Kiwi (bird): New Zealand’s small flightless emblem

Kiwis are not only the smallest of all ratites, but their biology differs greatly from the other families of ratites. They are 35 to 65 centimeters long, up to 35 centimeters tall, and weigh one to five kilograms. Females are on average slightly larger and 10 to 20 percent heavier.

They wear brown plumage, which almost looks like hairiness. Like all ratites, kiwis lack the pectoral crest, where the flight muscles normally attach. Thus the kiwis still have small, four to five centimetre long wings, but they are not able to fly with them. The wings have small claws at the ends and remain hidden under the plumage. The claws have no discernible function and are apparently rudiments found equally in some emus and cassowaries.

Kiwis have no externally visible tail, which contributes to the fact that they have an unusual oval body shape. Contributing to this appearance are the legs, which are shifted far back. These powerful legs, like those of most birds, have four toes, which enable kiwis to run well and quickly. Longer flight distances, however, are usually unnecessary in their confusing habitat. The head of the kiwi is relatively small, the beak very long and curved downwards. The beak of the striped kiwi is over 20 centimetres long. It is a good 30 percent larger in females than in males. The upper beak is slightly longer than the lower beak. Kiwis often lean on their beaks to keep their balance when standing. Kiwis cannot see very well, but they can hear very well and - a special feature among birds - they can smell very well. The nostrils are located at the tip of the beak, not at the base as in most birds. At the base of the beak, kiwis have "bristles" that resemble the vibrissae (whiskers) of mammals, but are actually modified feathers.

A further characteristic is the body-temperature, that lies with 38 °C far under that of most birds (42 °C) and rather resembles that of a mammal.

Because of their nocturnal and hidden lifestyle, vocalizations are often the only thing people hear from kiwis. Kiwis call all year and all night, except during strong winds and on very bright full moon nights.

The calls are shrill whistles that carry up to five kilometers in favorable conditions. As kiwis emit them, they stretch their necks and beaks upwards. Males call more often than females, and their whistles sound different in pitch and pitch length.

The calls seem to play a role mainly in territorial defense. They are often answered by kiwis of neighbouring territories.