The rhea, a ratite native to South America

Knowledge of Greater (Rhea americana) and Lesser (Pterocnemia pennata) rheas, both native to South America, are important for the purpose of conservation of wild populations as well as the potential commercialisation of captive bred animals.Whereas the different subspecies of Greater rheas are distributed through Argentina, Bolivia, Brazil, Paraguay and Uruguay, habitat of Lesser rheas are mainly limited to the Argentine and Chilean Patagonia.The two Andean subspecies (Pterocnemia pennata garleppi and Pterocnemia pennata tarapacensis) of Lesser rheas are endangered in the wild. Information on divergences between rhea and other ratite taxa are still inconclusive. Anatomy and standard metabolism of rheas in general are in agreement with that of other ratite and avian species.Vigilance is an important component of daily activities. In contrast to adult birds, several different vocalizations can be distinguished in young chicks. Rheas, that reach sexual maturity between 20 and 24 months of age, can be described as polygynandric in that males are simultaneously polygynous, whereas the females are sequentially polyandrous. Only 5 to 6% of the male population bred successfully each year in the wild. Rheas are ground-nesting birds with females laying eggs for up to 12 different males during the laying season, and males incubating the eggs for a period of around 42 days. Rheas are characterised by high rates of nest desertion (65%) commonly associated with egg predation, orphan eggs laid far away from active nests, and egg stealing between males. In the wild males took care of the chicks for 4 to 6 months, with chick adoption from other broods a common phenomenon. As with other ratites rheas grow at exceptionally slow rates, with a final mature live weight of around 25 kg, depending on gender. The digestive system of the rhea is characterised by a relative huge caeca and colon, which may serve as fermentation chambers for the utilisation of fibre. Diseases and parasites commonly found in other ratites also occur in rheas. Conservation and commercialisation of rheas are hampered by a lack of knowledge about the biology and requirements of these species.