Siamang

Characteristics

The gibbon family consists of lesser apes who spend their days in the trees. Their fur tends to be thicker and denser than other apes, giving them a heavy appearance. They are generally monogamous and very territorial of their group's area, though usually in non-violent expressions unlike other apes who may be physically aggressive or violent towards intruders.

Species Specifics

The siamang is the largest of the lesser apes; they are about twice the weight as the other gibbons in their family. They are jet black with a mostly hairless face. Their fur is long and somewhat shaggy. Their arm span can reach 5 feet. The hair on their forearms grows towards the elbow, like it does in humans and great apes. Siamangs have webbing between their second and third toes and fingers, something that sets them apart from other gibbon species.

Physical Characteristics

Siamang can carry objects with their feet because they have opposable big toes, in addition to opposable thumbs. Their arms are longer than their legs to help them climb and swing through the canopies. Their wrists are a ball and socket joint which makes the joint much more flexible than our hinged human wrists. They use their hands as hooks when brachiating. Siamang rarely descend to the ground but when they do, they walk upright with their arms above their heads to help them balance. Their gular sac, the inflatable vocal sac on the front of their neck, is unique among gibbons. It allows their song in both sexes to amplify and carry over a much longer distance than other gibbons.

Ecology

Habitat

Upper forest canopies

Distribution

Their territory ranges from 40 to 115 acres. During the course of a day, a siamang family will travel up to a mile foraging. The group will travel less distance during the wet season. Individuals will stay close to one another during their daily activities. When an adult disperses they usually do not travel more than 2 miles from their natal family group.

Diet

Siamang eat fruits, leaves, and other plant products. Fruit seems to be preferred when it is available. They also eat insects, birds, and birds' eggs.

Ecological Web

Because so much of their diet is fruit, siamang are thought to be important in dispersing seeds.

Activity and Behavior

Activity Pattern

The family group sleeps together in the upper canopy. They sleep upright in the foliage, unlike the great apes who build nests and platforms.

Behavior

Siamang spend most of their life in the trees and seem strongly averse to water. Females will lead a vocal territory defense while males will lead non-vocal defense. Siamang pairs will make male-female duet calls in the morning; these are used to maintain territory and help with cohesion in the family unit. The song can be heard from 2 miles away; they are considered the loudest land mammal.

Social Behavior

Siamang live in bonded pairs with up to three offspring. Offspring will leave the family group at 6-8 years of age.

Reproductive Behavior

Siamang are mostly monogamous, though there have been instances of polygamy in wild populations. Conception usually occurs between May and July, with births occurring between December and February. Offspring are spaced about three years apart. A female will usually have no more than ten pregnancies in her lifetime.

Offspring

Siamang have a single offspring who is born weighing 6 oz and without fur. The shaggy coat will come in at 2-3 years of age. The infant is weaned at 1 year old. The father exhibits more paternal care than other gibbon species. They may carry the infant while moving from tree to tree and even take over most of the daily care when the infant is 1 year old.

Conservation

Status

Listed on Appendix I of CITES. Listed as Endangered by the IUCN.

Historical

The population of siamang may have declined 50% over the last 40 years because of the pet trade and habitat loss. They may have lost 50% of their historical habitat but they are very adaptable to environmental changes.

Current Threats

Our Role

Oakland Zoo has projects to help end the exotic pet trade and to curb palm oil production, both of which affect siamang in the wild.