Darwin's Rhea, also known as the Lesser Rhea, is the smaller of the two extant species of rhea.

Description

It stands at 90"?100 cm (35"?39 in) tall and wighs 15"?25 kg (33"?55 lb), and has larger wings than other ratites, enabling it to run particularly well. It can reach speeds of 60 km/h (37 mph), enabling it to outrun predators. The sharp claws on the toes are effective weapons. Their plumage is spotted brown and white, and the upper part of their tarsus is feathered.

Taxonomy

The Lesser Rhea gets its name from Rhea, a Greek goddess, and pennata means winged. The name was bestowed by Darwin's contemporary and rival Alcide d'Orbigny who first described the bird to Europeans. As late as 2008 it was classified in the Pterocnemia Genus. In 2008 the SACC merged the two genera. This word is formed from two Greek words pteron meaning feathers, and kn?m? meaning the leg between the knee and the ankle, hence feather-legged, alluding to their feathers that cover the top part of the leg. They were named in 1834 by d'Orbigny.

There are three subspecies :

• Puna Rhea (R. pennata garleppi) located in the desert puna of southeastern Peru, southwestern Bolivia, and northwestern Argentina.
• R. pennata tarapacensis located in the puna of northern Chile from Tarapacá province to Atacama.
• R. pennata pennata located in the Patagonian steppes of Argentina and Chile.

There is a school of thought that R. pennata tarapacensis should be its own species but this is not widely accepted.

Behavior

The males of this species become aggressive once they are incubating eggs. 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 form 5-55 eggs. The eggs are 87"?126 mm (3.4"?5.0 in) and are greenish yellow. 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, through the countries of Argentina, Bolivia, Chile, and Peru. It is known locally by various names, depending on the location: suri, choique, ñandú petiso, or ñandú del norte. all sub-species prefer grasslands and brushlands and marshland. However the nominate subspecies prefers elevations less than 1,500 m (4,900 ft), where the other sub-species range from 3,000"?4,500 m (9,800"?15,000 ft) down to 1,500 m (4,900 ft) in the south.

Rhea and people Illustration of Darwin's Rhea, published in 1841 in John Gould's decription of birds collected on the Beagle voyage.

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 it to John Stevens Henslow in Cambridge. On 26 January they 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 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, but they were too wary to be approached closely or caught. Darwin at first thought that the larger and smaller rheas could be two varieties of the same bird, but by the later stages of the voyage he became convinced that they were distinct species.

In 1837 the bird was described by the ornithologist John Gould in a presentation to the Zoological Society of London in which he was followed Darwin reading a paper on the eggs and distribution of the two species.

When Gould classified what he called Rhea americana and Rhea darwinii as distinct species, he created a serious problem for Darwin. As these birds lived in different parts of Patagonia, there was a also an overlapping zone where the two birds species coexisted. 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 weren't fixed at all, but that another mechanism might be at work.

Conservation

The lesser rhea is Near Threatened with the threats coming from hunting, egg-collecting, fragmentation of habitat, and the fact that the two populations are isolated from each other. Farming and ranching are the greatest threat to their survival due to habitat loss. Their occurrence range is 1,100,000 km2 (420,000 sq mi).