Temporal range: pleistocene–present Pleistocene to present
|American Rhea, Rhea americana|
The rheas are ratites (flightless birds with unkeeled sterna) in the genus Rhea, native to South America. There are two extant species: the Greater or American Rhea and the Lesser or Darwin's Rhea. The genus name was given in 1752 by Paul Möhring and adopted as the English common name. Möhring's named the rhea based on the Greek Titan Rhea, whose name is derived from the Greek Rhea (῾Ρέα) by metathesis from έρα "ground". This was fitting, the rhea being a flightless ground bird. Depending on the South American region, the rhea is known locally as ñandú guazu (Guaraní, meaning big spider, most probably in relation to their habit of opening and lowering alternatively wings when they run), ema (Portuguese), suri (Quechua), or choique (Mapudungun).
Taxonomy and systematics 
The recognized extant species are:
- Greater Rhea Rhea americana
- R. a. americana, found in the cerrados (bushlands) of central and eastern Brazil.
- R. a. intermedia, southeastern Brazil in Rio Grande do Sul and Uruguay.
- R. a. nobilis, eastern Paraguay, east of Rio Paraguay.
- R. a. araneipes, chaco of Paraguay to Bolivia and Mato Grosso in Brazil.
- R. a. albescens, plains of Argentina south to Rio Negro.
- Lesser Rhea Rhea pennata
Rhea pennata was not always in the Rhea genus. In 2008 the SACC, the last holdout, approved the merging of the genera, Rhea and Pterocnemia on August 7, 2008. This merging of genera leaves only the Rhea genus. A third species of rhea, Rhea nana, was described by Lydekker in 1894 based on a single egg found in Patagonia, but today no major authorities consider it valid.
Rheas are large, flightless birds with gray-brown plumage, long legs and long necks, similar to an ostrich. Large males of R. americana can reach 170 cm (67 in) tall at the head, 100 cm (39 in) at the back and can weigh up to 40 kg (88 lb), The Lesser Rhea is somewhat smaller as they are only 90 cm (35 in) tall at the back. Their wings are large for a flightless bird (250 cm (8.2 ft)) and are spread while running, to act like sails. Unlike most birds, rheas have only three toes. Their tarsus has 18 to 22 horizontal plates on the front of it. They also store urine separately in an expansion of the cloaca.
Distribution and habitat 
Rheas are from South America only and are limited within the continent to Argentina, Bolivia, Brazil, Chile, Paraguay, Peru, and Uruguay. They are grassland birds and both species prefer open land. The Greater Rhea live in open grasslands, pampas, and chaco woodlands. They prefer to breed near water and prefer lowlands, seldom going above 1,500 metres (4,900 ft). On the other hand, the Lesser Rhea will utilize most shrubland, grassland, even desert salt puna up to 4,500 metres (14,800 ft).
Behavior and ecology 
Individual and flocking 
Rheas tend to be silent birds with the exception being when they are chicks or when the male is seeking a mate. During breeding season, the male will attempt to attract females by calling. This call is a loud booming noise. While calling like this, they will lift the front of their body, ruffle their plumage, all while keeping their neck stiff. They will then extend and raise their wings, and run short distances, alternating with their wings. He may then single out a female and walk alongside or in front of her with a lowered head and spread wings. If the female notices him, then he will wave his neck back and forth in a figure-eight. Finally, a female may offer herself and copulation will commence. During the non-breeding season they may form flocks of between 10 and 100 birds, although the lesser rhea forms smaller flocks than this. When in danger they flee in a zig-zag course, utilizing first one wing then the other, similar to a rudder. During breeding season the flocks break up.
Rheas are polygamous, with males courting between two and twelve females. After mating, the male builds a nest, in which each female lays her eggs in turn. The nest consists of a simple scrape in the ground, lined with grass and leaves. The male incubates from ten to sixty eggs. The male will utilize a decoy system and place some eggs outside the nest and sacrifice these to predators, so that they won't attempt to get inside the nest. The male may utilize another subordinate male to incubate his eggs, while he finds another harem to start a second nest. The chicks hatch within 36 hours of each other. The females, meanwhile, may move on and mate with other males. While caring for the young, the males will charge at any perceived threat that approach the chicks including female rheas and humans. The young reach full adult size in about six months but do not breed until they reach two years of age.
Status and conservation 
Both the Lesser Rhea and the Greater Rhea are seeing shrinking wild numbers and shrinking habitat. Both are considered near threatened by the IUCN and have been for the last 15 years. The IUCN also states that they are both approaching vulnerable status.
Human interaction 
Rheas have many uses in South America. Feathers are used for feather dusters, skins are used for cloaks or leather, and their meat is a staple to many people. The Rhea is pictured on the coinage of Argentina's 1 Centavo coin minted in 1987.
- Brands, S. (2008)
- Clements, J. (2007)
- Remsen, Jr., J. V. (2008)
- Knox, A.; Walters, M. (1994)
- Davies, S. J. J. F. (2003)
- Martin, W. C. L. (1835)
- Davies, S. J. J. F. (1991)
- Birdlife International (2012)
- Birdlife International (2012) a
- Symes, A. & Butchart, S. (2008)
- Symes, A. & Butchart, S. (2008)a
- BirdLife International (2012). "Greater Rhea Rhea americana". Data Zone. Retrieved 15 Jun 2012.
- BirdLife International (2012a). "Lesser Rhea Rhea pennata". Data Zone. Retrieved 15 Jun 2012.
- Brands, Sheila (August 14, 2008). "Systema Naturae 2000 / Classification, Family Rheidae". Project: The Taxonomicon. Retrieved Feb 04 2009.
- Clements, James (2007). The Clements Checklist of the Birds of the World (6 ed.). Ithaca, NY: Cornell University Press. ISBN 978-0-8014-4501-9.
- Davies, S. J. J. F. (2003). "Rheas". In Hutchins, Michael. Grzimek's Animal Life Encyclopedia. 8 Birds I Tinamous and Ratites to Hoatzins (2 ed.). Farmington Hills, MI: Gale Group. pp. 69–71. ISBN 0-7876-5784-0.
- Davies, S. J. J. F. (1991). In Forshaw, Joseph. Encyclopaedia of Animals: Birds. London: Merehurst Press. pp. 47–48. ISBN 1-85391-186-0.
- Knox, A.; Walters, M. (1994). Extinct and Endangered Birds in the Collections of the Natural History Museum. British Ornithologists' Club Occasional Publications 1. British Ornithologists' Club.
- Martin, W. C. L. (1835). An introduction to study of birds. London, UK: Chiswick. p. 400
- Remsen Jr., J. V.; et al. (7 August 2008). "Classification of birds of South America Part 01:". South American Classification Committee. American Ornithologists' Union. p. Proposal#348. Retrieved 4 February 2009.
- Symes, A. & Butchart, S. (2008). Rhea americana. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 16 Jun 2012.
- Symes, A. & Butchart, S. (2008a). Rhea pennata. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 16 Jun 2012.
- Rhea videos on the Internet Bird Collection
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