The rhea, often called the South American ostrich, is a large, flightless bird native to the diverse landscapes of South America. As a member of the order Rheiformes, rheas are classified as ratites, a group of birds characterized by a flat breastbone that lacks the keel found in most flying birds. They share a distant ancestry with other prominent flightless birds such as the African ostrich and Australia’s emu.
Distinctive Features
The greater rhea (Rhea americana) typically stands between 1.4 to 1.7 meters (4.6 to 5.6 feet) tall and weighs between 20 to 27 kilograms (44 to 60 pounds). Some larger males can reach heights of 1.83 meters (6 feet) and weigh up to 40 kilograms (88 pounds). Their bodies feature long necks and strong, lengthy legs, ending in three-toed feet adapted for swift movement. Unlike ostriches, which have only two toes, rheas possess three toes with sharp claws, with the middle toe being notably larger.
Their plumage is generally a dull gray or brown, providing effective camouflage within their habitats. Despite being flightless, rheas have large wings, spanning up to 2.5 meters (8.2 feet) in some greater rheas. These wings are used for balance and steering during high-speed running, and also play a role in courtship displays.
Life in the Wild
Rheas inhabit a range of open environments across South America, including grasslands, savannas, pampas, and open woodlands, typically avoiding dense forests. They are found in countries such as Argentina, Bolivia, Brazil, Paraguay, and Uruguay. While they generally prefer lower elevations, some species, like the puna rhea, can thrive at altitudes up to 4,500 meters (14,800 feet).
These birds are omnivorous, consuming a varied diet that includes broad-leaved plants, seeds, fruits, roots, and insects like grasshoppers. They also prey on small vertebrates such as lizards, frogs, and small birds. To aid digestion of tough plant matter, rheas swallow small pebbles, similar to other birds that consume fibrous foods.
Outside of the breeding season, rheas are social animals, often forming flocks that can range from 10 to 100 individuals. They are diurnal and known for their running speed, capable of reaching up to 60 kilometers per hour (37 miles per hour). When threatened, they employ a zigzag running pattern, using their wings to assist in quick turns and maintain balance, helping them evade predators.
Breeding and Rearing
The reproductive cycle of rheas is notable for the prominent role of the male. Rheas exhibit a polygynous mating system where a single male mates with multiple females. During the breeding season, which typically runs from August to January, males develop a dark collar and engage in courtship displays, including booming calls and wing movements, to attract females.
After mating, the male constructs a nest, which is usually a shallow depression scraped into the ground and lined with vegetation. Several females will lay their eggs in this single nest, with a male incubating a large clutch that can number from 10 to 60 eggs, or even up to 80 eggs from a dozen different females. The eggs are large, averaging about 13 cm (5 inches) long, and are typically gold-colored or greenish-yellow, fading to cream upon exposure to light.
The male rhea takes on the primary responsibility for incubating the eggs for approximately six weeks, and then solely cares for the newly hatched chicks for several months. Male rheas are fiercely protective of their young, charging at any perceived threat. Chicks are gray with dark stripes and reach adult size within about six months, although they do not become reproductively mature until around two years of age.
Conservation and Human Interaction
Rhea populations face several challenges, primarily from habitat loss and fragmentation due to agricultural expansion and human development. Hunting also poses a threat, as rheas are sought after for their meat, eggs, feathers, and their skin, which is used for leather. The fat from rheas is also processed into oil.
The greater rhea is currently listed as “Near Threatened” by the International Union for Conservation of Nature (IUCN), due to a decreasing population trend. While some populations are recovering, others are approaching vulnerable status. Conservation efforts often focus on monitoring illegal trade, enforcing hunting restrictions, and preserving remaining natural habitats. Rheas are also farmed in some areas.