Greater rhea (Rhea americana)
|Also known as:||common rhea|
|Spanish:||Avestruz, Ñandú, Ñandú Común|
|Size||Head-body length: 127 - 140 cm (2) (3)|
|Weight||20 - 25 kg (2) (3)|
Classified as Near Threatened (NT) on the IUCN Red List (1) and listed on Appendix II of CITES (4).
The largest bird on the American continent (5) (6), the greater rhea belongs to a group of flightless birds known as ‘ratites’, which lack the keel of the breastbone to which the flight muscles attach in flying birds (5) (7). However, despite a superficial resemblance - which led Charles Darwin to describe the species as a “South American ostrich” (8) - the rhea is not thought to be closely related to the other members of this group, the ostrich, emu, cassowaries and kiwis (9). The plumage of the greater rhea is generally greyish-brown, with darker patches on the neck and upper back, and whitish feathers on the thighs and abdomen (2) (3) (9) (10). During the breeding season, a prominent black ring develops at the base of the neck (2). The greater rhea’s feathers, not needed for flight, are long and plume-like (10), and the grey legs are long and powerful, with strong toes, and are adapted for running and for ranging over large distances (6) (7). Rheas have a deep, resounding call, which resembles the roar of a mammal more than the call of a bird. Mainly produced by the male during courtship, the sound of this call gives the rhea its local name, “ñandú” (2).
The male greater rhea is slightly larger and greyer in colour than the female, with a more pronounced dark patch on the neck and upper back (11). Young birds are greyish, with dark stripes (2) (3) (6) (10). Five subspecies of greater rhea are recognised, based on variations in size and in the extent of black on the neck, although the exact characteristics and ranges of several of these subspecies are tentative (2) (3) (10). The greater rhea can be distinguished from the other rhea species, the lesser rhea (Rhea pennata), by its longer legs, lack of white spotting on the plumage, the more greyish than brownish colouration, and feathering on the legs which does not go below the tarsal joint (3) (11).
The greater rhea is distributed throughout Brazil, Bolivia, Paraguay, Uruguay and Argentina (3) (12). Rhea americana americana is found in northeast and southeast Brazil, Rhea americana intermedia in the south of Brazil and Uruguay, Rhea americana nobilis in eastern Paraguay, Rhea americana araneipes in western Paraguay, eastern Bolivia and southern Brazil, and Rhea americana albescens in Argentina as far south as the Río Negro (2) (5) (9).
The greater rhea typically inhabits tall grassland, open woodland and wooded savanna, such as the pampas, cerrado, and chaco woodland habitats of South America. The species can also be found in cultivated fields when the crop height is low (11), and occurs at elevations of up to 2,000 metres (2) (3) (12).
The greater rhea feeds mainly on plant matter, including leaves, roots, seeds and fruits. It also takes insects and small animals, such as lizards, frogs, small birds and even snakes, and sometimes catches flies that have gathered around carrion (2) (6) (13). Rheas also commonly swallow pebbles, which help to grind down food in the gizzard, and can often be seen feeding alongside herds of pampas deer, guanacos, or domestic livestock (2) (6). Rheas are good runners, capable of reaching speeds of over 60 kilometres an hour, and, perhaps surprisingly, are also good swimmers (2).
Outside of the breeding season, the greater rhea lives in mixed flocks of up to 30 or more individuals, though old males are often solitary (2) (6) (9). However, at the start of the breeding season, from August to January, breeding females separate into small groups. At the same time, the males become territorial, competing for territories with threats or fights, intertwining necks and biting or kicking at rival males (2) (6) (14). A successful male attempts to attract a group of females into the territory, performing an elaborate courtship display that involves calling, running around the females with feathers ruffled and wings spread, and then standing beside the females with the neck lowered, shaking the wings (2) (6). The nest is prepared by the male, and consists of a depression in the ground, around one metre wide and twelve centimetres deep, lined with dry vegetation and often hidden amongst bushes (2). The group of females all lay eggs in the same nest, so that a typical nest may contain between 20 to 30, or even up to 80, eggs, from up to twelve different females (2) (6) (15).
Unusually, it is only the male who incubates the eggs and rears the chicks, with the females leaving to mate with other males and lay eggs in other nests. The eggs, which are golden yellow but fade to a dull white over time, hatch after an incubation period of 35 to 40 days (2) (6) (9). The male is an attentive and protective parent (2) (9), and, soon after hatching, leads the young away from the nest, and cares for them for another four to six months. The young keep together in a group by means of plaintive contact whistles, and may shelter under the male’s wings if threatened, or if too hot or too cold. The male may even ‘adopt’ chicks that have become separated from other groups (2) (6) (16). The young generally remain together in a group long after the period of parental care is over, until reaching sexual maturity at around two years in females, and three years in males (2) (6) (11).
The greater rhea has undergone a marked decline as a result of hunting for meat, eggs and skins, and for its feathers, which are used to make feather dusters. In recent years, these threats have been compounded by habitat loss as vast areas of grassland are converted for agriculture and cattle ranching (2) (12) (17). Farmers and ranchers often accuse rheas of eating crops and competing with cattle for food, and chase the birds off their land (2), although there is evidence that the greater rhea actually feeds on important weed and pest species (18). Physical barriers like roads can also prevent the birds dispersing, so increasing the risk of inbreeding. In addition, the greater rhea can suffer serious injuries if it becomes caught up in barbed wire fences (2) (5).
The greater rhea is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in the species should be carefully controlled (4). However, levels of both international and domestic trade in the greater rhea may need further monitoring, and restrictions on hunting and trade need effective enforcement (12). As increasing grain production within the species’ range appears inevitable, education and outreach programmes may be needed to help ensure the long-term survival of the greater rhea in agricultural areas (17). In recent decades, commercial farming of rheas for feathers, meat and skin has become increasingly popular, and studies into captive breeding of the species have led not only to improved production (for example, by using ‘adoptive’ males rather than artificial systems to rear chicks (19) (20)), but also the possibility of reintroduction of captive-bred rheas into the wild. Captive breeding has therefore been suggested as a possible conservation tool as wild populations continue to decline (5) (21).
To read more about rhea species see:
del Hoyo, J., Elliott, A. and Sargatal, J. (1992) Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona.
To find out more about rhea conservation see:
Proyecto Ñandú: Manejo de Rhea americana y R. pennata en la Argentina (in Spanish):
Proyecto Ñandúes (in Spanish):
For more information on this and other bird species please see:
- BirdLife International:
Authenticated (11/08/09) by Joaquín L. Navarro, Universidad Nacional de Cordoba - CONICET. Proyecto Ñandúes.
- Carrion: the flesh of a dead animal.
- Cerrado: a vast, tropical woodland-savanna ecosystem of Brazil, the most extensive of its type in South America. Comprising around 21 percent of Brazil’s total land area, the cerrado includes savanna, woodland-savanna and dry forest ecosystems, and has a pronounced dry season.
- Chaco: an extensive flatland of dry, shrubby woodlands, marshes, gallery forest and palm savanna, occurring in Brazil, Paraguay, Bolivia and northern Argentina.
- Gizzard: in birds, a thick-walled muscular chamber in which tough food is ground up, sometimes with the aid of ingested pebbles or grit.
- Inbreeding: the breeding of closely related individuals. An inbred population usually has less genetic variability and this is generally disadvantageous for its long-term survival and success.
- Incubate: to keep eggs warm so that development is possible.
- Incubation: the act of incubating eggs, that is, keeping them warm so that development is possible.
- Pampas: the vast, grassy plains of temperate central and southern South America.
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- Territorial: an animal, a pair of animals or a colony that occupies and defends an area.
- Territory: an area occupied and defended by an animal, a pair of animals or a colony.
IUCN Red List (July, 2014)