• Source: North Island brown kiwi

The North Island brown kiwi (Apteryx mantelli; Apteryx australis or Apteryx bulleri as before 2000, still used in some sources) is a species of kiwi that is widespread in the northern two-thirds of the North Island of New Zealand and, with about 35,000 remaining, it is the most common kiwi species. The eggs laid by the North Island Brown Kiwi are among the largest eggs relative to its body size.




Genetics


The genome of Apteryx mantelli was sequenced in 2015.




Description


North Island brown kiwi display size sexual dimorphism, where the females are observably larger than the males.
Females stand about 40 cm (16 in) in height and weigh about 2.6 kg (5.7 lb) and the males about 2 kg (4.4 lb). The plumage is streaky red-brown and spiky. The North Island brown kiwi is the only species of kiwi found internationally in zoos.




Taxonomy



North Island brown kiwi or Brown Kiwi at the time was first described as Apteryx australis by Abraham Dee Bartlett, in 1813, based on a specimen from Dusky Sound, South Island, New Zealand. This is a monotypic species.
Brown Kiwi (then Apteryx australis) was originally thought to additionally include the rowi (Okarito kiwi) and the tokoeka species. However, through genetic testing in 1994, it was determined that the Tokoeka was a separate, distinct taxon. Once the Tokoeka was separated into its own species, it was given the name Apteryx australis, eventually leading to the official binomial name of Apteryx mantelli to describe the North Island brown kiwi. Soon after, in 2003, more comprehensive genetic tests were performed and it was definitively determined that Rowi was also a separate species and was later given the binomial name Apteryx rowi.
In 2004 an injured bird was found with streaked white around the head and identified by Massey University. The white feathering is likely due to a rarely seen genetic variation sometimes described as a partial albino. Few documented cases exist with only a painting of one found in Ōtorohanga in the 18th century and a specimen in the Canterbury Museum. The injured bird recovered and was introduced into a breeding programme.




Range and habitat



North Island brown kiwi (Apteryx mantelli) inhabit four primary regions within New Zealand’s North Island outside of sanctuaries and zoos. This includes Northland and it’s associated islands, the Coromandel, Eastern and Western North Island, New Zealand.
Historically, prior to human colonisation, New Zealand’s indigenous forests covered terrestrial land and provided the assumed primary habitat for all Kiwi species, which thrived in this ecosystem.
In modern day New Zealand, North Island brown kiwi appear to generally prefer densely vegetated lowland and coastal New Zealand indigenous forest as their population densities are highest in these habitats. However, due to wide spread deforestation and destruction of these native forests post colonisation, the availability and abundance of these preferred habitats has significantly decreased. Although the characteristics of North Island brown kiwi, such as a low reproductive rate and their longevity suggest this species is accustomed to a stable environment, the North Island brown kiwi has been shown to be adaptive to an array of habitat types outside of their historical, ideal habitats. Brown Kiwi can also be found utilising exotic pine forests, overgrown pasture, sand dunes, regenerating forests and forest remnants etc. This variety in potential habitat usage has been suggested to be possible by the North Island brown kiwi selectively utilising small patches of favourable or ideal habitats amongst other habitat type patches. North Island brown kiwi appear to thrive in exotic forests similarly to indigenous forests. Anecdotal evidence suggests that the population densities, body weights and productivity of North Island brown kiwi in exotic forests is comparable to those within New Zealand indigenous forests. However, as this evidence does not originate from published data, further research needs to be conducted to confirm this claim.
Although there is an acknowledged favourable habitat, the current primary driver of habitat usage in the North Island brown kiwi appears to be food and shelter site availability with purpose/need such as reproduction also being a factor. Not in relation to favourable habitat availability within a given territory. For example, nesting sites of the North Island brown kiwi in a territory (purpose – reproduction) containing patches of different habitat types typically were found within or 25m near secondary succession vegetation and/or native vegetation. Kiwi chicks shortly after hatching can only walk short distances and therefore require adequate nearby habitats, which are selected for by nesting parental North Island brown kiwi.




Behaviour






= Foraging

=
Kiwi species, such as the North Island brown kiwi, have been found to allocate the majority of their time to foraging, as compared to other behaviours such as vigilance, walking, socialising etc. Their diet primarily consists of invertebrate species, including spiders and worms, which make up 85-95% of their intake, with plant material comprising the remainder.
Over evolutionary history, the visual organs of Apteryx species have been greatly diminished, leading to an overall reduction in their visual field. In fact, Apteryx has the smallest visual field reported of any bird species that rely on non-visual cues for foraging purposes. It has been proposed that this adaptation arose due to their nocturnal, forest-floor foraging behaviour, where low light conditions render visual perception less critical. Under these conditions, a reduction in reliance of visual cues may increase overall fitness by lowering metabolic costs associated with maintaining visual functions and extracting visual information. This suggestion is further supported by the behaviour of other nocturnal, forest floor foraging species that similarly are unable to or do not rely on visual cues for foraging, suggesting convergent evolution across various orders, families and species.
Given the reduction in their visual senses, Apteryx species, including the North Island brown kiwi are required to utilise their additional senses, particularly remote touch and smell (olfaction), the most common sense used by North Island brown kiwi, to find prey. Remote touch foraging is facilitated by the bill-tip sensory organ found at the end of kiwi species long, narrow slightly down curved beaks. The bill-tip organ consists of mechanoreceptors, such as Herbst corpuscles and terminal cell receptors, found within sensory pits in the bone of the beak tip. These mechanoreceptors are sensitive to the vibrations and pressure gradients soil dwelling invertebrates make underground, allowing kiwi to detect their prey without visual or auditory cues.
The North Island brown kiwi's most common form of foraging has been observed to be tapping and probing the ground substrate with their beaks. This form of foraging is thought to allow for either olfaction or tactile sensing of prey, with the North Island brown kiwi capable of switching between these sensory modalities depending on the available stimuli.




= Courtship and Reproduction

=
The North Island brown kiwi has been found to primarily engage in monogamous, long term pairings regardless of the sex ratio within a population. During courtship and the breeding period, individuals can be observed softly grunting while exhibiting bill to bill raised stretching behavioural displays, thought to reinforce established bonds between pairs and has been observed to occasionally occur before copulation. Additionally, prior to copulation, North Island brown kiwi pairs have also been observed to engage in mutual chasing, leaping, loud screeches and snorting.
Once a partnership has formed, the pair prepares their nest for the breeding season within their territory, a process that spans around a 2-month period. This preparation includes burrowing and lining the nests walls and floors with plant material such as fern fronds. Nest sites are typically located underground, within rock crevices or hollowed areas of tree trunks and roots.
After the nest is prepared, the female within the pair contributes her sole parental effort by laying significantly energetically expensive, large, highly nutritious eggs. Female North Island brown kiwi can lay up to 5 eggs in a single clutch and up to seven eggs during a breeding season (multiple clutches), though a complete brood that can be properly incubated contains two eggs, which is the average amount of eggs produced by a female in a single clutch. Once the eggs are laid, the male within a pair solely provides incubation, starting one to seven days post hatch. During incubation, male North Island brown kiwi develop a brood patch, where feathers are shed from the lower abdomen, which has been assumed to facilitate more direct contact for enhanced heat transfer, as observed in other Kiwi species. The eggs are also regularly turned during incubation.
When males leave their nest for foraging and later return, they often conceal the nest's entrance using surrounding plant material, dirt and plant litter. This has been proposed as an anti-predator mechanism against the New Zealand native Weka bird species. However, it has been further proposed through observational research that this could be a technique utilised to control the amount of humidity within a nest. Generally, incubating males typically leave the nest to forage for roughly a 5-hour period, half of the time spent by non-incubating individuals, suggesting a reduction in foraging time due to parental duties.
Once a chick hatches, it consumes the remaining highly nutritious shell and egg contents. After hatching, chicks do not receive further parental care, as they are born precocious with near full senses and mobility. Chicks generally leave the nest within ten days of hatching and remain in their parent's territory, foraging and nesting independently, until they are large enough to establish their territory.




= Vocalisations

=
Kiwi species possess unique vocalisations that, like those of other bird species, are proposed to serve in a variety of different social functions. The most common distinctive sound produced by the North Island brown kiwi is termed the “whistle call”, which is performed solo or in a duet. Mates exclusively perform duets as a form of pair communication.
Generally, the vocalisations of the North Island brown kiwi are believed to play roles in territory defence, social communication and reproductive/ courtship purposes. It has been observed that call rates tend to increase during the breeding period and decrease during the incubation period. Corfield’s work has suggested that North Island brown kiwi vocalisation is suited for short-range calls to close-by individuals and territory neighbours.
There are notable differences between the two sexes' vocalisations. Male North Island brown kiwi calls produce high-pitched (≤36) multi-harmonic notes, whereas females typically emit low-frequency notes. These differences are attributed to differences in the structure and size of their sound producing throat organs. Additionally, males have been observed to have a significantly higher call rate compared to females.




Conservation


The North Island brown kiwi is Vulnerable, per the IUCN Red List, with the major threat coming from predators, such as dogs, cats, and stoat (Mustela erminea). 94% of chicks die before breeding in areas where mammalian pest control is not carried out. It has an occurrence range of 38,400 km2 (14,800 sq mi), with a population, estimated in 2000, of 35,000.
In 1996 there were around 35,000 North Island brown kiwi and in 2006 there were 20,000.
Nationwide studies show that on average only 5 percent of kiwi chicks survive to adulthood. However, in areas under active pest management, survival rates for North Island brown kiwi can be far higher. For example, prior to a joint 1080 poison operation undertaken by DOC and the Animal Health Board in Tongariro Forest in 2006, 32 kiwi chicks were radio-tagged. 57% of the radio-tagged chicks survived to adulthood. Thanks to ongoing pest control, the adult kiwi population at Tongariro has almost doubled since 1998.
In 2006, kiwi were released into Remutaka Forest Park by the Remutaka Conservation Trusts. As of 2024, the population has reached 300 individuals in the park and surrounding areas, extending to Upper Hutt and Whitemans Valley.
In 2022, 11 North Island brown kiwi were released on Wellington's South Coast after a 100 year absence. Fifty more kiwi were released into the hills of Wellington in May 2023.




References






Further reading


Davies, S.J.J.F. (2003). "Kiwis". In Hutchins, Michael (ed.). Grzimek's Animal Life Encyclopedia. Vol. 8 Birds I Tinamous and Ratites to Hoatzins (2nd ed.). Farmington Hills, MI: Gale Group. pp. 89–92. ISBN 978-0-7876-5784-0.




External links



ARKive - images and movies of the North Island Brown Kiwi (Apteryx mantelli)
Video of North Island Brown Kiwi feeding in full daylight
Taranaki Kiwi Trust

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