RHEAS: Rheidae

PHYSICAL CHARACTERISTICS

Rheas are similar in general appearance to the ostrich, except for the fact that they are smaller and do not have the large tail feather plumes of ostriches. Rheas are 4.5 to 5.6 feet (1.3 to 1.7 meters) tall from their feet to the top of their back and weigh 55 to 88 pounds (24.75 to 40 kilograms). Their head, neck, and bodies are covered with soft, loose feathers that are gray or spotted brown and white.

They have long legs with three toes and wings with a claw on the end, an effective weapon against predators. Males are larger than females and the lesser rhea is smaller than the greater rhea.

GEOGRAPHIC RANGE

Rheas are distributed in Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay.

HABITAT

Rheas live almost exclusively on grassland although two subspecies of the lesser rhea also inhabit desert areas.

DIET

Rheas are omnivores, meaning that they eat both plants and meat. Their diet consists mainly of grass, leaves, herbs, fruit, and seeds, as well as lizards, insects, and small animals.

BEHAVIOR AND REPRODUCTION

Rheas are the largest birds in South America. They are extremely friendly and sociable. In the non-breeding season, the lesser rhea usually live in flocks of five to thirty birds, while the greater rhea live in flocks of ten to one hundred individuals. They are often found grazing alongside herbivorous (plant eating) mammals, such as deer and alpacas. They are fast runners and can reach speeds of up to 37 miles (60 kilometers) per hour, usually running in a zigzag pattern.

Rheas belong to a group of birds called ratites, which are flightless birds that have a flat breastbone rather than a keeled, or curved breastbone like birds of flight. They have a simplified wing bone structure, strong legs, and no feather vanes, making it unnecessary to oil the feathers.

They are polygamous (puh-LIH-guh-mus), meaning they have more than one mate during the breeding season. During breeding season, the male rhea builds a nest in which between two and fifteen females lay their eggs. Nests contain ten to sixty eggs. The male cares for the chicks for about thirty-six hours after they hatch.

During the winter, the flocks split into three groups: single adult males, flocks of two to fifteen females, and yearlings two-years-old and younger. Males challenge each other and try to attract females. This behavior intensifies as the spring and summer breeding season approaches.

RED MEAT WITH FEATHERS

Rheas are raised commercially in the United States for their meat. However, although rheas are poultry, their meat is classified as red rather than white. Raw rhea meat is a dark cherry red. After it's cooked, it looks and tastes similar to beef, except it is a little sweeter. Rhea meat is sold as steaks, fillets, medallions (small coin-shaped pieces of meat), roasts, and ground meat. Rhea meat is lower in cholesterol and fat than beef and lower in calories than beef, chicken, and turkey, according to the United States Department of Agriculture (USDA). In 2002, the USDA instituted mandatory inspection of rhea meat in places where the birds are slaughtered.

RHEAS AND PEOPLE

Rheas are hunted in the wild by humans for their meat, skin, and feathers. They are raised commercially on farms in the United States and Canada for their meat. They are considered agricultural pests by farmers because they will eat almost any crop.

CONSERVATION STATUS

The greater rhea and lesser rhea are listed by the IUCN as Near Threatened, meaning they are in danger of becoming threatened. Their populations are declining throughout their range, because much of their habitat is shrinking due to conversion to farmland. The Puna rhea, a subspecies of the lesser rhea, has a total population in the wild of only several hundred.

LESSER RHEA (Pterocnemia pennata): SPECIES ACCOUNT

Physical characteristics: The lesser rhea is 36 to 39 inches (92 to 100 centimeters) in height and weighs 33 to 55 pounds (15 to 25 kilograms).

Geographic range: Lesser rheas are found in Argentina, Bolivia, Chile, and Peru.

Habitat: Lesser rheas live in the grassy, open high plains of South America.

Diet: Lesser rheas are omnivores, meaning they eat both plants and flesh. They primarily eat grasses, plants, leaves, roots, fruit, and seeds along with insects, lizards and small mammals. They drink little water and get most of the liquid they need from plants. They also swallow pebbles to aid with digestion.

Behavior and reproduction: Lesser rheas are social creatures that usually live in herds of five to thirty individuals. In the spring and summer breeding season, males become territorial by selecting an area of land as their territory and defending it against other males. Females also leave the larger group to congregate in smaller flocks.

The flightless birds are fast runners, capable of reaching speeds of up to 37 miles (60 kilometers) per hour. They are also strong swimmers, capable of crossing rivers. They have excellent eyesight and hearing. They often graze with smaller herbivores and are able to detect predators, animals that hunt them for food, from a long distance, thus alerting the other grazing animals to the danger.

Lesser rheas are polygamous, meaning they have more than one mate during the breeding season. During the spring and summer, the male lesser rhea builds a nest in which between two and fifteen females lay their eggs. Nests contain ten to sixty eggs. The male incubates the eggs by sitting on them for thirty-five to forty days in order to keep them warm, so that they may later hatch. After the eggs hatch, the male cares for the chicks for a few days. He then leads the chicks away from the nest but they stay in contact through a series of whistles.

Lesser rheas and people: Lesser rheas are hunted in the wild by humans for their meat, skin, and feathers. They are raised commercially on farms in the United States and Canada for their meat. They are viewed with mixed feelings by farmers and ranchers. Farmers consider them agricultural pests because they will eat almost any crop. Cattle ranchers consider them beneficial because they often graze with sheep and eat grasses that have sharp burrs that become entangled in sheep's wool.

Conservation status: The lesser rhea is listed by the World Conservation Union (IUCN) as Near Threatened, because their populations are declining throughout their range. Much of their habitat is shrinking due to conversion to farmland. The Puna rhea, a subspecies of the lesser rhea, has a total population in the wild of only several hundred. ∎

FOR MORE INFORMATION

Books:

Davies, S. J. J. F., et al. Bird Families of the World. Vol. 8, Ratites and Tinamous: Tinamidae, Rheidae, Dromaiidae, Casuariidae, Apterygidae, Struthionidae. Oxford, U.K.: Oxford University Press, 2002.

Elwood, Ann, and John B. Wexo. Ostriches, Emus, Rheas, Kiwis, and Cassowaries (Zoo Books). Mankato, MN: Creative Education, 2000.

Periodicals:

Bouzat, Juan L. "The Population Genetic Structure of the Greater Rhea (Rhea americana) in an Agricultural Landscape." Biological Conservation. (June 2001): 277–284.

Codenotti, Thais L., and Fernando Alvarez. "Mating Behavior of the Male Greater Rhea." Wilson Bulletin (March 2001): 85.

Fernánzez, Gustavo J., and Myriam E. Mermoz. "Group Copulation Solicitation Display Among Female Greater Rheas." Wilson Bulletin (December 2003): 467–470.

Fernánzez, Gustavo J., et al. "Effect of Group Size on Individual and Collective Vigilance in Greater Rheas." Ethology (May 2003): 413–425.

Navarro, Joaquín L., et al. "Fertility of Greater Rhea Orphan Eggs: Conservation and Management Implications." Journal of Field Ornithology. (January 1998): 117–120.

Zannini, Marie, and Greg Zannini. "Another Look at Rheas." Countryside & Small Stock Journal (January–February 1995): 28–30.

Web sites:

Cholewiak, Danielle. "Family Rheidae." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/information/Rheidae.html (accessed on July 13, 2004).

Ivory, Alicia. "Rhea pennata." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/information/Rhea_pennata.html (accessed on July 13, 2004).