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.

A  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.

Listen to a Brazilian free-tailed bat bat echolocation call.