Tinamous and Ratites: Struthioniformes

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TINAMOUS AND RATITES: Struthioniformes


Struthioniformes are divided into two groups: ratites (RAT-ites), which are flightless birds that have a flat breastbone rather than a keeled breastbone (shaped like a wishbone) like birds of flight; and tinamous (TIN-ah-mooz), which have a keeled breastbone and can fly. Ratites have a simplified wing bone structure, strong legs, and no feather vanes, making it unnecessary to oil the feathers. Consequently, they have no preen gland that contains preening oil. This group is composed of ostriches (Struthionidae), rhea (Rheidae), cassowaries (Casuari-idae), emus (Dromaiidae), and kiwis (Apterygidae).

Ratite sizes range from 10 inches (25 centimeters) to 9 feet (2.7 meters) and weight can be from 2.86 pounds (1.3 kilograms) to 345 pounds (155.25 kilograms).

Ostriches are the largest struthioniforms (members of the Struthioniformes order), with long legs and neck. They range in height from 5.7 to 9 feet (1.8 to 2.7 meters) and weigh from 139 to 345 pounds (63 to 157 kilograms). They have loose-feathered wings. Males have black and white feathers while the female has grayish brown feathers.

Emus are about 6.5 feet in height and weigh 51 to 120 pounds (23 to 55 kilograms). They have long, strong legs and can run up to 30 miles per hour (48 kilometers per hour). They have short wings and the adults have brown feathers.

Rheas are 4.5 to 5.6 feet (1.3 to 1.7 meters) and weigh 55 to 88 pounds (24.75 to 40 kilograms). Their feathers are gray or spotted brown and white.

Cassowaries are 3.3 to 5.6 feet (1 to 1.7 meters) in height and weigh 30 to 130 pounds (14 to 59 kilograms). They have tiny wings with black feathers.

Kiwis are the smallest of ratites, ranging in height from 14 to 22 inches (35 to 55 centimeters) and weight 2.6 to 8.6 pounds (1.2 to 3.9 kilograms). They have brown and black hair-like feathers.

The tinamous have a keeled breastbone (shaped like a wishbone) and can fly. They range in size from 8 to 21 inches (20 to 53 centimeters) and weigh 1.4 ounces to 5 pounds (43 grams to 2.3 kilograms).


Ostriches are found in parts of central and southern Africa. Emus are distributed in several small areas of Australia. Kiwis are found in New Zealand. Rheas are distributed in Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay. Cassowaries are found in northern Australia, New Guinea, and surrounding islands. Tinamous are found in southern Mexico and throughout Central and South America.


Habitat varies between families. Ratites live in grasslands, eucalyptus forests, woodlands, alpine plains, subtropical and temperate forests, coastal areas, shrubland, desert, and rainforests. Tinamous live in rainforests, deciduous forests, woodlands, grasslands, and croplands.


Largely herbivores (plant eaters), ratites and tinamous eat mostly plants, fruits, seeds, and flowers although several families also eat insects, snails, and earthworms.


Ratites and tinamous are diurnal, meaning they are most active during the day. The exception is the kiwi, which is nocturnal, meaning it is most active at night. Behavior and reproduction varies between families. All lay eggs in nests but there the similarities end. In tinamous, rheas, cassowaries, kiwis, and emus, the males incubate (sit on to keep warm) the eggs and raise the young chicks. In ostriches, the males sit on the eggs at night and the females during the day.

Ostriches are the largest living birds and live in flocks, families, and individually. They are diurnal, meaning that they are most active during the day. Ostriches can run at speeds of up to 45 miles per hour (70 kilometers per hour). Males are polygamous (puh-LIH-guh-mus), meaning they take more than one mate at a time. Ostriches have an average of thirteen eggs per nest, and a number of females will lay their eggs in a single nest. The eggs take about forty-two days to hatch. On average, only one chick per nest will survive to adulthood.

Emus are the largest bird native to Australia. They live in pairs and are nomadic, following the rain to feed. The female lays a large, thick-shelled, dark green egg. When a nest has about eight to ten eggs, the male incubates them, meaning he sits on the eggs to keep them warm until they hatch.

Kiwis are shy, night birds with a keen sense of smell. They pair up for life and are monogamous (muh-NAH-guh-mus), meaning they have a sexual relationship with only one partner. The female usually digs a nest in the ground where she lays one or two large eggs, weighing about 1 pound (0.45 kilogram) each.

Rheas are the largest birds in South America. They are polygamous. During breeding season, the male rhea builds a nest in which between two and fifteen females lay their eggs. Nests contain ten to sixty eggs. The male cares for the chicks for about thirty-six hours after they hatch.

Cassowaries are solitary birds except during mating and the egg-laying period. Although they do not fly, they are good swimmers and fast runners. The female lays three to eight large dark bright green eggs in a nest that is incubated by the male. He cares for the chicks for nine months after they hatch.


A ratite known as the elephant bird (family Aepyornithidae) of Madagascar was the largest bird known to exist. It reached a height of 10 feet (3 meters) and weighed up to 880 pounds (400 kilograms). Seven species of the elephant bird once existed and two survived into the first century. All are now extinct. The last species to survive was Aepyornis maximus, which became extinct around the year 1600 c.e. One egg of the elephant bird was so large it would take 150 chicken eggs to fill it.

Tinamous are one of the oldest families of birds. They are very shy and are rarely seen by humans. The male builds a nest and two or more females lay eggs in it. The male incubates the eggs and soon after they hatch and leave the nest, he signals for new females to lay eggs.


Ratites are raised by humans for their meat and feathers. Their eggs are used as food and as decoration. Tinamous are hunted in the wild by humans for their meat.


Two Struthioniformes species are listed by the World Conservation Union (IUCN) as Critically Endangered, facing an extremely high risk of extinction. Nine species are listed by as Vulnerable, facing a high risk of extinction. One species is Endangered, facing a very high risk of extinction and four species are listed as Near Threatened, in danger of becoming threatened.



Davies, S. J. J. F., et al., eds. Bird Families of the World. Vol. 8, Ratites and Tinamous: Tinamidae, Rheidae, Dromaiidae, Casuariidae, Apterygidae, Struthionidae. Oxford, U.K.: Oxford University Press, 2002.

Elwood, Ann, and John B. Wexo. Ostriches, Emus, Rheas, Kiwis, and Cassowaries (Zoo Books). Mankato, MN: Creative Education, 2000.

Fowler, Allan. These Birds Can't Fly. New York: Bt Bound, 2001.

Harris, Timothy. Ostriches, Rheas, Cassowaries, Emus, and Kiwis. New York: Beech Publishing House, 1997.

Sinclair, Ian, et al. Birds of Southern Africa. Princeton, NJ: Princeton University Press, 2002.


Owen, James. "Does Rain Forest Bird 'Boom' Like a Dinosaur?" National Geographic News (November 4, 2003).

Roach, John. "Female Moa Bird Liked the Little Guys, Studies Suggest." National Geographic News (September 11, 2003).

Wiley, C. B. "Dinosaurs to Ratites in Only 250 Million Years." Live Animal Trade & Transport Magazine (June 1993): 5–16.

Web sites:

American Ostrich Association. http://www.ostriches.org (accessed on July 13, 2004).