White-cheeked gibbons are small members of the ape family, and, as such, have no tail, which is a point of difference with monkeys. They are sexually dimorphic, meaning that males and females look different. Although they are all are born with a cream color, males become black (except for white cheek patches) when they are two years old. Females turn black at the same time, but once sexually mature, their color goes back to cream. Unweaned infants are a buff/white and juveniles are black. There are two species of these gibbons, being the Northern white-cheeked gibbon, as opposed to the Southern white-cheeked gibbon.
Southeast Asia is the only place that White-cheeked gibbons are found. The northern group inhabits only northern Laos and northern Vietnam. The southern group lives in central Vietnam and southern Laos, ranging in the north from the Rao Nay and Nam Theun (Khading) rivers to the Thach Han and Banghiang rivers in the south. These gibbons live in lowland subtropical rainforests and rarely come down from the canopy to the forest floor.
White-cheeked gibbons are arboreal diurnal animals that live mainly in forest canopies. They move from tree to tree by brachiation. They spend a lot of time eating. These gibbons live in small families, made up of an adult pair with their two young. Each family group is territorial and the beautiful songs of the gibbon are thought to enforce their territorial rights and reinforce the pair's bond. Singing normally happens in the early morning, taking about 10 to 20 minutes. The hierarchy within the family is in the order of the adult female being dominant, followed by the female offspring, then the male offspring, with the adult male being last. An important social activity is grooming between adults, between adults and young, and between sub-adults. Play behavior centered on an infant is another social activity common among these animals.
White-cheeked gibbons form monogamous pairs and have just one mate throughout their life. They breed at any time of the year. A single offspring is born, following gestation of seven month, every two or three years. From birth, an infant cling to its mother, and newborns are often seen clinging to their mother's abdomen in a horizontal position, which allows their mothers to sit, as most gibbons do, with their knees up. Older infants sit on their mother's abdomen in a vertical position. Young are weaned early on in their second year. While being cared for by their parents, infants learn how to groom, what to eat and about basic social interactions as regards playing and social dominance. On reaching full maturity and becoming independent, around 6 to 7 years old, the offspring usually depart from the family group and seek their own territory and a mate.
White-cheeked gibbons are hunted as a source of food, for the pet trade and as a source for traditional "medicines". The value for traditional "medicine" of these animals is a major threat to them throughout their range, and was probably the main cause for the species' decline, including their presumed extinction in China. Habitat loss is also a threat, with wild forest being used as fuel wood or converted into farmland.
According to the IUCN Red List, there are no available population estimates for White-cheeked gibbons. Their numbers are decreasing today and Northern white-cheeked gibbons are classified as critically endangered (CR), while Southern white-cheeked gibbons are classified as endangered (EN) on the list of threatened species.
Due to their diet, these gibbons are important as seed dispersers for certain plants.