Nomascus leucogenys

Geographic Range

Hylobates 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, H. leucogenys is found to the southwest of the Song Ma and Song Bo Rivers. A close relative, Hylobates 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 H. leucogenys and H. concolor are extremely similar in appearance.

• Biogeographic Regions
• oriental oriental
  • native native

Habitat

Hylobates leucogenys live in the canopy of subtropical rainforests. White-cheeked gibbons hardly ever descend to the forest floor.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• rainforest rainforest

Physical Description

Hylobates 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 H. 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. Hylobates leucogenys was considered a subspecies of crested gibbon, H. concolor , until 1989. The main difference between the two species is the “mohawk” tuft at the top of the head of H. leucogenys .

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes colored or patterned differently

Reproduction

Hylobates leucogenys are monogamous.

• Mating System
• monogamous monogamous

White-cheeked gibbons become sexually mature at about six to seven years of age. At this point, Hylobates 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.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Parental care in white-cheeked gibbons is not restricted to females. Unlike many mammals where the female is the primary care giver, H. 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 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

Lifespan/Longevity

The average lifespan of Hylobates leucogenys in the wild is twenty-eight years.

Behavior

Hylobates leucogenys individuals are arboreal and live mainly in the canopy of forests. They travel through the trees by brachiation. While in the trees, white-cheeked gibbons spend a great deal of time eating. White-cheeked gibbons live in small families comprising a male adult and a female adult that mate monogamously. They usually have three to four offspring within the group. There is a hierarchy among the family. The female is dominant followed by her female offspring, male offspring, and the adult male is last. Hylobates leucogenys individuals spend much of their free time playing and grooming. White-cheeked gibbons also use vocalizations throughout the day to signal territory, and they are used in mating rituals.

• Key Behaviors
• arboreal arboreal
• scansorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• territorial territorial
• social social
• dominance hierarchies dominance hierarchies

Home Range

Hylobates leucogenys live in an area that spans about seventy-five to one hundred acres. They defend their territory.

Communication and Perception

Hylobates leucogenys individuals signal territory by using vocalizations. They also use vocalizations in mating behaviors. In order to signal aggression, H. 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 visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• duets duets

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Hylobates leucogenys are primarily frugivorous. They especially enjoy eating the pulp of fruits. They are important seed dispersers for some plants. In general, H. 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.

• Primary Diet
• herbivore herbivore
  • frugivore frugivore

• Animal Foods
• insects

• Plant Foods
• leaves
• fruit
• flowers

Predation

The main threat to Hylobates leucogenys is forest clearing, and therefore, their main predator is humans. It has also been documented that in North Vietnam, some people have hunted H. leucogenys for their meat. Nothing is known about other specific predators of Hylobates leucogenys , but eagles of the family Accipitridae , owls of the family Strigidae , and Panthera pardus are known to prey on H. concolor . Hylobates leucogenys , like H. 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.

Ecosystem Roles

Hylobates 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

Economic Importance for Humans: Positive

Miles and Caldecott (2005) reported that Hylobates 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 Hylobates concolor or Hylobates leucogenys .

• Positive Impacts
• pet trade pet trade
• research and education

Economic Importance for Humans: Negative

There is no known evidence that Hylobates leucogenys effect humans in a negative manner. This is also true for members of the related species Hylobates gabriellae .

Conservation Status

Nothing is known about the conservation status of Hylobates leucogenys , but members of the related species Hylobates concolor are endangered due to deforestation, logging, hunting and military activities.

Other Comments

A great deal of molecular research has been done recently on Hylobates phylogeny and greater ape phylogeny. There are four discrete divisions of lesser apes and these four subgenera include Bunopithecus , Hylobates , Symphalangus , and Nomascus . These are monophyletic groups. Before there was thorough DNA evidence, all white crested gibbons were considered members of a single species Hylobates concolor . Chromosomal evidence that is available today allows scientists to distinguish the white cheeked gibbon as a member of the subgenus Nomascus , which are characterized by having a diploid number of 52 chromosomes. Nomascus is found from southern China to southern Vietnam, and is found on Hainan Island. Fur coloration, anatomical data, and vocal data are also used to identify different species of gibbons. Within the subgenus Nomascus , there are four separate species that include N. concolor , N. gabriellae , N. sp. cf. nasutus , and N. leucogenys . White-cheeked gibbons have therefore been re-named Nomascus leucogenys . There are also subspecies within each species. For example, recent DNA evidence has distinguished Nomascus leucogenys leucogenys as the northern white-cheeked gibbon and Nomascus leucogenys siki as the southern white-cheeked gibbon. Due to the recent taxonomic advancements using DNA, it is not clear what species is being discussed in much of the older literature.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Tommy Boyd (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

References

Cawthon Lang, K. 2006. "National Primate Research Center, University of Wisconsin-Madison" (On-line). Primate Factsheets: White-cheeked gibbon (Hylobates leucogenys) Taxonomy, Morphology, & Ecology.. Accessed March 21, 2006 at http://pin.primate.wisc.edu/factsheets/entry/white-cheeked_gibbon .

Crane, S. 2000. ""Hylobates concolor" (On-line)" (On-line). Animal Diversity Web. Accessed April 18, 2006 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hylobates_concolor.html .

Geissmann, T., N. Xuan Dang, N. Lormee, F. Momberg. 2000. Vietnam Primate Conservation Status Review 2000- Part 1: Gibbons.. Fauna and Flora International, Indochina Programme. , Volume 1/Issue 1: 1-130.

Geissmann, T. 2002. Taxonomy and Evolution of Gibbons. Evolution Anthropology , Volume 11/Issue S1: 28-31.

Miles, L., J. Caldecott. 2005. World Atlas of Great Apes and their Conservation . Los Angeles: University of California Press.

Muller, S., M. Hollatz, J. Wienberg. 2003. Chromosomal phylogeny and evolution of gibbons (Hylobatidae). Human Genetics , Volume 113/Issue 6: 493-501.

Quist, E. 2005. ""Hylobates gabriellae"" (On-line). Animal Diversity Web. Accessed April 18, 2006 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Hylobates_gabriellae.html .

Roos, C. 2001. Molecular Phylogeny of the Major Hylobatid Divisions. Molecular Phylogenetics and Evolution , Volume 19/Issue 3: 486-494.

Takacs, Z., J. Carlos Morales, T. Geissmann, D. Melnick. 2005. A complet species-level phylogeny of the Hylobatidae based on mitochondrial ND3-ND4 gene sequences. Molecular Phylogenetics and Evolution , Volume 36/Issue 3: 456-467.

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Wolfheim, J. 1983. Primates of the World- Distribution, Abundance, and Conservation . Seattle, Washington: University of Washington Press.

2006. "Smithsonian National Zoological Park" (On-line). Great Apes and Other Primates- White-Cheeked Gibbons. Accessed March 21, 2006 at http://nationalzoo.si.edu/Animals/Primates/Facts/FactSheets/Gibbons/WhiteCheeked/default.cfm .

UNEP-WCMC. 2006. "UNEP-WCMC Species Database" (On-line). CITES-Listed Species. Accessed March 21, 2006 at http://sea.unep-wcmc.org/isdb/CITES/Taxonomy/tax-species-result.cfm?displaylanguage=eng&source=animals&Genus=Hylobates&Species=leucogenys&Country=&tabname=names .