is mainly a herbivore, with the odd small animal (lizards, beetles, grasshoppers) eaten on occasion. It predominately eats saltbush and fruits from cacti, as well as grasses, roots, seeds, and leaves. They tend to be quiet birds, except as chicks when they whistle mournfully, and as males looking for a female, when they emit a booming call. The males of this species become aggressive once they are incubating eggs, even towards females. The females thus lay the later eggs near the nest, rather than in it. Most of the eggs are moved into the nest by the male, but some remain outside, where they rot and attract flies. The male, and later the chicks, eat these flies. The incubation period is 30–44 days, and the clutch size is from 5–55 eggs. The eggs are and are greenish yellow. Chicks mature by three years of age. Outside the breeding season, Darwin's rhea is quite sociable: it lives in groups of from 5 to 30 birds, of both sexes and a variety of ages. Distribution and habitat Darwin's rhea lives in areas of open scrub in the grasslands of Patagonia and on the Andean plateau (the Altiplano), through the countries of Argentina, Bolivia, Chile, and Peru. All subspecies prefer grasslands, brushlands and marshland. However, the nominate subspecies prefers elevations less than , where the other subspecies typically range from , but locally down to in the south. History of the discovery of the genus Rhea 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 (similar to a llama) 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