The breeding birds arrive at Taiaroa Head in September. The nest, built during early November, is formed by a bird sitting down and pulling vegetation and earth around itself with its bill. The white egg, weighing up to 500 grams, is laid during the first three weeks of November. The parents share incubation duty in spells of two to eight days over a period of 11 weeks - one of the longest incubation periods of any bird. The incubating bird sleeps much of the time its mate is away.