In Cat Tien National Park, we surveyed only the southern portion of the protected area where we focused on the southeast and central part areas from where the species has been reported (McGowan et al., 1999 and Robson et al., 1991). In the southeast part, two 2 km line transects, that were 540 m apart, were set along the road that runs parallel to Dong Nai River, demarcating the park boundary, through the grassland (Fig. 1a). Two observers walked each transect at the same time for seven consecutive days so that each transect was walked twice a day and 14 times in total. The survey in the central part was focused around Crocodile Lake where point transects were used instead of line transects as it was not possible to conduct line transect surveys because the topography made the area inaccessible. Around the lake three accessible point locations were established 400 m apart (Fig. 1a). Point counts were conducted twice a day by three observers for seven consecutive days giving 14 repeat surveys per point.