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Mating

Common ostriches become sexually mature when they are 2 to 4 years old; females mature about six months earlier than males. As with other birds, an individual may reproduce several times over its lifetime. The mating season begins in March or April and ends sometime before September. The mating process differs in different geographical regions. Territorial males typically boom (by inflating their neck) in defense of their territory and harem of two to seven hens; the successful male may then mate with several females in the area, but will only form a pair bond with a 'major' female.

The cock performs with his wings, alternating wing beats, until he attracts a mate. They will go to the mating area and he will maintain privacy by driving away all intruders. They graze until their behavior is synchronized, then the feeding becomes secondary and the process takes on a ritualistic appearance. The cock will then excitedly flap alternate wings again and start poking on the ground with his bill. He will then violently flap his wings to symbolically clear out a nest in the soil. Then, while the hen runs a circle around him with lowered wings, he will wind his head in a spiral motion. She will drop to the ground and he will mount for copulation. Common ostriches raised entirely by humans may direct their courtship behavior not at other ostriches, but toward their human keepers.

The female common ostrich lays her fertilized eggs in a single communal nest, a simple pit, 30 to 60 cm (12–24 in) deep and 3 m (10 ft) wide, scraped in the ground by the male. The dominant female lays her eggs first; when it is time to cover them for incubation, she discards extra eggs from the weaker females, leaving about 20 in most cases. A female common ostrich can distinguish her own eggs from the others in a communal nest. Ostrich eggs are the largest of all eggs, though they are actually the smallest eggs relative to the size of the adult bird – on average they are 15 cm (6 in) long, 13 cm (5 in) wide, and weigh 1.4 kg (3 lb), over 20 times the weight of a chicken's egg and only 1 to 4% the size of the female. They are glossy cream-colored, with thick shells marked by small pits.

The eggs are incubated by the females by day and by the males by night. This uses the coloration of the two sexes to escape detection of the nest. The drab female blends in with the sand, while the black male is nearly undetectable in the night. The incubation period is 35 to 45 days, which is rather short compared to other ratites. This is believed to be the case due to the high rate of predation. Typically, the male defends the hatchlings and teaches them to feed, although males and females cooperate in rearing chicks. Fewer than 10% of nests survive the 9-week period of laying and incubation, and of the surviving chicks, only 15% of those survive to 1 year of age. However, among those common ostriches who survive to adulthood, the species is one of the longest-living bird species. Common ostriches in captivity have lived to 62 years and 7 months.