Rhea

Rheas are ratites, a type of flightless bird with a flat breastbone with no keel. Other familiar ratites include ostriches, emus, and others. Rheas look most like ostriches, but smaller. There are currently three species of rheas, including the Greater Rhea, the Lesser Rhea or Darwin’s Rhea, and the Puna Rhea. All three species are native to South America. Rheas can reach heights of three to five feet and can run up to 37 miles per hour. Male rheas build a nest and take on all of the reproductive duties except actually laying the eggs. They incubate and hatch up to 80 chicks and care for them for six months. They even sometimes adopt lost chicks from another male’s brood.

Incredible Rhea Facts

• Rheas are both simultaneously polygamous and sequentially polyandrous.
• Rhea males can raise up to 80 chicks at a time.
• Adult rheas are quite quiet most of the time, but their chicks are noisy.
• Rheas eat each other’s poop.
• There are feral populations of Greater Rheas in Germany and England.
• Puna Rheas can be found at elevations of up to 14,700 feet.

Where to Find Rheas

Rheas live only in South America, except for a couple of feral populations of Greater Rheas in Germany and England. The Greater Rhea has the largest range by far, covering an estimated area of 1.2 million square miles. It lives east of the Andes Mountains and mostly south of the Amazon River basin. The range of the Greater Rhea includes much of Brazil, Uruguay, Paraguay, the eastern part of Bolivia, and the northern part of Argentina. It lives mainly in low-lying grasslands and savannas up to elevations of 3,900 feet, and prefers to stay near water.

The ranges of the Lesser Rhea and Puna Rhea are a little more complicated. The Puna Rhea, previously considered a subspecies of the Lesser Rhea, is now widely recognized as a unique species by major authorities. If treated as a separate species, the Puna Rhea takes the northern portion of the Lesser Rhea’s former range along with it. The Puna Rhea lives on the western side of the Andes, from the very southern tip of Peru to the northern part of Chile, including portions of Bolivia and Argentina on the west side of the mountains. It lives at high elevations of between 4,000 and more than 14,700 feet. The Lesser Rhea inhabits a range further south, in Chile and Argentina. It lives largely in the Patagonia region of South America and sticks to elevations below 5,000 feet.

Classification and Scientific Name

The Greater Rhea was the first species assigned to the genus Rhea in 1760 by the French zoologist Mathurin Jacques Brisson. It was given the scientific name, Rhea americana. The name Rhea was taken from Greek mythology; it was the name of the mother of Zeus, Poseidon, Hades, Hera, etc. It is believed to have derived from an ancient Greek word meaning “ground.” The specific epithet, americana, referred to the part of the world where the bird was found.

The Lesser Rhea, also known as Darwin’s Rhea, was named in 1834. Originally placed in its own genus and named Petrocnemia pennata, the Lesser Rhea was reclassified as Rhea pennata and added to the same genus as the Greater Rhea beginning with the 2004 report from the International Union for Conservation of Nature and Natural Resources, or IUCN. Other organizations have followed suit, officially reclassifying the bird over subsequent years. The specific epithet, pennata, means “winged.”  

Several subspecies of both the Greater and Lesser Rheas exist. The Puna Rhea, or Rhea tarapacensis, formerly considered a subspecies of the Lesser Rhea, is now recognized as a unique species by the IUCN and other major organizations.

Rheas are also known by the name ñandú, or simplified nandu, in various parts of the world.

Rhea Appearance

Rheas look a lot like female ostriches, but significantly smaller. They have a long neck, long legs, and fluffy gray or light brown feathers. Their wings are large and impressive, especially when they fan them out and use them to balance while running. They do not have tail feathers. Their feet have three large, clawed toes, the middle one being much larger than the others. They have large eyes that appear to have long lashes and a pointed, ostrich-like bill.

Rheas are large birds, but much smaller than ostriches, which are not found in South America. Ostriches easily grow to more than 6 feet in height, with males reaching more than 9 feet, and can weigh more than 300 pounds. However, even the largest rheas max out at around 5.5 feet and less than 90 pounds. According to the Smithsonian’s National Zoo, Greater Rheas average 3 to 5 feet in height and typically weigh between 33 and 66 pounds. Their wingspan can exceed 8 feet.

Lesser Rheas reach heights of about 3 feet and average weights between 33 and 55 pounds. As compared with Greater Rheas, their feathers feature lots of white spotting.

The Puna Rhea is about the same size as and can be difficult to distinguish from the Lesser Rhea. Its head is grayer, and it has less white spotting on its feathers.

Behavior

Rheas are not migratory birds. They are flightless, terrestrial birds that generally walk from place to place. When they run, they tend to zigzag, flapping their wings out alternately to balance as they reach speeds of up to 37 miles per hour.

These birds are diurnal, and they spend most of their time in small flocks of up to 30 birds. During breeding season, these flocks split and rearrange, with females forming groups and most males becoming solitary, at least while competing for the chance to mate.

Rheas walk with their necks down when foraging. They hold their heads up high when they swallow or when they are alert and vigilantly surveying their surroundings. The adults spend most of their time in silence, with the exception of mating calls and alert signals. Chicks, on the other hand, can be quite noisy.

Diet

Rheas are omnivores. They walk around, grazing on broad-leafed plants such as clover. They also eat roots, seeds, and fruits from a wide variety of plant species. In addition to plants, rheas eat insects and other invertebrates, as well as small animals such as lizards, snakes, birds, rodents, and frogs. They also sometimes eat dead fish. Male rheas often dine on hordes of flies attracted by rotting eggs that they purposely leave out of the nest.  

Like many other birds, rheas ingest small pebbles to help them digest their food. They are also coprophagic, which means they ingest their own feces or that of other animals. Many animals, including giant pandas and rabbits, consume their own feces or that of other members of their species. Plant-eating animals, especially, may need to do so to get all the nutrients they can out of the tough-to-digest food they eat.  

Reproduction

Rheas have rather peculiar habits when it comes to reproduction. They are not monogamous and do not form social pairs. During breeding season, males separate from their mixed flocks and then compete with one another for the chance to breed. Males build a nest, which is essentially a scraped-out indentation on the ground lined with grass and leaves. Then they perform mating rituals, complete with booming calls and elaborate wing displays, to attract females. Only a small percentage of males are successful in attracting mates in any given breeding season, and these dominant males may mate with anywhere from two to twelve females at a time.

Females lay from five to ten eggs, but they don’t lay them in the nest, which is guarded aggressively by the male. Instead, females lay their eggs near the nest and then leave. Their job is done, although they may move on to mate with up to a dozen males over the course of the breeding season.

The males then move the eggs, most of them anyway, into the nest. Some of the eggs are left outside the nest, at a distance, where they will rot. These sacrificed eggs are possibly used as decoys for potential nest predators and as bait for flies, which the male rheas and their offspring eat.

Incubation & Rearing

Males incubate up to 80 eggs at a time from as many as twelve different females. The average clutch size is approximately 26. Incubation takes 29 to 43 days. They spend about two-thirds of their time on the nest, leaving during the warmest part of the day to forage. Males can be very aggressive when tending their nests. Sometimes, though, the dominant male may recruit a younger male to incubate his nest while he builds another nest and begins courting females again to start a second brood.

As the chicks get ready to hatch, they begin to whistle inside their shells. The entire brood hatches within a span of about 36 hours. They leave the nest with the male in a few days, and he continues to care for them for another four to six months, until they reach independence. Small chicks often spend time nestled in the feathers on their father’s back.

Sometimes young chicks get separated from their brood, usually because of predators or distractions during feeding times. Often, these lost chicks will be adopted into another brood by a nearby male. These adopted chicks have as high a survival rate as the males’ own chicks.  

Once the young birds reach independence, they continue to grow slowly until they are fully mature. Most reach sexual maturity around two years of age.

Predators & Threats

Adult rheas are large enough to deter most predators. Jaguars, pumas, and feral dogs are among the only animals known to attack and eat full-grown birds. However, these birds do suffer from nest predation. Armadillos, lizards, foxes, including the Pampas fox, and raptors, such as the Chimango Caracara, are examples of wild predators that take eggs and chicks. Feral dogs also pose threats as nest predators.

According to research, Greater Rheas have rates of nest desertion up to 65 percent, due in large part to egg predators and other interference, including from humans.

Hunting by humans and degradation of their habitat are the biggest threats to these birds. They are hunted for meat, their feathers, their eggs, their skin, and oils. Changes to their native environment, particularly to make way for farming, have also damaged populations.

Lifespan

Not much is known about the maximum lifespan of any of the three species. Greater Rheas can live at least 15 years in the wild, perhaps much longer, but their population is unknown. Unfortunately, the numbers of all three species are believed to be in decline, and the IUCN Red List of Threatened Species categorizes only the Lesser Rhea as a species of least concern. The Greater Rhea and the Puna Rhea are both listed as near threatened, with the population of the Puna Rhea estimated at between 1,000 and 2,499 mature individuals.