Rhea (bird)

The rheas (/ˈriːə/) 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 IUCN lists the puna rhea (Rhea tarapacensis) as a separate species. 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.

Rheas
Temporal range: Pleistocene-Holocene 0.126–0 Ma
↓
Two greater rheas
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Rheiformes
Family: Rheidae
Genus: Rhea
Brisson, 1760
Type species
Struthio americanus
Species
  • †R. fossilis
  • †R. mesopotamica
  • †R. pampeana
  • †R. subpampeana
  • R. americana American rhea
  • R. pennata Darwin's rhea
Synonyms
  • Rhea Moehring 1758 nomen dubium
  • Pterocnemia Gray 1870
  • Toujou Lacépède 1801
  • Tujus Rafinesque 1815

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 Greek name (῾Ρέα) is thought to come from ἔρα "ground". This was fitting with 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 alternate wings when they run), ema (Portuguese), suri (Aymara and Quechua),[1][2] or choique (Mapudungun). Nandu is the common name in many European languages.

Taxonomy and systematics
Greater rheas (Rhea americana) dustbathing. The two individuals on the left are leucistic.

The genus Rhea was introduced by the French zoologist Mathurin Jacques Brisson in 1760 with the greater rhea (Rhea americana) as the type species.[3][4]

Extant species

The genus contains two extant species and eight subspecies:[5]

ImageScientific nameCommon NameSubspeciesDistribution
Rhea americana (Linnaeus, 1758)Greater rhea
  • R. a. americana (Linnaeus, 1758), live in the cerrados (bushlands) and caatinga of central and eastern Brazil.
  • R. a. intermedia Rothschild & Chubb 1914, intermediate rhea of southeastern Brazil in Rio Grande do Sul and Uruguay.
  • R. a. nobilis Brodkorb 1939, eastern Paraguay, east of Rio Paraguay.
  • R. a. araneipes Brodkorb 1938, chaco of Paraguay to Bolivia and Mato Grosso in Brazil.
  • R. a. albescens Lynch & Holmberg 1878, plains of Argentina south of Rio Negro.
 Argentina, Bolivia, Brazil, Paraguay and Uruguay
Rhea pennata d'Orbigny 1834Darwin's rhea or lesser rhea
  • R. p. garleppi (Chubb 1913), puna/Garlepp's rhea of southeastern Peru, southwestern Bolivia, and northwestern Argentina. It is included in R. tarapacensis by The International Union for Conservation of Nature (IUCN).
  • R. p. tarapacensis (Chubb 1913), Tarapacá Rhea of northern Chile from Atacama to Tarapacá. Regarded as a separate third species by the IUCN.[6]
  • R. p. pennata d'Orbigny 1834, Darwin's lesser rhea of Patagonian steppes in southern Argentina and southern Chile.
 Altiplano and Patagonia in South America.

Fossils
  • †R. fossilis Moreno & Mercerat 1891
  • †R. mesopotamica (Agnolín & Noriega 2012) [Pterocnemia mesopotamica Agnolín & Noriega 2012]
  • †R. pampeana Moreno & Mercerat 1891
  • †R. subpampeana Moreno & Mercerat 1891

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.[7] A former third species of rhea, Rhea nana, was described by Lydekker in 1894 based on a single egg found in Patagonia,[8] but today no major authorities consider it valid.

Description
Greater rhea head close up

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 170 cm (67 in) tall at the head, 100 cm (39 in) at the back[9] and can weigh up to 40 kg (88 lb),[10] The lesser rhea is somewhat smaller as they are only 90 cm (35 in) tall at the back.[9] Their wings are large for a flightless bird (250 cm (8.2 ft))[9] and are spread while running, to act like sails.[11] 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.[9]

Distribution and habitat
A rhea at the Parque Luro, Argentina

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 1,500 metres (4,900 ft). On the other hand, the lesser rhea will inhabit most shrubland, grassland, even desert salt puna up to 4,500 metres (14,800 ft).[9][12][13]

A small population of rheas has emerged in northeastern Germany, after several couples escaped from an exotic meat farm near Lübeck in the late 1990s. Contrary to expectations, the large birds have adapted well to the conditions in the German countryside.[14] Currently there is a population of well over 100 birds in an area of 150 square kilometres (58 sq mi) between the river Wakenitz and the A20 motorway, slowly expanding eastwards.[15] A monitoring system has been in place since 2008.[16] The population is steadily growing. After the relatively long and cold winter 2017/2018 the number of Rheas dropped slightly to 205 in March 2018. However, in autumn 2018 their number drastically increased to about 566. Therefore, local farmers are claiming increasing damages on their fields and some biologists claim the growing risk of Rheas becoming a threat for local wildlife. Still protected by German natural conservation law there is a local discussion how to handle the situation. Occasional farmers were allowed to hunt down male Rheas in small numbers as part of a compromise. Research on these bodies will hopefully encourage further knowledge about the influence of the German Rhea population on their new environment.

Behavior
Rhea skeleton

Individual and flocking
Feral greater rhea flock in Germany.

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.[9]

During the non-breeding season they may form flocks of between 20 and 25 birds,[17] although the lesser rhea forms smaller flocks than this. When in danger they flee in a zig-zag course, using first one wing then the other, similar to a rudder. During breeding season the flocks break up.[9]

Diet

For the most part, rheas are vegetarian and prefer broad-leafed plants but they also eat fruits, seeds and roots, as well as insects such as grasshoppers and small reptiles and rodents.[9] Young rheas generally eat only insects for the first few days. Outside of the breeding season they gather in flocks and feed with deer and cattle.[17]

Reproduction

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.[11] The male incubates from ten to sixty eggs. The male will use a decoy system and place some eggs outside the nest and sacrifice these to predators, so that they do not attempt to get inside the nest. The male may use another subordinate male to incubate his eggs, while he finds another harem to start a second nest.[9] 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.[11]

Status and conservation

The numbers of both the greater and puna rhea are decreasing as their habitats are shrinking. Both are considered near threatened by the IUCN. The IUCN also states that they are both approaching vulnerable status.[12][13][18][6] The lesser rhea is classified as least concern.[19]

Human interaction
Rhea meat

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.[9]

The gaucho people traditionally hunt rheas on horseback, throwing bolas or boleadoras — a throwing device consisting of three balls joined by rope — at their legs, which immobilises the bird.[17] The rhea is pictured on Argentina's 1 Centavo coin minted in 1987, and on the Uruguayan 5 peso coin.

References
  1. 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)
  2. Teofilo Laime Ajacopa, Diccionario Bilingüe Iskay simipi yuyayk'ancha, La Paz, 2007 (Quechua-Spanish dictionary)
  3. 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.
  4. Mayr, Ernst; Cottrell, G. William, eds. (1979). Check-list of Birds of the World. Volume 1 (2nd ed.). Cambridge, Massachusetts: Museum of Comparative Zoology. p. 5.
  5. Gill, Frank; Donsker, David, eds. (2019). "Ratites: Ostriches to Tinamous". World Bird List Version 9.1. International Ornithologists' Union. Retrieved 4 April 2019.
  6. BirdLife International (2016). "Rhea tarapacensis". IUCN Red List of Threatened Species. 2016: e.T22728206A94974751. doi:10.2305/IUCN.UK.2016-3.RLTS.T22728206A94974751.en.CS1 maint: uses authors parameter (link)
  7. 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.
  8. 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.
  9. Davies, S. J. J. F. (2003). "Rheas". In Hutchins, Michael (ed.). Grzimek's Animal Life Encyclopedia. 8 Birds I Tinamous and Ratites to Hoatzins (2nd ed.). Farmington Hills, MI: Gale Group. pp. 69–71. ISBN 0787657840.
  10. Martin, W. C. L. (1835). An introduction to study of birds. London: Chiswick. p. 400.
  11. Davies, S. j. j. f. (1991). Forshaw, Joseph (ed.). Encyclopaedia of Animals: Birds. London: Merehurst Press. pp. 47–48. ISBN 1853911860.
  12. BirdLife International (2012). "Greater Rhea Rhea americana". Data Zone. Retrieved 15 June 2012.
  13. BirdLife International (2012). "Lesser Rhea Rhea pennata". Data Zone. Retrieved 15 June 2012.
  14. Kulke, Ulli (2 January 2010). "Nandus - ein tierisches Einwanderungsproblem" [Rheas - an animal immigration problem]. Die Welt (in German). Retrieved 5 November 2014.
  15. "Mecklenburg-Vorpommern: Nandus vergrößern ihren Lebensraum weiter" [Mecklenburg-Vorpommern: Rheas further extend their habitat]. Spiegel online (in German). 5 November 2014. Retrieved 5 November 2014.
  16. "Informationen der Arbeitsgruppe Nandumonitoring" [Information of the rhea monitoring working group] (in German). Retrieved 5 November 2014.
  17. Coomber, Richard (1991). "Rheiformes: Rheas". In Gill Waugh (ed.). Birds of the World. Godalming, Surrey: Colour Library Books Ltd. pp. 8–9. ISBN 0862838061.
  18. BirdLife International (2016). "Rhea americana". IUCN Red List of Threatened Species. 2016: e.T22678073A92754472. doi:10.2305/IUCN.UK.2016-3.RLTS.T22678073A92754472.en.CS1 maint: uses authors parameter (link)
  19. BirdLife International (2016). "Rhea pennata". IUCN Red List of Threatened Species. 2016: e.T22728199A94974489. doi:10.2305/IUCN.UK.2016-3.RLTS.T22728199A94974489.en.CS1 maint: uses authors parameter (link)


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