New information about the social systems of the different kiwi varieties tells a different story – not only do some taxa share incubation, but not all of them live simply as pairs.
Only in the little spotted and brown kiwi species are eggs incubated just by the male parent. These species also live in pairs.
However, new information shows that both parents in the great spotted kiwi, rowi and tokoeka varieties share incubation to some extent.
Not only that, with Stewart Island tokoeka young birds stay in their parents’ territory for several years, and help raise their younger siblings, with Stewart Island tokoeka helpers even sharing in the incubation.
Sub-adult great spotted kiwi living in the mainland island at Lake Rotoiti, Nelson Lakes National Park, have also been found near their parents, and may help guard chicks against predators.
Kiwi that incubate eggs develop a bare patch of belly skin, known as a brood patch. Free of feathers, it exposes warm blood vessels close to the surface, ideal for keeping the egg warm.
The adult uses its long beak to keep the egg tucked beneath it. If the female kiwi lays a second egg, the nest can become crowded and eggs do get accidentally broken under the parents’ large feet.
If the male kiwi incubates the egg alone, he leaves the nest unattended to feed. Early on he can leave the nest for most of the night, covering the eggs and burrow entrance with litter.
Sometimes the male will bathe when out feeding. It is thought his damp feathers help maintain the correct humidity in the nest.
Close to hatching, the adult will sit tight for several days at a time, sustained by fat reserves. By the time the egg hatches, it will have lost a great deal of body weight.
A long incubation period
Kiwi invest a lot of energy in incubating their eggs. The average incubation time is 70-80 days, more than twice what is normal for a bird and about the same as the gestation period of a similar sized mammal.
It was once thought the incubation period was so long because the egg was too big for the kiwi to incubate properly. Now it seems more likely that it is due to the kiwi’s low body temperature.