Lesser rhea (Rhea pennata)
|Also known as:||Darwin's rhea, Puna rhea|
|Synonyms:||Pterocnemia pennata, Rhea darwini|
|Spanish:||Avestruz de Magallanes, Ñandú Cordillerano, Ñandú Petizo|
|Size||Head-body length: 92 - 100 cm (2) (3)|
|Weight||15 - 25 kg (2)|
Classified as Near Threatened (NT) on the IUCN Red List (4) and listed on both Appendix I and Appendix II of CITES (5).
The lesser rhea is a large bird belonging 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. However, rheas are not thought to be closely related to the other members of this group, the ostrich, emu, cassowaries and kiwis (6) (7) (8). The lesser rhea has greyish-brown plumage, whitish on the underparts, with white spots on the back and wings, which help distinguish it from the larger Rhea americana, or greater rhea (3) (8) (9). The feathers are long and plume-like and extend onto the thighs and the top parts of the lower legs (2) (3) (9). The legs of the lesser rhea are long and powerful, with strong toes, and are adapted for running and for ranging over large distances (6). The female is generally duller in colour than the male, with fewer and smaller white spots on the back (2) (3), while juveniles are browner and lack the white spotting (2), and generally attain full adult plumage in their first or second year (10). Young chicks are greyish brown with black stripes (2) (9).
Three subspecies of lesser rhea are usually recognised. Rhea pennata tarapacensis and Rhea pennata garleppi, sometimes collectively known as the Puna rhea, are highland forms with greyer plumage and less conspicuous white spotting than Rhea pennata pennata, or ‘Darwin’s rhea’ (1) (2) (9). Some do not consider R. p. garleppi as a separate subspecies, while others include it with R. p. tarapacensis and suggest that these may comprise a full species in their own right (2) (9).
The lesser rhea occurs in Peru, Bolivia, continental Argentina and Chile, and has also been introduced onto the island of Tierra del Fuego (1) (2) (9). R. p. pennata is found in southern Chile, west-central and southern Argentina, and on Tierra del Fuego, R. p. tarapacensis is found in northern Chile, and R. p. garleppi is found in southern Peru, south-west Bolivia and north-west Argentina (1) (2).
R. p. pennata inhabits grassland and shrub-steppe (arid grassland with scattered shrubs), up to elevations of around 2,000 metres, and normally breeds in upland areas. The two northern subspecies inhabit highland areas of desert salt puna, pumice flats, upland bogs and tola (Lepidophyllum) heath in altiplano, at elevations of between 3,000 and 4,500 metres, and from 1,500 metres in the south (1) (2). Although generally inhabiting arid areas, rheas prefer to breed near lakes, rivers or swamps (2).
Rheas are good runners and, surprisingly, have also been seen swimming across rivers, with the wings held high over the back (2) (8). The lesser rhea feeds mostly on plant matter, including grasses and seeds, but also takes some small animals, especially insects (2) (11). Rheas often associate with flocks of grazing llamas, guanacos, vicunas, or sometimes domestic livestock (2).
The breeding season of the lesser rhea typically starts from late July to August (10). Usually living in groups of between 5 and 30 birds, the females separate into smaller groups during the breeding season, while males become territorial, attempting to attract groups of females into a territory, which is defended against rival males (2) (8). The male mates with a number of females, all of which lay their eggs in a single nest, which comprises a scrape in the ground, built by the male and lined with dry grass or twigs. Each nest may contain between 10 and 30 eggs, which start yellowish green in colour, but fade to buff over time. After laying, the females leave and often mate with another male, laying more eggs in a different nest. Unusually for a bird species, it is the male lesser rhea who alone undertakes incubation of the eggs and care of the young. The eggs hatch after an incubation period of around 40 days, and the male leads the chicks away from the nest a few days later, caring for them for a further few months (2). The young reach 90 percent of adult size at around 8 to 9 months, but may not reach sexual maturity until about three years in males, and two years in females (10).
R. p. pennata is thought to still be fairly common, perhaps due to its often inaccessible and harsh habitat. However, all populations of lesser rhea have undergone marked declines, and R. p. tarapacensis and R. p. garleppi are thought to be in serious danger of extinction, with combined populations of only several hundred birds (1) (2). The main threats to the lesser rhea are hunting, for meat, skins and feathers, and egg collection, as well as the taking of young birds for domestication (1) (2). Habitat degradation, due to conversion to farmland, or desertification as a result of overgrazing, also threatens all three subspecies and their grassland habitats (1) (7) (12). The building of roads and fences further fragments lesser rhea habitat, as well as preventing the birds from dispersing, and barbed wire fences can cause serious injury if the birds become caught (2) (7). However, it is hunting and egg collection which have been shown to have the more severe impact on lesser rhea populations (13).
The lesser rhea occurs in some protected areas, such as Ischigualasto-Talampaya Natural Parks, Los Glaciares, Monte León, Laguna Blanca and El Leoncito National Parks, and Península Valdes and Punta Tombo Natural Protected Areas, in Argentina (10) (14) (15). The species is also afforded a measure of protection under its listing on Appendices I and II of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in the lesser rhea should be carefully controlled, or, in the case of some populations, almost totally banned (5). Other conservation measures suggested for the species include increasing awareness amongst farmers and the public, in an attempt to reduce illegal hunting and egg collection. It will also be particularly important to monitor the remaining populations of P. p. tarapacensis and P. p. garleppi (1).
In recent decades, commercial farming of rheas has been expanding, and it is thought that in future this may serve as a source of individuals for reintroduction into the wild (7) (16). It has also been suggested that ‘orphan eggs’, those sometimes laid by females outside of nests, could be collected from the wild and artificially reared, before release back into the wild. Such eggs may represent up to seven percent of the total eggs laid in a breeding season, and, since they would otherwise not hatch, this measure may go some way towards helping to build up wild populations of the lesser rhea (17).
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 (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.
- Altiplano: Spanish for ‘high plain’; a high-elevation flat plain between eastern and western ridges of the Andes mountains, in South America.
- Desertification: a process of sustained decline of the biological productivity of arid and semiarid land; the end-result is desert, or skeletal soil that is irrecoverable.
- Incubation: the act of incubating eggs, that is, keeping them warm so that development is possible.
- Puna: a high-elevation grassland found throughout the Andes mountains, in 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)