Herding mechanisms to maintain the cohesion of a harem group: two interaction phases during herding

In animal groups, individual interactions achieve coordinated movements to maintain cohesion. In horse harem groups, herding is a behavior in which males chase females from behind; it is considered to assist with group cohesiveness. However, the mechanisms by which the individuals move to maintain group cohesion are unknown. We applied novel non-invasive methods of drone filming and video tracking to observe horse movements in the field with high temporal and spatial resolution. We tracked all group members and drew trajectories. We analyzed the movements of females and found two phases of interactions based on their timing of movement initiation. The females that moved first were those nearest to the herding male, while the movement initiation of the later females was determined by the distance from the nearest moving female, not by the distance from the herding male. These interactions are unique among animal group movements and might represent a herding mechanism responsible ...在动物群体中，个体间的交互行为可促成协调一致的群体运动，以此维持群体凝聚力（cohesion）。在单雄多雌马群（horse harem groups）中，驱赶行为（herding）指雄马从后方追逐雌马的行为，该行为被认为有助于维持群体凝聚力。然而，当前学界仍未明确个体通过运动维持群体凝聚力的具体机制。我们采用无人机拍摄与视频追踪这两种新型非侵入式研究方法，以高时空分辨率在野外观测马群的运动。我们对群体内所有个体进行追踪并绘制其运动轨迹。通过分析雌马的运动行为，我们基于其运动启动的时间节点，识别出两类交互模式：率先启动运动的雌马均为距离驱赶雄马最近的个体；而后续启动运动的雌马，其运动时机由自身与最近已启动运动的雌马之间的距离决定，而非与驱赶雄马的距离。这类交互模式在动物群体运动中独具特色，或可代表负责维持该群体凝聚力的驱赶机制……