Bats are a fascinating group of animals. Of the some 900 species of bats, more than half rely on echolocation to detect obstacles in flight, find their way into roosts and forage for food. A few species, though, click their tongues. These noises resemble the sounds made by hitting two round pebbles together.
Some bats have specialized structures for emitting echolocation calls.
Most bats produce a complicated sequence of calls, combining CF and FM components. Thus, these sounds are used more often. In terms of loudness, bats emit calls as low as 50 dB and as high as 120 dB, which is louder than a smoke detector 10 centimeters from your ear. That's not just loud, but damaging to human hearing. The good news is that because this call has an ultrasonic frequency, we are unable to hear it.