When we talk, yell, or sing, our larynx is vibrating in our throat, causing pressure variation in the air passing through it. These pressure vibrations are picked up in the ear drums of the listener and interpreted by the listener as sound. Although the range of sound we can make is limited, the range we can hear is quite broad. For humans, the range of audible sound runs from a low of 20 cycles (vibrations) per second to a high of 20,000 cycles per second. For centuries we thought what we heard were the only sounds. Then with the development of high frequency (ultrasonic) sound detection systems, we stepped into the auditory world of bats, porpoises, 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. A "Hertz" is not transportation you rent while on vacation. In this case it is 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.

Over the years bats have learned how to interpret these sounds and use them to hunt insects and maneuver in darkness. How do they do it? 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. It is much like counting off the seconds between when lightning strikes and thunder is heard. Since sound travels approximately 1100 feet for each second that passes, one can estimate how far away the lightning was when it struck. This 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. As a bat flies about searching for food it is usually making 10 to 50 calls per second. When it's sonar picks up a nearby insect, things begin to happen rapidly. The bat adjusts it's course toward 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. 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 very useful animals to have around.

Look toward the sky just after sunset and watch the bats chasing insects. Think how amazing it is that they are doing it with their ears!