Nomascus nasutus
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 nasutus

description: 13.
Eastern Black Crested Gibbon
Nomascus nasutus
French: Gibbon du Tonkin / German: Ostlicher Schopfgibbon / Spanish: Gibon de cresta negra oriental
Other common names: Cao Vit Black Crested Gibbon, Cao Vit Crested Gibbon
Taxonomy. Hylobates nasutus Kuinckel d’Herculais, 1884,
Vietnam, Along (= Ha Long) Bay.
Based on vocal and genetic evidence, N. nasutus is now differentiated from N. concolor and N. hainanus, to which it is most closely related. Monotypic.
Distribution. Restricted to a small area along the Sino-Viethamese border in Trung Khanh District (Cao Bang Province, NE Vietnam) and Jingxi County (Guangxi Province, SE China); the historical distribution stretched from SE China to N Vietnam as far S and W as the Red River.
Descriptive notes. No specific measurements are available, but the Eastern Black Crested Gibbon is similar in size to other species of Nomascus. As with those species of gibbons, the Eastern Black Crested Gibbon is sexually dichromatic. Males are predominantly black, with a brown tinge on the chest, and females are yellow to beige brown. Females have a wide, white face-ring, and a long, black crown-streak that extends past the nape and may cross the shoulders. The chest is sometimes adorned with a patch of gray, brown, or blackish hairs. Infant Eastern Black Crested Gibbons are born black, unlike all other Nomascus gibbons. Females transition to yellow-beige-brown when subadult.
Habitat. Previously in montane and limestone forests across northern Vietnam and south-eastern China at elevations of 50-930 m but now restricted to remnant tropical monsoon limestone forests at 500-930 m in the Cao Vit Gibbon Conservation Area, Vietnam, and the adjacent Bangliang Nature Reserve, China. The total remaining habitat in this area is only ¢.2000 ha.
Food and Feeding. Preliminary and cursory studies indicated that the Eastern Black Crested Gibbon was very frugivorous, but long-term observations have shown that while levels of fruit (36-1%) and fig (21:9%) consumption are high, substantial portions of the diet are leaves (16:9%) and buds (14:4%), with the supplementary consumption of animals (7%), flowers (3%), and other plant parts (0-7%). Diets have included 81 plant species, which was about half the known species at one studysite, but 19 species, many of them locally rare, made up the bulk of the diet. The animal component of the diet consists largely of invertebrates, but lizards are also eaten.
Breeding. Four births of Eastern Black Crested Gibbons have been recorded in the wild in October-February; seasonality of breeding is unknown.
Activity patterns. The Eastern Black Crested Gibbon is diurnal and arboreal. Activity begins just before dawn, often with loud vocalizations.
Movements, Home range and Social organization. The Eastern Black Crested Gibbon forms groups that defend exclusive territories, although there is some, minimal, overlap in home ranges. Initial estimates of home ranges from three focal groups were 128 ha, 130 ha, and 133 ha, which is large for gibbons. Formation of a new territory has only been observed once and appeared to consist of the codispersal of an adult male and two juveniles into an unoccupied territory, after which they were joined by a female. It has been suggested that codispersal aids in territorial defense. The first longterm studies on the Eastern Black Crested Gibbon, along with survey data, suggest that it may be polygynous, in contrast to most other gibbons but similar to Western Black and Hainan crested gibbons. The group structure consists of an adult male and one or two adult females and offspring. A group structure with two females appears to be stable, and concurrent, dependent infants have been observed in two focal groups. The average group size of four focal groups was six individuals.
Status and Conservation. CITES Appendix I. Classified as Critically Endangered on The IUCN Red List. The Eastern Black Crested Gibbon is legally protected in China and Vietnam. It has a tiny distribution, inhabiting only ¢.2000 ha of degraded limestone forest along the Sino-Vietnamese border. It occurs in two protected areas, which are contiguous: Cao Vit Gibbon Conservation Area in Vietnam and Bangliang Nature Reserve in China. Population estimates based on auditory surveys suggest the total transboundary population may total only 110 individuals in 18 groups, four of which occur totally or partially in China, with the remainder in Vietnam. This population was discovered in 2002 on the Vietnamese side of the border, where the majority of the population resides. Four groups were discovered on the Chinese side of the border in 2006. Cao Vit Gibbon Conservation Area in Vietnam was designated in 2007, and the contiguous Bangliang Nature Reserve in China was designated in 2009. Additional survey work in other areas of the Eastern Black Crested Gibbon’s former distribution in Vietnam has returned no more records, and it is likely that it has been extirpated in all other locations for which historical records exist. All conservation efforts are, therefore, focused on the one remaining transboundary population. Threats include ongoing degradation of the remaining habitat by local communities that use the area for collection of non-timberforest products and timber for construction and firewood. Hunting appears to be controlled, with no known cases since enforcement began in 2003. The small size of the population raises questions about its long-term genetic viability. It is vulnerable to inbreeding depression, disease outbreaks, and extreme weather events. Conservation interventions, mainly by Fauna and Flora International, on both sides of the border include working with local communities and government agencies to increase enforcement, reduce reliance of the local communities on forest resources, and build protected area management capacity. Forest regeneration and extension activities have been initiated and are likely to be important conservation actions in the future, given the highly restricted area of habitat available for the remaining Eastern Black Crested Gibbons.
Bibliography. Chan Bosco Pui Lok & Ng Sai Chit (2006), Chan Bosco Pui Lok et al. (2008), Chivers (2001), Dao Van Tien (1983), Fan Pengfei, Fei Hanlan, Scott et al. (2011), Fan Pengfei, Fei Hanlan, Xiang Zoufu et al. (2010), Geissmann (1989), Geissmann, La Quang Trung et al. (2002), Geissmann, Nguyen Xuan Dang et al. (2000), Groves (2001), Insua-Cao et al. (2010), La Quang Trung & Trinh Dinh Hoang (2004), Le Trong Dat & Le Huu Oanh (2008), Mootnick & Fan Pengfei (2011), Nguyen Thi Hien (2007), Tan Bangjie (1985), Van Ngoc Thinh, Mootnick, Geissmann et al. (2010), Van Ngoc Thinh, Mootnick, Vu Ngoc Thanh et al. (2010), Vu Ngoc Thanh et al. (2005).
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 pages 787-788, DOI: 10.5281/zenodo.6727957