Light and ultrasonic noise pollution displaces trawling Daubenton's bats

Bats evolved the ability to echolocate prey in night sky, but this dark and quiet sensory niche is increasingly encroached upon by anthropogenic light and noise pollution. Here, we test the hypotheses that such pollutions displace bats from their foraging sites and that the displacement increases with stressor intensity. To do so we exposed wild Daubenton's bats (Myotis daubentonii) to controlled levels of light or ultrasonic broad-band noise and recorded bat activity levels via passive acoustic monitoring at different distances to the stressors. We find that light-, and noise-exposures reduced bat activity by 43% and 49% respectively compared to control periods within 6m of the stressor source. The displacement effect decreased with increasing distance to the light and noise sources. At 20m from the source, light levels of 1 Lux still exerted a modest reduction in bat activity. By contrast, at 20 m, noise levels of 56 dB re. 20μPa RMS no longer elicited a measurable displacement of bats. We conclude that moderate anthropogenic light- and noise pollution can displace bats from their foraging sites and that light and ultrasonic noise pollution should be mitigated around critical bat habitats.