Kiwi are flightless birds found only in New Zealand. They belong to the order Apterygiformes. The five species that still exist today are part of the family Apterygidae and the genus Apteryx. Kiwi are about the same size as a domestic chicken and are the smallest of the ratites, a group that also includes ostriches, emus, rheas, cassowaries, and the extinct elephant birds and moa.
DNA comparisons show that kiwi are more closely related to the extinct Malagasy elephant birds than to the moa, even though both groups lived in New Zealand. There are five recognized kiwi species. Four of these are currently listed as vulnerable, and one is near threatened. All species have been harmed by past deforestation, but their remaining habitats are now protected in large forest reserves and national parks. Today, the biggest threat to their survival is predation by invasive mammals.
Kiwi have very small wings that are nearly invisible under their bristly, hair-like feathers. Their eggs are among the largest in relation to body size in the world, reaching up to 20% of the female's weight. Other unique features, such as short, strong legs and the use of nostrils at the tip of their long beaks to find prey, have made kiwi well known worldwide.
The kiwi is a symbol of New Zealand. The connection is so strong that the word "kiwi" is commonly used as a nickname for people from New Zealand.
Etymology
The Māori word "kiwi" is generally believed to come from the sound of the bird's call. Some experts think the word originated from an ancient language called Proto-Nuclear Polynesian, where it referred to a bird called Numenius tahitiensis, also known as the bristle-thighed curlew. This bird has a long, curved bill and a brown body, and it migrates to tropical Pacific islands during winter. When early Polynesian settlers arrived in New Zealand, they may have used the word "kiwi" to describe the new bird they found there. However, some linguists, like Robert Blust, suggest the word "kiwi" might have come from an older name for the Pacific golden plover in another ancient language called Proto-Oceanic.
The word "kiwi" is usually spelled with a lowercase "k." In English, it typically does not change when referring to more than one bird, just like it is used in the Māori language. This is different from when "kiwi" is used to describe a group of people from New Zealand, which is usually spelled as "kiwis" in that case.
Taxonomy and systematics
The name Apteryx comes from Ancient Greek words meaning "without wing": "a-" meaning "without" or "not," and "pteryx" meaning "wing."
For a long time, scientists believed the kiwi was closely related to other New Zealand ratites, such as the moa. However, recent DNA research has shown that the kiwi is most closely related to the extinct elephant bird of Madagascar. Among living ratites, the kiwi is more closely related to the emu and cassowary than to the moa.
A study published in 2013 examined an extinct bird called Proapteryx, found in ancient deposits from the Saint Bathans Fauna in the Miocene period. This bird was smaller than the kiwi and likely could fly. This discovery supports the idea that the kiwi's ancestor arrived in New Zealand separately from the moa, which were already large and flightless when kiwis first appeared.
There are five living species of kiwi, along with several subspecies. One species is no longer living.
Relationships in the genus Apteryx
Description
Kiwi birds have many adaptations for living on land. Like other flightless birds (ostriches, emus, rheas, and cassowaries), they lack a keel on the sternum, which is a bone that helps attach wing muscles. Their wings are very small and covered with tiny, hair-like feathers, making them hard to see. Most birds have hollow bones to help with flight, but kiwis have marrow inside their bones, like mammals and young birds of other species. They also lack a preen gland, which helps birds clean their feathers. Kiwis have long, flexible bills that are sensitive to touch, and their eyes have a reduced pecten, which is a structure in the eye. Their feathers do not have barbules or aftershafts, and they have large vibrissae (whisker-like hairs) around their beak area. They have 13 flight feathers, no tail, and a small pygostyle (a bone at the end of the spine). Their gizzard is weak, and their caecum is long and narrow.
Kiwi eyes are the smallest compared to their body size among all bird species, leading to the smallest visual field. Their eyes have some features suited for night activity, but they rely more on other senses, such as hearing, smell, and touch. Their eyesight is so poor that some kiwis are born blind, showing how little they depend on vision for survival and finding food. In one study, one-third of a kiwi population in New Zealand had eye injuries, and three individuals were completely blind but otherwise healthy. A 2018 study found that kiwis’ closest relatives, the extinct elephant birds, also had poor eyesight despite their large size.
Unlike most other paleognath birds, which generally have small brains compared to other birds, kiwis have larger brains relative to their body size. Their brain hemispheres are similar in proportion to those of parrots and songbirds, but there is no evidence that kiwis have the same level of complex behavior.
Behaviour and ecology
Before humans arrived in the 13th century or earlier, New Zealand’s only native mammals were three types of bats. In other parts of the world, animals like horses, wolves, and mice filled certain roles in the environment, but in New Zealand, these roles were taken by birds, along with some reptiles, insects, and snails.
The kiwi is mostly active at night, which may be because of predators, including humans. In areas where introduced predators have been removed, such as protected areas, kiwi are often seen during the day. They live in subtropical and temperate forests with podocarp and beech trees, but they are now adapting to other environments, such as sub-alpine scrub, grasslands, and mountains. Kiwi have a very good sense of smell, which is unusual for birds, and are the only birds with nostrils at the tip of their long beaks. They eat small insects, seeds, grubs, worms, fruit, small crayfish, eels, and amphibians. Because their nostrils are at the end of their beaks, kiwi can find insects and worms underground using their sense of smell, without seeing or touching them. This ability is due to a highly developed part of their brain called the olfactory chamber. It is commonly believed that kiwi rely only on their sense of smell to find food, but this has not been proven in natural settings. Laboratory tests suggest that some kiwi species can use smell alone, but this is not always the case in the wild. Instead, kiwi may use sounds or vibrations to find prey.
Once a male and female kiwi form a bond, they often stay together for their entire lives as a monogamous pair. During the mating season, which runs from June to March, the pair calls to each other at night and meet in their nesting burrow every three days. These pairings can last up to 20 years. Unlike most birds, kiwi and some birds of prey have two functioning ovaries. In most birds and in platypuses, only the left ovary works, while the right one does not develop.
Typically, kiwi lay only one egg each season. Kiwi lay one of the largest eggs in proportion to their body size of any bird. Even though kiwi are about the size of a domestic chicken, their eggs can be six times the size of a chicken’s egg. A kiwi egg can weigh up to one-quarter of the female’s body weight. This is possible because kiwi cannot fly, which limits how much weight they can carry. Brown kiwi females may lay eggs weighing up to 450 grams (16 ounces). Kiwi eggs are smooth and have an ivory or greenish-white color. The male usually incubates the egg, except in the great spotted kiwi (A. haastii), where both parents help. The incubation period lasts 63 to 92 days. Laying such a large egg puts a lot of stress on the female. For 30 days, she must eat three times her usual amount of food to grow the egg. Two to three days before laying the egg, there is little space inside the female for her stomach, so she must stop eating.
It was once thought that kiwi inherited their large eggs from larger ancestors, like moas, and that the trait remained unchanged as kiwi became smaller. However, research from the early 2010s suggests that kiwi evolved from smaller, flying birds that traveled to New Zealand and Madagascar, where they gave rise to kiwi and elephant birds. The large egg size is now believed to be an adaptation that allows kiwi chicks to hatch strong and mobile, with enough yolk in the egg to survive for about two and a half weeks. Large eggs were safe in New Zealand because there were no ground predators that ate eggs, and the mobile chicks could avoid flying predators that hunted young birds.
Pests
Lice in the group Apterygon and the smaller group Rallicola (Aptericola) are only parasites that live on the outside of kiwi birds' bodies.
Status and conservation
Studies across New Zealand show that about 5 to 10 out of every 100 kiwi chicks survive to become adults without help. In 2018, more than 70% of kiwi populations lived in areas without special protection efforts. However, in places where pest control is active, survival rates for North Island brown kiwi are much higher. For example, before a 2006 poison operation by the Department of Conservation and the Animal Health Board in Tongariro Forest, 32 kiwi chicks were tracked with radio tags.
Protecting kiwi has improved their status. In 2017, two kiwi species were moved from "endangered" to "vulnerable" by the IUCN. In 2018, the Department of Conservation shared its current Kiwi Conservation Plan. In 2000, the Department of Conservation created five kiwi sanctuaries to test ways to protect and grow kiwi numbers.
Other areas with large kiwi populations include mainland conservation islands and fenced sanctuaries. North Island brown kiwi were moved to the Cape Sanctuary in Hawke’s Bay between 2008 and 2011. This sanctuary raised chicks in captivity and later released them into Maungataniwha Native Forest. Kiwi sanctuaries are also called "kōhanga sites," a Māori word meaning "nest" or "nursery."
Operation Nest Egg is a program run by the BNZ Save the Kiwi Trust, which includes the Bank of New Zealand, the Department of Conservation, and the Royal Forest and Bird Protection Society. This program takes kiwi eggs and chicks from the wild, raises them in captivity until they weigh about 1,200 grams (42 ounces), and then returns them to the wild. A kiwi raised through this program has a 65% chance of surviving to adulthood, compared to 5% for kiwi raised in the wild. This method is used for all kiwi species except the little spotted kiwi.
In 2004, a man named Phillip Anderton falsely claimed a kiwi had been poisoned by 1080 (sodium fluoroacetate) poison. An investigation showed he lied and used a kiwi that had been caught in a possum trap. Studies confirm that kiwi are not harmed by the use of biodegradable 1080 poison.
Main threats to kiwi include introduced mammals like stoats, dogs, ferrets, and cats. Stoats are the biggest danger to kiwi chicks, killing about half of them in many areas. Kiwi chicks are vulnerable to stoats until they weigh about 1 to 1.2 kilograms (2.2 to 2.6 pounds). Cats also hunt kiwi chicks, but to a lesser extent. Dogs are the main threat to adult kiwi because they are attracted to kiwi’s strong scent and can kill them quickly. Motor vehicle accidents also harm kiwi where roads cross their habitat. Poorly set possum traps can injure or kill kiwi.
Habitat loss is another major threat. Small, isolated kiwi populations are more likely to face inbreeding. Research shows that the combined effects of predators and other causes (like accidents) result in fewer than 5% of kiwi chicks surviving to adulthood.
Relationship to humans
The Māori traditionally believed that kiwi birds were protected by Tāne Mahuta, the god of the forest. Kiwi were used for food, and their feathers were made into kahu kiwi, which are ceremonial cloaks. Today, kiwi feathers are still used, but only from birds that die naturally, from road accidents, or from predators, and from birds in captivity. Kiwi are no longer hunted, and some Māori consider themselves the birds’ guardians.
In 1813, George Shaw named the genus Apteryx when he described the southern brown kiwi, which he called “the southern apteryx.” Captain Andrew Barclay of the ship Providence gave Shaw a kiwi specimen. Shaw’s description included two plates, drawn by Frederick Polydore Nodder, and they were published in volume 24 of The Naturalist’s Miscellany.
In 1851, London Zoo became the first zoo to keep kiwi. The first kiwi breeding in captivity happened in 1945. As of 2007, only 13 zoos outside New Zealand had kiwi. These included Frankfurt Zoo (12), Berlin Zoo (7), Walsrode Bird Park (1), Avifauna Bird Park in the Netherlands (3), San Diego Zoo (5), San Diego Zoo Safari Park (1), National Zoo in Washington, DC (11), Smithsonian Conservation Biology Institute (1), and Columbus Zoo and Aquarium (3).
In 2023, Zoo Miami apologized for mistreating a kiwi after videos showed visitors touching the nocturnal bird under bright lights, which upset people in New Zealand.
The kiwi first appeared as a symbol in the late 19th century on New Zealand military badges. It was later used on the South Canterbury Battalion badge in 1886 and the Hastings Rifle Volunteers badge in 1887. Soon after, the kiwi appeared on many military badges. In 1906, when Kiwi Shoe Polish was sold widely in the UK and the US, the symbol became more well-known.
During World War I, New Zealand soldiers were called “Kiwis,” and a large kiwi (now called the Bulford kiwi) was carved on a hill in England. The term “Kiwis” is now used to describe all New Zealanders living abroad or at home.
The kiwi is now New Zealand’s most well-known national symbol. It appears on the coat of arms, crests, and badges of many New Zealand cities, clubs, and organizations. At the national level, the red outline of a kiwi is in the center of the Royal New Zealand Air Force’s roundel. The kiwi is also in the logo of the New Zealand Rugby League, and the team is called the Kiwis.
A kiwi has been on three New Zealand coins: the one florin (two-shilling) coin from 1933 to 1966, the twenty-cent coin from 1967 to 1990, and the one-dollar coin since 1991. The New Zealand dollar is sometimes called “the kiwi” in currency trading.
A song called “Sticky Beak the Kiwi,” written by Bob Edwards and with music by Neil Roberts, was recorded in 1961. It was sung by Julie Nelson (14 years old) and accompanied by the Satins and the Don Bell Orchestra. A Christmas song, it tells the story of Sticky Beak wanting to pull Santa’s sleigh when giving gifts near the equator.
“How the Kiwi Lost Its Wings” is a fable written by Alwyn Owen in 1963. It uses Māori mythology, such as Tāne Mahuta, and references the World War I symbol of cowardice, white feathers, to explain features of New Zealand birds. Owen describes the kiwi as giving up its wings and flight to protect trees from ground-dwelling animals, earning its unique reputation. The story is sometimes called “A Māori Legend.” It has been recorded as a children’s story, published as a book, made into an animated film in 1980, set to music by Thomas Goss for the Auckland Philharmonia Orchestra in 2002, and performed as a ballet by the Royal New Zealand Ballet in 2022.