NORTHERN WHITE-CHEEKED GIBBON

Nomascus leucogenys

Geographic Distribution and Habitat
​The northern white-cheeked gibbon (Nomascus leucogenys) is today found only in northwestern Vietnam and northern Laos. A small population was recorded in southern China as recently as the 1980s, but more recent surveys have failed to find any trace of them in the area; they are therefore now considered extinct in China. They inhabit both subtropical, evergreen, and deciduous forests at altitudes ranging from 656 to 5,250 ft (200–1600 m). Most of the areas where they are now found are relatively inaccessible and uninhabited by humans, which is probably why they have survived in these areas.

Northern white-cheeked gibbon range, IUCN 2020

Size, Weight, and Lifespan
Adult male and female northern white-cheeked gibbons are similar in both size and weight. Head and body length ranges between 19.3 and 24 in (49–61 cm) and adults weigh on average 16.5 lb (7.5 kg) but can range from 13.2 to 17.6 lb (6–8 kg). Both sexes have long canines, with the males’ canines being slightly longer on average (0.5 in; 12.3 mm) than the females’ (0.42 in; 10.7 mm).

The lifespan of these gibbons can be up to at least 28 years in the wild, although exact lifespans are not well known. Individuals in captivity generally reach higher ages; one white-cheeked gibbon in captivity reached 51 years of age.

Appearance
Despite being of similar size, northern white-cheeked gibbons show distinct sexual dimorphism in their coloration; adult males are almost entirely black, with stripes of white hair along their cheeks and a noticeable crest on top of their heads. Females, on the other hand, are a pale golden color with a dark brown patch on top of their heads, although females can vary in their coloration. Interestingly, all infants of this species are born a golden color and then turn black with white cheek patches during their first year of life. When they reach sexual maturity, the females then turn golden again while the males remain black. Both sexes have dark faces, which are sometimes framed by white in females.

Gibbons, as lesser apes, have no tails, and northern white-cheeked gibbons have extremely long arms in comparison to their body length, longer even than many other species of gibbon.

What Does It Mean?

Brachiation:
Also called arm swinging, is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms.

Monogamy:
A mating system in which a male and female mate exclusively with each other.

Olfaction:
The action or capacity of smelling; the sense of smell.

Sexual dimorphism:
Distinct difference in size or appearance between the sexes of an animal in addition to difference between the reproductive organs themselves.

Visit the Glossary for more definitions

Female northern white-cheeked gibbon. Photo credit: Bilby/Creative Commons

​Diet
​Northern white-cheeked gibbons are omnivores and eat a range of plant materials and small animals. Fruits are their preferred foods, but they will also eat leaves, flowers, and insects. During the rainy season they eat a lot of fruit, but when it is less available in the dry season, they will feed more on leaves. Other, closely related, species of gibbon are also known to eat bird eggs, chicks, and lizards.

Behavior and Lifestyle
Northern white-cheeked gibbons are exclusively arboreal in the wild, spending all their time high up in the canopy (although in captivity they will spend some time on the ground). Their main form of locomotion is through brachiation, swinging themselves through the trees by gripping branches overhead. They have very strong, long arms and are able to throw themselves between gaps in branches of up to 30 feet (9 m).

Gibbons are diurnal primates and sleep at night, usually on branches near the tops of trees, and usually huddled together. Like many other primates, this species tends to do most foraging in the morning and afternoon, while resting around midday. During the rainy season, they will travel less as fruits are more readily available—whereas they will travel further during the dry season. They tend to travel between .62 and .93 miles (1–1.5 km) each day within their home ranges, which usually span only about a quarter of a square mile (0.4 sq km).

Daily Life and Group Dynamics 
Northern white-cheeked gibbons are monogamous, which means that an adult male and female pair usually stay pair-bonded for life. They live in small family groups consisting of the adult pair and their offspring and group size is typically 3–5 individuals. Offspring of both sexes can stay in their natal group up until 10 years of age. Although most northern white-cheeked gibbons exhibit monogamy, there are some rare reports of groups containing one male and 2–3 adult females, suggesting that their mating system may actually be somewhat flexible.

Similar to many other primates, northern white-cheeked gibbons engage in social grooming to enhance social bonds. Juveniles also participate in both solitary and social play, including grabbing or pulling group mates, or soliciting chasing.

Communication
Gibbons are very famous for their singing, a form of vocal communication, and northern white-cheeked gibbons are no exception. Pair-bonded adult males and females sing duets with each other, often starting at dawn and then singing at intervals throughout the day. Males begin their song by inflating their throat sac to produce a “booming” sound and then follow this with a series of other sounds including the “long” call. Females produce “great” calls, as well as “twitter” notes and the pair take it in turns to sing. The songs are accompanied by body movements and often end with the male swinging between branches and shaking them rigorously. The song structures are not fixed, can vary with context, and can last between 5 and 17 minutes. Juveniles may also join in the couple’s duet, making it a chorus, and daughters will synchronize their great calls with their mothers’.

Facial expressions, gestures, and olfaction also play a role in gibbon communication, although much less is currently known about these than the gibbons’ famous songs.

Reproduction and Family
Northern white-cheeked gibbons reach sexual maturity between 4 and 8 years of age, although it tends to occur earlier in captivity than in the wild. Although adults tend to be monogamous, some mating with extra-pair partners has been recorded in similar species of generally monogamous gibbons.

Females give birth to one infant every 2–3 years after a gestation period that lasts for approximately 200 days. The newborn infant clings to its mother’s belly before traveling independently by around 3 years of age. Both sexes disperse to new territories once they are sexually mature, although they can stay with their parents until they are up to 10 years of age.

Male

Ecological Role
Northern white-cheeked gibbons have a diet that is high in fruit. They, therefore, likely play an important role in the ecosystem via seed dispersal.

Conservation Status and Threats
The northern white-cheeked gibbon is currently classified as Critically Endangered by the International Union for Conservation of Nature (IUCN, 2015) and their numbers continue to be in decline.

In Vietnam, populations are small and isolated. They are threatened by hunting and habitat loss through logging, expansion of agriculture, and gold mining. More natural habitat remains in Laos and the population numbers there are higher than in Vietnam. There are also some taboos against killing gibbons in Laos due to beliefs that they may seek revenge on the hunter; this may also partially explain why the populations in Laos are in less steep decline than those in Vietnam.

Conservation Efforts
​The northern white-cheeked gibbon is currently listed in the Convention on International Trade in Endangered Species (CITES) Appendix A. While this species is legally protected in Vietnam, protections against habitat destruction and poaching are often not enforced. More efforts are required to protect the habitat of the northern white-cheeked gibbon across its range. Additionally, more research is required to better understand how this species is distributed and greater enforcement of protections are needed to prevent hunting and further habitat loss.

​References:

  • ​Bolechová, P., Chaloupková, H., Hradec, M., Jánová, E., & Doležalová, J. (2019). Fur color change and hormonal development in captive females of northern white-cheeked (Nomascus leucogenys) and buff-cheeked (Nomascus gabriellae) gibbons. General and comparative endocrinology, 113210.
  • Fan, P. F., Fei, H. L., & Luo, A. D. (2014). Ecological extinction of the critically endangered northern white-cheeked gibbon Nomascus leucogenys in China. Oryx, 48(1), 52-55.
  • Geissmann, T., Geschke, K., & Blanchard, B. J. (2009). Longevity in gibbons (Hylobatidae). Gibbon J, 5, 81-92
  • Geissmann, T. (1993). Evolution of communication in gibbons (Hylobatidae) (Doctoral dissertation, Ph. D. thesis, Anthropological Institute, Philosoph. Faculty II, Zürich University. 374 pp.(English text, German summary)).
  • Harding, L. E. (2012) Nomascus leucogenys (Primates: Hylobatidae). Mammalian Species, 44(890), pp 1-15. 
  • Alltheworldsprimates.org
  • https://nationalzoo.si.edu/animals/white-cheeked-gibbon
  • ​https://www.iucnredlist.org/species/39895/10272040#conservation-actions

Written by Jennifer Botting, PhD, January 2020