Beyond noise playback: the effect of an audible and visible sound source on bird flushing behavior
摘要
Studies investigating the effects of ambient noise on animals’ tolerance to predators and risk assessment typically rely solely on sound playbacks, neglecting multimodal perception by omitting visual or other contextual cues. To address this limitation, we tested whether the faster escape responses from an approaching potential predator observed in isolated noise playback studies—commonly attributed to heightened vigilance—actually result from the absence of typical contextual cues, such as the visible noise source (the “cross-modal sensory dissonance” hypothesis). If true, pairing noise with its typical cues should reduce or eliminate the difference in flight initiation distances (FIDs) between noise-exposed and non-noise-exposed individuals. We simultaneously exposed male barn swallows Hirundo rustica to both acoustic noise and its visual source—an agricultural tractor. Subsequently, we compared these results with those from our previous research, which utilized only tractor noise playbacks. Birds initiated flight at significantly greater distances when the noisy tractor was nearby. This effect was significantly greater than in the experiment that used only isolated noise playback. We conclude that the longer FIDs observed in barn swallows during noise-playback experiments reflect increased vigilance, rather than merely a response to the “dissonance” of hearing noise without seeing its source.