GIBBONS: Hylobatidae

PHYSICAL CHARACTERISTICS

Gibbons have a thick coat that ranges in color from black to silvery gray to ash blond. They have a slender body and no tail. The bare face is framed in white fur or other markings. The extremely long arms, with hooklike fingers, are used for brachiating (BRAKE-ee-ate-ing), or swinging from branch to branch. Scientists consider gibbons as the only true brachiators, having powerful shoulder joints for reaching overhead and a wrist that can be rotated 180 degrees for switching position without tiring the arms and upper body. Gibbons are the only apes with skin pads on their buttocks that allow them to sleep comfortably sitting up.

GEOGRAPHIC RANGE

Gibbons are found in Southeast Asia, including China, India, Bangladesh, Myanmar, Thailand, Cambodia, Laos, Vietnam, Malaysia, and Indonesia.

HABITAT

Gibbons prefer the upper forest canopy, where fruits are abundant and spreading branches allow for continuous travel. They also thrive in surviving areas of forests that have been logged.

DIET

Ripe fruits are gibbons' main diet. Figs are their favorite. They also feed on leaves, flowers, buds, shoots, bird eggs, young birds, and insects.

BEHAVIOR AND REPRODUCTION

Gibbons are predominantly arboreal (tree-dwelling), defending their territory by chasing intruders and shaking branches. They sing to advertise ownership. Gibbons brachiate by grasping one branch after another or by propelling themselves through the air, loosening their grasp. They walk upright on wide branches or on the ground, arms held overhead to avoid tripping. They are diurnal (active during the day), but go to sleep before dark, sleeping in a sitting position.

The family consists of the parents and one to four juveniles. Females have single births every two or three years. The mother carries the infant around her waist for the first two months. When a juvenile reaches the age of five, the parent of the same sex may start chasing it off. Offspring who refuse to leave home stay in the vicinity of the family, but keep a distance when feeding and sleeping. Most leave home when they become sexually mature, or able to reproduce, at age seven or eight.

GIBBONS AND PEOPLE

Gibbons are popular zoo animals. The Ibans, the native people of Borneo, believe gibbons are human reincarnation, or the reappearance of a loved one's soul in the animal's body. Infants are captured for the pet trade.

SINGING GIBBONS

Gibbons typically begin their day by singing. It is thought that singing serves to advertise territory ownership or readiness to mate. It also reinforces pair bonds and family ties. Songs are loud and long, lasting up to an average of fifteen to thirty minutes. The songs, either solos or duets, follow certain complicated patterns and are specific just to a particular species. Siamangs sing hooting-bark notes made louder by their inflated throat sacs.

CONSERVATION STATUS

The IUCN lists the Moloch gibbon and the eastern black gibbon as Critically Endangered, facing an extremely high risk of extinction in the wild, due to hunting, as well as habitat loss and degradation from logging and human settlement. The hoolock gibbon and the black crested gibbon are listed as Endangered, facing a very high risk of extinction, due to habitat loss and degradation from human activities. The pileated gibbon, the Kloss gibbon, and the golden-cheeked gibbon are classified as Vulnerable, facing a high risk of extinction, due to habitat loss and degradation from human activities.

PILEATED GIBBON (Hylobates pileatus): SPECIES ACCOUNTS

Physical characteristics: Pileated gibbons have dense, woolly fur. Males are black, with a black face framed in white. Hands and feet are white. Females are silvery beige or ash blond, with a black face and chest. The top of females' head is also black. The body is slender and the small head is rounded. Very long arms have hooklike fingers for brachiation. Thick skin pads line the rears for prolonged sitting. Males weigh 17 to 23 pounds (7.7 to 10.4 kilograms), and females about 14 to 19 pounds (6.3 to 8.6 kilograms). The average head and body length is 17.5 to 25 inches (44 to 63.5 centimeters).

Geographic range: Pileated gibbons are found in Thailand, Cambodia, and Laos.

Habitat: Pileated gibbons prefer primary forests with well-developed canopies. They live in evergreen and semi-evergreen forests. They also occupy monsoon deciduous forests that have periods of heavy rainfall and dry spells, causing leaves to fall.

Diet: Pileated gibbons eat predominantly ripe fruits, supplemented with flowers, leaves, and insects.

Behavior and reproduction: The family consists of an adult pair and up to four offspring. The gibbons are arboreal and diurnal. Upon waking, the mated pair sings a duet, in which the offspring may join. The family forages soon after. Gibbons are territorial, defending their home against outsiders. They mostly travel by brachiating, but sometimes walk on two feet or leap through wide forest gaps. The family almost never goes down to the forest floor. They sleep before sundown, sitting on tree branches.

Females give birth to an infant every two or three years. The mother is the principal caregiver. The young tend to stay with the parents until they are ready to start their own family at seven or eight years of age. However, the parents may try to expel them when they reach the age of five.

Pileated gibbons and people: Poachers (illegal hunters) kill gibbons for food and capture the young for pets.

Conservation status: The IUCN lists the pileated gibbon as Vulnerable due to habitat loss from logging and human settlement. ∎

LAR GIBBON (Hylobates lar): SPECIES ACCOUNTS

Physical characteristics: Lar gibbons have thick, shaggy fur that is dark brown, beige, or a combination of both. The hands and feet are white. The black naked face is surrounded by a ring of white hair. Extremely long arms end in slender fingers that hook over branches when brachiating. The buttocks have thickened pads, adapted for prolonged sitting while asleep. Males weigh 11 to 16.8 pounds (5 to 7.6 kilograms), and females about 9.7 to 15 pounds (4.4 to 6.8 kilograms). The average head and body length is 16.5 to 23 inches (42 to 58 centimeters).

Geographic range: Lar gibbons are found in China, Indonesia, Malaysia, Myanmar, and Thailand.

Habitat: Lar gibbons prefer the high forest canopy where plentiful fruits are found. They occupy evergreen and semi-evergreen forests. They also inhabit monsoon deciduous forests, characterized by heavy rainfall and dry periods during which leaves fall.

Diet: Lar gibbons feed mainly on fruits, supplemented with flowers, leaves, and insects.

Behavior and reproduction: Lars gibbons are arboreal and diurnal. Brachiation is their chief means of moving through the forest. On the ground and on wider branches, they walk on two feet, holding their long arms over their heads for balance and to avoid tripping over the arms. They are territorial, chasing neighbors off their home boundaries and advertising ownership by loud singing.

The family consists of the mated pair and their young. However, there have been reports of the adult male or female moving in with the neighbors. Some stay permanently; others eventually return home. Females give birth to one infant every two or three years. When a juvenile reaches the age of five, the parent of the same sex may force it to leave. The young may continue to stay in the vicinity of the family, but keeps a distance when feeding and sleeping. Young females typically leave home by age eight.

Lar gibbons and people: The young are captured for the pet trade, and the mothers are usually killed.

Conservation status: The IUCN lists the lar gibbon as Near Threatened, not threatened, but could become so, due to habitat loss and degradation from agriculture, logging, and capture for the pet trade. ∎

SIAMANG (Symphalangus syndactylus): SPECIES ACCOUNTS

Physical characteristics: Siamangs are the largest gibbons, weighing about 18 to 29 pounds (8 to 13 kilograms), with a head and body length of 29.5 to 35.5 inches (75 to 90 centimeters). Their black fur is long and shaggy, making them look larger. The face is reddish brown. Both sexes have a pinkish throat sac that can be inflated to magnify the siamangs' booming and barking calls. Thick skin pads on the rear provide comfort when sleeping in a sitting position. Hooked fingers at the end of long arms allow for brachiation. The second and third toes are fused by a webbing of skin.

Geographic range: Siamangs are found in Indonesia and Malaysia.

Habitat: Siamangs are found in the lower canopy of evergreen forests. They also occupy mountain forests and monsoon deciduous forests, characterized by heavy rainfall and dry periods during which leaves fall.

Diet: Siamangs consume ripe fruits, leaves, flowers, shoots, and insects.

Behavior and reproduction: Siamangs are arboreal and diurnal. Upon waking, they sing harsh barking and booming notes, made louder by their inflatable throat sacs. Brachiation is the chief mode of locomotion among siamangs, who are capable of gliding over a forest gap of 25 to 32 feet (8 to 10 meters). They walk upright when on the ground or when branches are too wide for grasping.

The family consists of the parents and up to four offspring of different ages. Females have single births every two or three years. The mother carries the infant around her waist for the first two months. The father may help carry the infant when it stops nursing at two years of age. Offspring who reach sexual maturity at ages seven or eight leave the family to form their own.

Siamangs and people: Some local people revere siamangs for their impressive songs. Poachers hunt them to sell the meat for food and body parts for medicinal use.

Conservation status: The IUCN lists the siamang as Near Threatened due to habitat loss and degradation from human activities. ∎

FOR MORE INFORMATION

Books:

Fleagle, John G. Primate Adaptation and Evolution, 2nd ed. San Diego, CA: Academic Press, 1999.

Hunt, Patricia. Gibbons. New York: Dodd, Mead, & Company, 1983.

Kavanagh, Michael. A Complete Guide to Monkeys, Apes and Other Primates. New York: The Viking Press, 1983.

Nowak, Ronald M. Walker's Primates of the World. Baltimore: The Johns Hopkins University Press, 1999.

Periodicals:

Brockelman, Walter Y., and Ulrich Reichard. "Dispersal, Pair Formation and Social Structure in Gibbons, (Hylobates lar)." Behavioral Ecology and Sociobiology (1998): 329–339.

Geissman, Thomas, and Mathias Orgeldinger. "The Relationship between Duet Songs and Pair Bonds in Siamangs, Hylobates syndactylus." Animal Behaviour (2000): 805–809.

Gibbons, Ann. "Monogamous Gibbons Really Swing." Science (1998): 677–678.

Web sites:

"Gibbon." American Zoo and Aquarium Association Ape Taxon Advisory Group (AZA Ape TAG). http://www.apetag.org/Ape%20Tag/gibbon.html (accessed on July 6, 2004).

"Great Apes & Other Primates: Siamangs." Smithsonian National Zoological Park. http://natzoo.si.edu/Animals/Primates/Facts/FactSheets/Gibbons/Siamang/ (accessed on July 6, 2004).

"White-Handed Gibbon." Honolulu Zoo. http://www.honoluluzoo.org/whitehanded_gibbon.htm (accessed on July 6, 2004).

Other sources:

Gibbon Research Lab and Gibbon Network. http://www.gibbons.de (accessed on July 6, 2004).

Gibbon Conservation Center. http://www.gibboncenter.org (accessed on July 6, 2004).