page_title: Darwin's rhea
section_title: History of the discovery of the genus Rhea
hierarchical_section_title: Darwin's rhea / History of the discovery of the genus Rhea
caption_attribution_description: Pterocnemia pennata (Original description: Rhea darwinii)
context_page_description: Darwin's rhea, also known as the lesser rhea, is a large flightless bird, but the smaller of the two extant species of rheas. It is found in the Altiplano and Patagonia in South America.
context_section_description: During the second voyage of HMS Beagle, the young naturalist Charles Darwin made many trips on land, and around August 1833 heard from gauchos in the Río Negro area of Northern Patagonia about the existence of a smaller rhea, "a very rare bird which they called the Avestruz Petise". He continued searching fruitlessly for this bird, and the Beagle sailed south, putting in at Port Desire in southern Patagonia on 23 December. On the following day, Darwin shot a guanaco which provided them with a Christmas meal, and in the first days of January, the artist Conrad Martens shot a rhea which they enjoyed eating before Darwin realised that this was the elusive smaller rhea rather than a juvenile, and preserved the head, neck, legs, one wing, and many of the larger feathers. As with his other collections, these were sent to John Stevens Henslow in Cambridge. On 26 January, the Beagle entered the Straits of Magellan and at St. Gregory's Bay Darwin met Patagonians he described as "excellent practical naturalists". A half Indian, who had been born in the Northern Provinces, told him that the smaller rheas were the only species this far south, while the larger rheas kept to the north. On an expedition up the Santa Cruz River, they saw several of the smaller rheas, which were too wary to be approached closely or caught.
  In 1837, Darwin's rhea was described as Rhea darwinii (later synomized with R. pennata) by the ornithologist John Gould in a presentation to the Zoological Society of London in which he was followed by Darwin reading a paper on the eggs and distribution of the two species of rheas.
  When Gould classified Darwin's rhea and the greater rhea as separate species, he confirmed a serious problem for Darwin. These birds mainly live in different parts of Patagonia, but there is also an overlapping zone where the two species coexist. As every living being had been created in a fixed form, as accepted by the science of his time, they could only change their appearance by a perfect adaptation to their way of life, but would still be the same species. But now he had to deal with two different species. This started to form his idea that species were not fixed at all, but that another mechanism might be at work.
caption: Illustration of Darwin's rhea, published in 1841 in John Gould's description of birds collected on the voyage of HMS Beagle
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