Though soundless to our ears, bats are actually filling our night skies with noise. Bats fly with their mouths open and emit a constant stream of cries. They interpret the echos which bounce back from objects in their path. These sounds are so intense, that if humans could hear them, it would be comparable to the roar of a jet engine. Yet bats can pick up faint echoes amid all the noise, like hearing someone whispering over the roar of a crowd at a Bronco game.
Bats have sound-dampening structures in their ears which make their own calls tolerable.
Though we sometimes hear the low frequency calls of bats flying overhead, we are deaf to the high pitches used for echolocation. Bats use ultarsonic sounds not to avoid disturbing humans, but because higher frequencies can be beamed like a searchlight, producing sharper echo images. The Lubee Foundation. Swift Shadows in the Twilight, 1994. A Creativity Book for Young Conservationists, 1997.