The southern cassowary is a solitary bird, which pairs only in breeding season, in late winter or spring. The male builds a nest on the ground, a mattress of herbaceous plant material thick and up to wide. This is thick enough to let moisture drain away from the eggs. The male also incubates the eggs and raises the chicks alone. A clutch of three or four eggs are laid measuring . They have a granulated surface and are initially bright pea-green in colour although they fade with age. Cassowaries make a thunderous call during mating season and hissing and rumblings otherwise. Chicks will make frequent high-pitched contact whistles and chirps to call the male.