The greater rhea (Rhea americana) is a flightless bird found in eastern South America. Other names for the greater rhea include the grey, common, or American rhea; ñandú (Guaraní); or ema (Portuguese). One of two species in the genus Rhea, in the family Rheidae, the greater rhea is endemic to Argentina, Bolivia, Brazil, Paraguay and Uruguay. It inhabits a variety of open areas, such as grasslands, savanna or grassy wetlands. Weighing 50–55 pounds (23–25 kg), the greater rhea is the largest bird in South America. In the wild, the greater rhea has a life expectancy of 10.5 years. It is also notable for its reproductive habits, and for the fact that a group has established itself in Germany in recent years.
The adults have an average weight of 20–27 kg (44–60 lb) and often measure 127 to 140 cm (50 to 55 in) long from beak to tail; they usually stand about 1.5 m (4.9 ft) tall to the top of the head. The males are generally bigger than the females. Large males can weigh up to 40 kg (88 lb), stand nearly 1.83 m (6.0 ft) tall and measure over 150 cm (59 in) long, although this is rare.
The head and bill are fairly small, the latter measuring 8–10.4 cm (3.1–4.1 in) in length. The legs are long, with the tarsus measuring between 33.5 and 37 cm (13.2 and 14.6 in), and strong and have 22 horizontal plates on the front of the tarsus. They have three toes, and the hind toe is absent. The wings of the American rhea are rather long; the birds use them during running to maintain balance during tight turns, and also during courtship displays.
Greater rheas have a fluffy, tattered-looking plumage, that is gray or brown, with high individual variation, The head, neck, rump, and thighs are feathered. In general, males are darker than females. Even in the wild—particularly in Argentina—leucistic individuals (with white body plumage and blue eyes) as well as albinos occur. Hatchling greater rheas are grey with dark lengthwise stripes.
The greater rhea derives its scientific name from Rhea, a Greek goddess, and the Latinized form of America. It was originally described by Carolus Linnaeus in his 18th-century work, Systema Naturae under the name Struthio camelus americanus. He identified specimens from Sergipe, and Rio Grande do Norte, Brazil, in 1758. They are from the family Rheidae, and the order Struthioniformes, commonly known as ratites. They are joined in this order by emus, ostriches, cassowaries, and kiwis, along with the extinct forms moas, and elephant birds.
There are five subspecies of the greater rhea; their ranges meet around the Tropic of Capricorn:
- R. a. americana – campos of northern and eastern Brazil
- R. a. intermedia – Uruguay and extreme southeastern Brazil (Rio Grande do Sul state)
- R. a. nobilis – eastern Paraguay, east of Rio Paraguay
- R. a. araneipes – chaco of Paraguay and Bolivia and the Mato Grosso state of Brazil
- R. a. albescens – plains of Argentina south to the Rio Negro province
Main subspecific differences are the extent of the black coloring of the throat and the height.
However, subspecies of the greater rhea differ so little across their
range that, without knowledge of the place of origin, it is essentially
impossible to identify captive birds by subspecies.
