With a known population of only 110 individuals, the cao vit gibbon, also names eastern black crested gibbon, is one of the rarest ape species in the world, second only to its closest relative, the Hainan gibbon. In 1960s’, they were considered distinct, but was rediscovered along the northern border of Vietnam in 2002. According to an updated survey conducted by the research team of Fauna and Flora International’s Vietnam primate programme, 129 individuals have been recorded from one patch of karst forest on the China-Vietnam border and indicate a 17% increase in population since the censors of 2007.
Typically, an adult male cao vit gibbon has all black body with a crest on the head, while a female vary in color from yellow to beige with a black patch on the chest and on the top of the head and a large black triangle on her nape and back. Infants are born black and females only get their light color when they reach maturity.
In general, the top killer of cao vit gibbon population decrease is lacking of habitats. With characterizations of short of water and exceptional thin soil layer, the habitats of cao vit gibbons, karst forests are quite vulnerable and fragile. Under the interventions of human activities, such as fuelwood collection and livestock grazing, the recoveries of destroyed forest environments are extremely difficult.
Besides of the habitats withdrawal, the behaviours of cao vit gibbons also limit the population propagation, such as mature female may only give birth to one infant every two to four years. Moreover, cao vit gibbons are canopy dwellers with strong bonds to their territory and tend to avoid lower forest stratum. For example, in a recent study undertook by collaborations of Dr. FAN Pengfei from Dali University and Dr. REN Guopeng from the Kunming Institute of Zoology, Chinese Academy of Sciences, during their 2096 hours spent observing the behavior of threecao vit gibbon groups, only one juvenile male walked on a stone for few seconds was witnessed. Todate, no study has reported the ability of gibbons to disperse acrossrivers or roads, suggesting that the population of cao vit gibbon cannot naturally disperse out of their territory even if it is under threat.
To protect the remaining population and its karst forest habitat, the Cao Vit Gibbon Conservation Area in Vietnam and Bangliang Gibbon Nature Reserve in China were established in 2007 and 2009, respectively. Meanwhile, a wide range of activities have been implemented, such as improved forest protection, community outreach, livelihood development, environmental education, habitat restoration and ecological research.
In Dr. FAN and Dr. REN’s study, the high-resolution satellite images have been used to evaluate the habitat quality and to predict the potential gibbon habitats of the gibbon in the area immediately surrounding the last population. Then Vortex has been implied to simulate population responses to changes in the habitat’s carrying capacity. Their results indicate that the gibbon population is approaching the carrying capacity of their current habitat, and carrying capacity has a significant impact on population changes. And two potential habitats are located in a forest connected to the current habitat by a narrow forest corridor, situated above an underground river. Their research both provides important insight into sustaining the current gibbon population as well as suggestions for both Vietnamese and Chinese local governments planning habitat restoration at the study site.
The main findings of this study have been published on Biological Conservation（http://www.sciencedirect.com/science/article/pii/S0006320713000621）.
(By Su-Qing Liu)
