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Scientific Name: Hylobates syndactylus

Photo courtesy of ©Columbia Metropolitan CVB.


Siamangs are the largest species in the gibbon family. They weigh 18-29 pounds and reach approximately 2½ to 3 feet tall. They have an arm spread of as much as 5 feet, allowing them to be spectacular brachiators (arm-over-arm swinging used for locomotion).

Siamangs are arboreal (tree-dwelling) primates that consume leaves fruits, flowers and insects from the upper canopy of mountainous forest regions. They live in monogamous family groups where the adult males and females are bonded for life. Normally a single offspring is born to each family, and it is initially cared for by the mother. Adult males take over raising the young by two years of age, teaching them the necessary socialization and locomotive skills.

One feature that distinguishes siamangs from other primates is the duet song that marks their territory with sound. It consists of loud booms and barks, amplified by resonating sounds across their inflated throat sacs. This vocalization can be heard several miles away.


Siamangs live in the forests of Sumatra and Malaysia.

Status in the Wild

Siamangs are endangered because they are directly affected by habitat destruction from logging and agriculture practices. The pet trade is also responsible for their decline. Young siamangs are obtained as pets, and their owners often find they mature into aggressive and unpredictable adults.

In captivity, siamangs are managed under the Association of Zoos & Aquariums (AZA) Gibbon Species Survival Plan (SSP). Its mission is to maintain a healthy and self-sustaining captive population that is both genetically diverse and demographically stable to ensure the survival of these remarkable species. Riverbanks Zoo has maintained siamangs since 1974.