![]() The anti-predator effect of aggregating is important in the evolution of group-living, particularly for species which are regularly preyed upon. To counteract this, predators may attempt to split up their target groups for instance, an avian predator may attack an airborne flock several times, while gaining altitude in order to dive and intersect it at high speed (a hunting strategy called ‘stoop’). ![]() These patterns often confuse the predator and increase the prey's survival. Patterns of collective escape of animals are some of the most complex and mesmerizing displays in nature: when a moving group is under attack by a predator, the group changes its shape and internal structure rapidly. ![]() Our study highlights the importance of discrete and uncoordinated manoeuvres in the collective escape of bird flocks and advocates the systematic study of their patterns across species. We confirm this association in the empirical data. Their relative frequency depends on the angular velocity and position of the initiator in the flock: sharp turns by individuals at the periphery lead to more splits than collective turns. Both splits and collective turns emerge from this rule. To examine their formation, we extend an agent-based model of pigeons with a ‘discrete’ escape manoeuvre by a single initiator, namely a sudden turn interrupting the continuous coordinated motion of the group. By analysing GPS trajectories of flocking individuals, we identify two new patterns of collective escape: early splits and collective turns, occurring even at large distances from the predator. Here, we study airborne flocks of homing pigeons attacked by a robotic falcon, combining empirical data with a species-specific computational model of collective escape. These rules have not yet been systematically studied for bird flocks under predation. To understand what behavioural rules underlie these patterns, computational models are often necessary. Complex patterns of collective behaviour may emerge through self-organization, from local interactions among individuals in a group.
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