Either of two ostrich-like species of South American three-toed ratite birds (family Rheidae).
The common rhea ( Rhea americana ) is about 4 ft (120 cm) tall and weighs about 50 lbs (20 kg). It has luxuriant plumage, brown or gray above and whitish below. Darwin's rhea ( Pterocnemia pennata ) is smaller and has white-tipped brownish plumage. Rheas live in open country, often among grazing animals, and run from predators. They eat a wide variety of plants and animals. Both species are listed as endangered.