# The bats

In science, the revealed mystery often turns into a new mystery. So, for a long time the mysterious ability seemed like bats can navigate in the dark, until they showed up that they are armed with peculiar locators.

Everything became clear. However, only at first glance.

For example, one hundred bats fly. A hundred squeals are heard in the air. Every mouse, apparently, should hear ninety-nine others. A terrible cacophony must attack her ears.

Try it, take care of it. But the bat is flying. So, she somehow knows how to sing out her squeak, or rather, his echo, against the backdrop of numerous jamming. How? Unclear.

And here's another problem. The bat radiates its "detective" squeaks with a very wide front. This is not a radar antenna with its narrow needle beam. Hence, the mouse must simultaneously hear an echo reflecting immediately from several objects. How does she distinguish a fixed leaf on a tree branch from a flying butterfly? Or echoes from several butterflies?

It turns out that the whole thing is in the Doppler effect. If you forgot what it is, let's look at the encyclopedia. It says that the Doppler effect consists in the fact that the frequency of oscillations perceived by the observer depends on the speed and direction of motion of the observer and the source of oscillations. When the source of the waves and the receiver approach each other, their frequency increases, and when it is removed, it decreases. Accordingly, in acoustics, when the source of sound and the observer approach each other, the tone of the sound increases, and when it is removed, it decreases.

For a long time researchers have noticed that a bat in flight for some reason changes the frequency of squeaking. And in this, as it turned out and lies the clue.

The bat sings only when it flies. 3nachit, the returned echo she perceives is no longer on the frequency of a squeak, but on a slightly higher one. Affects the effect of Doppler: the bat, as it were, stumbles upon the waves of the echo. However, if the movement of the target is added to the movement of the target, the frequency of the signal perceived by the mouse will be different than when the echo is reflected from the stationary object. Therefore, it is not so difficult to distinguish a flying butterfly from a leaf that perch on a branch. Just as it is not difficult to separate signals from several butterflies flying at different speeds or in different directions.

But how can one explain the indifference of a bat to other people's signals?

The frequency to which the ear of the bat is most sensitive, every animal has its own definite, its own. A squeak mouse at different frequencies. That's why a bat and hears the signals of his neighbors very dully, like through cotton wool. And your own squeak, which, taking into account the Doppler effect, adjusts so that the reflected signal falls on the maximum of audibility, stands out very clearly against this background.