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(rheas), an order of three-toed ratite birds. The wings are developed but incapable of flight. When running swiftly, the birds extend their neck horizontally and raise one wing like a sail. The top of each wing has a horny process that apparently is used in fighting during mating season. The bill is broad and flattened.
There are two species of rheas. The common rhea (Rhea americana) is up to 170 cm tall and weighs up to 25 kg or greater. Its feathers are brownish or, sometimes, nearly white. The common rhea is found in the pampas and savannas of eastern South America, between 10° and 40° S lat. The bird is polygamous. Three to eight females lay 13 to 30 eggs in a single nest, which is constructed by the male. The male incubates and protects the eggs for 35 to 40 days. The smaller and more darkly colored long-billed rhea (Pterocnemia pennata) inhabits the arid mountain plateaus of the Andes from Peru to Patagonia. Rheas feed on leaves, shoots, and seeds, as well as on small vertebrates and insects. Because of intensified hunting, the number of rheas has sharply declined. In the USSR, rheas have been acclimatized to Askaniia-Nova.