Patterns of collective escape of bird flocks under predation by a RobotFalcon

Collective behaviour often functions to avoid predation, and is therefore especially conspicuous and complex in flocks of birds under attack by raptors. However, studying collective behaviour experimentally in natural conditions is challenging. Here, we used an artificial predator, the RobotFalcon, developed after a peregrine falcon, a cosmopolitan raptor hunting a wide variety of birds. We hunted with the RobotFalcon flocks of corvids, gulls, starlings and lapwings in an agricultural area in The Netherlands, while recording the collective escape responses of the flocks with a camera. We compared collective escape responses from the RobotFalcon with those from a drone. Flocks of all species responded to the RobotFalcon most often by collectively turning, compacting and splitting in subflocks. The frequency of collective escape was highest in starlings and corvids and lowest in gulls. For starlings only, we also compared their response to a live peregrine falcon using observational data. Similar to hunts by the real falcons, the collective escape response depended on the level of predatory threat. Flocks of all species except starlings responded less often and less intensively to the drone compared to the RobotFalcon. These results give novel insights in the predator-prey dynamics between raptors and bird flocks, and illustrate how artificial predators can be used to study prey-predator interactions experimentally in the field.