Common ostrich

Name and taxonomy

Carl Linnaeus described the ostrich in his Systema Naturae in the 18th century under the name it still carries. Struthio is Late Latin for ostrich. The species name camelus recalls the ancient Greek word strouthokamelos, the camel sparrow, a nod to its dry home. Modern Greek still uses that word for the bird. In German it is the Strauss, in French the autruche d'Afrique and in Spanish the avestruz comun.

The ostrich is the only living member of the family Struthionidae and the order Struthioniformes. Four subspecies are accepted. The Somali ostrich was a fifth until 2014, when BirdLife International and other authorities raised it to a full species. The Arabian subspecies died out around 1966, and a Sahara form from Rio de Oro vanished later in the 20th century.

Evolution and relatives

The ostrich is a ratite, one of the flightless birds in the infraclass Palaeognathae. Its relatives include the emus, rheas, cassowaries, kiwis, the flying tinamous and the extinct moa and elephant birds. Genetic studies show that the ostrich line split off before any of the others, so it is the sister group to all of them. The order Struthioniformes once held every ratite, but that grouping proved paraphyletic, and now it holds only the ostriches.

The Somali ostrich probably split from the common ostrich about 4 million years ago, when the East African Rift formed. The two rarely cross, because the Somali bird browses bushland while the common ostrich grazes open savanna. Fossil eggshell from India shows that ostriches lived there 25,000 years ago, with 92% genetic similarity to the North African form. As the largest living bird, the ostrich is also the largest living dinosaur, and scientists use it to model how extinct dinosaurs moved.

Appearance

A male stands 210 to 275 centimetres tall and weighs 100 to 130 kilograms. A female is smaller, at 175 to 190 cm and 90 to 120 kg. The long neck and legs lift the head up to 2.8 metres above the ground. The eye is 50 millimetres across, the largest of any land vertebrate, and it is shaded from the sun above. The head and the flat, broad bill are small for such a big bird, and the bill measures 12 to 14.3 cm.

An adult male is mostly black with white wing tips and a white tail. Hens and young cocks are grey-brown with white. The neck and head are almost bare, with only thin down, and the neck skin is pinkish grey in the female. The bare legs carry scales on the lower part, red in the male and black in the female. The lower leg bone is the longest of any living bird, at 39 to 53 cm.

Each foot has two toes, and the nail on the big inner toe looks like a hoof. The feathers lack the tiny hooks that zip a flying bird's feathers together, so they are soft and loose. The wings span about 2 metres, and the breastbone has no keel because there are no flight muscles to anchor. Chicks are fawn with dark brown spots, reach adult height at one year and full weight at 18 months.

Habitat and range

Ostriches once ranged across Africa north and south of the Sahara and into Asia Minor and Arabia. Hunters wiped out the Arabian birds by the middle of the 20th century, and an attempt to bring them back to Israel failed. Today the species lives in the savannas and the Sahel on both sides of the equatorial forest belt. In south-west Africa it lives in semi-desert and true desert. It prefers open ground, where its eyes can see a predator from a long way off.

The range still covers about 9,800,000 square kilometres, which is why the IUCN keeps the species at Least Concern. Birds have been seen on islands of the Dahlak Archipelago in the Red Sea. Farmed ostriches in Australia escaped, and a small feral population lives in the outback. GBIF holds records from 76 countries, but many of those are farms and zoos rather than wild birds. A male's territory covers 2 to 20 square kilometres.

Diet and feeding

The ostrich eats mainly seeds, shrubs, grass, fruit and flowers. It is a picky feeder and picks out grass seed heads and particular flowers rather than whole plants. Now and then it eats locusts, mice, lizards and scraps left by big cats. A captive bird needs about 3.5 kilograms of food a day.

The bird has no teeth, so it swallows pebbles that grind food inside the gizzard. It packs food into its gullet and sends it down the neck as a ball that can hold 210 millilitres. The gizzard can hold 1,300 grams, and up to 45% of that can be sand and stones. Like other ratites, the ostrich has no crop.

It can go several days without drinking, because it draws water from its food and from its own metabolism. Some of its food plants hold up to 87% water. It survives the loss of 25% of its body weight through dehydration. Even so, it enjoys water and bathes whenever it can.

Behaviour and social life

Ostriches are active by day and busiest early and late, though they may move about on moonlit nights. In winter they live alone or in pairs, and only 16 percent of sightings show more than two birds. In the breeding season, and in long droughts, they form wandering bands of five to 100, and a dominant hen leads each one. These groups often travel with zebras and antelopes, and each species watches for danger on behalf of the rest.

When a predator appears the ostrich runs. It holds a steady 50 kilometres per hour and bursts past 70 km/h, covering 3 to 5 metres in a stride. The wings act as stabilisers and help it brake, turn and zigzag at speed. If it cannot run it lies flat with its neck along the ground. In the heat haze it then looks like a mound of earth. If cornered it kicks forward, and a kick can deliver about 225 kilograms of force.

The ostrich copes with a daily swing of 40 degrees Celsius by changing its posture. It drapes its wings over the bare skin of its thighs to keep heat in, or lifts them to let heat out. It fluffs its feathers to trap a 7 cm layer of air in the heat. It pants at 40 to 60 breaths a minute without upsetting its blood chemistry. It has no sweat glands, so panting and a network of vessels behind the eye that cools the brain do the work.

Communication and senses

The ostrich relies on sight and hearing, and it can spot a lion at a great distance. The eyes are the largest of any land animal, and they sit high on a neck that gives a view over the grass. Groups grazing with zebras and wildebeest pick up a threat sooner than a lone bird would.

A territorial male booms by filling his neck with air, and the sound warns rivals off his ground and his hens. Males hiss and make other noises to intimidate each other. In courtship the male beats one wing and then the other, and the female runs a circle around him with her wings lowered. A parent whose nest is threatened may feign injury to draw a predator away, a display common to many ground-nesting birds. Ostriches raised by people alone may aim their courtship at their keepers instead of other ostriches.

Reproduction and life cycle

Ostriches mature at 2 to 4 years, and females about six months before males. The season runs from March or April to some time before September. A territorial male fights for a harem of two to seven hens and mates with several, but he bonds with only one major female. He clears a nest in the soil with hard wing beats and pokes the ground with his bill. Then he spirals his head as the hen circles him with lowered wings.

The male scrapes the nest, a pit 30 to 60 cm deep and 3 metres wide, in bare ground. Every hen in the group lays in it, and the major female lays first. She can tell her own eggs from the rest, and when incubation starts she rolls out the extra eggs of weaker hens, leaving about 20. Each egg is about 15 cm long and 13 cm wide and weighs about 1.4 kg. The thick, glossy cream shell is marked with small pits. It is over 20 times the weight of a hen's egg. Yet at 1 to 4% of the female's weight it is the smallest egg of any bird relative to its layer.

The drab females sit by day and blend with the sand, and the black male sits by night when he is almost invisible. The eggs hatch after 35 to 45 days, a short time for a ratite, probably because predators find so many nests. Fewer than 10% of nests survive the nine weeks of laying and incubation, and only 15% of the chicks that hatch reach one year. The male usually guards the chicks and teaches them to feed, though both parents help. A bird that reaches adulthood can live a long time. AnAge gives a captive record of 50 years, and Wikipedia reports one bird that lived to 62.

Predators and threats

Cheetahs, lions, leopards, wild dogs and spotted hyenas can take an ostrich of any age. Jackals, warthogs, mongooses and birds of prey raid nests and take chicks. The Egyptian vulture throws stones at ostrich eggs to break the shell. About 90% of chicks die, most of them to predators.

An adult that has seen a predator is almost impossible to catch, so most hunters try an ambush from cover. In the Kalahari, groups of male cheetahs hunt ostriches at night, when the birds keep a poorer watch. Lions there also take ostriches, but elsewhere the bird is a small part of any predator's diet. A parent defending chicks has killed hyenas and even lions with its kick. On farms in North America an adult ostrich has no natural enemy, and one is recorded killing a coyote.

Hunting for plumes almost wiped the species out in the 18th century, and hunting and habitat loss remain the main threats.

Population and conservation

The IUCN lists the common ostrich as Least Concern. The wild population has fallen sharply over the last 200 years, and most surviving birds live in reserves or on farms. The very large range keeps the species off the threatened lists. South Africa also lists it as Least Concern.

The North African subspecies is on Appendix I of CITES, which bans commercial trade across borders. The Arabian subspecies went extinct around 1966. Feather farms appeared in the 19th century, and they eased the pressure on wild birds because a farmed bird can be plucked and kept. By the start of the 20th century over 700,000 birds lived in captivity. iNaturalist holds 15,368 observations, and many of those come from parks in eastern and southern Africa.

Relationship with humans

People and ostriches go back at least 60,000 years. Engraved eggshell from Diepkloof Rock Shelter in South Africa dates to that age. Kalahari hunter-gatherers still punch a hole in an eggshell and use it as a water flask, and they make beads from the pieces. One egg holds as much as about 24 hen's eggs, and people and animals both eat them. Romans wanted ostriches for arena games, for the kitchen and for medicine.

Farming began in South Africa at the start of the 19th century, when settlers near Cape Town raised captured chicks. A farmed bird can be plucked again after seven or eight months. The feather market collapsed after the First World War, and farming for skins and meat spread in the 1970s. Ostrich leather is claimed to be the strongest on the market, and the meat is lean and dark red like beef. Farms offer tours and rides, and people race ostriches in South Africa and at festivals in the United States.

Wild ostriches avoid people, but a cornered bird or one guarding chicks will attack. A kick from the clawed foot can disembowel or kill a person with one blow. Around Oudtshoorn in South Africa, where farms sit beside wild birds, two to three attacks a year cause serious injury or death. By that count the ostrich is the most dangerous bird in the world.

In culture and myth

Ostriches have appeared in art for 5,000 years in Mesopotamia, Egypt and the Kingdom of Kush. A statue found in an Egyptian tomb shows Queen Arsinoe II riding one. In Egyptian belief the ostrich feather of the goddess Ma'at was weighed against the heart of the dead to judge a life. In Eastern Christian churches, decorated ostrich eggs hang on the chains of oil lamps. One story says the hen stares at her eggs without a pause until they hatch, a picture of the attention a Christian owes to prayer.

The claim that an ostrich buries its head in the sand is false. It probably began with Pliny the Elder, who wrote that the bird hides its head in a bush and thinks itself unseen. Lying flat with the neck along the ground, or turning eggs in a sand pit, may have looked like burying from a distance. The image now stands for denial, and economists call the avoidance of bad news the ostrich effect. An African folktale says the ostrich got its long neck in a quarrel between mates over whose turn it was on the nest.