Natural distribution is in the drier regions of Africa,
including southern Africa, the Sahel, Sudan, Ethiopia, Kenya and Tanzania. Once
occurred in Arabia and Syria. It generally prefers open savanna woodland, arid and
semi-arid grassland and shrubland, and open desert plains.
Herbivorous, eating green plant food predominantly, with a
preference for small herbs and grasses. Pooled observations of ostriches by
Milton et al. (1994) across a range of vegetation types showed that they eat 39%
green shoots, 12% leaves, 17% flowers, 4% fruits and seeds, and 28% small,
uprooted plants. Unpalatable and toxic plants avoided by ostriches tend to be
similar to those avoided by mammalian herbivores such as sheep (Milton et al.,
1994).
Under artificial conditions, young birds have
eaten Harvester termites Microhodotermes viator and tenebrionid beetle
larvae but this is unknown in wild birds.
Breeding
One male holds a territory and mates with up to
four females (i.e. he is polygamous). The females each have home
ranges that they do not defend and which overlap with one another. Their
home ranges do not coincide with the male territories and are larger.
A territorial male drives other males out of his
territory but displays to females he encounters. Successful displaying can
be followed by copulation.
A nest consists of a scrape in the ground, 2-3 m
across. Nests are made by the male and he makes a number of them within his
territory.
A male shows a female the nests in his territory. If
the female accepts a scrape, she lies in it and she is termed the 'major'
female if she is the first to do so.
The major female starts the egg laying, laying
them at 2-3 day intervals. Minor females also lay eggs in the nest, usually
on days when the major is not laying.
Clutch size can range from 4 to 78 eggs per
nest, but in South Africa, normal clutch size range is 4-26, averaging
13. Large clutches are the result of additional eggs laid by minor
females.
Eggs each weigh 1.22 - 1.75 kg, have a volume of
0.742 - 1.420 litres, and measure 12.2 - 15.8 mm long by 11.0 - 13.0 cm
wide.
Incubation of the eggs by the major female
starts about 16 days after she laid the first egg and lasts 39 - 53 days.
She incubates for most of the day and then the male takes over from late
afternoon and continues through the night. He also sometimes relieves the
female from incubating on very hot days.
Evidently the major female recognizes her own eggs and
keeps them near the centre of the clutch, pushing minor female eggs to the
periphery where they are not incubated and usually fail to hatch.
The chicks hatch out over a period of 3-5 days.
Chicks do not have an egg tooth and instead break out of their eggs by
contracting their muscles - this takes a long time: about nine hours.
Young are nourished through their first four
days by yolk reserves inside them which take up about a quarter of their
body mass.
After three days in the nest, the young leave the
nest with the adults and feed with the adults. Sometimes they form up
into creches with up to 60 young of different ages from different
nests.
Parents care for young for about nine months.
Potential predators are warded off by the adult pretending to be injured and
drawing the predator away from the young. They can also threaten the
predator by running towards it with opened wings and lowered head.
Survival rates can be low. A study in Kenya
showed that only 36% of the eggs in a nest were incubated (the rest were
eggs laid laid by minor females). Of the incubated eggs, only 33% hatched,
resulting in 7.5 young on average being produced per nest. Only about 12% of
these young survived to adulthood (0.9 survivors per nest). In South Africa,
chicks die from the sudden onset of cold, wet spells and they are also
susceptible to internal parasites.
References
Hockey PAR, Dean WRJ and Ryan PG (eds) 2005. Roberts
- Birds of southern Africa, VIIth ed. The Trustees of the John Voelcker
Bird Book Fund, Cape Town.
