The North Island brown kiwi (Apteryx mantelli) 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. The plumage is streaky red-brown and spiky. The North Island brown kiwi is the only species of kiwi found internationally in zoos.

Taxonomy

thumb|left|Brown kiwi chick

The 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.

The 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. 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.

{| class=wikitable

|+Breeding population and trends

|-

!Location

!Population

!Date

!Trend

|-

|North Island|| 24550 || 2016 || Increasing

|-

|Little Barrier Island || 2000 (*Hybrid) || 2024 || Increasing

|-

|Kapiti Island || 2015 ||Decreasing −2% yr

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 widespread 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. 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.

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. 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.

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. 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. Eggs are 12.5 x 7.8 cm and weigh 430 grams. Once the eggs are laid, the male within a pair solely provides incubation, starting one to seven days post hatch. The eggs are also regularly turned during incubation. 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. 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. Corfield's work

Nationwide studies show that on average only 5% 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, eleven 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

  • 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