The rheas are ratites (flightless birds, with unkeeled sterna) in the genus Rhea, native to South America. There are two existing species: the Greater or American Rhea and the Lesser Rhea.
Rheas tend to be silent birds with the exception being when they are chicks or when the male is seeking a mate. During the non-breeding season they may form flocks of between 10 and 100 birds, although the lesser rhea forms smaller flocks than this. When in danger they flee in a zigzag course, utilizing first one wing then the other, similar to a rudder. During breeding season the flocks break up.
They are omnivorous and prefer to eat broad-leafed plants, but also eat seeds, roots, fruit, lizards, beetles, grasshoppers, and carrion.