Gibbon

Order: Primates
Suborder: Haplorhini
Infraorder: Catarrhini
Family: Hylobatidae

Physical Description
The 12 species of gibbons are classified, referring to their size, as lesser apes. They exhibit many of the general characteristics of primates: flat faces, stereoscopic vision, enlarged brain size, grasping hands and feet, and opposable digits; and many specific characteristics of apes: broad chest, full shoulder rotation, no tail, and arms longer than legs.
Gibbons are relatively small, slender, and agile. They have fluffy, dense hair. They are not sexually dimorphic in size. Mature females usually weigh more than mature males. They have very long arms, which they use in a spectacular arm-swinging locomotion called brachiation. Their hands and fingers are also very long. The relatively short thumb is set well down on the palm, and their fingers form a hook, which is used during brachiation. Gibbons have very good bipedal locomotion, which they use on stable surfaces too large to grasp. When walking bipedally, arms are held up to keep from dragging and to assist with balance. Gibbons are sometimes observed putting their weight on their hands and swinging their legs through as if using crutches.
Gibbons do not build nests like the great apes. They sleep sitting up with their arms wrapped around their knees and their head tucked into their lap. They have ischial callosities (fleshy, nerveless pads attached to the hip bones, a characteristic otherwise found only in Old World monkeys).

Social Structure
Gibbons live in small, monogamous families composed of a mated pair and up to four offspring. Less than six percent of all primate species (more than 300) are considered monogamous.
Gibbons are one of the few apes where the adult female is the dominant animal in the group. The hierarchy places her female offspring next followed by the male offspring and finally by the adult male.
Gibbons are physically independent at about three, mature at about six, and usually leave the family group at about eight, though they may spend up to ten years in their family group.

Communication
Gibbons are known for their beautiful song. Their loud vocalization can be heard up to one mile away and is used to announce location, defend territory, and maintain bonds with the family unit. The adult pair, sometimes joined by practicing juveniles, sing duets. Each individual can be identified by his or her song.
Siamangs have a louder call than white-cheked gibbons, amplified by a throat sac. Their call can be heard up to two miles away. Also used to defend territory, it includes more of a boom, bark, and a loud call increasing in speed as the call goes on, as compared to the chatter and calling of the other gibbon families.

Life span
Longevity in the wild is 25 to 30 years and can be as long as 40 years in captivity.

Conservation
All gibbons are endangered, largely due to deforestation. They are also hunted and trapped for the pet trade.

Fact sheets for other gibbon species :

White-cheeked Gibbons
Siamangs