Behavioral plasticity in jackdaw flocks

Bird flocks are a classic example of collective behavior, where the cohesive motion of the flock as a whole is presumed to arise purely from local interactions. Flocking models tend to assume that every individual is an identical agent that plays by the same rules, and these rules are usually assumed to be immutable. In reality, however, interactions may be influenced by many factors, such as external stimuli and social relationships. I will present evidence from field studies of jackdaws, a highly social corvid species, that indeed flocks of this single species display different interaction rules in different ecological contexts. During the roosting season, large flocks spontaneously form in the evening as the birds return to their roosts. In these transit flocks, individual jackdaws interact topologically with a fixed number of their neighbors. Jackdaws also gather together in mobbing flocks to drive away predators, and such flocks can be induced experimentally using a model predator and playbacks of scolding and recruitment calls. In these mobbing flocks, jackdaws interact metrically over a fixed physical distance. This change in interaction type leads to a clear ordering phase transition as a function of group density in mobbing flocks that is absent in transit flocks.