these increases now predominate as populations at unmanaged sites are now extinct or functionally extinct. The species is entirely conservation-dependent, each population requiring ongoing (preferably annual) control of introduced pest mammals, or protection against pest mammal invasion if on a pest-free island. Populations are surveyed annually up to 25 breeding pairs, followed by surveys each 3 years thereafter (Scofield et al. 2020).

This species is endemic to New Zealand. The species was formerly common throughout the island's forests, but now only survives in the Hunua Ranges, Mataraua, Kaharoa, Rotoehu, Pureora and Mapara forests, and Te Urewera National Park (Rasch 1991, Moore and Innes 1996). The largest population is on predator-free Little Barrier to which it was successfully translocated. Additional translocated populations occur on Kapiti and Tiritiri Islands, as well as Mount Bruce Scenic Reserve (Wairarapa), Boundary Stream Mainland Island (Hawkes Bay), Ngapukeriki (East Cape), Ark in the Park (Waitakeres, west Auckland), Whirinaki and Otanewainuku (Bay of Plenty), Maungatautari (Waikato) and Puketi (Northland) (Innes 2019).

The species prefers lowland, tall podocarp/hardwood forests with a high diversity of plant species. It is rarely found in modified forests, including selectively logged forests (Heather and Robertson 1997). Its diet varies seasonally. It prefers fruit, but also eats leaves, invertebrates, buds, flowers and nectar (Powlesland 1987). Shrub hardwoods are a particularly important food source (Rasch 1991). It breeds mainly from October to March, usually laying three eggs (Heather and Robertson 1997, Bain 2008). In years of high food availability, pairs will raise several clutches.

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. At Mapara Wildlife Management Reserve, just 8% of nesting attempts successfully fledged young in the absence of predator control, versus 61% when predators were intensively trapped (Flux et al. 2006). Although the population is increasing overall, this remains highly dependent on pest control. Trichosurus vulpecula also competes for many preferred food items, and introduced goats and Red Deer Cervus elaphus 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) is likely to be the most effective way of dealing with the predator threat once managed populations have reached a certain size (Bassé et al. 2003). Birds have been reintroduced to Little Barrier, Kapiti and Tiritiri Islands, as well as Mount Bruce Scenic Reserve (Wairarapa), Boundary Stream Mainland Island (Hawkes Bay), Ngapukeriki (East Cape), Ark in the Park (Waitakeres, west Auckland), Whirinaki and Otanewainuku (Bay of Plenty), Maungatautari (Waikato) and Puketi (Northland) (Innes 2013). Populations are encouraged to stay in protected areas using playback of their calls, attracting individuals to key areas (Anon. 2008). Genetic research has been undertaken to ensure sufficient genetic diversity in each subpopulation (Bain 2008).

Conservation Actions Proposed
Improve understanding of the Te Urewera population, the management of which was recently returned to local indigenous people (J. Innes in litt. 2022). Modify management developed in smaller forest blocks, to assist large-scale protection and enhancement. Develop sustainable long-term management practices by research and mathematical modelling, and implement them. Support and develop captive breeding programmes, and aim to reintroduce birds to newly-managed forest areas (I. A. Flux in litt. 1999). Ensure pest control intensity is maintained at all key subpopulations.

Text account compilers
Vine, J.

Contributors
Benstead, P., Bird, J., Calvert, R., Flux, I.A., Innes, J., Khwaja, N., McClellan, R., Stringer, C., Taylor, J., Temple, H. & Westrip, J.R.S.

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Recommended citation
BirdLife International (2024) Species factsheet: North Island Kokako Callaeas wilsoni. Downloaded from https://datazone.birdlife.org/species/factsheet/north-island-kokako-callaeas-wilsoni on 21/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org/species/search on 21/12/2024.