These large South American birds roam the open pampas and sparse woodlands of Argentina and Brazil. The greater rhea is the largest of all South American birds and is related to ostriches and emus. These flightless birds use their long, powerful legs to outrun trouble. Although their large wings are useless for flight, they are used for balance and for changing direction as the bird runs.

The Greater Rhea is among the largest living birds. Its long, powerful legs carry a football-shaped body with a long protruding neck that can dip to the ground to feed and rise above tall grass to scan for danger. The plumage is gray, with black around the head, neck, and shoulders, lighter gray feathering the legs, and white on the underparts. The rhea, like all ratites, cannot fly, but retains large wings with which it supports bursts of running and performs impressive displays for mates and competitors. Its distinctive profile can be identified from a distance, and in its native habitat could only be mistaken for its sister species, the Lesser Rhea (Rhea pennata).