Factors influencing the population density of the hanuman langur (Presbytis entellus) in Sariska Tiger Reserve

We carried out a study of Hanuman langurs in Sariska Tiger Reserve, Rajasthan, India during three months in 1990. The area surveyed included habitat disturbed by human activity, with both the grazing of livestock and firewood collecting resulting in degraded forest. Langur population density was estimated to be between 19 and 36 animals/km². The density of langurs in disturbed areas was significantly lower than in undisturbed areas. Both tree cover, total tree, and shrub cover were positively correlated with langur density, suggesting that a lack of trees in disturbed areas may have caused the lower langur densities. Although bisexual groups were significantly more common in undisturbed areas the distribution of all male groups did not appear to be affected by human disturbance, suggesting that male bands are likely to inhabit more disturbed habitats than bisexual groups. We suggest that either a lack of food trees or the high density of predators in Sariska may prevent bisexual groups from inhabiting areas where tree cover is low, although the more mobile male groups can survive in these areas. Although Hanuman langurs are a relatively common species in India, these results suggest that they are not, as is commonly assumed, immune to the effects of human disturbance. In areas where langurs appear to survive in disturbed habitats the different response of bisexual and all male groups to disturbance may still result in serious disruption to the population structure.