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| subdivision_ranks = Subspecies | subdivision = ''S. c. camelus'' Linnaeus, 1758〔 North African ostrich ''S. c. australis'' Gurney, 1868〔 Southern ostrich ''S. c. massaicus'' Neumann, 1898〔 Masai ostrich †''S. c. syriacus'' Rothschild, 1919〔 Arabian ostrich ''S. molybdophanes'' Reichenow, 1883〔 Somali ostrich }} 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 ,〔 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, with its leanness a common marketing point.〔 ==Description== Ostriches usually weigh from , or as much as two adult humans.〔Brinkley, Edward S., and Jane Beatson. "A World of Birds." Birds. Pleasantville, N.Y.: Reader's Digest Children's Books, 2000. 9. Print.〕〔 Ostriches of the East African race (''S. c. massaicus'') averaged in males and in females, while the nominate subspecies (''S. c. camelus'') was found to average in unsexed adults.〔 Exceptional male ostriches (in the nominate subspecies) can weigh up to .〔 At sexual maturity (two to four years), male ostriches can be from in height, while female ostriches range from tall.〔 New chicks are fawn in colour, with dark brown spots.〔 During the first year of life, chicks grow at about per month. At one year of age, ostriches weigh approximately . 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. Afrikanischer Strauss Portrait.jpg|Close-up of head: Note the highly modified feathers Ostrich, mouth open.jpg|Close-up of head: Note the long eyelashes to protect the eyes Ostrich foot.jpg|Foot: Note the frequently missing nail on the outer toe File:The Childrens Museum of Indianapolis - Ostrich skull.jpg|Ostrich skull OstrichWing.jpg|Claws on the wings The long neck and legs keep their head up to above the ground, and their eyes are said to be the largest of any land vertebrate: 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 .〔 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 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.〔(【引用サイトリンク】publisher=TheWonderofBirds.com )〕 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 and can cover in a single stride.〔(San Diego Zoo's Animal Bytes: Ostrich ). Sandiegozoo.org. Retrieved on 21 August 2012.〕 The wings reach a span of about 2 metres (6 ft 7 in), and the wing chord measurement of 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 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 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.〔(Ostrich Wings Explain Mystery of Flightless Dinosaurs )〕 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 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 long. Their palate differs from other ratites in that the sphenoid and palatal bones are unconnected.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ostrich」の詳細全文を読む スポンサード リンク
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