Therhea (/ˈriːə/REE-ə), also known as theñandú[a] (/njænˈduː/nyan-DOO) orSouth American ostrich,[3][4] is aSouth Americanratite (flightless bird without akeel on thesternum bone) of the order Rheiformes. Rheas are distantly related to the two Africanostriches and Australia'semu (the largest, second-largest and third-largest living ratites, respectively), with rheas placing just behind the emu in height and overall size.
Most taxonomic authorities recognize twoextant species: thegreater or American rhea (Rhea americana), and thelesser or Darwin's rhea (Rhea pennata). TheInternational Union for Conservation of Nature (IUCN) classifies thepuna rhea as another species instead of a subspecies of thelesser 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, having recovered from past threats to its survival. In addition, the feral population of the greater rhea in Germany appears to be growing. However, control efforts are underway and seem to succeed in controlling the birds' population growth. Similarly to ostriches and emus, rheas are fairly popular livestock and pets, regularly kept and bred on farms, ranches, private parks, and byaviculturists, mainly in North and South America and Europe.
The name "rhea" was used in 1752 byPaul Möhring and adopted as theEnglish common name. Möhring named the bird after theGreek TitanRhea, whoseAncient Greek name (Ῥέα) is thought to come fromἔρα (éra, "ground"). This was fitting with the rhea being a flightless ground bird. Depending on the South American region, the rhea is known locally asñandú guazu (Guaraní –or related Tupinhandú-gûasú– meaning "big spider"[5] most probably concerning their habit of opening and lowering alternate wings when they run),[citation needed]ema (Portuguese),suri (Aymara andQuechua),[6][7] orchoique (Mapudungun).Nandu is the common name in many European languages and may sometimes be heard in English.[3]
R. p. garleppi(Chubb 1913),puna/Garlepp's rhea of southeasternPeru, southwestern Bolivia and northwestern Argentina. It is included inR. tarapacensis by The International Union for Conservation of Nature (IUCN).
R. p. pennatad'Orbigny 1834, Darwin's lesser rhea ofPatagoniansteppes in southern Argentina and southern Chile
Rhea pennata was not always in the genusRhea. In 2008, theSACC, the last holdout, approved merging the generaRhea andPterocnemia on August 7, 2008. This merging of genera leaves only the genusRhea.[11] A former fourth species of rhea,Rhea nana, was described byLydekker in 1894 based on a singleegg found inPatagonia,[12] but today no major authorities consider it valid.
Rheas are large,flightless birds with grey-brownplumage, long legs, and long necks, similar to anostrich. Large males ofR. americana can reach 170 cm (67 in) tall at the head, 100 cm (39 in) at the back[13] and can weigh up to 40 kg (88 lb).[14] The lesser rhea is smaller, with a height of 100 cm (39 in).[13] Their wings are large for a flightless bird (250 cm (8.2 ft))[13] and are spread whilerunning, to act likesails.[15] Unlike most birds, rheas have only three toes. Theirtarsus has 18 to 22 horizontal plates on the front of it. They also storeurine separately in an expansion of thecloaca.[13]
Rheas are fromSouth America only and are limited within the continent toArgentina,Bolivia,Brazil,Chile,Paraguay,Peru andUruguay. They are grassland birds, and both species prefer open land. The greater rheas live in open grasslands,pampas andchaco 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 inhabit mostshrubland, grassland, even desert saltpuna up to 4,500 metres (14,800 ft).[13][16][17]
A small population of rheas has emerged inMecklenburg-Western Pomerania, northeasternGermany, after several couples escaped from an exotic meat farm nearLübeck in the late 1990s. Contrary to expectations, the large birds adapted well to conditions in the German countryside.[18] A monitoring system has been in place since 2008.[19] By 2014, there was already a population of well over 100 birds in an area of 150 square kilometres (58 sq mi) between the riverWakenitz and theA20 motorway, slowly expanding eastward.[20]
Feral greater rhea flock in Germany
The population grew steadily for several years. By autumn 2018, their numbers had significantly increased to about 600. As such, local farmers claim increasing damage to their fields, and some biologists say the rheas pose a growing risk to local wildlife. Still protected by German natural conservation law, a local discussion developed regarding how to handle the situation. Eventually, Mecklenburg-Western Pomerania's government allowed limited hunting of the birds, explicitly to just reduce the population's growth and not to wipe them out. At this point, it was generally agreed that the rheas should be allowed to stay in the region. By spring 2021, just 247 rheas were counted; this development was attributed to both the hunting and the increased caution of the animals. Several had begun to avoid humans more than previously and retreated into the woods.[21][22] Some members of this rhea population have also expanded into other areas; at least twice individual rheas who probably originated in Mecklenburg-Western Pomerania were sighted inBrandenburg'sHigh Fläming Nature Park, over 200 kilometres (120 mi) from their usual range.[23] By early 2023, 91 rheas were counted in Mecklenburg-Western Pomerania; the population decline was attributed to both hunting as well as harsher weather of previous years. By this point, German authorities believed a stable population of 50 adult birds would be optimal for the local ecosystem and agriculture. Researchers concluded that the feral population was subject to substantial fluctuations but remained healthy, adaptable, and entrenched in the area.[24]
There also appears to be a small population of wild rheas in theUnited Kingdom. In March 2021, about 20 rheas were reportedly running free on a residential estate inHertfordshire. Local police could not identify any owner, so they assumed they were wild birds. Once caught, authorities intend to place them in a suitable nature reserve to allow them to develop as a colony.[25]
Rheas tend to be silent birds, except when they are chicks or the male seeks a mate. During the 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 and 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, he will wave his neck back and forth in a figure eight. Finally, a female may offer herself, and copulation will commence.[13]
During the non-breeding season they may form flocks of between 20 and 25 birds,[26] although the lesser rhea forms smaller flocks than this. When in danger, they flee in azigzag course, using one wing and the other, similar to a rudder. During the breeding season, the flocks break up.[13]
Mostly, rheas are herbivorous and prefer broad-leafed plants, but they also eat fruits, seeds, roots, and insects such as grasshoppers, small reptiles, and rodents.[13] Young rheas eat only insects for the first few days. Outside the breeding season, they gather in flocks and feed with deer and cattle.[26]
Rheas are polygynandrous, with males courting between two and twelve females and females commonly mating with multiple dominant males during the breeding season. After mating, the male builds a nest where each female lays eggs. The nest is a simple scrape in the ground, lined with grass and leaves.[15] The male incubates from ten to sixty eggs. The male will use a decoy system and place some eggs outside the nest, then sacrifice these to predators so they do not attempt to get inside the nest. The male may use another subordinate male to incubate his eggs while he finds another group of females to start a second nest with.[13] The chicks hatch within 36 hours of each other. Right before hatching, the chicks begin to whistle.[27] The group of females, meanwhile, may move on and mate with other males. While caring for the young, the males will charge at any perceived threat approaching 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.[15]
The numbers of the greater and puna rhea are decreasing as their habitats shrink. Both are considerednear threatened by the IUCN. The IUCN also states that they are both approachingvulnerable status.[28][16][17][29] The lesser rhea is classified asleast concern.[30]
Rheas have many uses in South America. Feathers are used for feather dusters, skins are used for cloaks or leather, and their meat is astaple to many people.[13]
Gauchos traditionally hunt rheas on horseback, throwingbolas orboleadoras—a throwing device consisting of three balls joined by rope—at their legs, which immobilises the bird.[26] The rhea is pictured onArgentina's 1-centavo coin minted in 1987, and on theUruguayan 5-peso coin.
^Radio San Gabriel, "Instituto Radiofonico de Promoción Aymara" (IRPA) 1993, Republicado por Instituto de las Lenguas y Literaturas Andinas-Amazónicas (ILLLA-A) 2011, Transcripción del Vocabulario de la Lengua Aymara, P.Ludovico Bertonio 1612 (Spanish-Aymara-Aymara-Spanish dictionary)
^Brisson, Mathurin Jacques (1760).Ornithologie, ou, Méthode Contenant la Division des Oiseaux en Ordres, Sections, Genres, Especes & leurs Variétés (in French and Latin). Paris: Jean-Baptiste Bauche.Vol. 1, p. 46,Vol. 5, p. 8.
^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. Retrieved4 February 2009.
^Knox, A.; Walters, M. (1994).Extinct and Endangered Birds in the Collections of the Natural History Museum. British Ornithologists' Club Occasional Publications. Vol. 1. British Ornithologists' Club.
^abcdefghijDavies, S. J. J. F. (2003). "Rheas". In Hutchins, Michael (ed.).Grzimek's Animal Life Encyclopedia. Vol. 8 Birds I Tinamous and Ratites to Hoatzins (2nd ed.). Farmington Hills, MI: Gale Group. pp. 69–71.ISBN0-7876-5784-0.
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