Bats have an enormous volume of sounds. To do this, the animals use different parts of their larynx. And for the lowest part of their vocal range they apparently use a technique like interpreters of Mongolian throat singing or death metal – meaning the so-called growling. This is reported by a working group led by Coen Elemans from the University of Southern Denmark in Odense in the specialist journal “Plos Biology”.

For their study, the researchers examined the vocal tract of water bats (Myotis daubentonii). They removed the larynx from five animals and passed air through them to mimic breathing and vocalization. The scientists recorded the process with a slow-motion camera, and then evaluated the images with the help of an AI.

They found that the bats vibrate very thin membranes that extend from their vocal folds. They use this to generate their high-frequency ultrasonic calls for echolocation. These membranes do not exist in the human larynx.

For the lower range of the vocal range, the animals use their pouch bands, or “false vocal cords,” located above the vocal folds needed for normal sounds. This part of the larynx allows bats — and humans too — to make a growling sound. Death metal singers, for example, use this growling to hit a very low, rough pitch.

Water bats growl in this manner when approaching their roosts and a dense flock of conspecifics. According to the researchers, it is not yet clear what the bats are communicating with these calls, which are in a frequency range of one to five kilohertz. The tones may be an expression of aggression.

According to the Elemans group, bats can cover seven octaves, while most other mammals can cover three to four octaves. Humans have an average vocal range of three basic intervals, some singers even four to five.

With their calls, bats produce sound frequencies in the range of 1 to 120 kilohertz. Their ultrasonic echolocation sounds go beyond the human hearing range. However, these tones can be made audible with special detectors.

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