Many animals produce sound to communicate with each other, and bats are no exception.
They can produce a range of frequencies, also known as the vocal range, that far exceeds vertebrates including humans. While researchers do not yet know the meaning of all their sounds and songs, they are learning more and more about how all these sounds are made.
According to a new study of Daubenton’s bats, for some sounds, they use the same technique as human death metal singers and throat singing members of the Tuva people in Siberia and Mongolia.
Researchers from the University of Southern Denmark, led by Professor Coen Elemans, department of biology, have for the first time filmed what goes on in a bat’s voice box (larynx) when it produces sound. Prof Elemans, said: “We identified for the first time what physical structures within the larynx oscillate to make their different vocalisations. “For example, bats can make low frequency calls, using their so-called ‘false vocal folds’ – like human death metal singers do.”
Together the normal vocal range for a bat spans 7 octaves, the research team reports.
Prof Elemans added: “That is remarkable. Most mammals have a range of 3-4, and humans about 3. “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.”
False vocal folds are called so because they look like vocal folds – tissues located in the voice box – but they are not used in normal human speech and song. Only death metal growlers and throat singers from a few cultures around the world use their false vocal folds like the bats. Humans move the vocal folds down so that they oscillate together with the vocal folds.
The researchers say growling sounds are often produced when bats fly in or out from a densely packed roost. They do not know for sure what a growling bat intends to communicate. “Some seem aggressive, some may be an expression of annoyance, and some may have a very different function. “We don’t know yet”, said biologist and study co-author Lasse Jakobsen from University of Southern Denmark.
Bats hunt insects in complete darkness using echolocation, and send out very short, very high frequency calls. They listen for echoes reflected from objects in the surroundings to find and capture insects. Researchers say their findings reveal for the first time how bats are able to make high frequency echolocation calls.
They do so by vibrating very thin vocal membranes – structures that humans also once had but were lost in our evolution.
The findings are published in the PLOS Biology journal.