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

<p>In animal groups, individual interactions achieve coordinated movements to maintain cohesion. In horse harem groups, herding<br> is a behavior in which males chase females from behind; it is considered to assist with group cohesiveness. However,<br> the mechanisms by which the individuals move to maintain group cohesion are unknown. We applied novel non-invasive<br> methods of drone filming and video tracking to observe horse movements in the field with high temporal and spatial resolution.<br> We tracked all group members and drew trajectories. We analyzed the movements of females and found two phases<br> of interactions based on their timing of movement initiation. The females that moved first were those nearest to the herding<br> male, while the movement initiation of the later females was determined by the distance from the nearest moving female, not<br> by the distance from the herding male. These interactions are unique among animal group movements and might represent a<br> herding mechanism responsible for maintaining group cohesion. This might be due to long-term stable relationships within<br> a harem group and strong social bonds between females. This study showed that the combination of drone filming and video<br> tracking is a useful method for analyzing the movements of animals simultaneously in high resolution.</p>