Estimation of large herbivore densities in the tropical forests of southern India using distance sampling

Ecological densities of large herbivores were estimated using the line transect method in the tropical moist forests of Bhadra Tiger Reserve, southern India, during November 2000. The species of interest were chital Axis axis, sambar Cervus unicolor, muntjac Muntiacus muntjak, gaur Bos gaurus and Hanuman langur Presbytes entellus. Six permanent transects, ranging from 2.6 to 3.6 km (totalling 18.2 km) were each walked 26 times. A total of 473 km was walked during the surveys. Numbers of detections were generally low (51, 25, 68, 17 and 302 for chital, sambar, muntjac, gaur and langur, respectively). Mean estimated densities of different species were [(D) over cap (+/- SE)]: 4.51 (+/- 1.05) chital km(-2), 0.89 (+/- 0.23) sambar km(-2), 3.64 (+/- 0.63) muntjac km(-2), 1.48 (+/- 0.63) gaur km(-2) and 22.62 (+/- 2.64) langur km(-2). Possible shortcomings of our estimates are considered and suggestions made for improving future surveys. A comparison with densities estimated for these species in other well-protected parks showed that the chital, gaur and sambar densities in Bhadra were extremely low. The main causal factors for these low densities seem to be poaching and livestock grazing.