Rudmer Zwerver

How bats use SONAR

The bat is one of the world’s most incredible animals and is largely misunderstood. The common bat is really known for two things; giving rise to the greatest superhero of our time (thanks batman) and the “expression blind as a bat”. In reality, bats aren’t actually blind at all, and depending on the species some have much better sight than humans do. However never let the truth get in the way of a good expression. Bats do have some other tools that they use to see and this is where the expression comes from as they are not reliant on sight like we are. Bats use echolocation to understand their surroundings and it is an incredible skill. Let’s look at it in a little more detail.

To understand a bat’s echolocation skill simply think of any submarine war movie that you may have seen. In submarines, they use something called SONAR. SONAR stands for SOund NAvigation and Range) this is where a submarine sends out a small signal under the water usually a high-pitched beep. It then listens to determine where that signal bounces. If it passes through the water unphased then there is no object in the water. If it bounces off something then there may be an enemy boat nearby. Bats use the same process.

A bat will produce a sound from its throat and emit it from either its mouth or nose. The bat then listens to the echoes this sound forms as it bounces around the cave. The bat can use this to form a complete mapping of their entire surroundings instantly. A bat is not blind but this tool allows it to see everything despite being in complete darkness. A bat’s hearing is so good that it can detect the movement of bugs on the ground and even the flutter of the wings of an insect.

The bat is able to do these things because it has a specially shaped nose that will project the sound far and wide. The bat’s ear is designed to receive tiny sounds and detect small frequency changes. Bats use two forms of echolocation, one to map the cave and surrounding area and one to find prey and predators. The first form is an incredibly loud sound similar to a smoke detector. It is the loudest noise that any animal is known to make relative to their size. However, we don’t hear them. The sounds register so high on the frequency scale that we can’t even hear them. Humans have a limit of 20,000 Hz while bats can emit frequencies as high as 100,000 Hz.

The second noise that bats use is a lower frequency one. It is a continuous call that is emitted and then bats listen to hear how the sound changes. They can hear a difference as small as 0.1 Hz. There are other bats that use tongue clicks to do the same task. In general though bats use high frequencies for prey as it provides detailed information on speed, direction, and size while they use low frequencies for mapping their surroundings and things that don’t move.

Nature is an amazing thing and while bats have evolved to have these special skills their prey have evolved to overcome it. The moth is the most common bat food and some species are able to jam the bat signal, other moths have a special organ that responds to ultrasound by twitching. When the bat sends out its signal to find the moth, the moth flies unpredictably and can’t be caught. The next time you think blind as a bat is an insult, think again.