The ostrich or common ostrich (Struthio camelus) is either one or two species of large flightless birds native to Africa, the only living member(s) of the genus Struthio, which is in the ratite family. Starting in 2014, the Somali ostrich is now considered a full species separate from the common ostrich.
The ostrich shares the order Struthioniformes with the kiwis, emus, rheas and cassowaries. However, phylogenetic studies have shown that it is the basal extant member of Palaeognathae and is thus equally closely related to flighted tinamous. It is distinctive in its appearance, with a long neck and legs, and can run at up to about 70 km/h (19 m/s; 43 mph), the fastest land speed of any bird. The 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 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 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.
Ostriches usually weigh from 63 to 145 kilograms (139–320 lb), or as much as two adult humans. Ostriches of the East African race (S. c. massaicus) averaged 115 kg (254 lb) in males and 100 kg (220 lb) in females, while the nominate subspecies (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 ostriches can be from 2.1 to 2.8 m (6 ft 11 in to 9 ft 2 in) in height, while female ostriches range from 1.7 to 2.0 m (5 ft 7 in to 6 ft 7 in) tall. New chicks are fawn in colour, with dark brown spots. During the first year of life, chicks grow at about 25 cm (9.8 in) per month. At one year of age, 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 greyish-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 blue-gray, 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 colour 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 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 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. 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 wings are used in mating displays and to shade chicks. 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. Ostriches can tolerate a wide range of temperatures. In much of their habitat, temperatures vary as much as 40 °C (100 °F) between night and day. Their temperature control mechanism relies on action by the bird, which uses its wings to cover the naked skin of the upper legs and flanks to conserve heat, or leaves these areas bare to release heat. They have 50–60 tail feathers, and their wings have 16 primary, four alular and 20–23 secondary feathers.
The 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 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.
The ostrich was originally described by Linnaeus in his 18th-century work, Systema Naturae under its current binomial name. Its scientific name is derived from Latin, struthio meaning "ostrich" and camelus meaning "camel", alluding to its dry habitat.
The ostrich belongs to the ratite order Struthioniformes. Other members include rheas, emus, cassowaries, moa, kiwi and the largest bird ever, the now-extinct elephant bird (Aepyornis).
However, the classification of the ratites as a single order has always
been questioned, with the alternative classification restricting the
Struthioniformes to the ostrich lineage and elevating the other groups.
Five subspecies are recognised:
- Common ostrich (S. camelus) complex:
- S. c. camelus, North African ostrich, or red-necked ostrich, North Africa. Historically it was the most widespread subspecies, ranging from Ethiopia and Sudan in the east throughout the Sahel to Senegal and Mauritania in the west, and north to Egypt and southern Morocco, respectively. It has now disappeared from large parts of this range, and it only remains in 6 of the 18 countries where it originally occurred, leading some to consider it Critically Endangered. It is the largest subspecies, at 2.74 m (9.0 ft) in height and up to 154 kilograms (340 lb) in weight. The neck is pinkish-red, the plumage of males is black and white, and the plumage of females is grey.
- S. c. australis, Southern ostrich, southern Africa. It is found south of the rivers Zambezi and Cunene. It is farmed for its meat, leather and feathers in the Little Karoo area of Cape Province.
- S. c. massaicus, Masai ostrich, East Africa. It has some small feathers on its head, and its neck and thighs are pink. During the mating season, the male's neck and thighs become brighter. Its range is essentially limited to southern Kenya and eastern Tanzania and Ethiopia and parts of southern Somalia.
- S. c. syriacus, Arabian ostrich or Middle Eastern ostrich, Middle East. Was formerly very common in the Arabian Peninsula, Syria, and Iraq; it became extinct around 1966.
- S. molybdophanes, Somali ostrich, southern Ethiopia, northeastern Kenya, and Somalia. The neck and thighs are grey-blue, and during the mating season, the male's neck and thighs become brighter and bluer. The females are more brown than those of other subspecies. It generally lives in pairs or alone, rather than in flocks. Its range overlaps with S. c. massaicus in northeastern Kenya.
Some analyses indicate that the Somali ostrich may be better
considered a full species, but there is no consensus among experts about
this. The Tree of Life Project and IOC recognize it as a different species, but The Clements Checklist of Birds of the World, Howard and Moore Complete Checklist of the Birds of the World do not. BirdLife International has reviewed the proposed split and accepted it. Mitochondrial DNA haplotype comparisons suggest that it diverged from the other ostriches not quite four mya due to formation of the East African Rift. Hybridization with the subspecies that evolved southwestwards of its range, S. c. massaicus,
has apparently been prevented from occurring on a significant scale by
ecological separation, the Somali ostrich preferring bushland where it
browses middle-height vegetation for food while the Masai ostrich is,
like the other subspecies, a grazing bird of the open savanna and miombo habitat.
The population from Río de Oro was once separated as Struthio camelus spatzi
because its eggshell pores were shaped like a teardrop and not round.
However, as there is considerable variation of this character and there
were no other differences between these birds and adjacent populations
of S. c. camelus, the separation is no longer considered valid.
This population disappeared in the latter half of the 20th century.
There were 19th-century reports of the existence of small ostriches in
North Africa; these are referred to as Levaillant's ostrich (Struthio bidactylus) but remain a hypothetical form not supported by material evidence.
