Ultrasonic deterrents have been experimented with, and have shown reduction in bat kills, but there are many challenges with respect to efficiency and reliabili

Ultrasonic deterrents have been experimented with, and have shown reduction in bat kills, but there are many challenges with respect to efficiency and reliability. Technically, ultrasound is attenuated significantly in the atmosphere, so it takes a lot of amplification to broadcast ultrasound significant distances. Not to mention that the bats are often flying with the wind, not against it, which means the ultrasonic transducers are projecting into the wind. Certain signals and sample playbacks might be effective for one bat species, say Hoary Bats, but not deter another species like Red Bats. Detecting bats' echolocation calls, however, is much easier. A brilliant researcher in Arcata CA has a working system installed in a commercial wind farm which detects the presence of migratory bats, and brakes the wind turbines until no bat calls have been detected for some some period of time. Bats don't fly all night, and migrating bats may travel together.