Contrary to popular belief bats are
not blind! They have perfectly functioning eyes and in many fruit bats the eyes
are very large and are used to find food. However, many nocturnal bats, like
those in Britain, also use echolocation to hunt.
Echolocation is a means of navigating and hunting using sound pulses which works
in the same way as sonar and could be more accurately described as 'echo
imaging'. The bat generates a high pitched squeak in its larynx
and simultaneously pulls a muscle over its ear to block out the sound. The squeak
travels forward and rebounds off anything it touches, like trees or insects.
These rebounded sound waves are received by the bat's ear and are used to make a
mental map of the area. This method of hunting is not just restricted to bats:
whales, dolphins and shrews are all known to echolocate. This fact supports the
theory that bats may have evolved from a small, shrew-like animal during the
Eocene period (approximately 50 million years ago).
The noises produced during echolocation are too high-pitched for most humans to
hear (although we can often hear the social calls made between bats). Bat
workers use a device called a bat detector to pick up echolocation calls and to
find bats. Bat detectors work by translating the noises produced during
echolocation to an audible sound and each bat has a distinctive 'call signature'
in the way that birds have distinctive songs.