rhea (bird)

The rheas ( ), also known as ñandus ( ) or South American ostriches, are large ratites ( flightless birds without a keel on their sternum bone) in the order Rheiformes, native to South America, distantly related to the ostrich and emu. Most taxonomic authorities recognize two extant species: the greater or American rhea (''Rhea americana''), and the lesser or Darwin's rhea (''Rhea pennata''). The International Union for Conservation of Nature (IUCN) classifies the puna rhea as another species instead of a subspecies of the lesser rhea. The IUCN currently rates the greater and puna rheas as near-threatened in their native ranges, while Darwin's rhea is of least concern. In addition, a feral population of the greater rhea in Germany appears to be growing, though control efforts are underway, and seem to be succeeding in controlling the birds' population growth.

Etymology

The name "rhea" was used in 1752 by Paul Möhring and adopted as the English common name. Möhring named the rhea after the Greek Titan Rhea, whose Ancient Greek name () is thought to come from "ground". This was fitting with the rhea being a flightless ground bird. Depending on the South American region, the rhea is known locally as ( Guaraní, meaning big spider, most probably in relation to their habit of opening and lowering alternate wings when they run), ( Portuguese), ( Aymara and Quechua), or ( Mapudungun). is the common name in many European languages and may sometimes also be heard in English.

Taxonomy and systematics

The genus ''Rhea'' was introduced by the French zoologist Mathurin Jacques Brisson in 1760 with the greater rhea (''Rhea americana'') as the type species.

Extant species

The genus contains two extant species and eight subspecies, although one subspecies is disputed:

''Rhea pennata'' was not always in the genus ''Rhea''. 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 genus ''Rhea''. A former fourth 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.

Fossils

* †'' R. anchorenense'' (Ameghino & Rusconi 1932) 'Rhea americana anchorenense'' Amcghino & Rusconi 1932* †'' R. fossilis'' (Moreno & Mercerat 1891) 'Pterocnemia fossilis'' (Moreno & Mercerat 1891); ''Rhea pampeana'' (Moreno & Mercerat 1891)]
* †''Rhea mesopotamica, R. mesopotamica'' (Agnolín & Noriega 2012) [''Pterocnemia mesopotamica'' Agnolín & Noriega 2012]
* †''Rhea subpampeana, R. subpampeana'' Moreno & Mercerat 1891

Description

Rheas are large, flightless birds with grey-brown plumage, long legs and long necks, similar to an ostrich. Large males of ''R. americana'' can reach tall at the head, at the back and can weigh up to . The lesser rhea is smaller, with a height of . Their wings are large for a flightless bird () 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 rheas live in open grasslands, pampas, and chaco woodlands. They prefer to breed near water and prefer lowlands, seldom going above . On the other hand, the lesser rhea will inhabit most shrubland, grassland, even desert salt puna up to .

Feral populations in Europe

A small population of rheas has emerged in Mecklenburg-Western Pomerania, northeastern Germany, after several couples escaped from an exotic meat farm near Lübeck in the late 1990s. Contrary to expectations, the large birds adapted well to conditions in the German countryside. A monitoring system has been in place since 2008. By 2014, there was already a population of well over 100 birds in an area of between the river Wakenitz