Abstract
Documented bat fatalities from collisions with wind turbines have prompted the search for a means to discourage bats from approaching them. Because echolocating bats depend upon sensitive ultrasonic hearing for orientation and prey capture, broadcasting ultrasound from turbines may disrupt or “jam” their perception of echoes and serve as a deterrent. I tested the response of bats to a prototype eight speaker deterrent emitting broadband white noise at frequencies from 12.5 to 112.5 kHz at about 100 dB SPL per speaker at 1 m. I tested the effect of broadcasting ultrasound on bats flying in feeding or non-feeding trials with the acoustic deterrent device placed among four quadrants in a flight chamber. In half the trials, the acoustic deterrent broadcast broadband noise, and in half the trials, the device remained silent. Bats in feeding trials were presented with a tethered meal worm in the same quadrant as the device.
In non-feeding trials, bats landed in the quadrant containing the device significantly less when it was broadcasting broadband noise (1.7% vs. 22.4%, p = 0.00375). In feeding trials, bats never successfully took a tethered mealworm when the device broad cast sound but captured mealworms near the device in about 1/3 of trials when it was silent. Bats in both feeding and non-feeding trials flew through the quadrant containing the device significantly less when it broadcast noise than when it remained silent (non-feeding trials: n =136, p = 0.0035, one-sided test; feeding trails: n = 132, p = 0.0103, one-sided test). While bats’ avoidance of the active device was not absolute, these results indicate that broadcasting broadband noise shows promise as a means to deter bats from approaching wind turbines.