Greater rheas (Rhea americana) are found in the Neotropical region. Their general range is the southeastern area of South America. They range as far north as the south-central region of Brazil and as far south as the southern point of Argentina. Their range reaches to the eastern coastline of South America and as far west as the western border of Argentina. (BirdLife International, 2016; Erize and Villafane, 2016; Giordano, et al., 2008; Sampaio, et al., 2015)
Greater rheas typically inhabit low vegetation grasslands and pampas areas of South America. They have also been found in open woodlands and saline marshes. Due to wild habitat loss, they have also adapted to agricultural developed areas, which replace the native plants with crops. Rheas spend more time in pasture like lands due to the availability of their food and good visibility. The greater rheas also select habitats closer to water bodies, as the tend to breed in more wet habitats. Minimum and maximum elevations have not been reported.
Rheas are ground-nesting birds and tend to go to areas with more vegetation coverage to provide nest protection. The males are the ones to find a location and build a nest. The better the nest location, the more success the male has at breeding. Factors that go into nest-site selection are distance to food and vegetation height and density. Males also tend to build their nests not too far from others, due to the polygamous nature of greater rheas. (BirdLife International, 2016; Erize and Villafane, 2016; Martella, et al., 1996; Sales, 2006; Schetini De Azevedo, et al., 2010)
Greater rheas are flightless birds. They are a ratite bird, along with emus (Dromaius novaehollandiae) and ostriches (Struthio camelus). Their body shape is ovular with a long protruding neck. Their head, neck and posterior are covered by brownish gray colored feathers, while the base of the neck, anterior, and dorsal feathers are black, and their ventral feathers are white. Their bills and scaled legs are yellowish-brown. Despite the inability to fly, these birds possess relatively large and powerful wings. Greater rheas use their wings like sails for bursts of speed during running and assistance in turning. They also create displays for potential mates or competitors.
Although adult males and females do not greatly differ in height or weight, juvenile females tend to grow and develop at a faster rate. Adult males tend to be from 1.34 to 1.70 meters tall and weight 26 to 36 kilograms. Females average 1.35 meters in height and a weight around 32 kilograms. Their wingspan has not yet been reported.
Greater rhea chicks incubate in their eggs for about 38 to 40 days. de Almeida et al. (2015) studied the morphological changes during embryonic development from the fifth to the 27th day. During development the chicks form the necessary skin, heart, and blood vessels first. At around 12 days they start to develop feather follicles, and at 14 to 18 days they have claws and scales. Near the end of their incubation at 27 days, the chicks have developed long down feathers, full claws, and the beginning of their bills. (Beletsky, 2006; BirdLife International, 2016; de Almeida, et al., 2015; Forshaw, 1998; Hodes, 2010; Picasso, 2014; Roots, 2006; Sales, 2006; Sampaio, et al., 2015)
The breeding season of greater rheas begins with the males fighting, then courtship, followed by copulation. Greater rheas are polygynandric. Males are simultaneously polygynous, mating with multiple females at one time. Females are sequentially polyandrous, mating with one male, then moving on to another. Male greater rheas fight for territories and, once they have established their territory, build a nest. The nest is a shallow dip in the ground filled and lined with leaves and grass. This nest is where the males attract females. Males compete against other males, court potential females, then finally end up with a subgroup of two to 12 females. Female greater rheas will sometimes display for nearby males by forming a closed circle. Once the male approaches the circle, he pulls a female from the circle and mounts her. While copulation occurs, the other females are still, and once copulation ends the rheas disperse and feed. Males will copulate with females once every two to three days. Females can lay 20 to 40 eggs per season, and nest can hold up to 30 eggs. Once the males deem the nests full, they drive away the females and begin to incubate. Once this happens, the flock of females move on to another male. This continues for the rest of the season, each female laying multiple eggs in six or more nests per season. (Fernández and Mermoz, 2003; Fernández and Reboreda, 2003; Forshaw, 1998; Sales, 2006; Valdez, et al., 2014)
Greater rheas reproduce seasonally; their reproductive period begins in July and ends in January. During the season, males and females copulate to establish a multitude of nests with eggs. Female rheas start laying eggs around 25 days after copulation and lay them every 48 hours for 10 to 12 days. Females can lay 20 to 40 eggs per season and nests can contain up to 30 eggs. Egg weight and size can depend on temperature and humidity. Because egg mass varies according to these factors, chicks mass at birth has not been reported, but has been reported as 60 to 70 percent of their egg weight. Once the eggs are laid, the females move on and the males stay to care for the offspring. Five to eight days after the eggs are laid, the males start incubating and incubate for 20 to 30 days, until the eggs hatch. The reason for delay of incubation is unknown. After hatching, the males care for the young for six months. Chicks grow quickly, becoming fledglings around four to six months and growing to full size in about six months. Once they turn around two years old they start to breed. (Beletsky, 2006; Fernández and Reboreda, 2002; Fernández and Reboreda, 2003; Forshaw, 1998; Sampaio, et al., 2015; Valdez, et al., 2014)
Male greater rheas build the nests, incubate the eggs and take care of the chicks. After the females lay the eggs in the nest, the males incubate the eggs for 20 to 30 days. Once the eggs hatch, the males look after the chicks for about six months. There are occurrences of males from one nest taking on chicks from another nest that has been abandoned by males that were hunted by humans. These nests can contain chicks of different ages, but the males still care after them until they are independent. During the reproduction season, males spend around 97% of their time at the nest looking after the chicks and keeping a close watch of the surrounding areas for predators. As the chicks get older this vigilance decreases. The chicks are fully grown and independent around six months old, at this time they leave and join groups of adult rheas until the age of sexual maturity. (Fernández and Reboreda, 2003; Sampaio, et al., 2015; Valdez, et al., 2014)
The maximum longevity of greater rheas in the wild and in captivity is unknown. They are known to live for up to 13 years in captivity, but it is possible for them to live much longer. (Navarro and Martella, 2002)
Greater rheas are terrestrial, walking birds, using their long, strong legs to cover greater distances. Rheas only run during social activities, like impressing a potential mate, or when threatened. Greater rheas run in a zigzag pattern, using their wings and necks to steer them in different directions. During the non-breeding season, greater rheas forage diurnally, individually or in groups. While the rheas feed, they are vigilant. This vigilance decreases as group become larger, but a solitary rhea will spend more time in vigilance than feeding.
During the breeding season, rheas form social groups of (1) individual males, (2) reproductively-active female groups, and (3) flocks of young coupled with adult non-reproductive males. Rheas will court each other with displays, and copulate multiple times. Also during this season, vigilance increases and feeding time decreases in both sexes. Greater rheas only vocalize as chicks. Adult rheas make no vocal sounds except for the low booming that males use while courting and to respond to chicks.
Rheas feed by walking slowly with their heads around 50 centimeters above the ground. The rheas only raise their head in vigilance and when swallowing food. Rheas sleep at night; their common posture when resting is with the neck in an s-shaped loop, with their bill resting on their throat. They frequently preen and dust-bathe after sleeping. This preening is done by twisting their necks to reach their wings and moving their bill among their feathers. Dust-bathing is done by crouching and scooping dust or dirt with their bill, then using their necks to toss it on their wings. (Hodes, 2010; Sales, 2006)
Greater rheas have a maximum home range of 2.6 square kilometers. They are more commonly found in areas with both food accessibility and safety from predators. In these areas the rheas claim their territory and build their nests. Their nest circle ranges from one to 1.6 meters in diameter. Greater rheas do not show territorial behavior except in nest defense. They guard their nest and a few meters around it, making their territory size two to three square meters. (Bellis, et al., 2004; Fernández and Reboreda, 2002; Sampaio, et al., 2015)
Greater rheas are mostly silent. As chicks, they utilize specific calls which sound like small higher-pitched chirps. These chirps are used as signals for contact, danger, feeding, and contentment. As the chicks grow, once they are about seven weeks old, the bronchial passage becomes less intruded by their internal membranes. This causes deterioration and silencing as adult rheas. The only sound an adult makes is during breeding season, this is when the male gives a low booming sound. This sound can be heard as far as one kilometer away, and is a sign of male to male competition, and used to attract females. Adult males will also respond to chicks with a light snap of their bill.
During breeding season, male greater rheas will court females with displays. These displays involve three activities, a call posture, the call itself, which is the low booming sound, and running toward the female. Males also conduct a wing display to lead to copulation. Males approach females with a low loop of their neck, bobbing the head. After several minutes, males spread their wings and walk beside or ahead of the female with their anterior end of the body slightly lowered. Occasionally, females will also display for males. They perform a solicitation display by forming a closed circle close to a feeding male. (Beaver, 1978; Codenotti and Alvarez, 2001; Fernández and Mermoz, 2003; Hodes, 2010)
Greater rheas are omnivores. They primarily eat both wild and cultivated plants. They feed on grass, leguminous crops, and agricultural grain. These plants and seeds make up 99% of their diet. Rheas will also consume small vertebrates like small birds, fish, and snakes, and will also sometimes eat insects. These animals account for the remaining one percent of their diet. Rheas are also coprophagous and occasionally consume fresh fecal matter of other rheas. Rheas also ingest small stones to aid their gizzard in grinding their food. Comparatore and Yagueddu (2016) studied the seasonal diet of greater rheas. They found that in the spring, when vegetation availability was high, the birds show affinity mainly to legumes. In the winter, when availability is low, they will eat grasses, wheat and any type of flowering plant. (Comparatore and Yagueddu, 2016; Giordano, et al., 2008; Hodes, 2010; Sampaio, et al., 2015)
Greater rheas and lesser rheas (Pterocnemia pennata) have been hunted for meat, feathers, and their eggs. These human (Homo sapiens) activities have caused free-ranging populations to decline. Egg predation is the leading cause of reproductive failure. If the eggs are not constantly guarded, they are preyed on by species like big hairy armadillos (Chaetophractus villosus) and Pampas foxes (Dusicyon gymnocercus). Adult rheas' only known predators are cougars (Puma concolor), Pampas cats (Leopardus colocolo) and humans. The latter predator is the rheas' main threat.
Greater rheas are constantly vigilant, when they do spot a predator, their tactic is a zigzag run using their wings to help them turn. This deters the predators from chasing after them. (Bellis, et al., 2004; Fernández and Reboreda, 2002; Sales, 2006)
Greater rheas are susceptible to multiple parasites. Parasites have been found in their feather barbs, small and large intestine, gizzard, air sacs, caeca, and oesophagus. Ectoparasites that have been found are lice (Struthiolipeurus rheae and Struthiolipeurus nandu). Endoparasites that have been found include protozoans in the apicomplexa group (Cryptosporidium parvum and Eimeria), protozoans in the ciliophora group (Balantidium struthionis), protozoans in the sarcomastigophora group (Entamoeba, Endolimax, Trichomonas gallinae, Tetratrichomonas gallinarum, Giardia, and Pleuromonas jaculans), nematodes (Sicarius uncinipenis, Torquatoides crotophaga, Deletrocephalus dimidiatus, Deletrocephalus cesarpintoi, Paradeletrocephalus minor, Capillaria venteli, and Dicheilonema rheae), and cestodes (Houttuynia struthionis, Chapmania tauricolis, and Monoecocestus cf rheiphilus). (Sales, 2006)
Greater rheas are hunted for their meat, eggs, feathers, and fat which is used to make oils. Their skins are used for leather in South America and the United States. The greater rheas are kept in captivity and farmed for their eggs and feathers. Empty rhea eggs can be bought for around 25 dollars and their feathers for 50 dollars. The price for their leather ranges about 100 dollars. (Floeck's Country Ranch, 2018; Sales, 2006)
Greater rheas that live in agricultural areas will graze on crops. Other than this, they are not known to have a negative impact on humans. (Sales, 2006)
Greater rheas are a "Near Threatened" species according to the IUCN Red List of Threatened Species. They are located on Appendix II on the CITES website, which classifies them as not close to extinction but trade must be controlled. They have no special status on the US Migratory Bird Act, US Federal List, and the State of Michigan List because they do not live in these regions.
Greater rheas have a large geographic range, but their population is declining rapidly. Their primary threats include hunting and conversion of their natural habitat to agricultural land. Farming has affected the greater rheas habitat by fragmenting it, forcing greater rheas to relocate. Trade for greater rheas' meat, eggs, skin, and oils from their fat is a huge contributor to the population decline. Large amounts of rhea skins are transported out of South America. The primary buyers of rheas are in Japan and the United States as of the 1990s.
The current actions being taken against the greater rhea population decline are to monitor illegal trade, enforce restrictions on hunting and trade, and to preserve the remaining natural habitat. (BirdLife International, 2016; Hodes, 2010)
Kelly Hodges (author), Radford University, Alex Atwood (editor), Radford University, Layne DiBuono (editor), Radford University, Lindsey Lee (editor), Radford University, Karen Powers (editor), Radford University, Joshua Turner (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
living in landscapes dominated by human agriculture.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
an animal that mainly eats the dung of other animals
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
A substance that provides both nutrients and energy to a living thing.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
parental care is carried out by males
marshes are wetland areas often dominated by grasses and reeds.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats all kinds of things, including plants and animals
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
uses sight to communicate
young are relatively well-developed when born
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