Rheidae is a family of large, flightless birds commonly known as rheas. They are native to South America and are primarily found in open grasslands and savannas. Rheas are characterized by their long legs, large bodies, and soft, grayish-brown feathers. They are similar in appearance to ostriches but are smaller in size. These birds are omnivorous, feeding on a diet that includes plants, seeds, and insects. Rheas are social animals, often seen in groups, and they are known for their unique mating system, where males incubate the eggs and care for the young after hatching.