Primates’ social interactions are grounded in temporal and spatial relationships, with physical proximity commonly used to assess affiliation, dominance, and tolerance. Yet proximity is often treated as a static, categorical measure rather than a dynamic, continuous process. Here, we combine computer vision and environmental markers to precisely quantify short-range social distances in two groups of Japanese macaques housed in large outdoor enclosures. Our social tolerance test results show that, when entering a food-baited circle, macaques positioned themselves at greater-than-chance distances from conspecifics, particularly to dominants. Furthermore, lower-ranking individuals tended to follow more indirect paths before approaching the food resource, suggesting they weigh social risks alongside physical positioning. By treating social proximity as a dynamic process, our study provides new insights into how primates navigate social and physical environments. This illustrates the potential of our method for more nuanced measures of group organization, tolerance, and decision-making.
Fig. 1 | Diagram of normalized entry distance (NED) metric and liminal path distance (LPD). When analyzing NED, we remove all data where the occupier was near the exact center. (B) Estimated trajectories of Masanobu, Jo, and Marge from Session 3 in Northwest. The alpha, Masanobu, takes a direct path to the resource circle while Jo takes a circuitous path. Masanobu chases Jo away while tolerating Marge’s proximity. (C) Time spent inside the circle in Session 3 in Northwest and (D) LPD from Session 3 in Northwest.
Fig. 2 | (A) A permutation test showing actual NED (red) is significantly greater than bootstrapped permutations of NED (black). (B) The estimated marginal mean NED by the social rank of the occupier (is group alpha or not) and whether the entering macaque and occupier are the same sex (green) or not (black). (C) Liminal path length by social rank of the enterer and occupier and whether the entering macaque and occupier are the same sex (green) or not (black).
Fig. 3 | Box plots of mean time in seconds macaques spent inside the circle per session grouped by enclosure and sex. Individual mean times are plotted as points with shapes corresponding to rank categories and color to sex.
