Description:
The siamang is by far the largest species of the gibbon family. Standing erect it is almost one meter high. Its arms have a stretch of nearly double this length. with a maximum weight of 20 kilos the male is nearly twice as heavy as the other species of gibbons. The females are somewhat smaller.

Vocalizations:
One feature that distinguishes siamangs from other primates is their duet song. A mature male and female pair of siamangs sing a duet song that lasts approximately 15 minutes. The duet song in composed of specific loud calls by both the male and female. The male typically brachiates (swings arm over arm) during portions of the sequence. Their incredible loud voice is amplified by a conspicuously large larynx sac which can be inflated like a ballon. Listen to a male siamang calling.

"At dawn and sunset, when agitated or confronted with an unusual situation, the siamangs' complicated chorus with its set sequence of calls, whereby male and female have a differ vocal pitch and motif and a repertory of five different kinds of sounds, can be heard for miles. Sometimes they hold their hands in front of their mouths when singing. It is thought that this is intended to cloak or dispel the intimidating effect on their partner of a wide open mouth that utters loud calls. With the aid of these noisy competitions the individual family groups vocally mark their territory and consequently the places where they forage, sleep and rest. The noisier groups usually assert themselves successfully against the less loud. The duets sung by male and female help to stabilize the pairs. Because of their piercing voices the siamangs are sometimes called the "howler apes" of the Old World." (Berger, 1985)

Locomotion:
Siamangs swing through the trees using a hand over hand movement called brachiation. View a small animation of a siamang brachiating or see a real animated gif "movie" of siamangs at the Oakland Zoo

Range:
Siamangs are only found in the Barisan Mountains of Sumatra (Indonesia) and in the mountains of Malay Peninsula south of Perak River.

Habitat:
Upper canopy of lowland and mountain forests from 500 to 2500 feet.

Diet:
Leaves, fruits, flowers and insects

Social Organization:
Siamangs live in monogamous family groups. There is one adult male and one adult female with up to four offspring. According to David Chivers, the male helps to raise the offspring. At night the male sleeps with the young offspring, while the female sleeps with the baby.

Reproduction:
Since siamangs are monogamous (have only one mate), an adult female mates with only one adult male. Gestation is seven months (230 days). Typically an single infant is born, but there have been twins births reported in zoos.

Population Status:
CITES - Appendix I; U.S. Endangered Species Act - Endangered

Threats to Survival:
Since siamangs are primarily arboreal (live in the trees), they are directly affected by habitat destruction from logging and agriculture practices. They are also potentially threatened by the pet primate trade. The adults are killed so people can have a cute young siamang as a pet.

Conservation - Species Survival Plan:
Siamangs are listed under the Gibbons Species Survival Plan of the American Zoo and Aquarium Association. The mission of the American Zoo and Aquarium Association's Species Survival Plan (SSP) Program is to help ensure the survival of selected wildlife species.

The Species Survival Plan, or SSP, began in 1981 as a cooperative population management and conservation program for selected species at North American zoos and aquariums. Each SSP carefully manages the breeding of a species in order to maintain a healthy and self-sustaining captive population that is both genetically diverse and demographically stable.

Information Source:
This information is provided as a courtesy of Tim Knight, Research Volunteer at the Woodland Park Zoological Gardens in Seattle, Washington.

References:
Berger, G. 1985. Monkeys and Apes. Arco Publishing, Inc., New York.

American Zoo and Aquarium Association Web site.

Related Web pages:

• Asian Rainforest: Siamang
  Hear siamang calls and view a large gif animation of a siamang brachiating. This is a great resource for students interested in learning about the siamangs at the Oakland Zoo. Information includes: description; geographical range and habitat, diet, life cycle/social structure; special adaptations; interpretitive information; status in the wild; and evolution.

• Siamang Facts - Woodland Park Zoo
  Information about siamang life cycle, reproduction, and singing behavior.

• Siamang Photos by Tim Knight
  Photos of a siamang pair.