Optimal foraging can drive emergent initiator-follower dynamics in social groups

Deciding when and where to move is a challenge for group-living animals as differences in preferences must be resolved for the group to maintain cohesion. In many species, consensus is reached through shared decisions-making, whereby group members initiate group movements by stopping foraging and making directed movements away from a feeding source. Yet, despite being widespread, it is unclear how this initiation process has emerged in animal groups, and theory has yet to resolve the paradox of why some individuals forego foraging to instigate collective movements. By applying theoretical predictions from the marginal value theorem to heterogeneous foraging groups, we show that (i) movement initiations can reduce subsequent within-group conflict over when to depart, (ii) habitat heterogeneity and within-group differences in foraging rate shape who initiates, and (iii) different forms of collective decision-making can emerge under different environmental conditions. These results demonstrate that optimal foraging theory can resolve outstanding questions about leadership in collective movements of animal groups.