Ostriches are ratites, flightless birds that have a flat breastbone rather than a keeled or curved breastbone like birds of flight. They have a simple wing bone structure, strong legs, and no feather vanes, making it unnecessary to oil the feathers. Therefore, ostriches have no preen gland that contains preening oil.
Ostriches are the largest birds in the world, with long legs and necks. They range in height from 5.7 to 9 feet (1.8 to 2.8 meters) and weigh from 139 to 345 pounds (63 to 157 kilograms). They have loose-feathered wings. Males have black and white feathers while females have grayish brown feathers. They have powerful legs, each with two toes. One of their two toes has a strong 4-inch (10-centimeter) claw while the other toe is usually clawless.
There are four living subspecies of ostrich: North African, Somali, Masai, and South African. Skin color is usually light but varies among subspecies, including pink in the North African ostrich and blue in the Somali ostrich.