Rheas: Profile and Information

Rheas are large flightless birds that lack a keel in their sternum bone.

They are also called ratites, a genus under the order Rheiformes, endemic to South America, distantly related to the emu and ostrich.

Most taxonomic authorities recognize two extant species: the American or greater rhea (Rhea Americana) and the lesser or Darwin’s (Rhea pennata).

The IUCN recognizes the puna rhea (Rhea tarapacensis) as a separate species.

The IUCN currently rates Darwin’s rheas as Least Concern, while the puna and greater rheas are Near-Threatened in their native ranges.

Scientific Classification

Species Classification

Extant species

Extinct species

• †R. fossilis 
• †R. mesopotamica
• †R. pampeana
• †R. subpampeana

Characteristics

Rheas are large, flightless birds with long legs, long necks, and grey-brown plumage, similar to the ostrich. Large males of the species R.

Americana can reach 67 in (170 cm) tall at the head, 39 in (100 cm) at the back, and can weigh up to 88 lb (40 kg).

The lesser/Darwin’s rhea is smaller as they are only 39 inches (100 cm) tall at the back. The wings of a rhea measure up to 8.2 ft (250 cm), which are spread while running to act like sails (for more speed).

Distinct from most birds, rheas possess only three toes. Their tarsus has 18 – 22 horizontal plates on the front of it.

Reproduction

Rheas practice polygamy, with males courting 2 to 12 females. After mating, the males show paternal care by building a nest where all their partners lay their eggs.

The male incubates from 10 – 60 eggs. The male sacrifices a few eggs as a decoy to predators, preventing them from getting to the nest.

The paternal male may use a subordinate male to incubate the eggs while he searches for another harem to build a second nest.

The chicks hatch within 2160 minutes (36 hours) of each other. The females show no maternal care and move on to mate with other males.

While caring for or protecting the young, the male will charge at any threat approaching the chicks, including humans and female rheas.

The young reach full size in about 6 months but do not breed until they reach 2 years of age.

Diet

During most of their life, rheas are vegetarians and prefer broad-leafed plants, but they also eat roots, seeds, fruits, grasshoppers, rodents, and small reptiles.

After birth, the young rheas (chicks) feed on only insects for the first few days. Outside the mating season, they gather in flocks and feed cattle and deer.

Behavior

Rheas are silent birds, except a male seeking a mate or when they are chicks. During the mating season, the male tries to attract females by calling (a loud booming noise).

While calling, they will lift the front part of their body, ruffle their plumage, and keep their neck stiff. They will then spread and raise their wings and run short distances.

During the non-mating season, they may form flocks between 20 – 25 birds, although the lesser rhea (Rhea pennata) forms smaller flocks than this.

Habitat and Distribution

Rheas are native to South America only and are limited within the continent to Bolivia, Argentina, Chile, Bolivia, Paraguay, Brazil, Uruguay, and Peru.

Both species prefer open land as they are grassland birds. The greater rheas live in pampas, open grasslands, and Chaco woodlands. They usually breed near water and prefer lowlands, seldom going above 4,900 ft (1,500 meters).

However, the lesser rhea will inhabit most grassland, shrubland, and even desert salt puna up to 14,800 ft (4,500 meters).