The Lar gibbon is a beautiful and captivating primate and a master of agility, being remarkably fast when swinging through the trees from branch to branch. It has long arms and hands, perfectly adapted to this means of locomotion. Despite having no tail, the Lar gibbon has an acute sense of balance, and it sometimes walks along branches high up in the trees on its hind legs, characteristically lifting its arms up above its head to balance. Individuals range in color from dark brown or black to pale fawn and red-buff, always having a white fringe around their black face and white hands and feet on the upper sides.
Lar gibbons are found throughout Southeast Asia, mainly in Thailand, Malaysia and Sumatra Island of Indonesia. Their habitats include tropical and subtropical dry and moist broadleaf forests with dipterocarpaceae being dominant in. They are a species that lives in the high canopy and are seldom found in the understory.
Lar gibbons are social, diurnal and arboreal animals. On average, 15.5 hours are spent up in 'sleeping trees', from a few hours before dusk comes, until the following morning, a behavior which is an adaptation to minimize risk of predation. They are usually active for an average of 8.5 hours during the day, spend their days feeding (32.6%), resting (26.2%), traveling (24.2%), in social activities (11.3%), vocalizing (4.0%) and in intergroup encounters (1.9%), although actual proportions of activities can change significantly over the course of the year. Gibbons use vocalization to communicate with others of their species. Duets are sung to announce territoriality, sending a signal to groups nearby who pose a threat. An individual defends his home range during intergroup encounters at overlapping zones of ranges, males singing together to chase away intruders.
Lar gibbons are largely frugivorous, eating ripe fruit from tropical trees and woody climbers, and being very selective about which types of fruit they eat. They also eat flowers, leafy plants, and insects.
Lar gibbons have a flexible mating system. They are monogamous but show some serial monogamy by occasional changes of partner, and there are some non-monogamous groupings as well. Generally, a group consists of a mated pair with their offspring. However, females may exhibit a polyandrous mating system, when one female has an exclusive relationship with two or more males. This is seen among females who have larger home ranges where good resources are not so available. Lar gibbons breed at any time of the year, usually producing one offspring each two to three years. Gestation lasts for 7 to 8 months, with young being weaned at 18 months. The mother provides most of the parental care but the father and older siblings help to raise the young. Adult size is gained at 6 years but offspring remain in their natal group until around 9 years old, when they reach sexual maturity.
Rapid loss of habitat is the main threat to Lar gibbons, which puts their future in great danger. The forests in Southeast Asia are being logged and cleared for agriculture at a very rapid pace, reducing the area where forest inhabitants can live. Sometimes lar gibbons are hunted for their meat. In some countries, Thailand in particular, the capture of juvenile gibbons to be sold as pet trade is widespread.
According to the IUCN Red List no population estimates are currently available for Indonesia, Malaysia, and Myanmar. There are estimates in Thailand: in Kaeng Krachan National Park - 3,000-4,000 individuals; the Western Forest Complex - 10,000 animals; in the western part of Khao Yai National Park – around 1, 000 animals. Overall Lar gibbons’ numbers are decreasing currently and they are classified as endangered on the list of threatened species.