Death metal fans just got a new mascot, as it’s been revealed that bats can vibrate folds in their larynx in a way similar to death metal singers to make sounds. Exactly what these roars are meant to communicate isn’t yet clear, but it demonstrates the vast range of these animals who are better known for their ultrasonic echolocation.
Both death metal growlers and throat singers both use an anatomical quirk known as false vocal folds to create sound by oscillation. They’re “false” because, although they can make sound, they’re not used in typical speech and song.
When a human lets a death metal growl rip, they move their false vocal folds so they oscillate with the vocal folds, which makes them “heavy and therefore they vibrate at very low frequencies” explained Jonas Håkansson, first author of the new study. This is why the growls of good death metal and throat singers can go so low.
To see what was going on with the many vocal folds of bats, the new study got up close and personal with the bat’s throat anatomy.
“We have directly filmed these vocal membranes for the first time,” explained Håkansson. “To show their vibrations we needed to film at extremely high rates, up to 250,000 frames per second. We see many adaptations in the larynx, that we think are responsible for the bat’s ability to make very high frequency calls very fast, so that they can catch insects while flying.”
As well as making high-frequency calls, the bats were capable of spanning a vocal range of 7 octaves, putting their skill even above some of the great vocal gymnasts of the Homo sapiens.
“That is remarkable. Most mammals have a range of 3-4, and humans about 3,” said Professor Coen Elemans, Department of Biology at the at University of Southern Denmark. “Some human singers can reach a range of 4-5, but they are only very few. Well-known examples are Mariah Carey, Axl Rose and Prince. It turns out that bats surpass this range by using different structures in their larynx.”
As for what the bats are saying with all this range, it’s hard to know. Observations of the death metal growl behavior were made while the bats were returning to the roost, which could indicate irritation if there are other bats in the way.
“Some seem aggressive, some may be an expression of annoyance, and some may have a very different function,” said biologist and bat expert Lasse Jakobsen from University of Southern Denmark, co-author on the study. “We don’t know yet.”