White-cheeked gibbons are sexually dimorphic. Both sexes are born blonde and start to turn black at around 12 months of age. The females turn back to blonde at sexual maturity (6-8 years). The colour change can take up to two years to complete. An adult White-cheeked gibbon weighs between 8 to 10 kilos and the male is only slightly larger. Males have very distinct white patches on their cheeks and an obvious scrotal tuft of hair. Females have an elongated clitoris which looks very similar to the male’s penis. Differentiating between juveniles can be difficult. The adult female has a small black crest and lacks a cranial tuft (Harding et al. 2012)
They have long arms (1.2-1.4m) and legs, long fingers and reduced thumbs, all of which are adaptations for brachiation. A form of locomotion where they swing by placing one arm in front of the other (Zilhman et al. 2011).
White-cheeked gibbons perform an elaborate duet, generally first thing in the morning which is thought to announce their territory and serve as a pair bonding exercise.
Habitat and Distribution
This species occurs in north-west Vietnam, northern Laos and southern Yunnan Province, China. It is restricted in the west by the Mekong River and limited in the east by the Black River (Groves 2001)
The population in Yunnan is effectively extinct with fewer than 10 individuals remaining.
Estimations for the population size of N. leucogenys in Vietnam are somewhere around 300 groups, representing an 80% decline in population size over the past 3 generations. (Rawson et al. 2011)
Although significant habitat remains in Laos, gibbons are widely hunted and populations are likely to be small. Further surveys are required in this region.
Prime habitat for this species is evergreen, subtropical forest with an elevation of between 200-1,650 meters (Harding et al.2012).
Declined over 80% in the last 45 years. It is envisaged a similar decline will result over the next 45 years. In both instances this is mainly due to habitat loss through the illegal timber trade and poaching for the pet trade. The mother is shot and if the baby survives the fall this is taken and sold on the illegal black market (IUCN 2011).
Other threats include gold mining and shifting cultivation.
Frugivorous diet consisting of; predominantly fruit, leaves and flowers with a small percentage of insects and small mammals such as birds (Harding et al. 2012)
Breeding and Lifecycle
White-cheeked Gibbons are monogamous, although recent research has indicated that this may not always be the case. They generally live in stable family units with up to three offspring (infant, juvenile and adolescent). Adolescent offspring reach maturity between 6-8 years of age and disperse from the group.
Gestation is 200-210 days.
The birth interval is generally 2-3 years. The average life expectancy in captivity is 30-40 years with the oldest recorded White-cheeked Gibbon being 46.
Conservation efforts and release programs for rescued gibbons exists in Vietnam however poaching and encroachment of remaining habitat continues to be a serious concern.
This species of gibbon has been shown to have a hand preference when brachiating, making individuals both left handed or right handed (Barker et al. 2008)
Historically, there have been issues with mothering in the captive population and there appears to a significantly learned component to maternal skills. Tooth eruption has been observed at birth in captive White-cheeked Gibbons.
Sexing infants can be difficult however males will generally have an obvious scrotum soon after birth and urination will generally differentiate between the penis and clitoris. The Northern White-cheeked Gibbon closely resembles the Southern White-cheeked Gibbon (Nomascus siki) however these are managed to species level in most regional captive populations. Vocalisation differs between the two species as well as some slight differences in pelage. Male Nomascus leucogenys have white cheek patches from the ears to corners of the mouth whereas Nomascus siki males white cheeks only reach half way to the ears and surround the entire mouth.
- www.iucnredlist.org (April 2011)
- Rawson B M, Insua-Cao P, Nguyen Manh Ha, Van Ngoc Thinh, Hoang Minh Duc, Mahood S, Geissmann T and Roos C (2011) The Conservation Status of Gibbons in Vietnam. Fauna & Flora International/Conservation International, Hanoi, Vietnam
- Groves C. P (2001) Primate taxonomy. Smithsonian Institution Press, Washington.
- Harding L E (2012) Nomascus leucogenys (Primates: Hylobatidae). Mammalian Species: January 2044, Issue 1. 1 – 15.
- Megan K. Barker, K (2008) Gibbon hand preference studies at the Endangered Primate Rescue Center, Vietnam. Vietnamese Journal of Primatology2, 41-45
- Zihlman A L et al. (2011) Anatomical contributions to hylobatid taxonomy and adaptation”. International Journal of Primatology32 (4): 865-877
The Zoo and Aquarium Association acknowledges Perth Zoo for providing the factsheet information above and Clare Campbell for the image.