Influence of proximate individuals on self-scratching behaviour in wild Japanese macaques

Abstract

In group-living animals, it is important to understand how individuals perceive the quality of social relationships because it subsequently affects their decision-making during social interactions. One way to assess how individuals perceive the quality of social relationships is to examine contexts and social factors affecting individuals' stress levels. In this study, we aimed to examine the influence of individuals in proximity (within 1 m) on stress levels during resting and foraging behaviour in wild Japanese macaques, Macaca fuscata, on Kinkazan Island, Japan. We collected data on self-scratching, a behavioural indicator of stress, from 11 adult females across 58 days. During rest, the frequency of self-scratching was higher in the absence of proximate individuals than in their presence. However, social relationships between the focal individual and a proximate female did not affect the frequency of self-scratching. In contrast, during foraging, there was no significant difference between the frequency of self-scratching in the absence and the presence of proximate individuals. However, the frequency of self-scratching was higher in proximity to a related female than in proximity to an unrelated female. These results suggest that stress levels due to proximity to other individuals are influenced by the focal individual’s activity. Furthermore, these results indicate that foraging competition among related individuals and spatial separation from other individuals is one of the causes of stress in this species.