A study from the University of Southern Denmark has revealed how bats growl similarly to death metal singers and Mongolian throat singers.
Sound is essential to how some species of bat hunt. By using ‘echolocation’, bats emit sounds that bounce and refract off surfaces and back into their ears, allowing them to map out objects in closed, dark spaces.
Now, researchers have said that the internal structures that bats use to create such sounds are “analogues to those used by death metal vocalists in their growls,” according to the news release.
“We identified for the first time what physical structures within the larynx oscillate to make their different vocalizations,” Professor Coen Elemans said. He led the study.
“For example, bats can make low-frequency calls, using their so-called “false vocal folds” – like human death metal singers do.”
Such false vocal folds aren’t used in normal human speech, and only in specific songs and genres. In humans, the false vocal cords are moved down so that they can oscillate with the other vocal folds, which allows the accumulative folds to become heavy and “vibrate at very low frequencies”, according to Elemans.
However, the research team isn’t sure what bats are trying to communicate when producing a sound in the range of one to five kHz.
“Some seem aggressive, some may be an expression of annoyance, and some may have a very different function. We don’t know yet,” Lasse Jakobsen added. Jakobsen co-authored the study.
It was also identified in the study that bats vibrate ‘vocal membranes’ to assist with echolocation. Interestingly, humans once had such membranes, but these were lost during evolution.
“We show that bats vibrate extremely thin and light membranes extending from their vocal folds to make their high-frequency ultrasonic calls for echolocation. To extend their limited lower vocal range, bats make aggressive calls with their ventricular folds – as in death metal growls,” the authors added.
You can read the study in PLOS Biology.