Data Zone
Justification of Red List category
Mainland populations of this species may be decreasing rapidly, based on annual declines, predation and loss of habitat. However, owing to the stability of island populations, and intensive predator control in select mainland populations, the overall decline is likely to be slower, but still rapid, thus warranting Vulnerable status.
Population justification
In 2015, the estimated number of individuals in the four main populations was: 8,200 in Northland, 1,000 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 ca 25,550 birds (H. Robertson in litt. 2016). More than 1,000 individuals of this species are also present on pest-free offshore islands, especially Hauturu-o-Toi/Little Barrier. The total population is therefore estimated to number 26,550 (rounded here to 26,600), which equates to approximately 17,700 mature individuals, placed here in the band 10,000-19,999 mature individuals.
Trend justification
Unmanaged mainland populations are declining at 2.5% per annum owing to introduced predators (Robertson et al. 2011). However, this is thought to be balanced by population increases in areas where predators are absent or managed to low densities (H. Robertson in litt. 2016). It is estimated that the population has undergone an overall reduction of 30-49% across three generations (26 years).
Apteryx mantelli (as defined following the taxonomic change) occurs in isolated and fragmented populations on the North Island and some adjacent islands of New Zealand. Birds are locally common in Northland, and mostly sparsely distributed in the Coromandel Peninsula, Bay of Plenty, Gisborne to the northern Ruahine Range, and from Tongariro to Taranaki. 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, the species has 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). The total population was estimated at 26,600 birds in 2015 (H. Robertson in litt. 2016), down from an estimated 35,000 (± c.25%) birds in 1996 (Robertson 2003). Numbers have probably declined by at least 90% since 1900, and are declining at 2.5% per annum in unmanaged mainland populations (Robertson et al. 2011). However, this is thought to be balanced by population increases in areas where predators are absent or managed to low densities (H. Robertson in litt. 2016).
It favours dense, subtropical and temperate forests, but is also found in shrublands, scrub, regenerating forest, exotic pine plantations and pasture (Marchant and Higgins 1990). Diet Invertebrates are the primary food (Heather and Robertson 1997). Breeding Clutch size is one or two (with single clutches more frequent in high-density populations [Ziesemann et al. 2011]) and there are up to three clutches in a year (Colbourne 2002, Ziesemann et al. 2011). The male carries out almost all of the incubation (Colbourne 2002), which is amongst the longest for any bird at between 74 and 84 days (Calder et al. 1978). Laying was recorded in every month between June and November in a high-density population in 2007 (Ziesemann et al. 2011). Chicks hatch fully-feathered, and first leave the nest unaccompanied after about a week. It is long-lived, with generation time taken to be 10-15 years (H. A. Robertson in litt. 1999). More chicks were found to hatch in reused nests than in previously unused burrows (Ziesemann et al. 2011).
The most significant threat to the survival of the species is predation of adults by dogs and ferrets Mustela furo (Robertson 2010), with predation of young kiwi by Stoat Mustela erminea and cats also affecting populations (McLennan et al. 1996, Basse et al. 1999, Holzapfel et al. 2008, Robertson 2010). Significant spikes of mortality can occur, for example, a single dog killed c.500 birds in six weeks (Taborsky 1988), and over 70 incidents of dogs killing kiwi in Northland occurred between 1990 and 1995 (Pierce and Sporle 1997). The smaller male kiwi may be at greater risk of predation by ferrets, resulting in a skewed sex ratio and reduced effective population size (Robertson 2010). In one population prior to management at least 94% of chicks died before reaching breeding age (McLennan et al. 1996). About half were killed by introduced predators, in particular, stoat Mustela erminea and cats (McLennan et al. 1996). Juvenile kiwi become too large for stoats above about 800g, which takes about four months to achieve (McLennan et al. 2004). The clearance of habitat fragments continues to threaten small populations (Hutching 1995, Miller and Pierce 1995), but the rate of loss of native habitat has declined markedly and this is not currently considered a driver for population reductions (Robertson 2010). New avian diseases and pathogens are a potential threat, particularly with the importation of non-native but closely related ratites to New Zealand (Holzapfel et al. 2008).
Conservation and research actions underway
Monitoring is intensive and nationally coordinated, and uses call-counts, specially-trained dogs searching for banded birds, and radio-tracking (Robertson et al. 2010). Key populations are managed by controlling predators by the use of trapping and poisoned baits (Robertson 1998), with leg-hold predator traps that are raised above the ground to prevent accidental trapping (H. A. Robertson in litt. 1999). Kiwi aversion training for hunters' dogs is being trialed, although there is no evidence that this is a viable long-term solution (Robertson et al. 2010).
A programme of removing and incubating eggs and returning subadults once these are large enough to fend off predators has been developed since 1995 under the name Operation Nest Egg (ONE, or BNZONE as the funding has been provided by the Bank of New Zealand) (Colbourne et al. 2005, Pickard 2009, Robertson et al. 2010). A dedicated rearing facility was constructed at which 942 eggs received from the wild produced 475 young released back into the wild between 1995 and 2008 (Pickard 2009), with survival in captivity greatly improving during this time (Colbourne et al. 2005, Pickard 2009). BNZONE has been demonstrated to be the most effective tool for the species, resulting in a 12.5% annual population increase within managed sites, due to 83% chick survival (Robertson et al. 2010). Due to the cost and need to locate nests this approach is only practical within areas up to 10,000 ha and should be used to turn around declines in the most threatened and restricted populations and subspecies (Colbourne et al. 2005). Many national and overseas captive populations are held (Heather and Robertson 1997).
40 cm. Medium-sized kiwi, flightless, no visible wings. Dark greyish-brown feathers streaked lengthways with reddish-brown. Long ivory bill. Similar spp. Differs from other kiwi taxa in brown rather than grey, rufous or dark brown plumage, stiff rather than soft feather tips, 17 large tarsal scutes (7 or less in other taxa) and long rather than short facial bristles. Voice Shrill, clear ascending then descending whistle (male), lower-pitched, hoarse cry (female). Note duration and inter-note interval increase during a calling bout, and there is evidence that the species may duet (Corfield et al. 2008). Hints Loud calls at night, especially first two hours of darkness.
Text account compilers
Symes, A., Benstead, P., Wheatley, H., Taylor, J., Martin, R, Mahood, S., McClellan, R.
Contributors
Germano, J., Robertson, H., Weeber, B.
Recommended citation
BirdLife International (2024) Species factsheet: North Island Brown Kiwi Apteryx mantelli. Downloaded from
https://datazone.birdlife.org/species/factsheet/north-island-brown-kiwi-apteryx-mantelli on 23/12/2024.
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 23/12/2024.