A number of bird species lost the ability to fly as they evolved, and about 40 flightless bird species exist currently. Most of these birds survived because they were in isolated areas with minimal predators, and many of them are being preserved through conservation programs, because they became close to being extinct. New Zealand and Australia both have a large number of flightless bird species, and some birds have also been found on remote islands and in parts of Africa and South America.
The size of a flightless bird can vary. The ostrich, for example, is the largest bird in the world, weighing in around 200 pounds (90 kilograms). The smallest flightless bird is the Inaccessible Island Rail, found in the Tristan Archipelago in the South Atlantic and weighing a little more than an ounce (30 grams). In a bid with the ability to fly, the breastbone has a large projecting keel, a bone to which flight muscles can be attached. Flightless birds have much less developed breastbones, and tend also to have vestigial wings.
The most famous living flightless bird group includes the ratites, all of which lack a keel altogether. Ostriches, emus, rheas, kiwis, and cassowaries are ratites. Emus, kiwis, and cassowaries can be found in Australia, New Zealand, and New Guinea, respectively, while rheas are native to South America and ostriches live in Africa. The ratites are among the largest of the flightless bird species, and they have well developed muscular legs with heavy claws to kick, claw, and defend themselves with.
The penguin, another flightless bird, can be found in many nations, and certain species of duck, teal, grebe, rail, and cormorant are also flightless. Many of these species are found in limited ranges on small islands which are often difficult to access. New Zealand boasts a large number of these species, along with the unique kakapo, the only flightless parrot, which also happens to be nocturnal. In addition, New Zealand hosts a small colony of takahe, another unique flightless bird which was thought to be extinct until 1948, when a small colony was found by a man who was out hiking.
Some flightless birds, such as the emu, are cultivated for their meat, eggs, or feathers. Because of their less developed breasts, the majority of the meat on flightless birds is found in their thighs. Emus also also raised for their oil, which is used as a moisturizer and leather conditioner. Emu oil is also believed to have other health benefits, and is widely available in many natural food stores.