North Island Brown Kiwi

Nostrils near the tip of the beak

The North Island brown kiwi (Apteryx mantelli) is a flightless bird that forages at night. Its long, curved bill is unique in the bird world in having the nostrils near the tip. A kiwi plunges that bill again and again into the leaf litter of the forest floor. It often snuffles audibly as it searches, a sound that may come from a valve behind the nostrils that stops it inhaling dirt.

Kiwi use that bill to sniff out food. Scientists compared kiwi with 55 other bird species, and the kiwi’s olfactory bulbs (the brain regions that process smell) were proportionately larger than any other bird’s in the study. Touch may help too. The bill tip holds mechanoreceptors, cells that sense vibration and pressure, set in pits arranged like those of sandpipers and snipe. A kiwi may be able to locate prey the same way.

Egg math A female kiwi lays an extremely large egg, an average of 15 percent of her body weight. It weighs about 450 grams and is over 60 percent yolk.

Size, menu and home

Kiwi are stout birds that stand 0.5 to 0.6 metres tall. Females are heavier than males, at 2 to 3.9 kilograms against 1.4 to 3.2 kilograms.

The menu is varied: earthworms, beetles, snails, crayfish, insects, fruits and berries. Kiwi forage actively from dusk to dawn.

Every brown kiwi lives on New Zealand’s North Island, in lowland and coastal native forest and subalpine areas. There are four distinct forms: the Northland, Coromandel, Western and Eastern brown kiwi. A territory covers 5 to 50 hectares depending on habitat quality, and each one holds several burrows.

Long lives, falling numbers

New Zealand’s Department of Conservation says other kiwi live to be 40 to 65 years old, but the Northland form of this species averages only 14 years.

After the female lays, she leaves the male to incubate the eggs, which takes about 68 to 91 days. Brown kiwi breed faster than other kiwi, with up to two eggs a clutch and one to two clutches a year.

Even so, numbers are falling. A 1996 estimate said North Island kiwi had probably declined by at least 90% over the previous century, and the Department of Conservation puts the population at about 26,000. Adults are usually feisty enough to defend themselves against smaller predators, but eggs and newly hatched young are very vulnerable. Predators include rats, weasels, cats, dogs and pigs. The IUCN Red List rates the species Vulnerable.