Greater Rhea

The greater rhea is a flightless bird native to eastern South America, found in Argentina, Bolivia, Brazil, Paraguay and Uruguay. Weighing 20–27 kg, it is the largest native bird in the Americas, and stands about 1.5 m tall. It inhabits open areas such as grassland, savanna, scrub forest and grassy wetlands, and stays near water during the breeding season. Its diet is mainly broad-leaved foliage, seeds and fruit, along with insects, scorpions, fish, small rodents, reptiles and small birds. It swallows pebbles to help grind tough plant matter. Outside the breeding season it forms flocks of 10 to 100 birds, and when chased it flees in a zigzag, alternately raising one wing then the other.

About the greater rhea

The greater rhea is a large, flightless bird of eastern South America and the largest native bird in the Americas. It is one of two living rhea species and belongs to the ratites, the group that also includes ostriches, emus, cassowaries and kiwi. It lives in open grasslands, savannas and grassy wetlands.

Carl Linnaeus described the bird in 1758, placing it with the ostriches as Struthio americanus. It is now known as Rhea americana, in a genus named in 1760 after Rhea, a goddess of Greek myth. In Spanish and Guaraní it is called ñandú, and in Portuguese, ema.

Adults usually stand about 1.5 m (4 ft 11 in) tall to the top of the head and measure 127 to 140 cm (50 to 55 in) from beak to tail. Average weight is 20 to 27 kg (44 to 60 lb). Males are generally bigger than females. Big males can reach 40 kg (88 lb) and nearly 1.83 m (6 ft) tall, though that is uncommon.

The plumage is soft, fluffy and somewhat ragged-looking, grey or brown, and it varies a lot from bird to bird. Males are usually darker than females. White, blue-eyed leucistic birds and true albinos occur even in the wild, especially in Argentina. Chicks are grey with dark stripes running along the body.

The head and bill are fairly small. The legs are long and strong, with 22 horizontal plates on the front of the lower leg, and each foot has three toes. The wings are fairly long for a flightless bird. Rheas spread them to keep their balance in tight turns while running, and in courtship displays.

Five subspecies are recognized, differing mainly in height and in how much black is on the throat. The differences are so slight that captive birds of unknown origin are essentially impossible to assign to a subspecies.

Behavior and diet

Greater rheas are built for running. In one case, a bird was clocked at more than 60 km/h (37 mph) running in front of a car. When chased, a rhea flees in a zigzag, lifting one wing and then the other.

Outside the breeding season, rheas gather in flocks of 10 to 100 birds. They are quiet birds. Adults make low booming calls during the mating season, and chicks give a mournful whistle.

The diet is mostly broad-leaved plants, especially seeds and fruit in season, from many plant families. Rheas generally avoid cereal grains and other grasses, though they eat large amounts of certain grass leaves. They also eat tough, spiny food such as tubers and thistles.

Animal food matters too, particularly for young birds. Rheas eat locusts, grasshoppers, beetles, cockroaches and bugs, along with scorpions, fish, small rodents, reptiles and small birds. They will even eat stinging wasps and bees, apparently without trouble.

Like many birds that eat tough plants, rheas swallow pebbles to help grind their food. They are attracted to shiny objects and sometimes swallow bits of metal by mistake.

Rhea breeding turns the usual roles around. In winter the big flocks break into lone males, groups of two to fifteen females, and flocks of yearlings. Each male courts females with calls, ruffled feathers, raised wings and figure-eight neck waves.

Males are polygynous, mating with several females, while females mate with one male after another. A female lays her eggs in a male's nest, then moves on to the next male. The male stays behind and does all the incubating and chick-rearing himself. Some dominant males even recruit a subordinate male to sit on the eggs while they start a second nest.

Because several females share each nest, it can hold as many as 80 eggs from a dozen females. The average is 26 eggs from seven females. Each egg measures about 130 by 90 mm (5.1 by 3.5 in) and weighs around 600 g (21 oz), less than half the size of an ostrich egg.

The nest is a shallow scrape. The male drags sticks, grass and leaves around the area surrounding it, so the edge resembles a firebreak as wide as his neck can reach. Incubation takes 29 to 43 days. Even though eggs may be laid two weeks apart, they all hatch within 36 hours. Hatching eggs give off a strong smell that attracts flies, which the chicks then eat. Rheas reach maturity at two to three years old.

The cougar is the main predator of adult rheas, and jaguars also hunt them in parts of Paraguay, Bolivia and Brazil. Feral dogs kill young birds, and crested caracaras are suspected of taking hatchlings. Armadillos sometimes dig under nests and break the eggs.

Range and habitat

The greater rhea is native to Argentina, Bolivia, Brazil, Paraguay and Uruguay, reaching south to about 40 degrees latitude. It is absent from Brazil's humid Atlantic coastal forests.

It lives in open country: grassland, savanna, scrub forest, chaparral and even desert and marshy ground, though it likes some tall vegetation. It prefers lower elevations and seldom goes above 1,200 m (3,900 ft). During the breeding season in spring and summer, it stays close to water.

A feral population also lives in northern Germany. In 2000, one male and five females escaped from a farm in Schleswig-Holstein, survived the winter and began breeding. By autumn 2018 the population had grown to 566 birds, and it is now treated as invasive and controlled.

Greater rhea vs lesser rhea

The greater rhea shares its genus with one other living species, the lesser rhea. The two can be similar in weight, but they are built differently.

Conservation status

The greater rhea is listed as Near Threatened on the IUCN Red List, most recently assessed by BirdLife International in 2022. Its range, about 6.5 million square kilometers (2.5 million sq mi), is shrinking, and numbers are believed to be falling.

The main causes are hunting and the conversion of central South American grasslands into farms and ranches. Farmers sometimes kill rheas as pests because they eat broad-leaved crops such as cabbage and chard, and crop burning has added to the decline. Populations in Argentina and Uruguay are the most seriously affected.

International trade in wild-caught birds is restricted under CITES Appendix II. Rheas are also farmed in North America and Europe, like the emu and the ostrich, for meat, eggs, oil and leather.

Captive-bred rheas tend to be fearless, which makes them easy prey if released into the wild. Researchers have trained young birds to avoid predator models before reintroduction, choosing the most cautious individuals for release.