Bats fly in pitch dark without trouble and they have a very interesting
navigation system to do this. It is what we call "sonar" system, a system
whereby the shapes of the surrounding objects are determined according to the echo of the
sound waves.
A young person can barely detect a sound with a frequency of
20,000 vibrations per second. A bat furnished with a specially designed "sonar
system", however, makes use of sounds having a frequency of between 50,000 and
200,000 vibrations per second. It sends these sounds in all directions 20 or 30 times each
second. The echo of the sound is so powerful that the bat not only
understands the existence of objects in its path, but also detects the location of its
swift-flying prey.