by Elena Suglia '15
Most people know that bats use echolocation to find prey and orient themselves in space, but did you know that bats use echolocation to communicate with each other? It turns out that there’s music in the air every night, except we can’t hear it! It’s a good thing too, because the intensity of the sound waves bats create would be deafening could we hear them. A bat’s screech, though inaudible to us, “rivals the intensity of a revved-up engine of an aircraft about to take off” .
Think whale or dolphin song: that’s what bats do, except at super ultrasonic frequencies which human ears are unable to decipher. This makes intuitive sense when you consider what high- and low-pitched sounds are made of: sound waves with different frequencies. Sound waves with high frequencies bend less as they travel and can therefore be used in a more precise manner to target an object. Bats use higher frequency waves because they operate in tight spaces and need to be more aware of their immediate surroundings so that they don’t run into obstacles or lose track of a quickly moving, small insect . Whales use lower frequency sound waves because they live in the open ocean, where they have much more space in which to maneuver.
But, as we all know, sounds can also be used for communication. This has been deemphasized in bats compared to other echolocating animals like dolphins and whales - probably because we can’t actually hear the noises bats make! Bats have been made out to be nature’s synesthetes, and indeed they do “see sounds” to a certain extent by mapping their surroundings using the information gleaned from echolocation.
We can understand this abstractly – if you put a metal pan in front of your face and yelled you would be able to tell that there was an object in front of you, and you might even be able to discern some details about the object.
However, bats also have very complex speech patterns, and they use sound waves to listen and speak in ways we are familiar with. For example, each bat has a unique courtship song, and patterns of speech between males and females are different . Bats speak to each other to define social status, deter intruders, draw territorial borders, and instruct offspring. Each bat has its own signature song and can thus recognize individuals .
Bats also eavesdrop on each other, using the information they obtain from intercepted sound waves to determine such things as what other bats are saying, how many bats are in a particular area, and where the best food is. Bats can even tune into their own frequency to “prevent their echolocation signal from being jammed by the cacophony of thousands of other bats also emitting many high-intensity pulses in close proximity at the same time” . According to bat echolocation researcher Michael Smotherman, “no other mammals besides humans are able to use such complex vocal sequences to communicate” .
Bats have had millions of years to evolve and perfect the sophisticated and versatile ways in which they use sounds. Did you know that bats compose at least one-fifth of all mammalian species? Bats are part of an extraordinarily speciose group of animals, all of which have evolved interesting variations of the “classic” bat. Some don’t even use echolocation at all!
In order to echolocate more effectively, bats’ brains have evolved computational circuits more advanced than the most powerful supercomputer ever built so that they can emit ultrasonic pulses of sound, process the return echoes, and react at high speeds. This increased brainpower means some bats have very high metabolic rates, and their hearts beat over 600 times a minute. “Place a baby stethoscope on a bat and it sounds like a motorcycle going down the street in third gear.” Some species of bats experience more heartbeats in one lifetime than would keep a human alive for “well over 300 years—without ever having to go to the hospital or see a specialist in cardiovascular surgery” .
Some bat species have such sophisticated auditory communication abilities that scientists are hoping that we can learn something about speech and how the human brain processes it. Interestingly, the fruits of these endeavors have helped the blind “see sounds” through the use of devices that essentially enable humans to echolocate by emitting sound pulses, processing the return echoes and “converting the information into a visual landscape” .
So as it turns out, “the bat says” a lot of things, and tells us much more, both about nature and about ourselves. But just because we can’t hear their song doesn’t mean we can’t appreciate how incredibly cool bats really are.