Hainan gibbon
Hainan gibbon
The Hainan black-crested gibbon or Hainan gibbon (Nomascus hainanus), is a species of gibbon found only on Hainan Island, China. It was formerly considered a subspecies of the eastern black crested gibbon (Nomascus nasutus) from Hòa Bình and Cao Bằng provinces of Vietnam and Jingxi County in Guangxi Zhuang Autonomous Region, China. Molecular data, together with morphology and call differences, suggest it is a separate species. Its habitat consists of broad-leaved forests and semi-deciduous monsoon forests. It feeds on ripe, sugar-rich fruit, such as figs (Ficus spp.) and, at times, leaves, and insects.
Current status
Hainan black-crested gibbons are under grave threat of extinction. They are currently identified as critically endangered on the International Union for Conservation of Nature’s Red List. Historically, they were widespread in China: Government records dating back to the 17th century state that their range used to cover half of China, although the records in question might represent multiple species, as some are from areas separated from each other by physical barriers such as large rivers that gibbons would have difficulty crossing. The gibbon population on Hainan Island has decreased precipitously over the last half century. While in the 1950s, more than 2,000 gibbons were found over the entirety of Hainan Island, a study in 2003 found 13 total gibbons split into two groups and two lone males, and in 2004 only 12-19 Hainan gibbons were found exclusively in the Hainan Bawangling National Nature Reserve.The most recent count found 22 Hainan gibbons split between two families, one of 11 and one of seven members, with four loners, all residing in Bawangling National Nature Reserve on Hainan Island. Habitat loss is the primary cause in the decline of the Hainan gibbon; poaching has also been a problem. Over 25% of the Hainan gibbon’s habitat has been reduced due to illegal pulp paper plantation growers. Originally denizens of lowland forest, logging has driven them to less suitable habitat at higher altitudes. The species is currently vulnerable to being eliminated by a single major storm or epidemic.
Physical and breeding characteristics
Sexual dichromatism is distinct in the Hainan gibbon. The males are all almost completely black, with sometimes white or buff cheeks. Females, conversely, are a golden or buff color with black patches, including a streak of black on the head. Both males and females are slender, with long arms and legs and no tail. The arms are used to swing from tree to tree, which is known as brachiation. The Hainan gibbon sings duets for bonding and mating.
The Hainan gibbons have acquired some reproductive adaptations in response to their drastically decreased natural habitat. The few remaining gibbons exhibit polygynous relationships; small families typically consist of one breeding male, two mature females, and their offspring. This stable pair bond relationship seems to have allowed the gibbons to decrease their interbirth interval, the length of time between births. Their two-year interbirth interval is shorter than that of most gibbon species and coincides with the blooming patterns of fruits on the Hainan Islands. The Hainan gibbon also has a shorter gestation period than other gibbon species. It has been observed that not all sexually mature females in the wild are breeding, however, the reasons for this are unclear.
Habitat selection
The Hainan gibbons reside in three different types of forests on the island. Their main area of occupancy is known as the primary forest (Old-growth forest). Within the primary forest the gibbons typically live in trees that are ten meters or taller. Along with offering sources of shelter and trees for singing rituals, the primary forests are also home to at least six species of plants eaten by the gibbons.When primary forests are destroyed, it takes the trees an extensive amount of time to regenerate to a state that is suitable as a home for the gibbons. In the 1960s, much of Hainan's lowlands were deforested to make way for rubber plantations and commercial logging, causing a dramatic decline in their population. These actions forced gibbon communities to higher elevations. By 1999, only 4% of the gibbons’ original habitat remained on the island.
Aside from primary forest, the gibbons split their time between two areas known as secondary forests and dwarf forests. The secondary forests are less suitable for the Hainan gibbons than the primary forests. Their trees are shorter in height, and they severely lack resources, such as food and shelter, needed by the gibbons to survive. The dwarf forest is even less favorable for the gibbons and a study by Fan et al. found that gibbons spent only 0.5% of the thirteen-month study period in dwarf forests. Nonetheless, the dwarf forests still account for a small portion of their habitat and are used by gibbons to move between primary forests. Even with the secondary and dwarf forests for the gibbons to reside in, the destruction of primary forests still severely impacts the gibbon population in a negative manner.
Resource availability, predation, and human expansion
A major result of habitat loss is the reduction of resources available to the Hainan gibbons. While lowland tropical forests are the most suitable habitat for the Hainan gibbon, much of this habitat and approximately 95% of the original vegetation on Hainan Island has been destroyed due to deforestation. This natural vegetation has been succeeded by pine and fir trees, which decrease the amount of food available for the gibbons.
Zhou et al. observed two unsuccessful hawk attacks on young gibbons, however, humans are the main threat to the Hainan gibbon. The human population on Hainan exploded 330% between 1950 and 2003, much of which was due to the open door policy implemented by the Chinese government in the late 1980s. Naturally, the population boom led to the construction of roads and towns to accompany the developing rubber and timber industry. Many of these projects led not only to the destruction of habitat where the gibbons were found, but also caused gibbon populations to split and become isolated from other groups of gibbons.
In addition to the economic development brought by the growing population, there is financial pressure to capture gibbons, since a female gibbon can be worth up to 300 US dollars. Gibbon bones are prized in traditional medicine and this belief led to many mass hunts between 1960 and 1980, leading to the death of approximately 100 gibbons. Aside from direct interactions between humans and gibbons, the low income of most residents of Hainan has led to their reliance on the forests for firewood, food, and herbs for use in traditional medicine, further amplifying human impact on the environment.
Ecological significance
The Hainan gibbon is considered an umbrella species for the Hainan Island. This designation indicates that status of the Hainan gibbon is a marker for the health and stability of its ecosystem. Alterations in the characteristics of the Hainan ecosystem that negatively affect the gibbons are indicative of negative impact on other species as well.
Other species of gibbons have been shown to be important factors in seed dispersal of several plant species, most notably figs and other fruit bearing plants. Therefore, the destruction of the natural vegetation on Hainan Island, coupled with the dwindling gibbon population bodes ill for the recovery of native plant species. This being said, no gibbon species has gone extinct in the modern world and no other primate has gone extinct since the 1700s, so there is little research on their ecological importance or methods of conservation. The impact that the extinction of the Hainan gibbon could have is not well characterized due to the limited amount of research.
Conservation
Reproduction limitations
The breeding characteristics for the Hainan gibbon do not lend themselves to rapid population growth. The breeding females have a single offspring every two years and the newborn has a dependence period of roughly a year and a half. Furthermore, there are currently no Hainan gibbons in captivity and all previous attempts to breed them in captivity have failed.
Conservation action plan
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.
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