SIXTH, how do bats use ultrasound to navigate?

We think we know all about bats- they’re nocturnal mammals. They fly in the dark without trouble and have a very interesting navigation system to do this - echolocation. It is what we call "sonar" system, a system whereby the shapes of the surrounding objects are determined according to the echo of the sound waves. Using the echolocation system, the bat can determine where an object is, how big it is and in what direction it is moving.

As bats fly, they emit a series of high frequency sounds. These sound waves are directed around them in different directions. The bat then listens for the echoes as the sound waves are reflected off nearby obstacles. They then process the time elapsed between the return of the echo and when emission of sound to calculate the distance between themselves and nearby obstacles.

 In addition, with regards to the horizontal position, the bat can tell if an insect is to the right or left by comparing when the sound reaches its right ear to when the sound reaches its left ear: If the sound of the echo reaches the right ear before it reaches the left ear, the insect is obviously to the right. To determine the vertical position of the object, bat's ears have a complex collection of folds that help it determine an insect's vertical position. The large variation in sizes, shapes, folds and wrinkles aid in the reception and funneling of echoes and sounds emitted from prey. Echoes coming from below will hit the folds of the outer ear at a different point than sounds coming from above, and so will sound different when they reach the bat's inner ear.



Bats can tell the size of these objects through listening for difference in intensity of the echoes as objects with a larger area for reflection of the ultrasound will produce a more intense echo.

They can also estimate direction in which other objects are moving relative to themselves as the pitches of the echoes will be higher if the object is moving towards the bat, whereas it would take on a lower pitch if the object is moving away. Essentially, as the object is moving towards the bat, the echoes that bounce off now are reflected from a position relatively closer to the bat, resulting in the time between arrival of successive wave crests to be reduced, leading to higher frequency of sound waves and thus a higher pitch.

Conversely, as the object moves away from the bat, the echoes that bounce off it are reflected from a position relatively further away, causing the time of the arrival of successive wave crests of the echo to be increased, causing a decrease in frequency and thus a lower pitch echo is perceived. Likewise, this also applies to the bat moving away from the object. Thus, through analysing a Doppler induced change in the echoes, bats are able to determine whether the object is stationary or not.

The bat continually repeats this cycle and thus is able to form a mental picture of its surrounding by piecing together all these aspects of sounds, and interpreting this information, enabling it to navigate safely in the dark.

Bat Detectors:
Nevertheless, the inaudibility of ultrasounds by bats has not hindered humans from wanting to know more about them. Bat detectors have been invented by making echolocation calls audible to humans. In addition, as different bat species hunt different prey and are of different sizes, they make different calls which helps in the identification process.

Echolocation allows bats to survive as they can now dominate the skies in darkness where there are lesser competitors and predators, and also when their prey are more active.

Here is a video provided for a concise summary on Bat Navigation! :)