The rheas are ratites (flightless bird

Flightless bird

Flightless birds are birds which lack the ability to fly, relying instead on their ability to run or swim. They are thought to have evolved from flying ancestors. There are about forty species in existence today, the best known being the ostrich, emu, cassowary, rhea, kiwi, and penguin...

s, with unkeeled sterna) in the genus Rhea, native to South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

. There are two existing species: the Greater or American Rhea and the Lesser or Darwin's Rhea

Darwin's Rhea

Darwin's Rhea, Rhea pennata, also known as the Lesser Rhea, is a large flightless bird, but the smaller of the two extant species of rheas. It is found in the Altiplano and Patagonia in South America.-Description:...

. The genus name was given in 1752 by Paul Möhring

Paul Möhring

Paul Heinrich Gerhard Möhring , aka Paul Mohr, was a German physician, botanist and zoologist.Möhring was physician to the Prince of Anhalt. In 1752 he published Avium Genera, an early attempt to classify bird species, which divided birds into four classes and shows the beginnings of the modern...

 and adopted as the English common name. Möhring's reason for choosing this name, from the Rhea

Rhea (mythology)

Rhea was the Titaness daughter of Uranus, the sky, and Gaia, the earth, in Greek mythology. She was known as "the mother of gods". In earlier traditions, she was strongly associated with Gaia and Cybele, the Great Goddess, and was later seen by the classical Greeks as the mother of the Olympian...

 of classical mythology, is not known. Depending on the South American region, the rhea is known locally as ñandú guazu (Guaraní

Guaraní language

Guaraní, specifically the primary variety known as Paraguayan Guaraní , is an indigenous language of South America that belongs to the Tupí–Guaraní subfamily of the Tupian languages. It is one of the official languages of Paraguay , where it is spoken by the majority of the population, and half of...

, meaning big spider, most probably in relation to their habit of opening and lowering alternatively wings when they run), ema (Portuguese

Portuguese language

Portuguese is a Romance language that arose in the medieval Kingdom of Galicia, nowadays Galicia and Northern Portugal. The southern part of the Kingdom of Galicia became independent as the County of Portugal in 1095...

), suri (Quechua

Southern Quechua

Southern Quechua , or only Quechua, is the most widely spoken of the major regional groupings of mutually intelligible dialects within the Quechua language family, with about 5 million speakers...

), or choique (Mapudungun).
Rheas are large, flightless birds with gray-brown plumage

Plumage

Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...

, long legs and long necks, similar to an ostrich

Ostrich

The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...

.