Nomascus siki
Creators: name: Russell A. Mittermeier
name: Anthony B. Rylands
name: Don E. Wilson
Publisher: name: Lynx Edicions
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Primates
Hylobatidae
Nomascus
Nomascus siki

description: 17.
Southern White-cheeked Crested Gibbon
Nomascus siki
French: Gibbon siki / German: Sudlicher WeiRwangengibbon / Spanish: Gibon de mejillas blancas meridional
Other common names: Siki Gibbon, Southern White-cheeked Gibbon
Taxonomy. Hylobates concolor siki Delacour, 1951,
Vietnam, Thua Luu.
Occasionally treated as a subspecies of N. leucogenys, but most authorities now recognize it as a distinct species based on genetic and morphological data. While the type locality is in the range of the newly described N. annamensis, the putative locality is disputed and the holotype morphologically represents N. siki. The recent description of N. annamensis and the southerly extension of the distribution of N. leucogenys have considerably reduced what was believed to be the distribution ofthis species. Monotypic.
Distribution. C Laos and C Vietnam,restricted by the Rao Nay River in Vietnam and the Khading River in Laos in the N, the Mekong River in the W, the Vietnamese coastal agricultural areas in the E, and around the Thach Han River (16° 40’-16° 50" N) in Quang Tri Province, Vietnam, and the Savannakhet Province in Laos, to the S.
Descriptive notes. No specific body measurements are available; weight of males 6-6 kg (SD 0-5 kg, n = 4) and of females 7-9 kg (SD 1-7 kg, n = 3). Adult males and juveniles of both sexes of the Southern White-cheeked Crested Gibbon are black with white cheek whiskers, which are similar to those of the Northern White-cheeked Crested Gibbon (N. leucogenys) but they reach only halfway up to the ears. Cheek whiskers have a pointed upper end and bracket the mouth, extending along the margin of the upper lips and onto sides of the chin and are not brushed outward as in the Northern Yellowcheeked Crested Gibbon (N. annamensis) and the Southern Yellow-cheeked Crested Gibbon (N. gabriellae). The crest is well developed, but less so than in the Northern White-cheeked Crested Gibbon. Females are pale yellow to orange-yellow, with a dark crown streak and white circumfacial hair, and are largely indistinguishable from female Northern White-cheeked Crested Gibbons.
Habitat. Tall primary tropical broadleaf evergreen forest and steep karst forest. The Southern White-cheeked Crested Gibbon occurs at 30-1800 m above sea level, but it may occur at higher altitudes.
Food and Feeding. There is no specific information available for this species, but it is presumably similar to other species of Nomascus (i.e. largely frugivorous with the diet supplemented mostly by leaves and flowers).
Breeding. There is no information available for this species.
Activity patterns. The Southern White-cheeked Crested Gibbon is diurnal and arboreal. Activity begins just prior to dawn, often with loud vocalizations.
Movements, Home range and Social organization. Very little is known about the Southern White-cheeked Crested Gibbon in the wild; no behavioral or ecological studies have been carried out. It is likely to be similar to the closely related Northern Whitecheeked Crested Gibbon and the two species of yellow-cheeked gibbons in being territorial and monogamous and living in family groups of one male, one female, and up to three offspring.
Status and Conservation. Listed on CITES Appendix I. Classified as Endangered on The IUCN Red List. The Southern White-cheeked Crested Gibbon may require reassessment based on a large reduction of its distribution caused by the description of the Northern Yellow-cheeked Crested Gibbon, which occupies much of what was formerly believed to be the southern part of its range. It occurs in much of what was formerly believed to be the southern distribution of the Southern White-cheeked Crested Gibbon. The Southern White-cheeked Crested Gibbon is known to occurin six protected areas: Phong Nha-Ke Bang National Park and Bac Huong Hoa Nature Reserve in Vietnam and Nam Kading, Phou Hin Boun, Hin Nam No and probably Nakai-Nam Theun national protected areas in Laos. Its status is not well documented at any site where it occurs. Key sites in Laos are likely to be the biodiversity conservation areas of Nam Kading, south of the Kading River, and Nakai-Nam Theun. Other areas such as Phou Hin Boun and Him Nam No biodiversity conservation areas likely have significant populations, being naturally well protected. The long-term financing of Nakai-Nam Theun from hydropower interests and poor access to Phou Hin Boun suggest these sites will be key for the long-term conservation of the Southern White-cheeked Crested Gibbon. The two protected areas where it occurs in Vietnam (Phong Nha-Ke Bang and Bac Huong Hoa), along with their adjacent forests, adjoin protected areas in Laos. The principal threat to the Southern White-cheeked Crested Gibbon is hunting. Hunting is largely opportunistic, with individuals being used locally for meat and traded for use in medicinal products and as pets (infants). This is exacerbated by habitat degradation and loss and, in some instances, infrastructure development, although disentangling these issues from hunting is problematic. Habitat fragmentation is more a serious threat in Vietnam than in Laos; human population pressure is greater in Vietnam, with correspondingly more widespread agriculture and logging. Reducing hunting and habitat loss are key for the Southern White-cheeked Crested Gibbon, especially controlling these threats in priority protected areas.
Bibliography. Chivers (2001), Dao Van Tien (1983), Deputte & Leclerc-Cassan (1981), Duckworth (2008), Geissmann (1991a), Geissmann et al. (2000), Groves (2001), Konrad & Geissmann (2006), Lao PDR, MAF (2011), Mootnick & Fan Pengfei (2011), Rawson et al. (2011), Streicher (2012), Van Ngoc Thinh, Mootnick, Geissmann et al. (2010), Van Ngoc Thinh, Mootnick, Vu Ngoc Thanh etal. (2010), Van Ngoc Thinh, Rawson etal. (2010).
description: Published as part of Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Hylobatidae, pp. 778-791 in Handbook of the Mammals of the World – Volume 3 Primates, Barcelona :Lynx Edicions on page 790, DOI: 10.5281/zenodo.6727957