Using Echo Location to actually capture an insect
Let us see how many of us can understand how a bat actually captures its prey using Echo Location.
Go through this carefully and see if you can explain this to your friend. Also see if you can answer some questions at the end.
So, let us follow the bat as it captures its prey.
We call their sound a “call” or “an echo-location call“.
It sounds like tick – silence – tick – silence – tick – silence.
Sometimes it gets shrill and sounds like click – silence – click – silence – click – silence
You can hear such sounds below :
Suppose the bat emits a call which sounds like : “click”.
A bat produces a click and then waits in silence for its echo to come back. After it receives the echo, it sends another click.
So , it emits a call, waits for a silent interval for the echo, receives it and then sends it back again.
It can produce many clicks in a second. If it produces 1000 clicks, the frequency of the sound is said to be 1000 Hertz.
( Question : What is the frequency if it produces 345 clicks in a second? )
Let us follow our bat as it comes out of the cave and gets ready to catch an insect.
At first, It is flying gently and keeps ticking constantly .
How fast does it click? It clicks 10 – 20 times in one second. Seems fast, but wait till you see him approach an insect!
Have you ever tried to sing while running fast? You soon go out of breath and need to stop singing or running. Doesn’t our bat get tired?
No! Its mouth is internally connected to its wings in a special way, such that it can produce sounds from its mouth just by beating its wings. This saves its effort of using its throat all the time while flying.
His clicks echo from nearby objects and come back to him. He finds everything usual, just keeps on changing his path gently so that he doesn’t stumble on a tree branch or wall.
Just then, he begins to get different kinds of echo which he knows from habit to be coming from a prey!
As we learned earlier, they immediately know if it is up/down, left/right, big/small, near/far, away/towards. It flies with great speed towards it, at the same time clicking faster and faster ( more and more clicks per second ). Just near the insect our bat manages to click 200 times per second!
If you shout words at a very fast rate in a hall, you will find their sound getting mixed with echoes of previous sounds you made.
But our bat, even at such high rate, is able to hear the produced clicks and their echoes distinct from each other.
A new echo brings to it the newest location from the insect.
A bat wants to be able to do two things with the help of his calls.
1. He wants to know about the latest location of the insect at small intervals .
2. He wants to be able to sense far away insects.
Can he do both these things at one time? Or can he do these, one at a time?
How should he produce sound to be able to do both of these tasks together?
Let us find out the answers to these question in our next page :