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Ostriches usually weigh from 63 to 130 kilograms (140–290 lb),[8][9] with exceptional male Ostriches weighing up to 156.8 kilograms (346 lb).[9] 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][10] The skin of the female's neck and thighs is pinkish gray,[10] while the male's is blue-gray, gray or pink dependent on subspecies.
The long neck and legs keep their head 1.8 to 2.75 m (6 to 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;[11] they can therefore perceive predators at a great distance. The eyes are shaded from sun light falling from above.[12][13]
Their skin varies in colour depending on the sub-species. 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.[9] 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.[14] The reduced number of toes is an adaptation that appears to aid in running. Ostriches can run at over 70 km/h (43 mph) for up to 30 minutes.[citation needed] The wings reach a span of about 2 metres (7 ft)[15] and 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. They have 50-60 tail feathers, and their wings have 16 primary, four alular and 20-23 secondary feathers.[9] 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] Contrary to all other birds who store the urine and faeces combined in the coprodeum, they store 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 8 in (20 cm) long. Their palate differs from other ratites in that the sphenoid and palatal bones are unconnected.[9]
At sexual maturity (two to four years), male Ostriches can be from 1.8 to 2.8 m (5 ft 11 in to 9 ft 2 in) in height,[9] while female Ostriches range from 1.7 to 2 m (5 ft 7 in to 6 ft 7 in). During the first year of life, chicks grow about 25 cm (10 in) per month. At one year of age, Ostriches weigh around 45 kilograms (100 lb). Their lifespan is up to 40 or 45 years.