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Flightless Birds

Ostriches

The ostrich is Earth's largest living bird. There is only one species, Struthio camelus. The specific name comes from the fact that these tall, desert-living birds have been called camel birds. They may be as much as 8 ft (2.4 m) tall and weigh up to 400 lb (181 kg). A prominent distinction among subspecies of ostrich is skin color. The long legs and long, straight neck show red skin in some subspecies and blue in others.

Natives of Africa, ostriches are found on the dry plains, where they seem more at home among big mammals, such as giraffes, than they do among other birds. They are currently found in three areas Western Africa, at the farthest western portion of the bulge; South Africa; and in East Africa from the Horn of Africa (Ethiopia). They were formerly found on the Arabian Peninsula, but this subspecies was hunted for sport and became extinct during the first half of the twentieth century. An effort is being made to re-introduce ostriches to this region, although of a different subspecies.

Generally, ostriches have whitish neck, head, and underparts, with a thick covering of black or dark-brown feathers crowning the entire back. The female's feathers are almost uniformly brown, while males have a black body with white wing and tail feathers. Ostrich plumage seems almost more like fur than feathers. Ostrich plumes, especially the long ones from the birds' tail and wings, have been popular for centuries, primarily for use on hats. Today, their softness makes them useful for dusting and cleaning delicate parts in machinery.

Ostriches have scaly legs and feet. There are only two toes on each foot, both of which hit the ground when the bird walks. Each toe ends in a thick, curved nail that digs into the soil as the ostrich runs. One toe is immense, almost the size of a human foot; the other is much smaller. Each toe has a thick, rough bottom that protects it.

There is a myth that ostriches put their heads in the sand when frightened, but this is not the case. In reality, ostriches can run faster than just about any predator, or they can stand their ground and kick with powerful slashing motions of their sharp-nailed feet. Ostriches can run at a steady pace of about 30 MPH (48 km/h), with a stride that can cover more than 20 ft (6 m). At top speed for a brief time, they can run almost 45 MPH (72 km/h).

There is little up and down motion as they run. Instead, their legs handle all of the motion and their body stays in one plane. Ostriches, as well as the slightly smaller rheas, use their wings rather like sails. When running, they hold them out from their bodies. This helps them balance and, by changing the level of one wing or the other, it helps them easily change direction as they run. If frightened, a running ostrich may swerve into a circular pattern that takes it nowhere.

These large birds have been farmed for more than 150 years, starting in Australia. Originally the birds were raised just for their plumes, but in recent years they have been raised for their large eggs, their skin, which tans into attractive leather, and their meat. The feathers are actually harvested, in that they are cut off before falling out as they would naturally. This harvesting keeps them from being damaged. New feathers grow in to replace the harvested ones.

Ostriches have the largest eyes of any land animal—a full 2 in (5 cm) in diameter. The eyes are shielded by eyelash-lined outer eyelids that blink from the top downward, as well as nictitating membranes that close from the bottom of the eye upward. This membrane protects the eye but is semitransparent so that the bird can still see.

Because a tall ostrich may get the first sight of approaching danger on the savannah, its alarm may alert other animals to the presence of danger. The birds are usually left undisturbed by herding mammals. The ostriches act as lookouts and the mammals stir up insects and other small animals with which the ostriches supplement their herbivorous diet. Actually, ostriches will eat just about anything, especially if it is shiny and attracts their attention.

During the dry season, herds containing as many as 500-600 ostriches may gather at a watering hole. The males, or cocks, tend to stay in one group, while the females, or hens, stay in their own groups. When the rainy season begins, however, they split into harem groups, consisting of one male and two to four females.

A male ostrich performs a courtship dance involving considerable puffing and strutting, accompanied by booming noises. At its conclusion, he kneels and undulates his body in front of his chosen female. If she has found the performance enchanting, she also bends her knees and sits down. The male's dance may be interrupted by a competing male. The two males then hiss and chase each other. Any blows are given with their beaks.

The male selects the nesting site for his several females. He prepares it by scraping a slight indentation in the soil or sand. The dominant female lays her eggs first, followed by the others, over a period of several weeks. Altogether, there may eventually be as many as 30 off-white, 8 in (20 cm) eggs in a single clutch, perhaps half of them belonging to the dominant female. However, all the eggs won't hatch because they cannot all be incubated. Abandoned eggs do not attract many scavengers because the shells are too thick to break easily.

Both the dominant female and the male take turns incubating the eggs, with their insulating feathers spread over the nest. The sitter also takes time to turn the eggs on a regular basis. The eggs hatch about six weeks after the start of incubation, but the hatching may be a slow process because the chicks are able to break only tiny bits of the tough shell at a time. The mottled-brown chicks, each about 1 ft (30.5 cm) tall, are tended by all the females in the group. The chicks are ready to feed on their own, but are protected by the adults as they grow. They develop adult feathers by their third year, and soon afterward are mature enough to mate. Ostriches can live to be more than 40-50 years old.


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Science EncyclopediaScience & Philosophy: Ferroelectric materials to Form and matterFlightless Birds - Ostriches, Rheas, Emus, Cassowaries, Kiwis