The Rheiformes, contain two species of Neotropical flightless birds in two genera. Common Rhea, Rhea americana, and the smaller Darwin's Rhea, Pterocnemia pennata.
The rheas rome the South American grasslands. Their sexes are not dimorphic. They are very tall, about 5 feet. When the rheas run, they do use their wings, but not to fly. As they turn they will use them as a sort of 'sail'. Like other large, fast land birds, their toes have been reduced to three, which helps in speed. They are gregarious birds, normally found in flocks. During the breeding season they will breed in harems.
By Rob Nelson
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