Abstract

Like humans, animals routinely make decisions. These decision-making opportunities can impact an individual’s survival and reproduction. Research has shown that nonhuman primates make intentional, directional movement choices when solving spatial navigation problems in foraging. However, few studies investigate contextual factors influencing an individual’s decision-making process. Here, I investigated the influence of social (dominance rank, intraspecies competition), individual (age, sex, physical impairment), and environmental (interspecies competition) variables on route choice decision-making in a large (400+) group of free-ranging Japanese monkeys who inhabit forests around the Awajishima Monkey Center in Japan. I used a multi-destination foraging experiment with 6 feeding platforms in a (4mx8m) Z-array, which was successfully completed by 29 identifiable individuals during solitary foraging trials (N=155 successful trials). The macaques: (1) did select optimal routes, and (2) used heuristics similar to primates in other studies. Linear mixed-effects models detected relationships: (1) between age and experiment run time (juvenile macaques completed the array significantly faster than adult and young adult participants); and (2) between route length and competition (trials with competitors nearby were significantly longer than those absent of competitors). Contextual factors led to variation in Japanese macaque decision-making. Participants preferentially used what I term a sweep strategy, which promoted food acquisition in the experiment. I argue this strategy was a response to the island’s topography and intragroup competition. My research on individual variation in route choice contributes to a better overall understanding of group-level movements and the processes underlying foraging decisions, which can contribute to conservation and management.