Democratic leadership controls intermittent collective motion

Most animal behavior studies consider collective motion as an uninterrupted, continuous process. Yet, in many animal systems, collective motion is not a continuous process, but occurs in bursts, which are preceded and followed by resting phases. The abrupt behavioral changes involved in this intermittent process might jeopardize group cohesion. Here, we study intermittent collective motion using sheep as model system. We discover that in this system, each collective motion phase possesses a temporal despotic leader that guides the group. We also show that group coordination and cohesion result from a strongly hierarchical interaction network, where each individual is attracted to, rather than aligned with, the individual directly in front. Consequently, there exists an information flow from the temporal leader to all group members. Importantly, individuals alternate in playing the roles of leaders and followers. We demonstrate that the unveiled democratic leadership mechanism – likely to be at work in other gregarious animal systems – confers the group with the capacity to pool information – known as collective intelligence– to perform a series of complex tasks, such as efficient target localization, consensus decision-making, and coherent group navigation.