Although rheas look very similar to their larger cousin the ostrich, there are several differences, including their size, toes, and child-rearing habits. Rheas’ plumage is typically in shades of gray and brown, with white underneath. Where ostriches have two toes on each foot, rheas have three toes per foot which allows them better balance.

The rhea participates in one of the most rare child-rearing practices. Once the female has laid her eggs, it is the father who incubates them and raises the fledglings. During this time male rheas are very protective, and will charge at anything or anyone who gets too close. Rheas are a species of ratite, a specific type of flightless bird which have a ratite skeleton. These birds have a flat, cartilaginous breastbone in place of the keel which allows most birds to fly. The keel is an anchor for a bird’s strong pectoral muscles. Without one, the bird does not have the muscle strength to fly. Other members of the ratite group include ostriches, emus, and kiwis.

Rheas have unusually long wings for flightless birds, and they use them like airplane rudders to balance while running and to help them dodge predators like cougars and pampas cats. Greater rheas are very fast, running up to 40 miles per hour. They will also swim to avoid predators.