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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)
Total population: Unknown
Regions: China, Laos, Vietnam
Gestation: about 7 months (200 to 212 days)
Height: 457 to 635 mm (M & F) or 1.50 to 2.08 ft (M & F)
Weight: 5.6 kg (M), 5.8 kg (F) or 12.3 lbs (M), 12.8 lbs (F)
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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).
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
CURRENT RANGE MAPS (IUCN REDLIST):
Nomascus leucogenys
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). IUCN reports no record of this species in China since 1990 (IUCN Redlist).
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
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: December 1, 2010
Written by Kristina Cawthon Lang. Reviewed by Alan Mootnick.
Cite this page as:
Cawthon Lang KA. 2010 December 1. Primate Factsheets: White-cheeked gibbon (Nomascus leucogenys) Taxonomy, Morphology, & Ecology . . Accessed 2020 July 7.
SOCIAL ORGANIZATION AND BEHAVIOR
Very little is known about the behavioral ecology of white-cheeked gibbons. Most information comes from the very small Chinese population and details about the Laotian and Vietnamese populations are based on anecdotal field observations (Geissmann et al. 2000). However, the available data suggest that the life history characteristics of the white-cheeked gibbon are similar to other gibbons (Geissmann et al. 2000). Historically, gibbons were thought to live only in monogamous social groups that include an adult male and female and their immature offspring. Recent research has shed light on the social structure of gibbons, though, and while many form long-term pair bonds, extra-pair copulations may occur (Palombit 1994; Reichard 1995). A gibbon family is territorial and defends its territory with regular morning songs performed by the breeding male and female (Leighton 1987). Groups have, on average, four individuals and usually include an adult male and female, one infant and one juvenile, although the group may also include one adolescent and one subadult (Leighton 1987). There is a high degree of social and behavioral equality between adult males and females and codominance is exhibited (Leighton 1987; Geissmann et al. 2000). Because of this egalitarian social atmosphere and no competition between males for access to females, white-cheeked gibbons are not sexually dimorphic.
Gibbons defend their territories both vocally and physically. The primary means by which adult males and females defend their territory is by ritualized morning duets. The morning duet occurs at dawn and is a long, loud, energetically expensive song in which the female and male sing individual notes in specific patterns. The duet lasts between 10 and 13 minutes but is longer during the rainy season and shorter during the dry season (Geissmann et al. 2000). This seasonal variation in song bout may be related to energy expenditure and food availability. During the rainy season, when fruit is widely available and foraging time is shorter, more time and energy can be allocated for singing whereas during the dry season, foraging time increases and more energy is expended on finding food rather than territory defense (Geissmann et al. 2000). The song is initiated by either sex but is always ended by the adult male (Schilling 1984). Females begin singing long notes of increasing frequency with note durations and intervals between notes continuously decreasing and reaching a climax of short barks that eventually trail off (Geissmann et al. 2000). Males sing three different notes that include boom notes, staccato notes, and high frequency modulated notes. During his part of the duet, a male continuously cycles through these three notes and his song is accompanied by locomotory displays including violent brachiation, branch shaking, or prancing (Deputte 1982; Geissmann et al. 2000). The other mechanisms by which gibbons defend their territories include aggression and physical contests. Intergroup encounters may include chasing, fighting, and loud-call displays as well (Leighton 1987). Reports of facial scars, broken canines, and open wounds have been documented in some but not all gibbon species and it is usually males that are afflicted (Leighton 1987). Females are usually involved in call displays, both morning duets and other calls during border disputes, while adult, subadult, and adolescent males of a gibbon group physically defend their territory from intruders or full takeovers (Leighton 1987).
Because of the monogamous social structure, both males and females leave their natal groups when they reach sexual maturity, and transfer is hastened by aggressive encounters between the subadult gibbon and its same-sexed parent (Leighton 1987; Macdonald 2001). Gibbon parents often become antagonistic towards their subadult offspring and evict them from the family group to decrease the possibility of inbreeding (Leighton 1987). Though young gibbons attempt to settle near their natal territories, the availability of vacant or appropriate habitat is a limiting factor. Females are more likely to remain close to their natal territories than males, and vagabond young males seek out females. Once paired, a gibbon couple then settles in an appropriate habitat and begins to defend it as their own territory (Leighton 1987).
REPRODUCTION
Limited data are available on reproductive parameters in both wild and captive white-cheeked gibbon. Sexual maturity occurs between six and eight years of age but captive white-cheeked gibbons have bred as early as four years-old (Geissmann 1991). With sexual maturity comes a change in pelage color of female white-cheeked gibbons from their black juvenile coat to the characteristic yellow or buffy coat of adults. Males remain black but develop the white cheek patches as they reach sexual maturity (Geissmann et al. 2000). The menstrual cycle of female gibbons lasts, on average, 21.6 days (between 12 and 27 days) and is accompanied by some genital swelling during estrus, though it is not as pronounced as that seen in chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) (Nadler et al. 1993; Lukas et al. 2002). During estrus, female gibbons entice males to mate with quick, jerking upper-body movements known as bobbing (Lukas et al. 2002). First parturition occurs between six and eight years of age and gibbons exhibit an interbirth interval of two to three years. A mating pair of gibbons will produce an average of five to six offspring over their reproductive lifetimes (Leighton 1987; Geissmann 1991; Macdonald 2001). There is no conclusive evidence for birth seasonality in white-cheeked gibbons, though some species of gibbon exhibit mild birth peaks at the end of the rainy season (Leighton 1987).
PARENTAL CARE
Though white-cheeked gibbons are monogamous and males have high paternity certainty, the majority of parental care is the responsibility of the female gibbon (Varsik 2001). Gestation lasts about seven months (Lukas et al. 2002). Infancy lasts from birth to about two years, at which time the infant is weaned and enters the juvenile period (Leighton 1987; Macdonald 2001). Juvenile gibbons move independently of their mothers and this period lasts from two to four years (Leighton 1987). The period of adolescence is from about four to six years of age in which the young gibbon is not yet adult-sized but is moving and sleeping independently from its mother and beginning to reach sexual maturity. According to Leighton (1987), young gibbons were not observed to play on a daily basis, this may be due to the small social groups and lack of play partners. Though white-cheeked gibbons are monogamous and males have high paternity certainty, the majority of parental care is the responsibility of the female gibbon (Varsik 2001). Gestation lasts about seven months (Lukas et al. 2002). Infancy lasts from birth to about two years, at which time the infant is weaned and enters the juvenile period (Leighton 1987; Macdonald 2001). Juvenile gibbons move independently of their mothers and this period lasts from two to four years (Leighton 1987). The period of adolescence is from about four to six years of age in which the young gibbon is not yet adult-sized but is moving and sleeping independently from its mother and beginning to reach sexual maturity. According to Leighton (1987), young gibbons were not observed to play on a daily basis, this may be due to the small social groups and lack of play partners.
COMMUNICATION
The territorial long call duets of white-cheeked gibbons serve an important function by communicating location and area of occupancy to other gibbon groups. The development of this duet begins during the juvenile period when young gibbons practice the songs and displays that they will one day perform as adults in their own territories (Deputte 1982). Juvenile males and females mimic portions of an adult female’s song while she is performing her great call. As they mature, adolescent females begin to hone their singing skills and eventually perfect the song of the adult female white-cheeked gibbon. Young males will eventually switch the type of call they give (usually coinciding with sexual maturity) and begin to sing the chorus of an adult male as they are gradually peripheralized from the family group (Deputte 1982; Geissmann et al. 2001).
LISTEN TO VOCALIZATIONS
- Hylobates (Nomascus) leucogenys: Sound Gallery (Thomas Geissman’s Gibbon Research Lab)
A form of visual communication in white-cheeked gibbons is the sexual dichromism exhibited by adult males and females. Coat color is an intraspecies cue that conveys information about age and reproductive status, and it may also function in mate choice (Gerald 2003). The differences in coat color and markings are important, for example, to distinguish sexually mature males from subadult males. Perhaps this cue is useful for dispersing females looking for a potential mate; they can quickly identify if males are mature enough to be potential mates (Gerald 2003).
SPECIAL NOTES
Other reasons that gibbons are separated from the great apes include the differences in intelligence and tool-using behaviors. Unlike chimpanzees (Pan troglodytes), bonobos (Pan paniscus), gorillas (Gorilla) and orangutans (Pongo), gibbons do not use tools in the wild and do not score as well on cognitive tests in captivity (Rumbaugh & Washburn 2003). In captivity, gibbons have been recorded using objects in their enclosures as tools, but short of dropping branches on human observers that follow them, they have not been seen using tools in the wild. On intelligence tests they do not generally perform as well as great apes but generally do better than monkeys (Rumbaugh & Washburn 2003). In recent tests, though, gibbons moderately scored higher in a cognitive task than chimpanzees and capuchins (Cebus) (Cuningham et al. in press).
Content last modified: December 1, 2010
Written by Kristina Cawthon Lang. Reviewed by Alan Mootnick.
Cite this page as:
Cawthon Lang KA. 2010 December 1. Primate Factsheets: White-cheeked gibbon (Nomascus leucogenys) Behavior . . Accessed 2020 July 7.
INTERNATIONAL STATUS
For individual primate species conservation status, please search the IUCN Red List.
Also search the current scientific literature for primate conservation status (overall as well as for individual species), and visit CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora).
Conservation information last updated in 2010 follows, for comparison:
CONSERVATION THREATS & POTENTIAL SOLUTIONS
Threat: Human-Induced Habitat Loss and Degradation
Increasing pressure on the forests for fuelwood collection, human settlement, agricultural production, and commercial timber extraction threaten the white-cheeked gibbon throughout its range (Geissmann et al. 2000). Gibbons are strictly arboreal and depend on stretches of forest to move between food patches, therefore fragmentation and degradation seriously inhibit the natural behaviors of these animals. Human population growth in all three of the white-cheeked gibbon’s range countries exacerbates the problems of habitat destruction. In China, where the range is already small and the population is classified as highly endangered, massive human population growth and encroachment as well as commercial logging endeavors are gravely threatening the last white-cheeked gibbons in that country (Geissmann et al. 2000; Zhang et al. 2002). In Laos, natural habitat is more abundant, but with no legal protection of this land the gibbons are likely to fall prey to the same pressures as in China and Vietnam.
Potential Solutions
Population censusing is vital to the protection of white-cheeked gibbons. Along with a broader understanding of the range area of these apes, protection must be extended to their habitats as soon as possible. The combination of lack of understanding of their range coupled with habitat degradation could lead to the annihilation of the species in a short amount of time. Immediate protection of the area where they range in China is necessary to save that population. Rather than ranging in a “paper park,” there should be some enforcement of protected area status. Moreover, the Laotian population should be surveyed and protected as it is likely this is currently the largest and least affected population of white-cheeked gibbons (Geissmann et al. 2000).
Threat: Harvesting (hunting/gathering)
Another salient threat to white-cheeked gibbon survival is the hunting and collection of apes for food, the pet trade, and medicinal purposes (Geissmann et al. 2000). The Laotian population is particularly threatened by poaching for the pet trade and the demand for gibbons in the Chinese and Thai markets is not decreasing (Geissmann et al. 2000). Being hunted for food is inextricably linked to collection for the pet trade because a poacher that shoots an adult male and female is likely to collect at least one immature gibbon for sale, but may catch up to four, because of the social structure of gibbons (Leighton 1987). By massacring entire family groups, poachers can have very significant impacts on the overall population in a short amount of time.
Potential Solutions
Establishing protected areas that are effectively guarded against poachers and other illegal incursions into the forest may alleviate the hunting and collection pressure on gibbons across their range. Decreasing the demand in the Thai and Chinese markets through education programs and public awareness campaigns may also help decrease the wildlife trade in this region. Moreover, cracking down on animal smugglers by decreasing the fluidity by which they cross borders could also help decrease the booming animal trade in Southeast Asia. Where gibbons are hunted for food, alternate protein sources could be provided through development programs, and local pride for such rare animals could be facilitated through education programs. Survey projects could be established that would serve two purposes: the evaluation and identification of the population and distribution of white-cheeked gibbons and the development of employment opportunities for local people as field assistants.
Threat: Intrinsic Factors
Inbreeding may have negative effects on the survival of small populations of gibbons (Leighton 1987). Because of their dispersal patterns, neighboring groups of gibbons have some likelihood of being related. Moreover, where population density is high or suitable habitat is limited because of habitat degradation young males and females are less likely to be able to establish their own territories and they may range closely to their natal territories. It has been observed in some species of gibbon that when a male or female is widowed, the offspring of the opposite sex inherits the territory and mating may occur between parent and offspring (Leighton 1987). Some potential problems with inbreeding that may affect population viability include genetic drift and deleterious allele fixation within the population.
Potential Solutions
If a population is restricted to a small fragment of forest and dispersal opportunities are limited or if the population density is so high that territories are not available, inbreeding may pose a problem. Protecting wide swaths of forest such that white-cheeked gibbons can disperse and establish territories may decrease the chance of inbreeding depression.
Threat: Human Disturbance
Human settlement and fuelwood collection are increasing in this area because of high population growth (Geissmann et al. 2000). Dependence on forest products increases as human populations come into increasing contact with the forest frontier and gibbon habitat suffers as a result.
Potential Solutions
Establishing protected areas immediately as well as enforcing the protected area status of parks may decrease human pressure on forests. Establishing research sites in villages that can involve communities in surveys and other research endeavors may also help in mitigating the burdens on the forest through alternate revenue generation and public awareness. Development programs that create alternate fuel sources and food programs may decrease fuelwood collection and agricultural encroachment.
LINKS TO MORE ABOUT CONSERVATION
CONSERVATION INFORMATION
- No current links for Nomascus leucogenys
CONSERVATION NEWS
- Largest population of rare gibbon found in Vietnam (Associated Press; July 18, 2011)
- Quang Binh: Largest group of Siki gibbon discovered (VietNamNet; March 24, 2009)
ORGANIZATIONS INVOLVED IN Nomascus leucogenys CONSERVATION
Content last modified: December 1, 2010
Written by Kristina Cawthon Lang. Reviewed by Alan Mootnick.
Cite this page as:
Cawthon Lang KA. 2010 December 1. Primate Factsheets: White-cheeked gibbon (Nomascus leucogenys) Conservation . . Accessed 2020 July 7.
REFERENCES
Cunningham CL, Anderson JR, Mootnick AR. In press. Object manipulation to obtain a food reward in hoolock gibbons (Hoolock hoolock). Anim Behav.
Dao Van Tien. 1983. On the north Indochinese gibbons (Hylobates concolor) (primates: Hylobatidae) in North Vietnam. J Hum Evol 12: 367-72.
Deputte BL. 1982. Duetting in male and female songs of the white-cheeked gibbon (Hylobates concolor leucogenys). In: Snowdon CT, Brown CH, Petersen MR, editors. Primate communication. Cambridge (England): Cambridge Univ Pr. p 67-93.
Geissmann T. 1991. Reassessment of age of sexual maturity in gibbons (Hylobates spp.). Am J Primatol 23: 11-22.
Geissmann T, Nguyen Xuan Dang, Lormée N, Momberg F. 2000. Vietnam primate conservation status review 2000. Part 1: gibbons. Hanoi (Vietnam): Fauna & Flora Int, Indochina Programme. 130 p.
Gerald MS. 2003. How color may guide the primate world: possible relationships between sexual selection and sexual dichromatism. In: Jones CB, editor. Sexual selection and reproductive competition in primates: new perspectives and directions. Volume 3, Special topics in primatology. Norman (OK): Am Soc Primatol. p 141-71.
Groves C. 2001. Primate taxonomy. Washington DC: Smithsonian Inst Pr. 350 p.
Leighton DR. 1987. Gibbons: territoriality and monogamy. In: Smuts BB, Cheney DL, Seyfarth RM, Wrangham RW, Struhsaker TT, editors. Primate societies. Chicago: Univ Chicago Pr. p 135-45.
Lukas KE, Barkauskas RT, Maher SA, Jacobs BA, Bauman JE, Henderson AJ, Calcagno JM. 2002. Longitudinal study of delayed reproductive success in a pair of white-cheeked gibbons (Hylobates leucogenys). Zoo Biol 21: 413-34.
Macdonald D, editor. 2001. The encyclopedia of mammals. Volume 2, Primates and large herbivores. New York: Facts on File. 930 p.
Nadler RD, Dahl JF, Collins DC. 1993. Serum and urinary concentrations of sex hormones and genital swelling during the menstrual cycle of the gibbon. J Endocrinol 136: 447-55.
Nowak RM. 1999. Walker’s mammals of the world. Volume I. Baltimore (MD): Johns Hopkins Univ Pr. 836 p.
Palombit R. 1994. Dynamic pair bonds in hylobatids: implications regarding monogamous social systems. Behaviour 128(1-2): 65-101.
Rowe N. 1996. The pictorial guide to the living primates. East Hampton (NY): Pogonias Pr. 263 p.
Rumbaugh DM, Washburn DA. 2003. Intelligence of apes and other rational beings. New Haven (CT): Yale Univ Pr. 326 p.
Schilling D. 1984. Song bouts and duetting in the concolor gibbon. In: Preuschoft H, Chivers DJ, Brockelman WY, Creel N, editors. The lesser apes: evolutionary and behavioural biology. Edinburgh (Scotland): Edinburgh Univ Pr. p 390-403.
Varsik A, compiler. 2001. North American regional studbook for white-cheeked gibbon Nomascus leucogenys and golden-cheeked gibbon Nomascus Gabriella. Santa Barbara (CA): Santa Barbara Zoo Gardens. 33 p.
Zhang Y, Chen L, Qu W, Coggins C. 2002. The primates of China: biogeography and conservation status. Asian Prim 8(1-2): 20-2.
Content last modified: December 1, 2010
IMAGES
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Nomascus leucogenys Photo: Alan Mootnick |
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Nomascus leucogenys Photo: Anne Savage |
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Nomascus leucogenys Photo: Bertrand L. Deputte |
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Nomascus leucogenys Photo: Bertrand L. Deputte |
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Nomascus leucogenys Photo: Bertrand L. Deputte |
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Nomascus leucogenys Photo: Bertrand L. Deputte |
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Nomascus leucogenys Photo: Bertrand L. Deputte |
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Nomascus leucogenys Photo: Bertrand L. Deputte |
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