Bats navigate by echolocation-- high frequency sound which is emitted by the bat, then bounces off of objects and is received by the ears of the bat. This gives bats a 3D sound picture.
Bats typically emit 30 sounds per second countinuously while flying.
When encountering an object, they emit 50-60 sounds/second.
The sound frequency of bat echolocation is 30,000 cycles (the extreme upper limit of human hearing) to 60,000 cycles.
examples of bat echolocation
(frequencies lowered to human-audible frequencies)
courtesy of UNM Batsound Library