The relationship between a troop of hanuman langur monkeys (Presbytis entellus) and chital deer (Axis axis) was examined in Kanha Tiger Reserve, Central Indian Highlands. The frequency distribution of closest approaches between the two species suggested that associations (defined as proximity < 25 m) were not chance encounters; 70.1% of all those herds observed within 200 m came within 25 m of the troop. Associations were more frequent and lasted longer during the hot and cold weather than in the monsoon. Chital initiated and terminated the majority of associations, whilst langurs terminated them more frequently than they initiated.

The langur troop dropped a mean of 4.0 kg vegetation fresh weight/day and chital were seen to scavenge or glean this forage in 38.2% of associations; more frequently in the hot and cold weather than in the monsoon. Chital gleaned items from 19 species of tree, with Shorea robusta the most frequently utilized.

Responses to potential predators suggested that chital and langur responded to each other's alarm behaviour. Chital alerted to langur alarm more frequently than vice versa. Antagonistic interactions between the two species were observed in 5.8% of associations, predominantly directed from langurs to chital.

The study suggests that chital-langur associations are asymmetrical mutualisms. Chital gained by opportunistically taking advantage of vegetation dropped by langurs, and by responding to langur alarm behaviour. The benefit, if any, to langurs was probably slight; they may have gained from responding to chital alarms but incurred costs of antagonism and feeding competition with chital.