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Greater Rhea
Rhea americana
Lesser Rhea (NT)
Rhea pennata
  Orbigny, 1834
 
  Owner:   C. Michael Hogan    

Lesser Rhea grazing in level grasslands of Chilean Patagonia
Lesser Rhea
Rhea pennata

C. Michael Hogan PhD
September 15, 2009

The Lesser Rhea is a flightless bird found in Patagonia and the Altiplano of southeastern South America. R. pennata can attain stature of slightly more than one metre and its muscular legs can propel it to land velocities in excess of 60 km/hr assisting in predator escape. The genus name is derived from the eponymous Greek goddess, while an alternate common name for the nominate subspecies is Darwin's Rhea, bestowed by Alcide d'Orbigny, a Patagonian explorer contemporary to Charles Darwin . The species is very sociable and is typically found in groups of four to 30.



SUBSPECIES AND DISTRIBUTION
R. pennata pennata is found on the grassland and scrubby steppes of Chile from the southern Aisén Region to the Straits of Magellan and in southern Argentina from southern Mendoza Province to Patagonia.(Sibley) One of the first places to be observed by Europeans was by a voyage of Charles Darwin up the Santa Cruz River in Patagonia in the year 1834. This nominate taxon typically is found at elevations less than 1400 metres. Many of these birds can be seen on the arid scrubby grasslands of Patagonia, while large numbers can also be seen on rocky, grassy slopes at 500 to 1000 metres in elevation. R. pennata tarapacensis occurs more northerly in puna, grasslands and mountains from the Atacama Region north through the Tarapacá, Antofagasta, and Arica/Parinacota Regions, and is usually found on high plateaus and mountains at elevations from 3000 to 4400 metres, although sometimes this subspecies is found as low as 1500 metres. R. pennata garleppi is found in northwest Argentina (e.g. Catamarca, Salta and Jujuy Provinces); in the Andean parts of southeast Peru; and in western Bolivia (Oruro, Potosi and LaPaz Departments).

Archaeological and taphonomic analyss of R. pennata remains at prehistoric human habitation sites indicate that the Lesser Rhea was hunted in Patagonian regions since the early Holocene. (Cruza and Elkin) For example, at Pali Aike within the lava tube habitation sites occupied by humans in the period 8000 to 12,000 years BC, there are remains of R. pennata along with those of Fox (genus Lycalopex), Giant Sloth (Smilodon populator), Guanaco (Lama guanicoe) and American Horse (Hippidion saldiasi). (Hogan)



MORPHOLOGY
Like all ratites Rheas lack a sternum keel, used for attaching flight propelling muscles. R. pennata manifests brown-gray plumage, with dirty whitish underparts; white blotches are evident dorsally and on the wings, distinguishing this taxon from the larger Rhea americana. Wings are large compared to other ratites. Feathers are quite long, covering thighs and upper reaches of the lower legs. The upper portion of the tarsus manifests plumage.The species has long legs and strong sharp claws. Females are characteristically more drab, and exhibit smaller and fewer white dorsal patches. Juveniles are more brown and have not attained the white spots until age one or two, whilst chicks sport black striping. Body mass of adults is typically in the range of 16 to 24 kilograms.



REPRODUCTION
Nest sites are associated with areas of heavier vegetation, especially humid meadows called "mallins". (Barri. 2009) Nest density has been measured in the region of 0.17 nests per square kilometre. (Barri. 2008) Clutch sizes vary from seven to 33 yellow-green eggs, with the male carrying out incubation for four to six weeks. (Davies) Hatching success was measured at 74.4 percent. Chicks are precocial to three months, during which time they are under paternal supervision.



CONSERVATION
The IUCN classifies the conservation status of the species as Near Threatened. (Birdlife International) While there may be up to several hundreds of thousand of the nominate subspecies grazing in the wild on Patagonian steppes; however, the other two subspecies have extremely low population numbers, possibly totally in the hundreds and are correspondingly critically endangered. All populations are severely diminished from prehistoric levels, mainly from successive conversion of natural grasslands for livestock. Chief ongoing threats to the Lesser Rhea are continued agricultural land conversion and egg harvesting by Aymará Indians and others. Chief reasons for nest site disturbance and resulting egg and chick mortality are human and livestock generated, both being mainly associated with cattle and sheep grazing operations.



REFERENCES

* Charles Gald Sibley and Burt Leavelle Monroe. 1990. Distribution and taxonomy of birds of the world, 1111 pages
* C. Michael Hogan. 2008. Pali Aike, The Megalithic Portal, ed. Andy Burnham
* Fernando R. Barri, Mónica B. Martella and Joaquín L. Navarro. 2009. Nest-site habitat selection by Lesser Rheas (Rhea pennata pennata) in northwestern Patagonia, Argentina, Journal of Ornithology, vol 150, no. 2, Springerlink,
* Fernando R. Barri, Monica B. Martella and Joaquín L. Navarro. 2008. Reproductive success of wild Lesser Rheas (Pterocnemia -Rhea- pennata pennata) in northwestern Patagonia, Argentina, Journal of Ornithology, published on line by Springerlink, June, 2008
* Birdlife International. 2009. IUCN Red List Category: Lesser Rhea. [http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3&m=0]
* S.J.J.F Davies. 2003. Rheas. in Hutchins, Michael. Grzimeks Animal Life Encyclopedia''. Tinamous and Ratites to Hoatzins (2 ed.). Farmington Hills, Michigan, Gale Group. pp. 69-74. ISBN 0 7876 5784 0.
* Isabel Cruza and Dolores Elkin. 2003. Structural Bone Density of the Lesser Rhea (Pterocnemia pennata) (Aves: Rheidae). Taphonomic and Archaeological Implications, Journal of Archaeological Science, Volume 30, Issue 1, January, pages 37-44



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