white-cheeked gibbon

Nomascus leucogenys   

Weight:15–20 lbs
Geographic Distribution:Historically, Vietnam, Laos, and southern China; currently their distribution is very fragmented in Vietnam and there have been no records from China since 1990.
Habitat:Tropical rainforest, semi-deciduous forest and montane forest; they prefer closed canopy forests
Wild Diet:80% ripe fruit, 20% leaves, buds and flowers; they occasionally eat eggs, young birds, and insects
Zoo Diet:Monkey chow biscuit, canned science diet, and a wide variety of fruits, vegetables, and leafy greens
Status in the Wild:Their population is estimated to be slightly greater than 1,000 individuals.
Location:Tropic World: Asia

Hylobatids, the lesser or smaller apes, differ from great apes by not building nests, being smaller-bodied, showing no size difference between genders, and consistently exhibiting ischial callosities. Adult white-cheeked gibbons exhibit dichromism (different color for each gender). Both genders are born a buff color. Juveniles turn black with a white cheek pattern between six months and a year. Females return to a buff hair color with a black crown patch when they become sexually mature. Males remain black with white cheek patches. Both sexes have very dense hair coat compared with other gibbon species living closer to the equator. Their face, palms and soles are bare and pigmented. Their elongated posture is a key adaptation for suspensory behavior. Their arms and hands are elongated and there is a deep cleft between the index finger and opposable thumb. This thumb is not used in brachiation (swinging by the arms from branch to branch), but is instead used to climb thick branches, groom, and manipulate food. They have a small throat sac used as a resonating chamber. Like all apes, they are tailless.

Gibbons live in monogamous family groups. Pairs remain together for many years. Both males and females are aggressive to conspecifics of the same sex. They defend a home range; its size depends on food resources and population density. They police the territory, which can lead to daily conflicts between rivals. Mutual grooming is of social importance, but they do not groom to the extent of most apes. They are arboreal and sleep among the dense foliage with their knees bent to their chin, their hands folded on their knees, and their face buried between their knees and chest in order to retain body heat. They are diurnal (active during the day) and are most active in the morning. Any play behaviors are usually centered around juveniles and sub-adults. Vocalizations are usually a duet between the male and female. The male makes grunts, squeals and whistles while the female makes a rising twitter note. When moving through the trees, they swing alternately with their arms (brachiation) and have their legs flexed under their body. Gibbons are brachiation specialists, able to swing up to 50 feet between handholds. All apes, greater and lesser, walk bipedally, however, gibbons are the most bipedal of non-human primates. For gibbons, bipedalism is thought to be an adaptation for arboreal feeding more than for terrestrial locomotion.

They feed up in the trees, rarely descending to the ground, and precisely pick fruit with their thumb and index finger or pull food to their mouth. They prefer to feed on small, scattered sources of pulpy fruit. Gibbons are specialists at terminal branch feeding, accessing fruits, buds, and leaves at the thinner outer branches, and suspensory feeding by hanging below branches. Other primate species do not use these terminal branch resources, therefore they are competing with small mammals and birds for terminal branch leaves, buds, and fruit. They spend 9 to 10 hours a day feeding. They drink water by licking wet leaves and bark or by scooping water up with their hand.