Response dynamics of jackdaw flocks to sudden perturbations

It is often suggested that an important benefit for animals of aggregating into groups is the "many eyes" effect, where the group perceives threats more effectively than any single individual. However, evidence of this effect in real animal groups is limited, and the impact of factors such as individual-level heterogeneity is not well understood. It is also difficult to quantify the details of how animal groups in the wild respond to threats. Under natural conditions, groups are often far from observers and move in complex, three-dimensional patterns, making quantitative measurements challenging, and it is difficult to pinpoint the exact moment when individuals first become aware of potential threats. To begin to address these gaps, we conducted field experiments during which we fired a projectile near wild flocks of jackdaws (Corvus monedula) while performing three-dimensional tracking of the individual birds. We find evidence that the individual response to the perturbation is not random but rather is consistent with social information propagation, a necessary condition for the many-eyes effect. However, we also find that different flocks do not respond consistently to the same stimulus. Our results are thus broadly consistent with the many-eyes hypothesis, but also highlight the importance of individual-level heterogeneity.