Southern white-cheeked gibbon  (Nomascus siki)

Classified as Endangered (EN) on the IUCN Red List (1) and listed on Appendix I of CITES (3).

The southern white-cheeked gibbon has only recently been recognised as a distinct species; previously it was believed to be a subspecies of the northern white-cheeked gibbon (Nomascus leucogenys) (4). Species belonging to the Nomascus genus (the crested gibbons) are distinctive due to their different colour phases.  Unweaned infants are buff/white and juveniles of both sexes are black. Females then change back to buff/white with a black streak on the crown or neck when they reach adulthood (2). The males remain black and can be identified by the striking white cheek whiskers that surround the corners of the mouth in a wide, bushy arc (5). Gibbons are infamous for their singing, with adult pairs performing complex duets that can be used to identify species (6).

The southern white-cheeked gibbon is found in southern Laos and central Vietnam. The northern limit of the distribution is the Nghe An Province of Vietnam, while the southern limit is unclear as there appears to be a hybridisation zone with the yellow-cheeked gibbon (Nomascus gabriellae) between the Quang Tri Province and the north of the Kon Tum Province (7).

The southern white-cheeked gibbon lives in tall primary broadleaf evergreen forest in the lowlands, which is a typically wet, tropical climate (1).

Like all gibbons, the southern white-cheeked gibbon is arboreal and spends most of its life in the canopy of the forest. It feeds on fruits and flowers and its diet is normally supplemented by young leaves and invertebrates (8). The southern white-cheeked gibbon is well adapted to this lifestyle, moving by a method known as brachiation, in which it swings between branches hanging by its elongated arms. This method of locomotion allows the gibbon to move very quickly through the forest and reach fruit that other primates are unable to (2).

Gibbons normally form groups consisting of an adult monogamous pair and two young. Each group is territorial and it is believed that the gibbons’ beautiful songs are used to enforce their territory, as well as reinforce the bond between the adult male and female (8). These songs normally occur in the early morning and last between 10 and 20 minutes (2).

The southern white-cheeked gibbon is one of the most endangered primates in Vietnam (9). It occupies an area where there is a high human population, meaning the threat of hunting, for food, the pet trade, and for use in traditional medicine, is prevalent. It is also threatened by habitat loss, as most of its natural range has been heavily fragmented through logging and agricultural encroachment (7). As a result, it is believed that the southern white-cheeked gibbon population has declined by 50 percent in the last 45 years (1).

This primate is protected from international trade as it is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), meaning that trade in this species is only permitted in highly exceptional circumstances (3). Its range covers protected areas and national parks, although there is not sufficient enforcement in these areas against forest encroachment and poaching (1). It is also protected in Vietnam at the highest level through the wildlife protection law (7).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on the conservation of gibbons visit:

• Gibbon Conservation Alliance:
  http://www.gibbonconservation.org
• The Gibbon Conservation Center:
  http://www.gibboncenter.org/