The common ostrich (Struthio camelus), or simply ostrich, is a species of large flightless bird native to certain large areas of Africa. It is one of two extant species of ostriches, the only living members of the genus Struthio in the ratite order of birds. The other is the Somali ostrich (Struthio molybdophanes), which was recognized as a distinct species by BirdLife International in 2014 having been previously considered a very distinctive subspecies of ostrich.

The common ostrich shares the order Struthioniformes with the kiwis, emus, rheas, and cassowaries. However, phylogenetic studies have shown that it is the sister group to all other members of Palaeognathae and thus the flighted tinamous are the sister group to the extinct moa. It is distinctive in its appearance, with a long neck and legs, and can run for a long time at a speed of 55 km/h (34 mph) or even up to about 70 km/h (43 mph), the fastest land speed of any bird. The common ostrich is the largest living species of bird and lays the largest eggs of any living bird (extinct elephant birds of Madagascar and the giant moa of New Zealand laid larger eggs).

The common ostrich's diet consists mainly of plant matter, though it also eats invertebrates. It lives in nomadic groups of 5 to 50 birds. When threatened, the ostrich will either hide itself by lying flat against the ground, or run away. If cornered, it can attack with a kick of its powerful legs. Mating patterns differ by geographical region, but territorial males fight for a harem of two to seven females.

The common ostrich is farmed around the world, particularly for its feathers, which are decorative and are also used as feather dusters. Its skin is used for leather products and its meat is marketed commercially, with its leanness a common marketing point.

Description
Common ostriches usually weigh from 63 to 145 kilograms (139–320 lb), or as much as two adult humans. The Masai ostriches of East Africa (S. c. massaicus) averaged 115 kg (254 lb) in males and 100 kg (220 lb) in females, while the nominate subspecies, the North African ostrich (S. c. camelus), was found to average 111 kg (245 lb) in unsexed adults. Exceptional male ostriches (in the nominate subspecies) can weigh up to 156.8 kg (346 lb). At sexual maturity (two to four years), male common ostriches can be from 2.1 to 2.8 m (6 ft 11 in to 9 ft 2 in) in height, while female common ostriches range from 1.7 to 2.0 m (5 ft 7 in to 6 ft 7 in) tall. New chicks are fawn in color, with dark brown spots.[10] During the first year of life, chicks grow at about 25 cm (9.8 in) per month. At one year of age, common ostriches weigh approximately 45 kilograms (99 lb). Their lifespan is up to 40–45 years.

The feathers of adult males are mostly black, with white primaries and a white tail. However, the tail of one subspecies is buff. Females and young males are grayish-brown and white. The head and neck of both male and female ostriches is nearly bare, with a thin layer of down. The skin of the female's neck and thighs is pinkish gray, while the male's is gray or pink dependent on subspecies.

The long neck and legs keep their head up to 2.8 m (9 ft) above the ground, and their eyes are said to be the largest of any land vertebrate: 50 mm (2.0 in) in diameter; helping them to see predators at a great distance. The eyes are shaded from sunlight from above. However, the head and bill are relatively small for the birds' huge size, with the bill measuring 12 to 14.3 cm (4.7 to 5.6 in).

Their skin varies in color depending on the subspecies, with some having light or dark gray skin and others having pinkish or even reddish skin. The strong legs of the common ostrich are unfeathered and show bare skin, with the tarsus (the lowest upright part of the leg) being covered in scales: red in the male, black in the female. The tarsus of the common ostrich is the largest of any living bird, measuring 39 to 53 cm (15 to 21 in) in length. The bird has just two toes on each foot (most birds have four), with the nail on the larger, inner toe resembling a hoof. The outer toe has no nail. The reduced number of toes is an adaptation that appears to aid in running, useful for getting away from predators. Common ostriches can run at a speed over 70 km/h (43 mph) and can cover 3 to 5 m (9.8 to 16.4 ft) in a single stride. The wings reach a span of about 2 metres (6 ft 7 in), and the wing chord measurement of 90 cm (35 in) is around the same size as for the largest flying birds.

The feathers lack the tiny hooks that lock together the smooth external feathers of flying birds, and so are soft and fluffy and serve as insulation. Common ostriches can tolerate a wide range of temperatures. In much of their habitat, temperatures vary as much as 40 °C (72 °F) between night and day. Their temperature control relies in part on behavioral thermoregulation. For example, they use their wings to cover the naked skin of the upper legs and flanks to conserve heat, or leave these areas bare to release heat. The wings also function as stabilizers to give better maneuverability when running. Tests have shown that the wings are actively involved in rapid braking, turning and zigzag maneuvers. They have 50–60 tail feathers, and their wings have 16 primary, four alular and 20–23 secondary feathers.

The common ostrich's sternum is flat, lacking the keel to which wing muscles attach in flying birds. The beak is flat and broad, with a rounded tip. Like all ratites, the ostrich has no crop, and it also lacks a gallbladder. They have three stomachs, and the caecum is 71 cm (28 in) long. Unlike all other living birds, the common ostrich secretes urine separately from faeces. All other birds store the urine and faeces combined in the coprodeum, but the ostrich stores the faeces in the terminal rectum. They also have unique pubic bones that are fused to hold their gut. Unlike most birds, the males have a copulatory organ, which is retractable and 20 cm (8 in) long. Their palate differs from other ratites in that the sphenoid and palatal bones are unconnected.
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