Incubation behaviour and egg physiology of kiwi (Apteryx spp.) in natural habitats

Incubation behaviour varies among the different taxa of kiwi. For North Island brown kiwi (Apteryx mantelli) and little spotted kiwi (A. owenii), only the male incubates the eggs, except for in the first week. Meanwhile, for Okarito brown kiwi (A. mantelli) and the tokoeka (A. australis), incubation is shared by both sexes. In addition, amongst southern tokoeka, family group members can assist with incubation to the extent that breeding males may take no part in incubation at all. This study shows that kiwi turn their eggs regularly, an observation that contradicts earlier findings. There is a mean incubation temperature of 36.5°C at the top of the egg but the bottom may be 10°C lower in North Island brown kiwi and 5-8°C lower in Okarito brown kiwi eggs. Experiments inducing water loss from fertile and infertile eggs show that the presence of an embryo does not influence rate of water loss. North Island brown kiwi, Okarito brown kiwi and tokoeka regularly have more than one clutch in a season, and some North Island brown kiwi females lay up to seven eggs each year.