Birds
Rhea
Rhea · also called rheas, nandu, South American ostrich
A rhea is South America’s big flightless bird — a grey-brown, long-necked ratite that runs the pampas with one wing raised like a sail for balance. It looks like a scaled-down ostrich, but its family life is its own: a single male mates with a whole harem, gathers all their eggs into one nest, incubates the lot, and then raises the creche of chicks alone, charging anything that comes near.
Overview
Rheas are the genus Rhea, two species — the widespread greater rhea and the smaller Darwin’s (lesser) rhea of Patagonia and the high Andes. The greater rhea stands about 1.5 m and 20–40 kg, the largest bird in the Americas. They are omnivores of leaves, seeds, fruit, grasshoppers, and small vertebrates on open grassland and scrub, and they have three toes (the ostrich has two).
Wings kept for other jobs
A rhea cannot fly, but it raises one wing like a sail to help it corner at speed and spreads both in courtship — flight feathers repurposed for balance and display. It runs at 50–60 km/h, usually fast enough to escape a puma or jaguar.
The father does everything
A dominant male gathers a harem, and each female lays into his single nest scrape — a clutch of 20–60 eggs from up to a dozen mothers. The females move on; the male incubates for six weeks and then raises all the chicks alone, brooding them at night and defending them fiercely.
Status
Both species are Near Threatened and decreasing, as the pampas and cerrado are ploughed for soybeans and cattle, and rheas are hunted and killed as supposed livestock competitors. A small wild population in northern Germany, descended from farm escapees around 2000, is the only one outside South America.
Rhea: common questions
Is a rhea the same as an ostrich?
No, though they look alike and fill the same role on different continents. Both are ratites, the group of large flightless birds that also includes the emu, cassowary, and kiwi, but the rhea is a South American bird and the ostrich is African, and they are on separate branches of the ratite family tree. The rhea is smaller, standing about 1.5 metres against the ostrich's 2.5 metres, has three toes on each foot rather than two, has feathered thighs and a feathered neck rather than bare skin, and lacks the ostrich's dramatic black-and-white male plumage, being a fairly uniform grey-brown. The old name South American ostrich reflects the resemblance, not a close relationship.
How does rhea breeding work, with the male raising the young?
Rhea breeding is polygynandrous, meaning both sexes have several mates. A dominant male courts and mates with a group of females, then makes a nest scrape, and the females of his harem each lay their eggs into that one nest over a week or two before leaving to mate with a different male and lay again. The first male is then left with a communal clutch of 20 to 60 eggs, which he incubates alone for about six weeks, and once they hatch he raises the whole creche of chicks by himself for several months, defending them aggressively. A female may contribute eggs to several males' nests in a season, and a male may recruit a young subordinate male to mind one nest while he starts another.
Can rheas fly, and how fast can they run?
Rheas cannot fly at all. Their wings are large for a flightless bird but the flight muscles and keeled breastbone that powered flight in their ancestors are gone. Instead the wings are used for balance and steering, held up like a sail on one side when the bird runs fast and turns, and for display during courtship. On the ground a rhea is quick, reaching around 50 to 60 kilometres per hour in a long-striding run and able to change direction sharply, which lets it outmanoeuvre the pumas and jaguars that hunt it on the open plains.
Why are there wild rheas in Germany?
In 1999 or 2000 a small number of greater rheas, kept on a farm in the northeastern German state of Mecklenburg-Vorpommern, escaped when a fence was damaged. The surrounding landscape of fields, meadows, and hedgerows near the Baltic coast suited them, the winters proved survivable, and with no natural predators the birds bred and spread, reaching a peak of several hundred by the late 2010s. They are now the only free-living rheas outside South America. Authorities monitor the population and control it where the birds damage crops, since a large flightless bird eating oilseed rape is an unusual agricultural problem for northern Europe.