Apterygidae

The primitive-looking kiwis are flightless birds with tiny, vestigal wings and long bills. Kiwis are ratites - relatives of Emus, cassowaries, rheas and ostriches - yet they have a very different morphology from these other families. The birds live mainly in forests. All five species have declined since New Zealand was colonized by Europeans, due to habitat loss and predation, particularly by introduced mammals.

Additional information

Kiwis have no keel on their sternum and therefore lack an anchor for wing muscles. The most pronounced external feature is the long slightly decurved bill, which can grow to 20 cm. Unusually for a bird, the bill has nasal openings located at near the tip; these have very large olfactory lobes that help the birds detect prey above or below the ground. A valve near the base allows the bird to eject water and detritus through the nostrils while foraging.

The birds are almost entirely nocturnal, emerging from their burrow systems to feed after sunset. They prefer to keep to cover when leaving their roosting burrows, although they may emerge into open areas such as shoreline to feed after dark. Kiwis forage in soil and leaf litter. They have poor eyesight, so locate their food by means of their highly developed sense of smell and sensitive, probing bill. Larger insects are also detected by sound.

Kiwis are highly territorial and, unusually for birds, mark their home range and their burrows with pungent droppings.

Uniquely among ratites, kiwis are monogamous for life. The courtship display involves the birds crossing bills while circling each other slowly. Breeding takes place in spring, around August, but the season may extend as late as February. Kiwis lay the largest egg, in proportion to their own body weight, of any living bird. The yolk is also proportionally 50 percent larger than those of other birds. Kiwi chicks lack an egg tooth, so break out of the shell using their feet.

Taxonomy

Kiwis all belong to a single genus, Apteryx. Some authorities recognize just three species: Little Spotted Kiwi, Great Spotted Kiwi and Brown Kiwi, with the last comprising North Island, South Island, and Okarito Island. Here I divide them over 5 species:

• A. haastii (Great Spotted Kiwi)
• A. owenii (Little Spotted Kiwi)
• A. rowi (Okarito Brown Kiwi)
• A. australis (Brown Kiwi)
• A. mantelli (North Island Brown Kiwi)

Evidence from their ancestors in the fossil record has been found as far back as the Eocene. Recent studies suggest that the kiwis do not have a common ancestral origin with the extinct moas of New Zealand, as was once thought.