Characterized by a body that can reach around 5 feet (152 cm) tall at the head, 3.5 feet (106 cm) at the back and weighing up to 40 kg (88 lb), equipped with long legs, a long neck, and three-toed feet, the Rheas, native to South America, resemble the ostriches of Africa and the emus of Australia. They are flightless birds, although their 8.2 feet (2.50 m) long wings are more than large for a flightless bird, which they spread while running to act like sails.
The genus Rhea contains two extant species. While the Common Rhea is found in abundance in the open country from northeastern Brazil southward to Argentina, Darwin’s Rheas, somewhat smaller in size, reside from Peru southward to Patagonia, at the tip of the continent. The upper parts of the common rheas are brown or grey and their underparts are whitish, while Darwin’s rheas have brownish plumage tipped with white.
The Rheas are grassland birds, and both the species prefer open land. However, while the greater rheas live in open grasslands, the Pampas and Chaco woodlands, the lesser rheas inhabit mostly in shrubland, grassland, even desert salt Puna grassland in the central Andes Mountains up to the height of 14,800 feet (4,500 m).
Although they are mainly vegetarian and prefer broad-leafed plants, roots, fruits and seeds, they also eat insects like grasshoppers, small reptiles like lizards, rodents, birds and other small games. Apart from that, Rheas have a taste for crops, for which they earn the ire of many South American Farmers. However, for the first few days, the young Rheas eat only insects. Outside the breeding season in spring, Rheas flock together and often congregate with other large animals like deer and guanacos to from mixed herds.
The rheas do not form lasting pairs. They are polygamous and the males usually court between two and twelve females in a season. Although they tend to be silent birds, during the breeding season, the males try to attract the females by calling, which is a loud booming noise. While calling, they keep their necks stiff, but lift the front of their bodies and ruffle their plumage.
If a male singles out a particular female, the male raises his wings, runs short distances, alternating the wings and then walk alongside or in front of her, with lowered head and wings spread out. If the female cares to notice him, the male waves his neck back and forth in a figure of eight and finally, the female may agree to commence copulation.
After mating, the male builds a nest consisting of a simple scrape in the ground, lined with soft grass and leaves. Several females deposit their eggs, each about 5 inches (13 cm) long, in the same shallow nest, which could hold anything between 50 and 60 eggs. The male takes the responsibility to incubate the eggs, and the chicks hatch in about six weeks. During that period, the male aggressively guards the young, ready to charge any animal, even a female rhea that may appear to approach too close. Meanwhile, the female may move on and mate with any other male, if she pleases. However, the male may also use the service of a subordinate male to incubate the eggs for him, while he finds another female to start a second nest. Nevertheless, the young birds reach full adult size in about six months, but they do not breed until they reach two years of age. The average life span of a rhea in the wild is said to be around 15 years.
Although Europe is not the natural habitat of the rheas, a small population of the big birds has emerged in northeast Germany after several of them escaped from a meat farm near Lubeck in the late 1990s. Despite the low temperature during the harsh winter days, the birds adapted to the weather condition and by the autumn of 2018, their numbers greatly increased to about 566.