Order of birds
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 (which also include ostriches, emus, rheas, cassowaries and the extinct elephant birds and moa).
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 (up to 20% of the female's weight) 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 language word is generally accepted to be "of imitative origin" from the call. However, some linguists derive the word from Proto-Nuclear Polynesian , which refers to "Numenius tahitiensis", the bristle-thighed curlew, a migratory bird that winters in the tropical Pacific islands. With its long decurved bill and brown body, the curlew resembles the kiwi. So when the first Polynesian settlers arrived, they may have applied the word kiwi to the newfound bird. The bird's name is spelled with a lower-case "k" and, being a word of Māori origin, normally stays as "kiwi" when pluralised. 
The genus name "Apteryx" is derived from Ancient Greek 'without wing': (), 'without' or 'not'; (), 'wing'.
Taxonomy and systematics.
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 species of kiwi, with a number of subspecies.
Description.
Their adaptation to a terrestrial life is extensive: like all the other ratites (ostrich, emu, rhea and cassowary), 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. With no constraints on weight due to flight requirements, brown kiwi females carry and lay a single egg that may weigh as much as . Like most other ratites, they have no uropygial gland (preen 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 (auditory, olfactory, and somatosensory system). 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 , 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 (and, to a lesser extent, reptiles, insects and gastropods).
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.
Once bonded, a male and female kiwi tend to live their entire lives as a monogamous couple. During the mating season, June to March, the pair call to each other at night, and meet in the nesting burrow every three days. These relationships may last for up to 20 years. They are unusual among other birds in that, along with some raptors, they have a functioning pair of ovaries. (In most birds and in platypuses, the right ovary never matures, so that only the left is functional.) 
Kiwi eggs can weigh up to one-quarter the weight of the female. Usually, only one egg is laid per season. The kiwi lays one of the largest eggs in proportion to its size of any bird in the world, so even though the kiwi is about the size of a domestic chicken, it is able to lay eggs that are about six times the size of a chicken's egg. The eggs are smooth in texture, and are ivory or greenish white. The male incubates the egg, except for the great spotted kiwi, "A. haastii", in which both parents are involved. The incubation period is 63–92 days. Producing the huge egg places significant physiological stress on the female; for the thirty days it takes to grow the fully developed egg, the female must eat three times her normal amount of food. Two to three days before the egg is laid there is little space left inside the female for her stomach and she is forced to fast.
It was believed that the large eggs were a trait of much larger moa-like ancestors, and that kiwi retained large eggs as an evolutionarily neutral trait as they became smaller. However, research in the early 2010s suggested that kiwi were descended from smaller flighted birds that flew to New Zealand and Madagascar, where they gave rise to kiwi and elephant birds. The large egg is instead thought to be an adaptation for precocity, enabling kiwi chicks to hatch mobile and with yolk to sustain them for two and half weeks. The large eggs would be safe in New Zealand's historical absence of egg-eating ground predators, while the mobile chicks would be able to evade chick-eating flying predators.
Lice in the genus "Apterygon" and in the subgenus "Rallicola" ("Aptericola") are exclusively ectoparasites of kiwi species.
Status and conservation.
Nationwide studies show that only around 5–10% of kiwi chicks survive to adulthood without management. As of 2018[ [update]] over 70% of kiwi populations are unmanaged. 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.
Efforts to protect kiwi have had some success, and in 2017 two species were downlisted from endangered to vulnerable by the IUCN. In 2018 the Department of Conservation released its current Kiwi Conservation Plan.
Sanctuaries.
In 2000, the Department of Conservation set up five kiwi sanctuaries focused on developing methods to protect kiwi and to increase their numbers.
There are three kiwi sanctuaries in the North Island:
*Whangarei Kiwi Sanctuary (for Northland brown kiwi)
*Moehau Kiwi Sanctuary on the Coromandel Peninsula (Coromandel brown kiwi)
*Tongariro Kiwi Sanctuary near Taupō (western brown kiwi)
and two in the South Island:
*Okarito Kiwi Sanctuary (Okarito kiwi)
*Haast Kiwi Sanctuary (Haast tokoeka)
A number of other mainland conservation islands and fenced sanctuaries have significant populations of kiwi, including:
North Island brown kiwi were introduced to the Cape Sanctuary in Hawke's Bay between 2008 and 2011, which in turn provided captive-raised chicks that were released back into Maungataniwha Native Forest.
Sanctuaries for kiwi are also referred to as 'kōhanga sites' from the Māori word for 'nest' or 'nursery'.
Operation Nest Egg.
Operation Nest Egg is a programme run by the BNZ Save the Kiwi Trust—a partnership between the Bank of New Zealand, the Department of Conservation and the Royal Forest and Bird Protection Society. Kiwi eggs and chicks are removed from the wild and hatched and/or raised in captivity until big enough to fend for themselves—usually when they weigh around 1200 grams (42 ounces). They are then returned to the wild. An Operation Nest Egg bird has a 65% chance of surviving to adulthood—compared to just 5% for wild-hatched and -raised chicks. The tool is used on all kiwi species except little spotted kiwi.
1080 poison.
In 2004, anti-1080 activist Phillip Anderton posed for the New Zealand media with a kiwi he claimed had been poisoned. An investigation revealed that Anderton lied to journalists and the public. He had used a kiwi that had been caught in a possum trap. Extensive monitoring shows that kiwi are not at risk from the use of biodegradable 1080 poison.
Threats.
Introduced mammalian predators, namely stoats, dogs, ferrets, and cats, are the principal threats to kiwi. The biggest threat to kiwi chicks is stoats, while dogs are the biggest threat to adult kiwi. Stoats are responsible for approximately half of kiwi chick deaths in many areas through New Zealand. Young kiwi chicks are vulnerable to stoat predation until they reach about in weight, at which time they can usually defend themselves. Cats also to a lesser extent prey on kiwi chicks. These predators can cause large and abrupt declines in populations. In particular, dogs find the distinctive strong scent of kiwi irresistible and easy to track, such that they can catch and kill kiwi in seconds. Motor vehicle strike is a threat to all kiwi where roads cross through their habitat. Badly set possum traps often kill or maim kiwi.
Habitat destruction is another major threat to kiwi; restricted distribution and small size of some kiwi populations increases their vulnerability to inbreeding. Research has shown that the combined effect of predators and other mortality (accidents, etc.)