Eastern chipmunks increase their perception of predation risk in response to titmouse alarm calls

Vocally signaling a predator's presence through alarm calls creates public information regarding risk in the environment. If having this information confers an advantage, eavesdropping behavior, the use of information in signals by individuals other than the primary target, is expected to evolve. Thus, eavesdropping for information on predation risk to avoid predators may be common. We describe the first study to quantify an effect of avian alarm calling on the perceived cost of predation in a mammalian receiver/eavesdropper using the eastern tufted titmouse--eastern chipmunk dyad. We used the technique of giving-up densities to quantify changes in chipmunks' perceived risk of predation while foraging under experimental playbacks of titmouse vocalizations (seet, mobbing, and contact calls), hawk calls, and wood thrush song (control). Titmouse mobbing calls significantly increased chipmunk's perceived risk of predation. Chipmunks also appeared to divert attention (i.e., cost of multitasking) to monitoring alarm call playbacks/assessing predation risk as shown by the absence of density-dependent foraging. In contrast, when foraging during hawk calls (a direct cue of predation risk), chipmunks showed no differences in foraging relative to controls. These results support other published studies that prey respond more strongly to indirect source of information about predation risk than to direct sources. Copyright 2008, Oxford University Press.