Conservation of the cao vit gibbon 777


FIG. 1 The study site and survey posts in the Trung Khanh Cao Vit Gibbon Species and Habitat Conservation Area, Viet Nam, and the Bangliang Gibbon National Nature Reserve, China.


border may overestimate total population size as individuals or groups travel across the border and are counted by both countries (Vitkalova et al., 2018), and researchers may underestimate total population size because areas adjacent to political borders are avoided because of security con- cerns. Since the rediscovery of the cao vit gibbon in 2002, several surveys and censuses have been conducted on the Vietnamese side of the border in the Trung Khanh Cao Vit Gibbon Species and Habitat Conservation Area. These surveys recorded a population with 26–28 individuals in 2002 (Geissmann et al., 2002), 37 in 2004 (Trinh Dinh, 2004), and 27–35 in 2005 (Vu et al., 2005). These surveys underestimated the species’ population size because three more groups also exist on the Chinese side, as was discov- ered in 2006 (Chan et al., 2008). To obtain an accurate estimate of the total population


size of the cao vit gibbon, two transboundary censuses were conducted, in 2007 and 2016, by the Management Board of Trung Khanh Cao Vit Gibbon Species and Habitat Conservation Area and the Administrative Bureau of Bangliang Gibbon National Nature Reserve, with the support of Fauna & Flora International (FFI) Viet Nam and China Programmes. Here, we report the results of these sur- veys, analyse population trends since the species’ rediscovery, discuss factors that limit gibbon population increase, and propose potential solutions.


Study area


We conducted surveys along the Chinese and Vietnamese international border in the Bangliang Gibbon National


Nature Reserve in Guangxi Province, China, and the Trung Khanh Cao Vit Gibbon Species and Habitat Conservation Area in Cao Bang Province, Viet Nam (Fig. 1). The study area is characterized by a typical karst limestone landscape consisting of densely packed outcrops, sharp-peaked moun- tains with steep slopes, ridges and vertical cliffs, interspersed with lowland valleys. Altitude is 400–950mand the vegeta- tion is monsoon tropical forest that has been degraded by selective logging, fuelwood collection, charcoal making, and agriculture prior to the establishment of the nature re- serves (Fan et al., 2011). On the Chinese side of the border, 113 tree species and 46 woody liana and epiphyte species were recorded in 44 20 × 20m plots, and mean canopy height was 10.5m (Fan et al., 2011). Diversity of tree and woody liana species was higher in the valleys and slopes than on the cols and ridges (Fan et al., 2011). Previous studies found cao vit gibbons consumed foods from .81 tree and liana species, with 19 species accounting for 77.8% of total feeding time (Fan et al., 2011). Fruits made up 58% of the gibbons’ diet, and leaves and buds accounted for 16.9 and 14.3%, respectively (Fan et al., 2011).Nocomparable informa- tion is available for Vietnamese cao vit gibbon groups, but we assume that habitat quality and gibbon ecology and behaviour are similar on both sides of the border.


Methods


We applied auditory techniques that were developed especially for gibbon surveys (Brockelman & Ali, 1987) and were used in this area in previous surveys (Geissmann et al., 2002, 2003; Chan et al., 2008). In 2007 we set up 18


Oryx, 2020, 54(6), 776–783 © 2019 Fauna & Flora International doi:10.1017/S0030605318001576


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