What can a bat tell about the insect from its echo and how ?

Is the insect small or big?

If the insect is small, less of the sound wave will be reflected.

Intensity ( similar to loudness of sound or “volume” of your tape recorder ) of the echo sound will be lesser. Bat immediately knows that less intense echo means smaller prey!

(See the illustration on right)

2. How far is the insect?

The bat knows the time after which it hears the echo, after having produced it. If it takes a lot of time to hear the echo, the prey is very far. If the echo comes immediately, the prey is very near. If it has to wait for a long time, he knows that the prey is far.

(Can you confirm this with walls of your hall? The wall farthest from you returns your echo in the longest time.)

(See the illustration below )

photo 7.2

(* ) Do you know the formula :

distance = speed multiplied by time

Suppose you are a bat, you hear the echo after 2 seconds of having produced the sound. How far is the bat? Speed of sound wave in air is 330 meters / second

(Can you confirm this with walls of your hall? The wall farthest from you returns your echo in the longest time.)

3. Is it to the right or to the left ?

If the sound of the echo reaches the right ear before it reaches the left ear, the bat knows

that the insect is to the right.

If you place a card board on the right side of your mouth, you will find the echo sound louder and reaching your right ear first.

{Can you locate the exit door of a hall blindfolded, simply by shouting and hearing your echo?}

4. Is the insect moving away from it or towards it?

If the bat finds the echo sound to be lower ( smaller frequency ) than the sound it produced at first, it knows that the insect is moving away from it. If echo is higher, the insect is moving towards the bat.

Can you reason why? First try to give an answer to yourself and then we will understand this together.

You may need to go back and read Teacher’s Scribbles on Waves, if you want to understand it properly.

Let us then see how this is so. Look at the illustration below and read on.

1. Suppose you are standing infront of your friend who throws balls at you. They take 2 seconds to reach you. In 6 seconds, how many balls do you collect? Answer is 6 divided by 2 which equals 3. So you collect 3 balls in 6 seconds.

2. Now, you start walking away from him. Balls will take longer time to reach you as you are now moving farther from your friend. Suppose they take 3 seconds to reach you. How many balls do you collect in 6 seconds? You collect 6 divided by 3 which equals 2 balls. You see that if you start moving away, you collect lesser number of balls in the same time.

3. Next, you start walking towards your friend. Now, balls will take lesser time to reach you as you are now closer to him when you collect them. Suppose they take 1 second to reach you. How many balls do you collect in 6 seconds now? You collect 6 divided 1 which equals 6 balls. So, if you start moving towards, you collect greater number of balls in the same time.

The way your friend sent you balls, a bat sends “ oscillations” of his call towards his prey.

If the prey is moving away he collects less number of oscillations in a second, just as you collected lesser number of balls. The echo which he reflects towards the bat also contain lesser number of oscillations than what the bat sent at first. You recall we learnt that lesser number of oscillations in the same time means less frequency. So if the bat finds that the echo has lesser frequency than his call, he knows that the insect is moving away.

If the prey is moving towards the bat he collects a greater number of oscillations, the way

you collected more balls. The echo which he reflects also contains greater number of

oscillations in the same time, which means greater frequency. Now, if the bat finds that

echo has greater frequency than his call, he know that insect is moving towards him.

Look at the figure above to see how the echo wave looks different from the call.

5. Is the insect up or down ?

The bat’s ears have a collection of folds that help it to know if the insect is up or down. This is how these folds serve them, as you were told when you saw pictures of their ears.

Echoes coming when the insect is down / below hit these folds at a different place than similar echoes coming when the insect is up/above. They reach the bat ‘s inner ear and sound differently to him. Thus he is also able to know if the prey is up or down.

You may have heard of the phrase “ as blind as bats“. But they are not at all blind. They can see in darkness much better than us. Some of the bats can even see colours. They use echo – location which is “seeing with sound ” together with the normal “seeing” with the help of eyes and light.

Till now we have learned how does a bat echo locate.

Let us present ourselves with something challenging now.

We will learn how bats actually use echo location to actually hunt for insects in real life. You will learn that it is not as easy as seeing and bats have to think about so many things to capture their prey.

See if you can understand and explain all of what is going to come, to your friend.

Let us brace up then and click : Using Echo Location to actually capture an insect