The purpose of this workshop is to advance the development of an efficient and effective ultrasonic acoustic deterrent to reduce bat fatalities at wind turbines. Discussions focused on how to develop a durable, easily mounted and maintained ultrasonic acoustic deterrent device that results in a significant reduction in bat fatalities, comparable to operational mitigation.
Bats depend on echolocation for navigation, orientation, prey capture and communication. A typical bats emit pulses at approximately 110 dB sound pressure level (SPL) at 10 cm at a rate of 12 pulses/sec, with each pulse lasting about 5 milliseconds long. Given the speed of sound at 340 m/sec and duration of an open air echolocation pulse, the bats own call will mask echoes returning from objects within about 1.5 m away (i.e., the bat cannot hear early return echoes while vocalizing). An echo from a target about 1.5 m away will return about 45 dB less than the original 110 dB signal, or about 65 dB. The bats next call would mask echoes returning from about 25 m away. A bat would theoretically perceive information from returning echoes with amplitudes of ≤65 dB over a range from about 1.5–25 m. Thus, broadband signal of ≥65 dB should ‘jam’ echolocation perception from targets beyond 1.5 m away.