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Gibbons: Hylobatidae

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.

Male and female siamangs have a pinkish throat sac that can be inflated to magnify the siamangs' booming and barking calls. (© R. Van Nostrand/Photo Researchers, Inc. Reproduced by permission.)

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. ∎



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.


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).

Additional topics

Animal Life ResourceMammalsGibbons: Hylobatidae - Physical Characteristics, Behavior And Reproduction, Gibbons And People, Conservation Status, Pileated Gibbon (hylobates Pileatus): Species Accounts - GEOGRAPHIC RANGE, HABITAT, DIET