Echolocation: What is it?
Ever lost your way in the dark? Finding your way in total
darkness is more than just difficult... It can be impossible! But, bats can
fly in total darkness and detect something as fine as a human hair. Today we
call this unique skill "echolocation", but it wasn't until the mid 1930's
that we had any idea what it was all about. During the thirties the first
scientific apparatus was developed to detect high frequency sounds and it was
then that the mystery of how bats could "see in the dark" was finally
When we talk, yell or sing our larynx is vibrating in our
throat causing pressure variations in the air passing through it. These
pressure variations are picked up by the ear drums of the listener and
interpreted by the listener as sound. Although the range of sounds we can make
is limited, the range we can hear is quite broad. For humans, the range of
audible sounds runs from a low of 20 cycles (vibrations) per second to a
high of 20,000 cycles (vibrations) per second. For centuries we thought
these were the only sounds to be heard. Then, with the development of high
frequency (ultrasonic) sound detection systems we stepped into the auditory
world of bats, dolphins, and a number of other animals. Bats have probably
developed the most sophisticated echolocation techniques of any animal on
earth. They started with the same mechanisms we use for vocalization and
listening and refined them into a highly sophisticated sonar system. As they
fly about in total darkness searching for insects they are calling out at
frequencies of 20,000 to 120,000 Hertz. No, a Hertz isn't something you rent
on vacation. In this case its a unit of measure equal to one cycle per second.
Scientists who study these things say that some species of bats making
echolocation calls a few inches from your ear would sound as loud as a smoke
detector going off the same distance away. So, as you can see, bats are
really very noisy animals. But the good news (or bad news, depending on how you
look at it) is that we can't hear them.
Over the years bats have learned how to interpret these
sounds and use them to hunt insects and maneuver in total darkness. How do they
do it? Well, the high frequency sounds are reflected back to the bat like
light from a mirror and the bat gains information from these reflected signals.
For example, the length of time it takes the sound to travel from the bat to the
object and back again reveals how close the object is. Its much like counting
off the seconds between when lightning strikes and thunder is heard. Since the
sound traveled approximately 1100 feet for each second that passed, one can
estimate how far away the lightning was when it struck. This, of course, is a
crude description of what the bat is doing with the reflected sounds.
Obviously, it is gaining much more information from what is being heard. It
might be helpful to imagine yourself tracking a mosquito by yelling at it with
your eyes closed. Today anyone can listen to bats foraging for insects. Bat
detectors can be purchased which pick up their high frequency calls and produce
an audible tick (that means we can hear it) for each call made. As a bat flies
about searching for food it is usually making 10 to 50 calls a second. When its
sonar picks up a nearby insect, things begin to happen rapidly. The bat adjusts
its course towards the insect. The insect initiates evasive maneuvers. The bat
increases the rate of calls to 200 or more per second until they sound like a
buzz on the detector. The insect darts to the side. The bat loops back. The buzz
ends abruptly. The bat continues on. There is one less insect in the world.
hungry bat can devour up to 600 insects an hour, which makes them pretty
useful animals to have around. So look toward the sky just after sunset and
watch the bats chasing insects and think how amazing it is that they are doing
it with their ears.