Relation between social tension and demographic density of commensal long-tailed macaques (Macaca fascicularis) in Bali (Indonesia)

In Bali, Indonesia, Macaca fascicularis groups are sometimes leaving in situations of high density or overpopulation. Previous researches established three models in order to explain how macaques cope with high-density conditions. We tested the validity of these models for free-ranging M. fascicularis, considered as less despotic than M. mulatta on which the models have been originally tested by comparing free-ranging and captive populations. Allowing the increasing ecological validity of our research’s conclusions, the free-ranging macaques we studied had a time window of life in high density condition long enough to set up an efficient and well-established social coping strategies. The study sites of Ubud and Uluwatu consisted of respectively six and five groups of M. fascicularis. We collected demographic data using a procession counting method, and behavioural data using focal and all-occurrence sampling methods. We assessed home range size using the daily group’s GPS location. Although Ubud is a crowded space while Uluwatu is not, we recorded less home range overlap between groups in Ubud in comparison to Uluwatu. Although global aggression did not differ between both populations, aggressive and submissive time increased whereas affiliative time decreased when density increased. According to the activity budget, while time spent in affiliative contacts was shorter in higher density condition, time spent in distant affiliative behaviours was longer. Females of both populations spent longer aggressive time than males but, although they increased more submissive time and decreased more affiliative time, their increase of aggressive time was lower than this of males when density increased. A plateau in aggressions occurred when density increased. In the study conditions, macaques seem to become more hierarchically structured that known for the species. However, some evidences seem to indicate they could become less despotic as well, supporting the coping model originally tested on M. mulatta. Macaca fascicularis could be expected to combine two different coping strategies to cope with high densities.