Kiwi

This is an article about the flightless birds native to New Zealand called kiwi. For information on the people of that country, who are nicknamed "Kiwis", see New Zealand. For information on the fruit of Chinese origin, see Kiwifruit.

The Kiwi is any of the species of small flightless birds native to New Zealand of the genus Apteryx. At around the size of a domestic chicken, kiwi are by far the smallest living ratites. Though they are thought to be most closely related to either cassowaries or moa, their evolutionary origin is still uncertain.

Prior to the arrival of humans in about 1300 CE, New Zealand had no mammals, 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).

Kiwi are shy, nocturnal creatures with a highly developed sense of smell and, most unusually in a bird, nostrils at the end of their long, sharp bill. They feed by thrusting the bill into the ground in search of worms, insects, and other invertebrates; though they also take fruit and, if the opportunity arises, small crayfish, amphibians and eels.

Their adaptation to a terrestrial life is extensive: like all ratities they have no keel on the breastbone to anchor wing muscles, and barely any wings either: the vestiges are so small that they are invisible under the kiwi's bristly, hair-like, two-branched feathers. While birds generally have hollow bones to save weight and make flight practicable, kiwi have marrow, in the style of mammals.

There are three species, one of which has two sub-species:

• The North Island Brown Kiwi, Apteryx australis mantelli is widespread in the northern two-thirds of the North Island and with about 35,000 remaining is the most common kiwi. Females stand about 40cm high and weigh about 2.8 kilos, the males about 2.2 kilos. The North Island Brown has demonstrated a remarkable resiliance: it adapts to a wide range of habitats, even non-native forests and some farmland. The plumage is streaky red-brown and spiky. The female usually lays two eggs, which are incubated by the male.

• The Okarito Brown Kiwi, Apteryx australis australis, is a recently identified sub-species of the North Island Brown, slightly smaller, with a greyish tinge to the plumage and sometimes white facial feathers. Females lay as many as three eggs in a season, each one in a different nest. Male and female both incubate. Only about 140 birds survive, in lowland forest to the north of Franz Josef.

• The largest species is the Great Spotted Kiwi, Apteryx hastii, which stands about 45cm high and weighs about 3.3 kilos. (Males about 2.4 kilos.) It has grey-brown plumage with lighter bands. The female lays just one egg, with both sexes incubating. Population is estimated to be over 20,000, distributed through the more mountainous parts of northwest Nelson, the northern West Coast, and the Southern Alps.

• The very small Little Spotted Kiwi, Apteryx owenii is unable to survive predation by imported pigs, stoats and cats and is extinct on the mainland and the most threatened of all kiwi. About 1000 remain on Kapiti Island and it has been introduced to other predator-free islands and appears to be becoming established. A docile bird the size of a bantam, it stands 25cm high and the female weighs 1.3 kilos. She lays one egg which is incubated by the male.