Reproduction
Siamangs mature sexually at 5 to 7 years of age. They form long-term monogamous bonds. Gestation period is seven to eight months (230 days). Females bear single young whose average birth weight is 6 ounces (170 gr). Females reproduce approximately every two to three years.

Life Cycle
Siamangs provide a high level of parental care for their young. Infants are born naked (hairless) but are soon covered with soft, dark hair. They will not grow their long, adult hair until 2 to 3 years old. During the first year, mothers closely guard and care for their infants. Young are weaned at about 1, at which time fathers take over their daily care until the juveniles can live without assistance at about age 3. Between 6 to 8 years old, subadult siamangs leave their family units to establish their own families.

The "Swinging" Life
All gibbon species use brachiation (hand-over-hand locomotion) as their primary means of travel through their forest habitat. Powerful upper limbs and limited body weight enable siamangs to swing on branches and vines with great agility. Siamangs hook, rather than grasp, branches with their hands. In the wild, siamangs rarely descend to the forest floor. When required, however, they are efficient at bipedal walking on the ground or along branches, holding their arms above their head for balance.

Of all the gibbon species, siamangs form the closest social ties within the family unit. The siamang family group consists of one adult male and one adult female (probably a monogamous pair), and two or three offspring. Siamangs are diurnal (active during the day), with family members remaining close together while they forage for food. Food is generously shared among all family members. Rarely will family members become separated from one another by more than 100 feet (30 m).

Grooming among family members is their most common social behavior, followed by play centered on the infant. Unlike the great apes (gorillas, chimpanzees and orangutans) which build sleeping nests or platforms, siamangs sleep sitting upright on a branch high in the forest canopy, with arms folded and head between their knees.

Singin' in the Rain
Early in the morning, the tropical rain forest usually resonates with "singing" siamangs. Described as a combination of a dog’s bark and a grouse’s hoot, siamangs sing (or call) to communicate between family groups. Singing communicates location between different family groups, establishes and maintains feeding area boundaries and is also for defensive posturing. It is believed that singing also helps form, maintain and further develop bonds between a mated pair.

Siamangs sing so loudly that it can be heard for up to 3 miles (4.8 km). To produce this loud call, siamangs have a hairless, reddish-brown or gray throat (laryngeal) pouch which acts as a resonator to enhance the carrying of their call. When not in use, the pouch is hidden under their long, shaggy, jet-black fur. When inflated, the pouch is about the size of a siamang’s head, and amplifies its hooting and barking to ear-splitting levels. Usually involving the adult pair, the male and female sing different but coordinated parts; songs have a definite beginning, middle and end. Each elaborate duet begins slowly, then accelerates in speed. A song lasts about 18 seconds and is repeated for about 15 minutes.

Woodland Park Zoo's siamang area, located at the Trail of Vines exhibit in the Tropical Asia bioclimatic zone, simulates their natural environment through the innovative use of dense foliage, vines, massive rock outcrops, pools and waterfalls.

Visitors can observe the siamangs as they may behave in the wild. The area also has a heated indoor enclosure where the siamangs can reside during inclement weather.

Siamangs are an endangered species.** Overpopulation, logging, agriculture and other human activities are rapidly destroying forest environments required by siamangs and other gibbon species for their survival.

Woodland Park Zoo is dedicated to conserving the siamang. The zoo supported a genetic analysis of captive North American siamangs to determine if there were distinct subspecies within the captive population. This study concluded that there was not sufficient genetic variation among siamangs to support subspecies designation. As a result, North American captive siamangs are managed as one population.

How You Can Help!
The effort to save threatened and endangered species requires cooperation and support at the international, national, regional and individual levels. You can help in this cause. Join and become active in Woodland Park Zoo and other conservation organizations of your choice. Please do not buy products made from wild animal parts. Let your elected representatives know your views about conservation of endangered species and wild habitats.

Contact Woodland Park Zoo at webkeeper@zoo.org to find out about ways you can support conservation programs at the zoo. Learn other ways you can help conserve wildlife and the habitats they require for survival by visiting our How You Can Help page.

Sources and Suggested Reading
Macdonald, David, ed. 1993. The Encyclopedia of Mammals. Facts on File, Inc., New York, NY. 895 p.

Nowak, Ronald M., ed. 1991. Walker’s Mammals of the World. 5th Edition. The John Hopkins University Press, Baltimore and London. 1,629 p.

For Kids!
Zoobooks. 1994. Apes. Wildlife Education, Ltd., San Diego, CA. 18 p.

More References

* Taxonomic classification varies between references. Classification information used in this fact sheet was taken from Mammal Species of the World: A Taxonomic And Geographic Reference, edited by Don E. Wilson and Dee Ann M. Reeder, Second Edition, 1993.

**Woodland Park Zoo identifies an animal or plant endangered if it is listed as endangered (in any part of its range) on the federal list of Endangered and Threatened Species, or if is listed on Appendix 1 of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

Facts About Woodland Park Zoo's Siamangs

Frequently Asked Questions About Siamangs