Ecological context shapes collective turns and velocity correlations in jackdaw flocks

Recently, ecological context has been shown to have a profound impact on the collective motion of wild animals. Animals in different contexts can use different inter-individual interaction rules, and consequently produce different group-level properties. In this talk, we report that ecological context can also influent collective turns and velocity correlations for flocks of jackdaws (Corvus monedula). We used a three-dimensional imaging system to track the movement of jackdaws in two different contexts: transit flocks where birds travel from one location to another, and mobbing flocks where birds respond to a predatory stimulus. We found that context may alter where turns were initiated in the flocks: for transit flocks in the absence of predators, initiators were located either at the front or at the back of the flocks, but for mobbing flocks with a fixed ground-based predator, they were always located at the front. In addition, we found that the correlation length of velocity was independent of the group density for transit flocks, but increased with increasing the group density in mobbing flocks. This result confirms a previous observation that birds obey topological interactions in transit flocks, but switch to metric interactions in mobbing flocks. Our results highlight the importance of ecological context when studying collective animal behaviour.