The taxonomy of the crested black gibbons, genus Nomascus is still in debate, but experts now believe there are three species: the Hainan gibbon, Nomascus hainanus, the most endangered of any of the gibbons and restricted to the island of Hainan (Geissmann 2003; Geissmann and Chan 2004; Wu et al. 2004; Zhou et al. 2004); the eastern black gibbon, Nomascus nasutus, occurring in northeast Vietnam (Nadler 2003), and adjoining Guangxi Zhuang Autonomous Region, China (Chan et al. in prep.); and the western black gibbon, Nomascus concolor, occurring in central Yunnan, China, and Indochina.

A recent study found no molecular differences between the putative subspecies of N. concolor, but significant genetic differences between the forms hainanus and nasutus (Roos et al. 2007). The Hainan gibbon and eastern black gibbon differ in their hair coloration (Geissmann et al. 2000; Mootnick 2006) and territorial calls (La Q. Trung and Trinh D. Hoang 2004). These characteristics, in association with the newly discovered genetic differences, suggest that the Hainan gibbon and eastern black gibbon be considered distinct species (Roos and Nadler 2005; Roos et al. 2007).

Adult male eastern black gibbons are black and can have a slight tinge of brown hair on the chest. Adult male Hainan gibbons are entirely black (Geissmann et al. 2000; Mootnick 2006). Adult female Hainan gibbons and eastern black gibbons vary from a buffish to a beige brown and have a black cap (Geissmann et al. 2000; Mootnick 2006). The adult female Hainan gibbon has a thin, white face ring that is thicker above the mouth and below the orbital ridge. The hair surrounding the face of the female Hainan gibbon creates a rounded appearance encircling the face. The hair grows outwards on the side of the face and in a more downward direction as it gets closer to the chin.

This contrasts with the female northern white-cheeked gibbon (Nomascus l. leucogenys), whose facial appearance is slightly similar to the female Hainan gibbon. The hair on the outer sides of the face of the female white-cheeked gibbon grows in a more upward direction giving the face a more triangular appearance. Depending on the amount of humidity, female Nomascus can acquire a more orangey color resulting from their sweat (Mootnick 2006). The only account of a live female eastern black gibbon in close proximity was of a female “Patzi” in the Berlin Zoo whose vocalizations were similar to that of the eastern black gibbon, but her pelage differed in that she had a very long and broad black crown streak that went past the nape, and extended to the brow, tapering to a thin face ring and becoming thicker at the chin (Geissmann et al. 2000; Mootnick 2006). This female had a narrow blackish-brown chest plate slightly wider than the face, beginning at the throat and tapering at the top of the abdomen. At this time Patzi had more black than what has been observed in the wild or in museum specimens of female eastern black gibbons.

The eastern black gibbon was thought to be extinct in southwestern provinces of China in the 1950s. In the 1960s, it was also feared extinct in Vietnam, but was rediscovered after intensive searches in January 2002 by Fauna and Flora International (FFI) biologists La Q. Trung and Trinh D. Hoang (2004). They found five groups totaling 26 individuals in the remaining 3,000 ha of limestone forest of Phong Nam-Ngoc Khe Mountains, Trung Khanh District, northern Cao Bang Province bordering Guangxi in China. Further surveys by the Vietnam Primate Conservation Programme of FFI and Trung Khanh District rangers in November 2004 located 37 individuals (VNA 2004).

Recently, a team of researchers from Kadoorie Farm & Botanic Garden (KFBG) and China confirmed 17 eastern black gibbons in three groups in the Bangliang limestone forest of Jingxi County in Guangxi, neighboring the Phong Nam-Ngoc Khe Mountains of Vietnam. Some of the gibbons observed in Bangliang may be the same individuals counted by Vietnamese counterparts as gibbon groups were seen traveling between the two countries (People's Daily Online 2006; Chan et al. in prep.). There is a rumor that there might be some eastern black gibbons in Kim Hy Nature Reserve, Bac Kan Province, Vietnam, as well as other border areas in Guangxi, China.

In the 1950s there were estimates of >2000 Hainan gibbons on the island of Hainan in 866,000 ha of forests across 12 counties (Wang and Quan 1986). By 1989, the Hainan gibbon population was reduced to only 21 gibbons in four groups restricted to Bawangling Nature Reserve (Liu et al. 1989). In 1998 the population was said to be 17 (Kadoorie Farm & Botanic Garden 2001). A gibbon survey in October 2003 found two groups, and two lone males, comprising a total of 13 individuals (Fellowes and Chan 2004; Geissmann and Chan 2004; Chan et al. 2005; Zhou et al. 2005); another survey in 2001–2002 estimated 12–19 individuals in four groups (Wu et al. 2004). In recent months three newborns and at least one lone female have been observed, bringing the world total to 17 individuals (Hainan Daily Online 2007a).

Gibbons generally establish long-term pair bonds, but in Bawangling National Nature Reserve (BNNR) there have been repeated observations of two females in the same group both carrying offspring (Liu et al. 1989; Bleisch and Chen 1991; Hainan Daily Online 2007a). This “non-traditional” group could be the result of older offspring being unable to locate appropriate mates (Wu et al. 2004), limited space to establish new groups (Liu et al. 1989), or could reflect habitual bigyny as in the crested black gibbons of Yunnan (Bleisch and Chen 1991; Fan et al. 2006). If fresh feces could be collected from these individuals, it is possible that nuclear DNA sequencing could determine the relationships and confirm if observations are being conducted on the same group in different locations.

Since 2003, when the first Hainan Gibbon Action Plan was launched (Chan et al. 2005), several teams have continued to work roughly in line with the Plan, though with limited coordination. Conservation actions include surveying the distribution of the Hainan gibbon, providing training of staff to monitor the gibbons, restoring the forest, and community conservation work. One team consists of the KFBG, the Hainan Wildlife Conservation Centre of the Hainan Provincial Forestry Department (HWCC), and BNNR. The second (Franco-Chinese) team consists of East China Normal University of Shanghai (ECNU), the Zoological Society of Paris (PZS), and BNNR. A third team from Fauna and Flora International (FFI) China has also conducted monitoring, training and community work in the recent past.

With only 17 Hainan gibbons and 54 eastern black gibbons confirmed, each surviving in just one small forest block, the Hainan gibbon and eastern black gibbon are among the most critically endangered primates in the world. It is important to gain full support from the surrounding community for conservation of the gibbons and their habitat, possibly by ensuring benefits linked to their compliance with conservation goals, and ensuring longer-term commitment from the government and outside partners. Efforts are underway to contribute to the conservation of the eastern black gibbon in Vietnam with the establishment of community-based protection activities. Since there are unconfirmed reports of gibbon occurrences from other forests, additional surveys need to be conducted in both Guangxi and Hainan (Hainan Daily Online 2007b). There is an urgent need to secure and expand suitable forest for the survival of the few remaining gibbons and their habitats, which will require continued effort and cooperation among all parties.

Alan R. Mootnick, Xiaoming Wang, Pierre Moisson, Bosco P. L. Chan, John R. Fellowes & Tilo Nadler