The degree of behavioural synchrony of animals within a group can be considered a reflection of how individuals adjust their behaviours to manage the costs/benefits accompanying group-living. In this study, we focused on activity synchrony and travel direction synchrony as behavioural synchrony. We aimed to quantify the degree of behavioural synchrony and identify which factors can affect the synchrony in wild females of Japanese macaques. Japanese macaques live in female philopatric multi-female and multi-male groups and have a linear dominance hierarchy. The groups are characterized by changing spatio-temporal cohesiveness among group members. Two observers conducted simultaneous focal animal sampling on adult females using global positioning system devices to record locations. The overall degree of activity synchrony was positive compared with random, and the degree was highest when macaques were located within visual range of each other. Both activity synchrony and travel direction synchrony were influenced by spatial cohesion, i.e. interindividual distance, which shows that the probabilities of synchrony were higher with individuals located closer. Activity synchrony was also influenced by activity type, showing that the probabilities of synchrony were higher when individuals engaged in foraging. These results suggest that synchronized foraging may be caused by enhanced feeding with other group members when they are closer to each other. Our approach to quantitatively measure spatial dispersal while observing group members simultaneously revealed the roles of spatial cohesion and activity types for determining the degree of behavioural synchrony.

一个群体内动物的行为同步程度可以被认为是个体如何调整他们的行为以管理伴随群体生活的成本/收益的反映。在这项研究中，我们将活动同步和行进方向同步作为行为同步。我们旨在量化行为同步的程度，并确定哪些因素会影响日本猕猴野生雌性的同步。日本猕猴生活在雌性多雌性和多雄性群体中，并具有线性优势等级。群体的特点是改变群体成员之间的时空凝聚力。两名观察员使用全球定位系统设备对成年女性进行同步焦点动物采样以记录位置。与随机相比，活动同步的整体程度是积极的，当猕猴位于彼此的可视范围内时，程度最高。活动同步性和行进方向同步性均受空间凝聚力即个体间距离的影响，表明个体距离越近，同步的概率越高。活动同步性也受活动类型的影响，表明当个体从事觅食时，同步的概率更高。这些结果表明，同步觅食可能是由于其他群体成员彼此距离较近时加强进食造成的。