Strategies used by bonnet macaques (Macaca radiata) to reduce predation risk while sleeping

Sleep results in a decrease in alertness, which increases an animal's vulne rability to predation. Therefore, choice of sleeping sites would be predict ed to incorporate predator-avoidance strategies. The current study, conduct ed in two national parks in southern India, examined the behaviors adopted by bonnet macaques (Macaca radiata) to reduce the risk of being preyed upon while sleeping. Bonnet macaques from an urban setting with a low predatory risk were included for comparison. The physical characteristics of the sle eping sites in the forest corresponded with features that were most difficu lt for predators to access; bonnet macaques selected emergent trees with hi gh boles near human settlements. These trees typically overhung water. With in the canopy, individuals slept in huddled subgroups near the terminal end s of branches, preferentially selecting branches over water. Subgroups were generally composed of members of the same age and sex, which likely promot ed social bonding. Adult males and females with infants selected branches h igher than members of other age and sex categories. The lateral distances o f individuals along branches from the main trunk were similar across demogr aphic categories. The size of a subgroup appeared to be limited by the weig ht a branch could supports lateral distances were maintained by regulation of mean subgroup weight, with heavier individuals forming smaller subgroups . The urban troop slept on the top of a building. Subgroup compositions at the urban site were similar to those at the forest sites. However, subgroup size, not restricted by branch fragility, resulted in larger subgroups tha n those found in the forest. Our results indicate that bonnet macaques adop ted a suite of behaviors that reduced their risk of being preyed upon at ni ght by selecting sleeping sites that minimized predator encounters and by s electing the safest locations within the canopy.