Justification of Red List Category
This species is listed as Near Threatened owing to the success of intensive conservation intervention which has established populations on eight islands and two mainland sites, in which numbers continue to increase or remain stable. Given the wide geographic spread of these populations the species is under no immediate threat, but populations, and the predator free status of the islands on which they live, still require monitoring.
The population is estimated to number at least 1,700 individuals in total, roughly equivalent to 1,400 mature individuals (Robertson in litt. 2016).
The species is now confined to a few offshore predator free islets where the population is stable, and one predator free location on the mainland.
Apteryx owenii (or allied species) occurred in forested areas throughout New Zealand prior to European settlement, but A. owenii is now restricted to eight offshore islands to which it has been introduced, and two mainland sites where it has been reintroduced (H. A. Robertson in litt. 2016). The stronghold is Kapiti Island (20 km2), where five birds are believed to have been introduced in 1912 (Ramstead et al. 2013). In the 1980s, birds were released on Red Mercury (2 km2), Hen (5 km2) and Long Islands (2 km2), and to Tiritiri Matangi Island (2 km2) in 1993 and 1995 (Colbourne and Robertson 1997). More recently, birds have been released on Motuihe Island (2 km2) in 2009 (Anon. 2009), Chalky Island (5 km2) in 2008-2010 (Edmonds 2010), Anchor Island (15 km2) in 2015-16 (ongoing) and at Cape Sanctuary (1 km2) near Napier in the North Island (ongoing). The population was estimated at 1,700 individuals in 2013 (Heather and Robertson 2015), with 1,200 on Kapiti and 500 spread amongst the other populations. This is an increase from the 1,500 individuals estimated in 2008 (Holzapfel et al. 2008), and from the estimated 1,150 individuals in 2000 (Robertson and Colbourne 2004). On Kapiti the species is considered to be at carrying capacity and annual survivorship is estimated at 97.5% (Robertson and Colbourne 2004). This population is being used to increase populations on other islands or to establish new populations (Holzapfel et al. 2008). At the same time more recently established populations are increasing.
It is present in all available habitats on Kapiti, including mature broadleaf forest, regenerating forest and grassland (Marchant and Higgins 1990). It eats invertebrates, but also fallen fruits and leaves (Heather and Robertson 2015). It lays one, sometimes two eggs, usually in a burrow. Chicks hatch fully-feathered, and first leave the nest unaccompanied after about a week. It normally begins to breed at around three years of age (H. A. Robertson in litt. 1999). Mean life expectancy is estimated at 45 (27-83) years (Robertson and Colbourne 2004).
Introduced predators except Weka Gallirallus australis are absent from all the islands where A. owenii occur. There are conflicting reports as to the extent and effect of predation (Jolly 1989, Marchant and Higgins 1990), although the A. owenii population appears to have grown from 5 birds in 1912 to reach carrying capacity at 1,200 birds in the presence of Weka (H. A. Robertson in litt. 2016). The island populations remain susceptible to accidental or deliberate introduction of mammalian predators.
Conservation Actions Underway
Translocations to predator-free offshore islands have done much to secure the survival of A. owenii. More islands have been examined for further introductions, but given the health of the present island populations, and their geographical spread, there is limited need for additional island populations; however, other secure mainland sites are being investigated to allow people access to the species. The genetic diversity of the species is very low, having passed through a bottleneck of just five individuals (including at least two females), and there has been further loss of genetic diversity with each transfer from Kapiti Island (Ramstad et al 2013). Research has shown that neither of the D'Urville Island birds placed on Long Island (Marlborough Sounds) with two Kapiti Island birds has left any descendants and so the entire population is derived from a single pair and is highly inbred (Taylor 2014). Two hybrid offspring from A. owenii x A. rowi pairings have been discovered in South Okarito forest since 1993, suggesting that A. owenii must have been present in the area until the mid-1990s and so nearby reports of kiwi are being checked, and elsewhere in the South Island, young (i.e. small) A. haastii are critically examined in case a few A. owenii persist on the South Island mainland. All populations are monitored using call-counts, and territory-mapping, and specially-trained dogs are used to locate banded birds (H. A. Robertson in litt. 2016).
30 cm. Smallest kiwi, flightless, no visible wings. Brownish-grey with fine, white horizontal mottling. Pale legs and long ivory bill. Voice High-pitched ascending whistle (male), lower and more tremulous, a rolling churr (female).
Text account compilers
Benstead, P., Mahood, S., Martin, R, McClellan, R., Taylor, J. & Stringer, C.
BirdLife International (2021) Species factsheet: Apteryx owenii. Downloaded from http://www.birdlife.org on 23/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/10/2021.