On the perception of targeting by predators during attacks on socially feeding birds

We examined the spatial perception of predator targeting by prey during simulated hawk attacks on house finch, Carpodacus mexicanus, flocks, with an overall goal of gaining insight into the targeting process itself. Predator targeting of specific prey during attacks determines how danger is distributed among group members, and thereby determines key aspects of the safety of feeding in groups, such as risk dilution and its relationship to antipredator vigilance. During the main experiment, a model hawk suddenly appeared at either 3 m or 9 m from finches feeding near protective cover. The 9 m attacks always caused nearly all birds to flee to cover. During 3 m attacks, only birds directly in the line of attack fled to cover; the other birds instead consistently flew nearly perpendicular to the attack and away from cover. These results suggest that most finches did not perceive themselves to be targeted for attack when the hawk appeared at close range; otherwise, all birds appeared to perceive themselves as potential targets. A second experiment demonstrated that information about predator targeting is derived from observation of the predator itself rather than the behaviour of flockmates in the direct line of attack. A third experiment demonstrated that distance to cover also influenced the birds’ response to targeting; thus, reactions to apparent nontargeting were not simply a matter of moving away from the line of attack. The differential perception of targeting during an attack is probably a widespread phenomenon in social birds and other animals.