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.

Greater rheas are polygamous, so males have many different mates. Females lay their eggs—one every other day for a week or ten days—in a ground nest of the male's design. Several females deposit their eggs in the same nest, which may hold 50 eggs or more.

The male rhea incubates the eggs of all its mates for six weeks and cares for the newly hatched young. They aggressively guard their young during this period and will charge any animal—even a female rhea—that approaches too closely.

Males are solitary in the spring breeding season, but in winter, rheas are social and flock together. They often congregate with other large animals, such as deer and guanacos, and form mixed herds.

Greater rheas are opportunistic eaters. They enjoy plants, fruits, and seeds but also eat insects, lizards, birds, and other small game. Rheas have a taste for agricultural crops, which earns them the ire of many South American farmers. As more open grasslands are converted to farmland, this problem grows.

Rhea eggs are collected for food and many people eat their meat. Their skins are used in the manufacture of leather, and hunting to supply this trade has thinned their numbers considerably. Today, regulations have limited both hunting and farming rhea for these commercial uses.