Nomascus gabriellae (Thomas, 1909)

Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Hylobatidae, Handbook of the Mammals of the World – Volume 3 Primates, Barcelona: Lynx Edicions, pp. 778-791 : 790-791

18.

Southern Yellow-cheeked Crested Gibbon

Nomascus gabriellae

French: Gibbon de Gabrielle / German: Sudlicher Gelbwangengibbon / Spanish: Gibon de mejillas beige meridional

Other common names: Buff-cheeked Crested Gibbon, Red-cheeked Crested Gibbon, Red-cheeked Gibbon

Taxonomy. Hylobates gabriellae Thomas, 1909 ,

Vietnam, Langbian, 460 m.

The taxon’s distribution was previously thought to include more northerly areas, including southern Laos and southcentral Vietnam, but this was reduced with the taxonomic split and subsequent description of N. annamensis . Monotypic.

Distribution. S Vietnam (from Ba River, 13° 00’-13° 10’ N, in Gia Lai and Phu Yen provinces in the N to the Nui Ong Nature Reserve, 11° 01’ N, in Binh Thuan Province in the S) and SE Cambodia (E of the Mekong River and S of the Srepok River).

Descriptive notes. Head-body 45.5-49.5 cm (males, n = 4) and 4647-5 cm (females, n = 2); weight of females 5-2 kg (SD 5-9 kg, n = 3). As with other species of Nomascus , the Southern Yellow-cheeked Crested Gibbon is sexually dichromatic. Males are predominantly black, and females are buffy-colored. Adult males are black with slightly rusty-colored chests, yellowish to orangey cheeks, and a partial beard, which is brushed outward. This is in contrast to the white cheeks of the Southern White-cheeked Crested Gibbon (N. siki ) and the Northern White-cheeked Crested Gibbon (N. leucogenys ). Adult females are pale yellow to orangey-yellow, have a variable black crown streak, and may show a slightly darker chest. Infants are born buffy-yellow and begin to transition to the same pelage as adult males at about six months old, maintaining this coloration as juveniles and subadults. Males maintain this pelage through to adulthood, but females change to their adult pelage color as they reach maturity.

Habitat. Wet evergreen and semi-evergreen forests of the Indochina lowlands and also in mixed deciduous and bamboo forests, but possibly limited to where these forest types are found in association with preferred habitats. The Southern Yellow-cheeked Crested Gibbon does not occur in dry deciduous dipterocarp forests that are common in its range. It occurs in higher densities in undisturbed habitats. It has been recorded at 100-2287 m above sea level, and reports indicate that it might occur at higher elevations but at lower densities.

Food and Feeding. Diets of Southern Yellow-cheeked Crested Gibbons are dominated by figs (38:6%) and otherfruits (43%), and supplemented with new and mature leaves (9:5%) and flowers (8:9%). This high degree of frugivory contrasts with the northerly distributed species of Nomascus that include more leaves in their diets.

Breeding. A single interbirth interval of 17-22 months was recorded in the wild.

Activity patterns. The Southern Yellow-cheeked Crested Gibbon is diurnal and arboreal. Activity beginsjust before dawn and often commences with loud calls, the majority of them in the 30 minutes around sunrise. Singing bouts average about twelve minutes.

Movements, Home range and Social organization. Groups of Southern Yellow-cheeked Crested Gibbons are socially monogamous, comprising an adult pair and offspring; groups average 4-5 individuals (range 3-6). Extrapair copulations have been recorded but are infrequent. Females tend to disperse to new territories near their natal territories after reaching maturity, while males emigrate more widely. Home ranges are 14-2-60-5 ha, averaging 41 ha. Defended territories are smaller, averaging 37 ha.

Status and Conservation. CITES Appendix I. Classified as Endangered on The IUCN Red List. The Southern Yellow-cheeked Crested Gibbon is legally protected in Vietnam and Cambodia. It occurs in 15 protected areas: Yok Don, Chu Yang Sin, Bi Dup-Nui Ba, Phuoc Binh, Bu Gia Map, and Cat Tien national parks and Hon Ba, Nam Nung, Ta Dung, Dong Nai, and Nui Ong nature reserves in Vietnam and Phnom Prich, Snoul, and Phnom Nam Lyr wildlife sanctuaries and Seima Protection Forest in Cambodia. The most significant Cambodian population is found in Seima Protection Forest, estimated at 432-972 groups based on surveys using a number of different techniques. While spot surveys have been conducted in several other protected areas, the only other population survey using an appropriate method and sample size is from Phnom Prich Wildlife Sanctuary, which resulted in an estimate of 15-273 groups. In Vietnam, areas with large and important populations are Cat Tien National Park with a minimum estimate of 149 groups and Bu Gia Map National Park with an estimated 124 groups. These two protected areas and surrounding forests are the priority sites for the species’ conservation in Vietnam, but other significant populations likely exist. Cat Tien National Park also houses the Dao Tien Endangered Primate Species Centre that holds confiscated gibbons and conducts reintroductions into the park. Hunting for the wildlife trade is a major threat, with individuals taken from the wild for zoos and private collections in southern Vietnam. There is a market for infants that are acquired by shooting the mother, which adversely affects population recovery. Habitat loss is also significant, with planned and unplanned forest conversion and severe degradation in and around some protected areas caused by infrastructure development, agricultural encroachment, and illegal logging. Populations in Seima Protection Forest and Phnom Prich Wildlife Sanctuary in Cambodia are under active and effective management, while populations in Cat Tien and Bu Gia Map national parks in Vietnam have been the focus of gibbon-specific conservation activities over recent years.

Bibliography. Chivers (2001), Clements et al. (2008), Geissmann et al. (2000), Kenyon (2007), Kloss (1929), Mootnick & Fan Pengfei (2011), Nguyen Xuan Dang et al. (2005), Phan Channa & Gray (2009), Rawson (2004, 2010b), Rawson & Traeholt (2012), Rawson, Clements & Nut Meng Hor (2009), Rawson, Insua-Cao et al. (2011), Traeholt et al. (2005), Van Ngoc Thinh, Mootnick, Geissmann et al. (2010), Van Ngoc Thinh, Mootnick, Vu Ngoc Thanh et al. (2010), WCS (2009).

Figures

12. Western Black Crested Gibbon (Nomascus concolor), 13. Eastern Black Crested Gibbon (Nomascus nasutus), 14. Hainan Crested Gibbon (Nomascus haimmanus), 15. Northern Yellow-cheeked Crested Gibbon (Nomascus annamensis), 16. Northern White-cheeked Crested Gibbon (Nomascus leucogenys), 17. Southern White-cheeked Crested Gibbon (Nomascus siki), 18. Southern Yellow-cheeked Crested Gibbon (Nomascus gabriellae), 19. Siamang (Symphalangus syndactylus)

Distribution. S Vietnam (from Ba River, 13° 00’-13° 10’ N, in Gia Lai and Phu Yen provinces in the N to the Nui Ong Nature Reserve, 11° 01’ N, in Binh Thuan Province in the S) and SE Cambodia (E of the Mekong River and S of the Srepok River).