Behavioural response of European starlings exposed to video playback of conspecific flocks: effect of social context and predator threat.

We studied the behavioural response of European starlings to a socially mediated predation event. Adult starlings were exposed to either a video of a flock attacked by a peregrine falcon or a video of a flock not under attack. We investigated whether the social condition affected the anti-predator response under the hypothesis that in such a gregarious species singletons would increase their anti-predator behaviour more than individuals in groups, to compensate for potential increased risk. The video of the flock under attack caused an increase in immobility and vigilance, more marked in singletons, both during and after the exposure. The video of the non-threatened flock caused an increase in activity levels, especially during the exposure. Furthermore, we observed a marked increase in comfort activities in singletons as well as in social interactions and vocalizations in mini-flocks. Only birds in mini-flocks vocalized, which may be explained by an audience effect, a process of social cognition mediated by the social context, and not only by the stimulus. The results are in line with previous field studies, which showed that isolated starlings are exposed to a higher risk of predation compared to individuals in flocks.