Plains zebra (Equus quagga) group movement decisions are associated with visual and tactile behaviours performed by initiators, followers and non-followers

Diverging needs often occurs among group members, prompting group-living animals to engage in collective decision-making, such as coordinating collective movement. Existing models classify these decision-making processes as unshared (despotic), shared (democratic), or partially shared (partially democratic). However, how specific communication contribute to different decision-making outcomes remains unclear. Here, we investigated the decision-making process underlying collective movement departure in South African plains zebras, focusing on visual, tactile and acoustic behaviours emitted by individuals playing various roles – initiators, followers, and non-followers. Our findings revealed that zebras use non-acoustic behaviours (i.e. visual and tactile) to make decisions about when to move as a group; namely, headshakes, head-bobs, contacts, grazing, standing, short walks, and direction changes were significantly associated with the decision-making process. Conversely, we did not detect an association between acoustic behaviours and collective movement departure. Our findings also suggest that zebras display role-differentiated behaviours associated with departure outcomes that are consistent with a partially shared-decision-making process, as the behaviours of not only initiators but also followers and non-followers were related to the decision-making process for group movement. Specifically, our analyses showed that the number of followers versus non-followers in a group movement decreased as the time non-followers spent standing before departure increased, while an increased rate of direction change of both initiators and non-followers was associated with shorter group movement duration. In conclusion, our study suggests that collective movement departure in zebras may arise from a partially shared decision-making process based mostly on non-acoustic behaviours. This research contributes valuable insights into the behavioural intricacies of group-living animals, laying the groundwork for further comprehension of social dynamics and collective decision-making processes.