Cries in the Night

We think of bats as mysterious creatures, fluttering silently on ghostly wings. You may be surprised to learn that bats are not so quiet. You learned in biology that bats use echolocation to navigate and catch prey in the dark, but have you ever thought about "echolocation" and what it really means?

We think of bats as mysterious creatures, fluttering silently on ghostly wings. You may be surprised to learn that bats are not so quiet. You learned in biology that bats use echolocation to navigate and catch prey in the dark, but have you ever thought about "echolocation" and what it really means?

In simple terms, bats have voices; they aren't silent at all! What's more, they use their voices for a variety of things, much as we do, but for much more than we can do. We cannot hear them because they are "speaking" in frequencies that are above the level of sensitivity of our ears, about 20 kilohertz (cycles per second). If we listen in, there is much to learn about bats and their voices. The best known use for these ultrasonic cries is navigation. Using the echoes of their own voices bats can fly through caves or into the darkest night, avoid obstacles, including each other, and find their way back again. And while they're at it they can locate and capture, in the air, flying insects for their food.

The only way I can visualize this for myself is to imagine that the bat's brain takes the information from the echoing cries and creates a mental scene that must be much like vision. Maybe it's like an arcade or computer game - images in black and white and shades of gray. But I do know this, a bat can learn a great deal about what's out there just from those echoes. It can tell whether an object is large or small, hard or soft, moving or stationary, something to eat, or something that might eat it.

What is echolocation, and how does it work? Most bats, and all bats in Missouri, emit ultrasonic cries through their mouths. These cries range from about 20 khz to 100 khz; in Missouri they don't rise much above 80 khz. Most bats have a mechanism for turning off their hearing at the moment they emit a cry, presumably to avoid being deafened by the outgoing sound. Their ears pick up the returning echoes and