Siamangs are members of the order Primates belonging to the “lesser ape” family or Hylobatidae. Their scientific name is Hylobates syndactylus, although up until 1972 it was Symphylangus syndactylus. Siamangs are the largest species in the gibbon family, with a height of 30-35 inches and a weight of around 18-35 pounds. Siamangs have long black hair and a chromosomal count of 52. Most of the other gibbons have chromosomal counts of 38 and 44, although one subgenus does have 52 chromosomes also. Siamangs differ from other members of their family by having a unique webbing of the skin between their second and third toes. There are two subspecies of siamangs, the Sumatran siamang (H. s. syndactylus), which is only found on the Indonesian island of Sumatra, and the Malaysian siamang (H. s. continentis), which is only found on the Malay Peninsula.
Siamangs mostly live in primary and some secondary forests. Their habitat ranges from lowland to mountainous forests, up to elevations of 12,468 feet. The majority of the siamang diet consists of leaves but also includes some fruits and flowers. Siamangs also have been known to prey on small animals. Siamangs spend the majority of their time feeding in the mid-canopy where common trees and leaves are abundant. They also feed at the tops of canopies and under cover near the ground. Members of a family group feed close together, usually staying within 100 to 200 feet of one another. Siamangs typically have smaller day and home ranges than other gibbon species due to the abundance of available leaves in their diet.
Like all hylobatids, siamangs live in monogamous families consisting of one female, one male, and offspring. Siamangs have a gestation period of 200-239 days, and females give birth every two to three years.
During the first year, siamangs spend most of their time with their mother, but during the second year they spend more time with their father. The offspring stay with their parents for up to nine years. When the juveniles become young adults, they leave their parents to start their own families.
Siamangs are an arboreal species and rarely walk on the ground. They brachiate using their long arms and long, skinny fingers. Siamang hands are cup-shaped, allowing them to swing freely through the trees without having to grasp firmly onto branches. Siamangs also locomote bipedally along tree branches, holding their arms in the air so they do not drag on substrates. All gibbons, including siamangs, are renowned for their great vocal calls. Siamangs, however, have the most powerful call of all. They have an enlarged vocal sac in which vocalizations reverberate, making them extremely loud. Every day, the male and female duet together in 20-second bouts that can continue for 15 minutes at a time. Like all species of gibbons, siamangs are threatened by habitat destruction on both Sumatra and the Malay Peninsula. In fact, both species of siamang are endangered.
References:
- Chivers, D. J. (1974). The siamang in Malaya: A field study of a primate in tropical rain forest. Switzerland: S. Karger.
- Preuschoft, H. (1985). The lesser apes: Evolutionary and behavioral biology. Edinburgh: Edinburgh University Press.
- Teleki, G. (1979). Aerial apes: Gibbons of Asia. New York: Coward, McCann & Geoghegan.
