Nomascus leucogenys is better known as the white-cheeked gibbon. This species is found only in Southeast Asia. They primarily populate Laos, Vietnam, and Southern China. In Vietnam, N. leucogenys is found to the southwest of the Song Ma and Song Bo Rivers. A close relative, Nomascus concolor, is found northeast of the Song Ma River and northeast of the Song Bo River. The geographical separation is crucial to distinguishing these two gibbon species because N. leucogenys and N. concolor are extremely similar in appearance.
Biogeographic Regions: oriental (Native )
Nomascus leucogenys are not sexually dimorphic in size. Both males and females grow to weigh an average of 5.7 kg. Likewise, both sexes reach similar lengths, from 45 to 63 cm long. White-cheeked gibbons are, however, dimorphic in fur color. All infants are born with cream-colored fur. At two years of age, the infants' fur changes from cream to black, and they develop white patches on their cheeks. At sexual maturity, males stay black with white cheeks. Females turn back to the original cream color and they lose the majority of their white cheek color. Like all species of gibbons, white-cheeked gibbons do not have tails. They have exceptionally long forelimbs and hindlimbs. Their bodies are built for an arboreal lifestyle. They have an opposable hallux and an opposable pollex. This makes grasping food and holding branches easy. Furthermore, their hands are hook shaped, facilitating brachiation. The body of N. leucogenys is small and they have a remarkably upright posture. Their molar teeth are bunodont and their canines are large and showy. The dental formula is 2/2, 1/1, 2/2, 3/3. Nomascus leucogenys was considered a subspecies of crested gibbon, N. concolor, until 1989. The main difference between the two species is the “mohawk” tuft at the top of the head of N. leucogenys.
Average mass: 5.7 kg.
Range length: 45 to 63 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes colored or patterned differently
Nomascus leucogenys live in the canopy of subtropical rainforests. White-cheeked gibbons hardly ever descend to the forest floor.
Range elevation: 300 to 600 m.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: forest ; rainforest
Habitat and Ecology
Gibbons are strictly arboreal and mainly frugivorous (Geissmann et al. 2000), but there is very little field data on the behavioral ecology of N. leucogenys. Dao Van Tien (1983) studied the content of the stomach of six wild-shot crested gibbons (genus Nomascus) from Viet Nam, including three N. leucogenys, and found 90-100% fruits, associated with some leaves and insects. This data cannot be directly compared to field observations, which usually measure the time spent eating various food items (Geissmann et al. 2000). Food composition in Xishuangbanna (southern Yunnan) included fruits (39%), leaves (36%), and flowers (5%) (Hu et al. 1989). During the rainy season (May-October), when many fruits are available, gibbons travel less, whereas in the dry season (November-April), the gibbons eat more leaves and travel for longer distances (Hu et al. 1989). Average group size in Yunnan province, China, was 3.78 (range 3-5, n = 9) (Hu et al. 1989). In anecdotal reports, group sizes of three gibbon groups from Thanh Hoa and Nghe An provinces (southern part of north Viet Nam) were specified as 3, 3, and 4 individuals, respectively (Nguyen Manh Ha et al. 2005).
Nomascus leucogenys are primarily frugivorous. They especially enjoy eating the pulp of fruits. They are important seed dispersers for some plants. In general, N. leucogenys eat and forage with their family. Unlike other primates that spend half of the day foraging and the other half of the day slumbering, white-cheeked gibbons search for food throughout the day. Early in the morning, they forage high in the canopy. When the sun begins to heat the canopy, they retreat to lower trees in the understory. They are frugivores, but along with fruit, white-cheeked gibbons also eat leaves, flowers, and insects. The type of food that they eat depends on precipitation. When there is a great deal of precipitation, fruit is plentiful and they do not have to travel far to find food. Conversely, they travel great distances in search of food when there is little rainfall.
Animal Foods: insects
Plant Foods: leaves; fruit; flowers
Primary Diet: herbivore (Frugivore )
Nomascus leucogenys are known to be excellent seed dispersers because they eat fruit. They drop seeds when they eat and when they excrete.
Ecosystem Impact: disperses seeds
The main threat to Nomascus leucogenys is forest clearing, and therefore, their main predator is humans. It has also been documented that in North Vietnam, some people have hunted N. leucogenys for their meat. Nothing is known about other specific predators of Nomascus leucogenys, but eagles of the family Accipitridae, owls of the family Strigidae, and Panthera pardus are known to prey on N. concolor. Nomascus leucogenys, like N. concolor, live in the canopy and that makes them easy prey for large birds and arboreal carnivores. Gibbons are very agile and remain vigilant in their high, inaccessible habitats, all of which help them avoid predation.
- humans (Homo sapiens)
- leopards (Panthera pardus)
- typical owls (Strigidae)
- large raptors (Accipitridae)
Life History and Behavior
Nomascus leucogenys individuals signal territory by using vocalizations. They also use vocalizations in mating behaviors. In order to signal aggression, N. leucogenys resort to the common threat of opening their mouth wide to show their teeth. White-cheeked gibbons spend much of their time grooming and playing. Grooming and playing allow individual gibbons to form bonds. It is also likely that chemical cues, such as pheromones, are used to communicate reproductive state.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: duets
Perception Channels: visual ; tactile ; acoustic ; chemical
The average lifespan of Nomascus leucogenys in the wild is twenty-eight years.
Status: wild: 28 years.
Lifespan, longevity, and ageing
Nomascus leucogenys are monogamous.
Mating System: monogamous
White-cheeked gibbons become sexually mature at about six to seven years of age. At this point, Nomascus leucogenys females have a menstrual cycle that lasts about twenty-eight days. They breed throughout the year. Once fertilization occurs, a female has a gestation period of seven months. When the infant is born, it holds on to the mother for nearly two years. After the two-year period, the infant is weaned.
Breeding interval: Nomascus leucogenys give birth to a solitary offspring once every two to three years.
Breeding season: A female white-cheeked gibbon has a twenty-eight day menstrual cycle. At this point she is fertile and ready to mate.
Average number of offspring: 1.
Average gestation period: 7 months.
Average weaning age: 24 months.
Range time to independence: 3 to 8 years.
Average time to independence: 6 years.
Range age at sexual or reproductive maturity (female): 5 to 8 years.
Average age at sexual or reproductive maturity (female): 7 years.
Range age at sexual or reproductive maturity (male): 5 to 8 years.
Average age at sexual or reproductive maturity (male): 7 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Parental care in white-cheeked gibbons is not restricted to females. Unlike many mammals where the female is the primary care giver, N. leucogenys share the responsibilities between males and females. An infant reaches physical maturity at three years of age and becomes independent at around six to seven years of age. During the period of parental care, the infant learns to groom, differentiate between food sources, and learns basic social interactions such as playing and social dominance.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Protecting: Male, Female); post-independence association with parents; extended period of juvenile learning
Molecular Biology and Genetics
Statistics of barcoding coverage: Hylobates leucogenys
Public Records: 0
Specimens with Barcodes: 3
Species With Barcodes: 1
Nothing is known about the conservation status of Nomascus leucogenys, but members of the related species Nomascus concolor are endangered due to deforestation, logging, hunting and military activities.
CITES: appendix i
IUCN Red List of Threatened Species: critically endangered
IUCN Red List Assessment
Red List Category
Red List Criteria
Recommended conservation measures include prevention of hunting and wildlife trade; minimization of habitat disturbance; and research and field surveys throughout the range, specifically tape recordings, genetic analysis and photographic recordings to help better define the distribution area of the taxon relative to N. siki. This is among the most common species of crested gibbon (genus Nomascus) maintained in zoos (Varsik 2000; Gibbon Network 2006; Moisson and Baudier 2005).
Relevance to Humans and Ecosystems
There is no known evidence that Nomascus leucogenys effect humans in a negative manner. This is also true for members of the related species Nomascus gabriellae.
Miles and Caldecott (2005) reported that Nomascus concolor are kept as pets in Vietnam when infants are plucked from their mothers. As the infant enters adulthood they become a problem and are often abandoned by their owners. They are also kept at zoos around the world. It is unclear whether these authors studied Nomascus concolor or Nomascus leucogenys.
Positive Impacts: pet trade ; research and education
Northern white-cheeked gibbon
The northern white-cheeked gibbon (Nomascus leucogenys) is a species of gibbon native to South East Asia. It is closely related to the southern white-cheeked gibbon (Nomascus siki), with which it was previously considered conspecific. The females of the two species are virtually indistinguishable in appearance.
The genome of N. leucogenys was sequenced and published in 2011.
A "substantial" population of 455 critically endangered northern white-cheeked crested gibbons (Nomascus leucogenys) have been recently found living in the Pù Mát National Park in Nghệ An Province, northern Vietnam, near the border with Laos. Conservation International report they are living at high altitudes, and far from human settlements. This population, representing two thirds of the total known in Vietnam are, apparently, the "only confirmed viable population" of this variety in the world.
Northern white-cheeked gibbons are sexually dimorphic, with males and females having different colourations and the former also being slightly larger. Males have black hair over their entire bodies, except for distinct white patches on their cheeks, as well as a prominent tuft of hair on the crown of head, and a gular sac. Females are reddish-tan in colour, lack a cranial tuft, and have a crest of black or dark brown fur running from the crown to the nape of the neck. They are reported to have an average weight of 7.5 kilograms (17 lb), although this is based on only a small number of wild individuals, and those in captivity appear to be larger. 
Like other members of their genus, both males and females have unusually long arms, even for gibbons, with the arms being 1.2 to 1.4 times as long as the legs. They are also more muscular, with heavier thighs and shoulders that suggest a greater bodily strength. Adults have been shown to demonstrate a hand preference while swinging through the trees, with individuals being equally likely to be right or left handed.
The species closely resembles the southern white-cheeked gibbon, but has slightly longer body hair and subtly different vocalisations. The males can also be distinguished by the shape of the white patches on their cheeks; in the northern species these reach the upper borders of the ears, and do not touch the corners of the mouth, whereas in the southern species, they reach only half way to the ears and entirely surround the lips.
Both males and females have been reported to produce reddish-brown secretions from glands around their upper chest, hips, and ankles. However, samples of sweat taken from the axillae and chest possess lower levels of steroids in white-cheeked gibbons than in many other species of ape, suggesting that olfactory signals may be less important in these animals than in their relatives.
Distribution and habitat
Today, the northern white-cheeked gibbon is found only in northern Vietnam and northern Laos. They were formerly also known from southern China, in Yunnan province, where they were reported to be on the edge of extirpation in 2008. No subspecies are currently recognised, although the southern white-cheeked gibbon was formerly considered to be a subspecies of N. leucogenys. The gibbon inhabits primary evergreen subtropical forest between 200 and 1,650 metres (660 and 5,410 ft) in elevation.
Behaviour and diet
The northern white-cheeked gibbon is arboreal in habits, and primarily herbivorous, feeding mainly on fruits, with some leaves, buds, and flowers. However, up to 10% of their diet may be composed of insects and other small animals. They are generally sociable, living in groups of up to six individuals. Individual groups do not travel far, and are believed to be territorial. They are diurnal, and spend the night sleeping in high branches, often embracing one another tightly. Behavioural studies have demonstrated that they are capable of self-recognition in mirrors.
The calls of northern white-cheeked gibbons are among the most complex of those produced by gibbons, and are significantly different between males and females. The most distinctive calls are those made as part of male-female duets. These begin with the female making a series of fifteen to thirty notes with an increasing pitch, followed by the male complex call with rapid changes of frequency modulation. The cycle, which lasts less than twenty seconds, then repeats with increasing intensity for anything from five to seventeen minutes. In the closely related southern species, such duets are most common at dawn, and are apparently only made on sunny days. In captive studies, males and females that sing duets together the most frequently are the most likely to mate, indicating that this may play a key role in pair-bonding.
Similar calls are sometimes made solo by both sexes, and juveniles sometimes join in, to create a full 'chorus'. In addition to the duet and solo great calls, males can also make booming sounds with their gular sacs, and short single notes.
At birth, both sexes are covered in yellow-buff fur, and weigh an average of 480 grams (17 oz). At around one year of age, the fur in both sexes changes to a black colour, with pale cheek patches, with the sexually dimorphic adult coats only growing when they reach four or five years. During this period, the juveniles sing the female form of call, and regularly engage in play behaviour.
Northern white-cheeked gibbons reach sexual maturity at seven or eight years, and have lived for at least 28 years in the wild.
- Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M, eds. Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press. OCLC 62265494. ISBN 0-801-88221-4.
- Bleisch, B., Geissmann, T., Manh Ha, N., Rawson, B. & Timmins, R. J. (2008). Nomascus leucogenys. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 4 January 2009.
- Geissmann, Thomas (December 1995). "Gibbon systematics and species identification" (PDF). International Zoo News 42: 472. Retrieved 2008-08-15.
- Ensembl entry
- "Community of rare gibbons found in Vietnam." AFP. July 17th 2011. 
- Harding, L.E. (2012). "Nomascus leucogenys (Primates: Hylobatidae)". Mammalian Species 44 (1): 1–15. doi:10.1644/890.1.
- Zihlman, A.L. et al. (2011). "Anatomical contributions to hylobatid taxonomy and adaptation". International Journal of Primatology 32 (4): 865–877. doi:10.1007/s10764-011-9506-y.
- Barker, M.K. (2008). "Gibbon hand preference studies at the Endangered Primate Rescue Center, Vietnam". Vietnamese Journal of Primatology 1 (2): 41–45.
- Fan, P.F. & Huo, S. (2009). "The northern white-cheeked gibbon (Nomascus leucogenys) is on the edge of extinction in China". Gibbon Journal 5: 44–52.
- Ujhelyi, M. et al. (2000). "Observations on the behavior of gibbons (Hylobates leucogenys, H. gabriellae, and H. lar) in the presence of mirrors". Journal of Comparative Psychology 114 (3): 253–262. doi:10.1037/0735-7036.114.3.253.
- Ha, N.M. (2007). "Survey for southern white-cheeked gibbons (Nomascus leucogenys siki) in Dak Rong Nature Reserve, Quang Tri Province, Vietnam". Vietnamese Journal of Primatology 1 (1): 61–66.
- Dooley, H. & Judge, D. (2007). "Vocal responses of captive gibbon groups to a mate change in a pair of white-cheeked gibbons (Nomascus leucogenys)". Folia Primatologica 78 (4): 228–239. doi:10.1159/000102318.
- Lukas, K.E. et al. (2002). "Longitudinal study of delayed reproductive success in a pair of white-cheeked gibbons (Hylobates leucogenys)". Zoo Biology 21 (5): 413–434. doi:10.1002/zoo.10040.
- Giessmann, T. & Ordeldinger, M. (1995). "Neonatal weight in gibbons (Hylobates spp.)". American Journal of Primatology 37 (3): 179–189. doi:10.1002/ajp.1350370302.
- Burns, B.L. et al. (2011). "Social dynamics modify behavioural development in captive white-cheeked (Nomascus leucogenys) and silvery (Hylobates moloch) gibbons". Primates 52 (3): 271–277. doi:10.1007/s10329-011-0247-5.
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