When moving in groups, social animals tend to follow a leader which successfully attracted them. Many variables are known to affect an individual’s propensity to act as a leader. Depending on their nature, these variables underlie two theoretical paradigms (i) ‘leadership according to social indifference’, characterised by differences in personality or sociability, or (ii) ‘leadership according to need’, characterised by differences in energetic requirements or information content. Currently, it is not clear under which circumstances each of the two paradigms plays a larger role. Here, we tried to understand these paradigms by observing collective movements in female mallards. Each of these mallards previously learned individually to associate one of four locations in a maze with food rewards. We then formed groups of various compositions (group size range: 2–5 individuals) with respect to personality, sociability, energetic requirements, motivation and information content. We found that groups remained cohesive, and that certain individuals were consistent leaders within and between trials. The order of entering the maze was mainly determined by energetic requirements. However, soon after entering the maze, the progression order changed. Then, more socially indifferent individuals took the lead and this new order remained constant until all individuals reached the final location, which was usually the one the leader had learned. In addition, we investigated the role of naïve individuals in group decision-making. In our setup, adding naïve individuals broke the leadership consistency between trials and increased fission events. Overall, our results show that the onset of collective movements may be driven by different mechanisms compared to the movement progression itself.
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