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. In 2014, the Somali ostrich (Struthio molybdophanes) was recognized as a distinct species.[2][3]
The 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.[4][5] 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),[6] the fastest land speed of any bird.[7] 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, with its leanness a common marketing point.
Description
Ostriches usually weigh from 63 to 145 kilograms (139–320 lb), or as much as two adult humans.[6][8] 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.[6] New chicks are fawn in colour, with dark brown spots.[9] 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.[8][9] The skin of the female's neck and thighs is pinkish gray,[9] 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;[10] helping them to see predators at a great distance. The eyes are shaded from sunlight from above.[11][12] 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).[6]
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.[6]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.[13] 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.[14] 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.[6] 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 (104°F) between night and day. Their temperature control relies in part on behavioural 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.[15] They have 50–60 tail feathers, and their wings have 16 primary, four alular and 20–23 secondary feathers.[6]
The ostrich's sternum is flat, lacking the keel to which wing muscles attach in flying birds.[16] The beak is flat and broad, with a rounded tip.[8] Like all ratites, the ostrich has no crop,[17] and it also lacks a gallbladder.[18] 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.[19] All other birds store the urine and faeces combined in the coprodeum, but the ostrich stores the faeces in the terminal rectum.[19] 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.[6]
Taxonomy
The ostrich was originally described by Carl Linnaeus from Sweden in his 18th-century work, Systema Naturae under its current binomial name.[20] Its scientific name is derived from Latin, struthio meaning "ostrich" and camelus meaning "camel", alluding to its dry habitat.[21]
The ostrich belongs to the ratite order Struthioniformes. Other members include rheas, emus, cassowaries, moa, kiwi and the largest known 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.
Subspecies
Four living subspecies are recognised:
- Common ostrich (S. camelus) complex:
| Subspecies | Description | Image |
|---|---|---|
| North African ostrich (S. c. camelus), also called the red-necked ostrich or Barbary ostrich | Lives in North Africa. Historically it was the most widespread subspecies, ranging from Ethiopia and Sudan in the east throughout the Sahel[22] 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,[23] and it only remains in 6 of the 18 countries where it originally occurred, leading some to consider it Critically Endangered.[24] It is the largest subspecies, at 2.74 m (9.0 ft) in height and up to 154 kilograms (340 lb) in weight.[25] The neck is pinkish-red, the plumage of males is black and white, and the plumage of females is grey.[25]
|  |
| South African ostrich (S. c. australis), also commonly known as black-necked ostrich or southern ostrich | 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.[26] | _male_(13994461256).jpg) |
| Masai ostrich (S. c. massaicus), also known as the pink-necked ostrich or East African ostrich | 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[22] and Ethiopia and parts of southern Somalia.[25] |  |
Arabian ostrich( S. c. syriacus), also known as Syrian ostrich or Middle Eastern ostrich | Was formerly very common in the Arabian Peninsula, Syria,[22] and Iraq; it became extinct around 1966.
|  |
| Subspecies | Description | Image |
|---|---|---|
| Somali ostrich (S. molybdophanes), also known as blue-necked ostrich | Found in southern Ethiopia, northeastern Kenya, and Somalia.[22] 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.[25] It generally lives in pairs or alone, rather than in flocks. Its range overlaps with S. c. massaicus in northeastern Kenya.[25] |  |
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, The Clements Checklist of Birds of the World and IOC recognize it as a different species, but Howard and Moore Complete Checklist of the Birds of the World does not. BirdLife International has reviewed the proposed split and accepted it.[3][27] Mitochondrial DNA haplotype comparisons suggest that it diverged from the other ostriches not quite 4 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.[28]
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.[29][30] 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.[31]
Evolution
The earliest fossil of ostrich-like birds are Paleocene taxa from Europe.[32] Palaeotis and Remiornis are birds from the Middle Eocene also cited as potential early ostriches. However, their exact status as such is controversial, and they have alternatively been considered more basal (or more derived) ratites. Other unspecified ratite remains are known from the Eocene and Oligocene of Europe and Africa; their status as early ostriches too is questionable, and may in fact represent multiple lineages of flightless paleognaths.[33][34] The African Eremopezus, when not considered a basal secretarybird or shoebill, is sometimes considered an ostrich relative or an "aepyornithid-like" taxon.[35]
Apart from these enigmatic birds, the fossil record of the ostriches continues with several species of the modern genus Struthio which are known from the Early Miocene onwards. While the relationship of the African species is comparatively straightforward, a large number of Asian species of ostrich have been described from fragmentary remains, and their interrelationships and how they relate to the African ostriches are confusing. In China, ostriches are known to have become extinct only around or even after the end of the last ice age; images of ostriches have been found there on prehistoric pottery and petroglyphs.[36][37][38]
Ostriches have co-existed with another lineage of flightless didactyl birds, the eogruids. Though Olson 1985 classified these birds as stem-ostriches, they are otherwise universally considered to be related to cranes, any similarities being the result of convergent evolution. Competition from ostriches has been suggested to have caused the extinction of the eogruids,[39][40] though this has never been tested and both groups do co-exist in some sites.[41]
Several of these fossil forms are ichnotaxa (that is, classified according to the organism's footprints or other trace rather than its body) and their association with those described from distinctive bones is contentious and in need of revision pending more good material.
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