How living beings tune into the sound surrounding them ?
The way every living being, looks, senses and behaves is just in such a way that it is able to find food and shelter in its surrounding. We say that the living being is “ adapted” to its environment.
Different types of bats produce calls of different frequencies. What frequency of sound they find useful to produce depends on
1. How big are the prey insects which live around them.
2. The frequency of noise of the environment, so that it does not disturb their calls.
So, we again see that even their calls are “ tuned to” their surroundings.
Most of the times, different living beings like birds, animals and reptiles have to share an environment.
There they use sound
– to find their way around ( like bats )
– to hunt for prey ( again like bats )
– to warn each other of dangers like bigger animals
– to tell their fellow kinds when they have found food
– to call their young ones or mates or expressing friendship
What if all the living beings in a forest start crying together? Will they be able to perform any useful activity which helps them find food, allows them to communicate or keeps them safe ?
No. They will just be disturbed by each other’s calls .
So, they should call at different times with “different sounding” calls so that they can be recognized by their fellow beings and not get disturbed by or sound similar to other animals around them.
They call at such frequencies and with such loudness that their fellow beings can hear them clearly. All these living beings produce sounds at frequencies as different as possible so that no two different animals produce similar sounds. This way, every animal can listen to and recognize the sound of his fellow animals clearly.
In the towns, there is so much noise. It is of a low frequency. So birds living in towns sing louder and at a higher frequency, so that their sounds do not get muffled.
We can say that these animals divide the available frequencies of the sound available in the environment among them. This is called an “Acoustic Niche”. We ‘ll learn more about it in the next article along with many more interesting purposes for which animals use their sounds.
We learnt just now that birds in town call at high frequency.
Do you know why birds in dense forests call each other at less frequency ?
You can think of the answer even now with what you have read.
As you learnt , when speed of the sound is divided by a low frequency, it gives you a long wavelength. A wave with long wavelength doesn’t get absorbed or muffled in the dense forests with thick vegetation. So, they can communicate up to a very long distance !
You cannot hear bat’s calls but you can record them using “ ultrasonic recorders ”, also called “bat detectors”. Then you can match the sound with “ Bat Call Libraries” on line which have sounds of all the bats around an area. If you find that the sound matches with one of those, you can identify the kind of the bat whose sound you have recorded, which is given in the tables along with the sounds. But, some kinds of bats do produce calls of same frequency!
One little thing : Some bats have strange noses that serve them to focus the calls they produce just like a lens focuses sunlight. This helps them to sense their prey more accurately. You will find it mentioned later in the article.
As the next topic, we will learn about a few life habits of bats .