Endangered Native Species of Patagonia: the Lesser Rhea

An ostrich-like bird, the Darwin’s or Lesser Rhea (Rhea pennata pennata) is one of the most distinctive, fabled and endangered residents of Patagonian steppe grasslands. Two species of rhea, the Greater and Lesser, occupy overlapping ranges in Patagonia. Lesser rheas typically weigh 35-55 lbs and have spotted dun, brown, grey and white feathers. Rheas are sociable birds, typically living in groups of five to fifteen. Rheas do not fly, but thanks to their unusually large wings, which they spread behind their bodies while running from predators, they can sprint at speeds over 35 mph.

Rheas are omnivorous, eating everything from herbs, shrubs, seeds and roots to insects, grasshoppers, and small vertebrates such as lizards or frogs. Their main predators are pumas, foxes, and birds of prey. Mating season lasts from September to December. During this time, one male will mate with several females, all of which deposit their eggs in the male’s nest site. The males incubate the eggs for 40 days. When one chick hatches, it begins to call, which stimulates the others to hatch. The whole brood will hatch within a period of 1-2 days. Males are then in charge of rearing the chicks, which will remain in his care until May or June.

Rheas attracted Charles Darwin’s attention when he visited Patagonia during his voyages on the HMS Beagle. Darwin had seen many Greater Rheas, but had only heard tell from gauchos of the existence of a smaller Rhea in southern Patagonia. Puzzled by the existence of two related but different species—which challenged the then-accepted theory that every animal was created in a fixed form, perfectly adapted to its place and life—Darwin went on the hunt for the fabled Lesser Rhea. He searched for months before recognizing the bird upon his dinner plate. The gentleman-ecologist put his dinner bones back together to form the skeleton, and with the help of ornithologist John Gould he confirmed that he had finally found the Lesser Rhea. With further examination it was clear that the Greater and Lesser Rheas were indeed two distinct, yet surprisingly similar species. This discovery helped spark his theory that species could change and diverge over time, and no creature is permanently fixed in its current state of life.

The bird’s scientific name comes from the Greek goddess Rhea. Known as “the mother of the gods,” Rhea gave birth to no less than six Olympian gods and goddesses: Zeus, Hera, Poseidon, Demeter, Hades, and Hestia. German naturalist P.H.G. Mohring bestowed this name on the birds in 1752 for reasons that remain unknown. In Patagonia the rhea is known as “Nañdu,” Guarani for “big spider,” possibly a reference to the manner in which it carries its wings while running.

Lesser rheas have faced serious threats from humans for over a century. In 1911, the Encyclopedia Britannica’s profile of the rhea stated, “the feathers of the ñandu have a considerable market value, and for the purpose of trade in them it is annually killed by the thousands, so that its total extinction as a wild animal is probably only a question of time.”
The rhea is listed in the “near threatened” category of the International Union for Conservation of Nature Red List, with regional populations considered ecologically extinct. Intensive hunting, egg collecting, competition with livestock, and the destruction of nests all contribute to the species’ imperiled status. Chile defines the species as “Endangered.” The Chacabuco Valley contains the most important population in the Aysen region.

In 2011, Conservacion Patagonica instituted an initiative to monitor and restore lesser rhea populations within the park. Project conservationists are teaming up with neighbors, including the police and army personnel stationed within the species’ range in the park’s eastern sector. The population of rheas within the range under observation is shockingly low, with just 74 individuals identified to date. These numbers are on the rise, however, and efforts to curb threats and expand the population look quite promising. With ongoing support from donors and the dedication of our conservation staff on the ground, one day the lesser rhea will thrive once more in Patagonia!

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