This discussion was first published as part of the 2016 Red List update. At the time a decision regarding its status was pended, but to enable potential reassessment of this species as part of the 2017 Red List update this post remained open and the date of posting was updated.
Apteryx mantelli occurs in isolated and fragmented populations on the North Island and some adjacent islands of New Zealand. Birds are locally common in Northland, the northern and central Coromandel Peninsula, southern Bay of Plenty, and in a triangle between Tongariro, Whanganui and Waitara in north Taranaki. They are more sparsely distributed in southern Coromandel Peninsula, western Bay of Plenty, north Taranaki, and from Motu to the northern Ruahine Range. Stable populations are present on Little Barrier/Hauturu-o-Toi (c.1,000 birds), Kawau and Ponui Islands (Heather and Robertson 2015, H. A. Robertson in litt. 2016). Since 1991, they have been successfully introduced to three pest-free offshore islands (Motukawanui, Motuora, and Motutapu), and translocated to many mainland sites that are either pest-free or where pests are maintained at very low densities. These translocations have established new populations (e.g. Marunui, Mataia, Tawharanui, Maungatautari, Lake Rotokare, Cape Kidnappers, Pukaha Mount Bruce and Rimutaka Range) or have bolstered severely depleted populations (e.g. Whangarei Heads, Mt Egmont National Park, Boundary Stream) (Heather & Robertson 2015, H. Robertson in litt. 2016).
In 1996, the total population of A. mantelli was estimated to number 35,000 individuals. In 2008, this was estimated at 25,000 (Holzapfel et al. 2008). In 2015, the estimated number of individuals in the four main populations was: 8,200 in Northland, 1000 on Little Barrier, 1,700 on the Coromandel Peninsula, 7,150 in the eastern North Island and 7,500 in the western North Island, giving a total of c.25,550 birds (H. Robertson in litt. 2016). This is consistent with the estimate in 2008, indicating that the population has remained stable for the last eight years.
Unmanaged mainland populations are still declining at 2.5% per annum owing to introduced predators (Robertson et al. 2011). However, this is now thought to be balanced by population increases in areas where predators are absent or managed to low densities (H. Robertson in litt. 2016). Since the overall population is no longer declining rapidly, this species no longer qualifies as Endangered under criteria A2bce+3bce+4bce under which it was previously listed. It is suggested therefore that A. mantelli be downlisted to Vulnerable under criterion A2bce as there has been a population reduction of more than 30% but less than 50% over three generations (26 years) and the causes of the reduction are understood but have not ceased and are not reversible. Introduced predators are still present in New Zealand, but it is clear that with good conservation management, kiwi populations can now be maintained and increased. More than 1,000 individuals of this species are also present on pest-free offshore islands, especially Hauturu-o-Toi/Little Barrier which gives the species some extra protection. It is clear that the continued stability of, and any future increase in A. mantelli population numbers will be dependent on the continuation of conservation action by government and community groups (Robertson in litt. 2016).
Additional information and comments on this proposal are welcomed.
Heather, B. D.; Robertson, H. A. 2015. The field guide to the birds of New Zealand. Penguin Random House NZ, Auckland, New Zealand.
Holzapfel, S., Robertson, H. A., McLennan, J. A., Sporle, W., Hackwell, K. and Impey, M. (2008) Kiwi (Apteryx spp.) recovery plan: 2008–2018. Wellington, New Zealand: Department of Conservation.
Robertson, H.A., Colbourne, R.A., Graham, P.J., Miller, P.J. and Pierce, R.J. 2011. Experimental management of Brown Kiwi Apteryx mantelli in central Northland, New Zealand. Bird Conservation International 21: 207-220.