Nine-year-old Emma would like to know… “DO BATS USE SONAR TO COMMUNICATE WITH EACH OTHER OR JUST TO LOCATE OBSTACLES AND FOOD?”
Before answering Emma’s question, it would perhaps be helpful to define some words and terms: sound travels in waves and is often referred to in terms of frequency. Frequency is really a measure of how often something vibrates. The frequency of sound is expressed in hertz (Hz).
Humans can usually hear sounds that have a frequency between 20 Hz and 20 kHz; however, many animals can make, and hear, sounds outside of this range. Some, like bats, make sounds above 20 kHz and this sound range is referred to as ultrasound (or ultrasonic sound).
WHAT IS SONAR?
Sonar, or bio-sonar, is a method of echolocation used in air or water, by animals such as whales or bats. Sonar may also refer to the man-made technology that uses instruments to emit sound and detect the returning echo.
Echolocation is the process whereby animals use sound to locate prey, navigate and generally map their surroundings. They send out high-frequency sounds and then determine the size and location of the objects by monitoring the echoing sound.
Most bats are nocturnal so they can use echolocation to allow them to see in the dark, except that they rely more on their sense of hearing than on their sense of sight to detect and track their prey. This gives them an advantage, as many bat species get to hunt at a time (night-time) when the food is plentiful and the competition is scarce.
Bats can use echolocation to such accuracy that they can literally tell the size, shape, location, distance and direction of objects around them.
Did you know that, apart from humans, bats are the most vocal mammals? Much of their communication is similar to bird song, except they use a higher frequency of sound.
They emit high-pitched noises, such as chirps, clicks and songs through their noses and mouths, but most of it is too high to be detected by the human ear. We can, however, hear these sounds if we use a device called a bat detector; this small hand-held piece of equipment converts these high-frequency (ultrasonic) sounds into sounds that are audible to humans.
Bats use a large variety of sounds to communicate with each other. There are different sounds made when males communicate, when females communicate, when both males and females communicate and when mothers communicate with their young. In fact, mothers can locate the sound of their own young in large maternity colonies that can contain hundreds of bats.
GETTING BACK TO THE QUESTION
So to answer Emma’s question, bats use high-frequency sounds to locate obstacles, to navigate and to eat; they also use high-frequency sounds to communicate with each other. However, if we take sonar to literally mean the detection of objects based on echoes of sound bouncing back from noises made by the animal itself, then I would say that bats use sonar for navigation and detection of prey only.
When they are communicating with each other they are hearing sounds made by the other bats, not just the echo of sounds that they make themselves. It is, however, very likely that echolocation (or sonar) contributes to, or enhances, these communications in some subtle ways.
Naomi is a science communicator and mother to three inquisitive children. She can be found at sciencewows.ie
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