Nomascus hainanus (Thomas, 1892)
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publication ID |
https://doi.org/ 10.5281/zenodo.6727957 |
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DOI |
https://doi.org/10.5281/zenodo.6728305 |
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persistent identifier |
https://treatment.plazi.org/id/03D787BA-0E33-FFCA-FF2E-F6BCF6BFC26B |
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treatment provided by |
Jonas |
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Nomascus hainanus |
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14. View Plate 54: Hylobatidae
Hainan Crested Gibbon
French: Gibbon de Hainan / German: Hainan-Schopfgibbon / Spanish: Gib 6n de Hainan
Other common names: Hainan Black Crested Gibbon, Hainan Black Gibbon, Hainan Gibbon
Taxonomy. Hylobates hainanus Thomas, 1892 ,
China, Hainan.
Now commonly recognized as a distinct species from N. nasutus based on vocal and genetic evidence. Monotypic.
Distribution. Endemic to Hainan I, China; once widespread, but today the only known population is restricted to Bawangling Nature Reserve in the W of the island. View Figure
Descriptive notes. Head-body mean 49-1 cm (males, n = 2) and mean 48-3 cm (females, n = 3); weight 5.8-10 kg. As with other species of Nomascus , the Hainan Crested Gibbon is sexually dichromatic. Males are completely black, and females are brownish buff with a black crown streak and a thin white face ring. Infants are born buff and transition to black by 5-6 months of age, which they maintain as juveniles and subadults. Males maintain this pelage through to adulthood, but females change to their adult pelage of brownish buff at maturity.
Habitat. Restricted to ravine microhabitats in montane forest at 700-1200 m above sea level. The lowland forests preferred by the Hainan Crested Gibbon are now largely destroyed on Hainan Island.
Food and Feeding. To date, the Hainan Crested Gibbon is known to select food items from 119 plant species. Food availability may be limited in February-April. At this time, they subsist on less preferred food sources. Restriction to less preferred montane forests due to the destruction of the lowland forests has implications for their feeding ecology, with lower plant diversity and fewer preferred tree species in these areas.
Breeding. Gestation period of the Hainan Crested Gibbon is estimated to be 136-173 days, and the interbirth interval is about two years, based on observations in the wild. Births are not seasonal, and infants are weaned at c.1-5 years. Survivorship of infants to subadulthood can be 92%. Between 1982 and 1989, nine of twelve infants born were male, skewing the sex ratio and potentially causing issues with mate choice within the population. Familial polygyny appears to be common. Femalesinitiate sexual encounters and are sexually receptive post-conception.
Activity patterns. The Hainan Crested Gibbon is diurnal and arboreal. Activity begins just before dawn and often commences with loud vocalizations. Adult males lead the group during travel.
Movements, Home range and Social organization. Group size of the Hainan Crested Gibbon is large; surveys in 2008 found that the last two groups of the species had nine and six individuals. The home ranges of these two groups are very large at 548 ha and 987 ha. It is unknown if these large home ranges are typical, are related to a lack of optimal habitat, or reflect home range expansion due to lack of competition from neighboring groups. Over 30 years of observation, these two groups of Hainan Crested Gibbons have maintained a polygynous mating strategy, with two adult females and a single adult male. Mating opportunities are restricted, however, and this may reflect abnormal behavior for the taxon—a point of contention over many years. Subadults are peripheralized until they leave the natal group. In one case, a subadult male was observed to be peripheral to his natal group for about six months before his expulsion at ¢.5-5 years old. Subadults leaving the natal group may be at high risk of mortality because many have dispersed but few have been observed to form new groups.
Status and Conservation. CITES Appendix I. Classified as Critically Endangered on The IUCN Red List. The Hainan Crested Gibbon is legally protected in China. It occurs in just one protected area, Bawangling Nature Reserve. Three hundred years ago it inhabited most of Hainan Island—some 27,784 km?*—but several waves of habitat destruction have reduced the available habitat to only ¢.66 km?*. Hainan Crested Gibbons are now restricted to a mere 14-16 km®. The population has declined from over 2000 individuals in the 1950s to a low point of 7-8 individuals in the 1970s, with a subsequent recovery to 21 individuals in the 1980s. Estimates since that time have varied between 13 and 20 individuals, with the current population estimated at 22; two groups of seven and eleven individuals and four solitary individuals. Although the population has increased through births in recent years, no new social groups have been formed since 2000. The small size of the population leaves it vulnerable to threats such as inbreeding depression, skewed sex ratios, disease outbreaks, and extreme weather. Other threats include habitat destruction and fragmentation, which in recent decades has been driven by agroindustry, small-scale farming, and infrastructure development. The continuing demand for Hainan Crested Gibbons for use in traditional Asian medicine also poses a threat to the remaining population, although there have been no known instances of hunting in recent years. Reducing risks from hunting and further habitat degradation through increased enforcement are priority conservation actions. Reforestation using native tree species, particularly those fed on by Hainan Crested Gibbons, will be important for the species’ survival, and some work has already begun in this area.
Bibliography. Bleisch & Chen Nan (1991), Chan Bosco Pui Lok et al. (2005), Chivers (2001), Fellowes et al. (2008), Geissmann et al. (2000), Groves (2001), Haimoff (1984a), Liu Zhenhe, Yu Simian & Yuan Xicai (1984), Liu Zhenhe, Zhang Yongzu et al. (1989), Ma Shilai et al. (1988), Mootnick & Fan Pengfei (2011), Mootnick et al. (2012), Roos et al. (2007), Smith & Yan Xie (2008), Stone (2011), Tan Bangjie (1985), Van Ngoc Thinh, Mootnick, Geissmann et al. (2010), Van Ngoc Thinh, Mootnick, Vu Ngoc Thanh et al. (2010), Wei Wu et al. (2004), Xu Longhui et al. (1983), Zhang Mingxia et al. (2010), Zhou Jiang, Wei Fuwen, Li Ming, Chan Bosco Pui Lok & Wang Deli (2008), Zhou Jiang, Wei Fuwen, Li Ming, Zhan Jianfeng et al. (2005).
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