rhea rē´ə [key], common name for a South American bird of the family Rheidae, which is related to the ostrich. Weighing from 44 to 55 lb (20–25 kg) and standing up to 60 in. (152 cm) tall, the rhea is slightly smaller than the ostrich and lacks that bird's extravagant plumelike tail feathers. The rhea also differs from the unrelated ostrich in structure of the palate, pelvis, and foot. It is yellow and gray above, with a black head and dirty-white underside. The greater, or common, rhea (Rhea americana) is found from northeastern Brazil to Argentina. The somewhat smaller lesser, or Darwin's, rhea (Pterocnemia pennata) occurs from Patagonia to the high Andes. The rhea is typically a creature of the pampas and savannas and may often be found feeding in mixed herds along with cattle or guanaco, occupying an ecological niche similar to that of the ostrich and the zebra of Africa. Rheas feed on several kinds of plants, insects, and small vertebrates. While the old males tend to stay solitary, the young male is aggressive and highly polygamous, gathering about itself from three to seven hens. The nest is built in a dry and protected area, preferably near water. The male excavates a shallow hole with his bill, lines it with dry vegetable matter, and assumes all the incubation duties. He may incubate as many as 50 eggs, produced by a number of females over a period of weeks. Incubation takes from 35 to 40 days. The eggs, lemon yellow when laid, or greenish in the case of Darwin's rhea, weigh up to 2 lb (almost 1 kg) each. When hatched, the chicks are gray with darker stripes. The rhea is one of the flat-breastboned, or ratite, flightless birds. Rheas are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Struthioniformes, family Rheidae.
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