Non‐additivity among multiple cues of predation risk: a behaviorally‐driven trophic cascade between owls and songbirds

Abstract

Non‐lethal effects of predators on prey are initiated in the form of responses to direct and indirect cues of predation risk. Like their lethal equivalents, non‐lethal effects may affect species further down the food web initiating a behaviorally‐driven trophic cascade. I presented a direct cue of predation risk, owl vocalizations, to white‐footed mice (Peromyscus leucopus) during either a new or full moon (indirect cue). Mice reduced their activity in space by nearly two‐thirds in response to playbacks of owl vocalizations during a full moon. However, neither moonlight (full vs new) nor the presence/absence of owl calls had an effect on space use when each cue varied singly. Previous studies have demonstrated a tight correlation between spatial activity in mice as used in the current experiment and nest predation rates on ground‐nesting birds. Because moonlight is a ubiquitous deterrent of activity in nocturnal rodents I used of long‐term nesting records the veery (Catharus fuscescens) to test whether nest predation rates were correlated negatively with moonlight. For half the lunar cycle (∼full moon to new moon) predation rates decreased with moonlight as predicted. During the second half of the lunar cycle predation and moonlight did not correlate as expected, but this was likely due to the depletion of vulnerable nests after a period of in which predation rates were at their maximum near the full moon. These studies suggest that the non‐lethal effects of predatory risk on mice (i.e. changes in space use) cascade to affect their prey. Through the mechanism of reduced space use by rodents, perceived predation risk has the potential to significantly and indirectly affect songbird nest predation rates.