White-cheeked gibbon
Nomascus leucogenys

TAXONOMY

Suborder: Haplorrhini
Infraorder: Simiiformes
Superfamily: Hominoidea
Family: Hylobatidae
Genus: Nomascus
Species: N. leucogenys

Other names: Hylobates concolor or Hylobates (Nomascus) leucogenys; Chinese white-cheeked gibbon, northern white-cheeked gibbon, or white-cheeked crested gibbon; vitkindad gibbon (Swedish)

Gibbons are members of the family Hylobatidae and though they are apes, they are known as lesser, or small, apes. The four genera of gibbons are differentiated on the number of chromosomes, among other things. The white-cheeked gibbon is in the genus Nomascus and has 52 diploid chromosomes (Rowe 1996).

MORPHOLOGY

One of the reasons gibbons are known as lesser apes is their diminutive body size in comparison with the great apes. White-cheeked gibbons do not exhibit sexual dimorphism and both males and females measure between 457 and 635 mm (1.50 and 2.08 ft). Males weigh, on average 5.6 kg (12.8 lb) while females have an average weight of 5.8 kg (Rowe 1996). Though the sexes are about the same size, white-cheeked gibbons do exhibit an interesting pattern of sexual dichromism. Males have coarse black fur and black skin with white fur on their cheeks and pronounced crests of hair on the crowns of their heads while females are golden or reddish buff-colored with black faces and dark brown or black fur on top of their heads, but no crown crests. Females do not have the characteristic white cheek fur but do have white fur in a halo around their faces (Rowe 1996; Groves 2001). All infants are born with a whitish buff coat that turns black over the first two years of life. When they reach sexual maturity, males remain black and females change back to a buffy color (Geissmann et al. 2000).

Photo: Bertrand L. Deputte

Gibbons are adapted for their arboreal lifestyle (Varsik 2001). Gibbons use a highly specialized mode of locomotion called brachiation. This hand-over-hand motion of swinging through the trees is their main pattern of movement. Gibbons have an unusually erect posture and are never seen moving quadrupedally and only rarely seen walking bipedally (Rowe 1996; Geissmann et al. 2000). When they are seen walking bipedally (usually over a wide branch) they hold their long arms above their heads for balance (Nowak 1999). They have proportionately long arms and hands with fingers that act like hooks as they swing through the forest, covering up to three meters per swing (Leighton 1987; Nowak 1999). Though they move with ease and grace through the trees, accidents still happen and it is very common to find healed bones in the corpses of wild gibbons (Rumbaugh & Washburn 2003). (Geissmann et al. 2000).

The average life span of the white-cheeked gibbon in the wild is 28 years (Rowe 1996).

RANGE

N. leucogenys range (in red)

White-cheeked gibbons are found in a stretch of forest that encompasses China (southern Yunnan province), northern Laos, and northwestern Vietnam (Geissmann et al. 2000). While the Chinese population is estimated to be about 100 animals in a 300 to 500 km² (116 to 193 mi²) area, there is no reliable estimate of range or population size in Vietnam. The population in Laos is estimated to be the largest (Geissmann et al. 2000). Lack of surveys in Vietnam have limited the ability to estimate population size, but given the highly fragmented habitat, intense hunting pressure, and the small size of the original range, the numbers are probably very low (Geissmann et al. 2000).

There have been very few ecological and behavioral studies and no long-term studies on white-cheeked gibbons because of their strictly arboreal lifestyle, difficult habitat terrain, and shyness of humans (Geissmann et al. 2000; Lukas et al. 2002).

HABITAT

The lowlands of northeastern Vietnam and northern Laos have a subtropical climate with an average annual temperature of 23.6° C (74.5° F) and average annual rainfall between 1364 and 1894 mm (4.48 and 6.21 ft) (Dao Van Tien 1983). The rainy season lasts from May to October and the dry season from November to April (Geissmann et al. 2000). There is a very short winter with no frost and summers are hot with dry westerly winds (Dao Van Tien 1983). White-cheeked gibbons live at elevations between 300 and 600 m (984 and 1969 ft) in primary and mature secondary forests (Geissmann et al. 2000).

ECOLOGY

Photo: Alan Mootnick

White-cheeked gibbons are frugivorous and spend most of their time in the forest canopy searching for food. Leaves are another important food item for gibbons as well as flowers, leaf buds and shoots, and insects. There is some evidence that white-cheeked gibbons are less frugivorous than other species of gibbons, though fruit still makes up the largest proportion of their diet (Geissmann et al. 2000). There are seasonal differences in food intake due to fruit availability or scarcity. During the rainy season, fruit is widely available and white-cheeked gibbons depend heavily on this resource and do not travel long distances. During the dry season they travel greater distances and spend more time foraging while increasing their dependence on leaves (Geissmann et al. 2000). Brachiation may be an adaptation for their frugivorous lifestyle. Gibbons are capable of fast, efficient travel through the forest canopy and this makes moving between highly dispersed food patches easy and minimally time-consuming (Leighton 1987).

Gibbons travel and sleep too high in the forest canopy to encounter felid predators, but raptors are a potential predatory risk (Leighton 1987). There are no field studies to confirm or illuminate the role of predators on gibbon populations.

Content last modified: July 3, 2005

Written by Kristina Cawthon Lang. Reviewed by Alan Mootnick.

Cite this page as:
Cawthon Lang KA. 2005 July 3. Primate Factsheets: White-cheeked gibbon (Nomascus leucogenys) Taxonomy, Morphology, & Ecology . <http://pin.primate.wisc.edu/factsheets/entry/white-cheeked_gibbon>. Accessed 2010 February 9.