On warm calm days from July until October, pairs are often seen doing their spectacular 'sky dance' or courtship diving, a series of U-shaped dives accompanied by loud calls. October, females start building the nest. I have never come across one of their nests but the books tell me it is a low platform of bracken, manuka, raupo and flax stalks, topped with rushes, cabbage tree leaves and grass. It is sited on the ground in swamps, in wet patches covered in rushes, in bracken fern, rank grass in young pine plantations or on road verges. Rarely are nests built on a platform in a tree.
Pairs return to the same territory year after year.
Only the female incubates the eggs but the male feeds the female throughout the incubation period of 31-34 days. Only the female feeds the chicks although the male gathers food for the female and the chicks. When the chicks are older, both adults hunt and when the female is away the male occasionally drops food at the nest but does not stay to feed them. At two to three weeks, the chicks clamber out of the nest and scatter widely in the surrounding vegetation. They fly at about 45 days old.