Rheidae (rheas; class Aves, order Rheiformes) A family of large, ostrich-like birds which have long necks, wide, flat bills, short wings with soft feathers, and no tail feathers. Their body plumage is grey-brown and loose-webbed. Their legs are powerful, with three toes, enabling them to run swiftly. They are terrestrial and flightless, inhabit grassland and open brush, feed on vegetable matter and insects, and nest on the ground. Rhea americana (common rhea) has grey upper-parts and white under-parts, the male having a black base to its neck. Pterocnemia pennatus (Darwin's rhea) is similar, but smaller and with white spots. There are two monotypic genera, found in S. America.

Rheiformes (rheas; class Aves) An order which comprises one family, Rheidae.

rheas See RHEIDAE.