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 synonymized 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. Conservation Darwin's rhea is categorized as least concern by the IUCN. The former southern nominate subspecies remains relatively widespread and locally fairly common. Its range is estimated at . The situation for the two former northern subspecies is more worrying, with their combined population estimated as being possibly as low as in the hundreds. However, they are classified as Rhea tarapacensis by the IUCN, which regards it as being near threatened, with the primary threats being hunting, egg-collecting, and fragmentation of its habitat due to conversion to farmland or pastures for cattle-grazing. Patagonia National Park in Chile's Aysén Region hosts the Centro de Reproducción para la Conservación del Ñandú ('Reproduction Centre for Darwin's rhea Conservation'). The centre is run by Tompkins Conservation with the support of the National Forest Corporation. Footnotes Notes References Rheidae Ratites Domesticated birds Flightless birds Birds of the Altiplano Birds of Patagonia Birds of Argentina Birds of Peru Birds of Chile Birds of Bolivia Darwin's rhea