Kiwi (bird)
Kiwi are flightless birds endemic to New Zealand of the order Apterygiformes. The five extant species fall into the family Apterygidae and genus Apteryx. Approximately the size of a domestic chicken, kiwi are the smallest ratites.
DNA sequence comparisons have yielded the conclusion that kiwi are much more closely related to the extinct Malagasy elephant birds than to the moa with which they shared New Zealand. There are five recognised species, four of which are currently listed as vulnerable, and one of which is near threatened. All species have been negatively affected by historic deforestation, but their remaining habitat is well protected in large forest reserves and national parks. At present, the greatest threat to their survival is predation by invasive mammalian predators.
The vestigial wings are so small as to be invisible under their bristly, hair-like, two-branched feathers. Kiwi eggs are one of the largest in proportion to body size of any order of bird in the world. Other unique adaptations of kiwi, such as short and stout legs and using their nostrils at the end of their long beak to detect prey before they see it, have helped the bird to become internationally well known.
The kiwi is recognised as an icon of New Zealand, and the association is so strong that the term Kiwi is used internationally as the colloquial demonym for New Zealanders.
Etymology
The Māori word kiwi is generally accepted to be "of imitative origin" from its call. Some linguists derive the word from Proto-Nuclear Polynesian *kiwi, which refers to Numenius tahitiensis, the bristle-thighed curlew, a migratory bird that winters in the tropical Pacific islands that kind of resembles with its long decurved bill and brown body. So when the first Polynesian settlers arrived, they may have applied the word kiwi to the newfound bird. Some linguists like Robert Blust however propose that kiwi originated from Proto-Oceanic name for the Pacific golden plover, *kiwiwi.The bird's name is usually spelled with a lower-case k. It normally stays unchanged when pluralised in English, mirroring its usage in the Māori language itself. This contrasts with when kiwi is used to refer to a group of New Zealanders, which is typically pluralised as kiwis.
Taxonomy and systematics
The genus name Apteryx is derived from Ancient Greek 'without wing': a-, 'without' or 'not'; ptéryx, 'wing'.Although it was long presumed that the kiwi was closely related to the other New Zealand ratites, the moa, recent DNA studies have identified its closest relative as the extinct elephant bird of Madagascar, and among extant ratites, the kiwi is more closely related to the emu and the cassowaries than to the moa.
Research published in 2013 on an extinct genus, Proapteryx, known from the Miocene deposits of the Saint Bathans Fauna, found that it was smaller and probably capable of flight, supporting the hypothesis that the ancestor of the kiwi reached New Zealand independently from moas, which were already large and flightless by the time kiwi appeared.
Species
There are five known extant species of kiwi, with a number of subspecies. One extinct species is also known.Relationships in the genus Apteryx
| Image | Scientific name | Common name | Distribution | Description | Population | IUCN Status | Population Trend |
| Apteryx haastii | Great spotted kiwi or roroa | New Zealand | The largest species, standing about tall, with females weighing about and males about. It has grey-brown plumage with lighter bands. The female lays one egg a year, which both parents incubate. The population is estimated at over 20,000, distributed through the more mountainous parts of northwest Nelson, the northern West Coast, and the Southern Alps of the South Island. | 9,300 | |||
| Apteryx owenii | Little spotted kiwi | Kapiti Island | A small kiwi the size of a bantam, standing tall, with the female weighing. She lays one egg, which is incubated by the male. This small, docile kiwi is unable to withstand predation by introduced pigs, stoats and cats, leading to its extinction on the mainland. There are about 1350 on Kapiti Island and it has been introduced to other predator-free islands, where it appears to be getting established with about 50 on each island. | 1,500 | |||
| Apteryx rowi | Okarito kiwi, rowi or Okarito brown kiwi | South Island | The Okarito kiwi, first identified as a new species in 1994, is slightly smaller than the North Island brown kiwi, with a greyish tinge to the plumage and sometimes white facial feathers. Females lay up to three eggs in a season, each one in a different nest. Male and female both incubate. Distribution is now limited to a small area on the West Coast, but studies of ancient DNA have shown that, in prehuman times, it was far more widespread on the western side of the South Island and lived in the lower half of the North Island, where it was the only kiwi species detected. | 350-400 | |||
| Apteryx australis | Southern brown kiwi, tokoeka or common kiwi | South Island | Almost as big as the great spotted kiwi and similar in appearance to the brown kiwi, though its plumage is lighter in colour. It is relatively numerous. Ancient DNA studies have shown that, in prehuman times, the distribution of this species included the east coast of the South Island. Several subspecies are recognised:
| 16,500 | |||
| Apteryx mantelli or Apteryx australis | North Island brown kiwi | North Island | A. mantelli females stand about tall and weigh about, while the males weigh about. The plumage is streaky red-brown and spiky. The female usually lays two eggs, which are incubated by the male. The North Island brown has demonstrated a remarkable resilience: it adapts to a wide range of habitats, including non-native forests and some farmland. It is widespread in the northern two-thirds of the North Island and is the most common kiwi, with about 35,000 remaining. | 10,000-19,999' | |||
| Apteryx littoralis | "Kiwi of the shore" | North Island | A. littoralis is the only known extinct species of Apteryx, known from Pleistocene-age rocks that are roughly one million years old. The holotype, NMNZ S.36731, is a tarsometatarsus. The holotype was found to be most similar to the Okarito and North Island brown kiwi, although it was stouter and proportionally more narrow. It is thought to have been restricted to coastal habitats due to volcanism present on the North Island at this time. |
Description
Their adaptation to a terrestrial life is extensive: like all the other ratites, they have no keel on the sternum to anchor wing muscles. The vestigial wings are so small that they are invisible under the bristly, hair-like, two-branched feathers. While most adult birds have bones with hollow insides to minimise weight and make flight practicable, kiwi have marrow, like mammals and the young of other birds. Like most other ratites, they have no uropygial gland. Their bill is long, pliable and sensitive to touch, and their eyes have a reduced pecten. Their feathers lack barbules and aftershafts, and they have large vibrissae around the gape. They have 13 flight feathers, no tail and a small pygostyle. Their gizzard is weak and their caecum is long and narrow.The eye of the kiwi is the smallest relative to body mass in all avian species, resulting in the smallest visual field as well. The eye has small specialisations for a nocturnal lifestyle, but kiwi rely more heavily on their other senses. The sight of the kiwi is so underdeveloped that blind specimens have been observed in nature, showing how little they rely on sight for survival and foraging. In an experiment, it was observed that one-third of a population of A. rowi in New Zealand under no environmental stress had ocular lesions in one or both eyes. The same experiment examined three specific specimens that showed complete blindness and found them to be in good physical standing outside of ocular abnormalities. A 2018 study revealed that the kiwi's closest relatives, the extinct elephant birds, also shared this trait despite their great size.
Unlike virtually every other palaeognath, which are generally small-brained by bird standards, kiwi have proportionally large encephalisation quotients. Hemisphere proportions are even similar to those of parrots and songbirds, though there is no evidence of similarly complex behaviour.
Behaviour and ecology
Before the arrival of humans in the 13th century or earlier, New Zealand's only endemic mammals were three species of bat, and the ecological niches that in other parts of the world were filled by creatures as diverse as horses, wolves and mice were taken up by birds.The kiwi's mostly nocturnal habits may be a result of habitat intrusion by predators, including humans. In areas of New Zealand where introduced predators have been removed, such as sanctuaries, kiwi are often seen in daylight. They prefer subtropical and temperate podocarp and beech forests, but they are being forced to adapt to different habitat, such as sub-alpine scrub, tussock grassland, and the mountains. Kiwi have a highly developed sense of smell, unusual in a bird, and are the only birds with nostrils at the end of their long beaks. Kiwi eat small invertebrates, seeds, grubs, and many varieties of worms. They also may eat fruit, small crayfish, eels and amphibians. Because their nostrils are located at the end of their long beaks, kiwi can locate insects and worms underground using their keen sense of smell, without actually seeing or feeling them. This sense of smell is due to a highly developed olfactory chamber and surrounding regions. It is a common belief that the kiwi relies solely on its sense of smell to catch prey, but this has not been scientifically observed. Lab experiments have suggested that A. australis can rely on olfaction alone but is not consistent under natural conditions. Instead, the kiwi may rely on auditory and/or vibrotactile cues.