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Species Profile: Darwin’s Rhea

By Bolton Howes (Macalester College ’15)


Darwin’s Rhea (Rhea pennata), also known as the Lesser Rhea, is a large flightless bird that lives in the Patagonian steppe. Rheas belong to a group called ratites, which include other large flightless birds such as ostriches, emu, kiwis, and cassowaries. They typically grow to be about three feet tall and three feet wide and can weigh over 50 pounds. Darwin’s Rheas are often observed grazing alongside guanaco or sheep in groups of up to 30 individuals and are typically herbivores, but also eat the occasional insect or small lizard.

Although Darwin’s Rheas are not commonly found inside Valle Chacabuco, I chose to study them for my species presentation because they have become an iconic species in Patagonia and due to the unique place Darwin’s Rheas have in scientific history. When Charles Darwin was traveling in Patagonia on the second voyage of the HMS Beagle, he heard rumors of a rare second, smaller species of rhea (there is a Greater Rhea in northern Patagonia). He later “found” a Lesser Rhea in southern Patagonia after a member of his party shot it and was preparing the rhea for dinner. Since the ranges of the two species of rhea are largely separated, it suggests that the two species differed due to adaptations to their different environments.  About a hundred years after Darwin’s discovery of the Lesser Rhea, the theory of plate tectonics and former supercontinents developed. On one of these former supercontinents lived an ancestor to the modern ratites and when the continent split and isolated different populations, the populations adapted to their environments resulting in the differences between ostriches, emus, cassowaries, and rheas. In this, way Darwin’s Rhea provides a wonderful case study for the theory of evolution and allopatric speciation.

In the process of studying Darwin’s Rhea, I struggled with the lack of information that was available.  It was a struggle that I believe a lot of my classmates also experienced, and ultimately demonstrates the Northern Hemisphere-bias in scientific research. Many of the species studied in our project have been poorly studied by scientific researchers, which means there is still a lot of work for scientists to do in South America.


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