frequency spectrum
Bats have a much larger vocal range than humans. While using high-frequency signals to hunt their prey, they use the lower voice ranges for social calls. The sound and production of the low tones is similar to human throat singing – like the growl of “death metal” singers, according to a new study.
The voice is a vital tool for bats, they locate their prey in the dark with the help of sound waves. For echolocation, the animals usually use high-frequency ultrasound that is inaudible to humans. The tonal range of the flying robbers is considerable and extends over seven octaves. Most mammals, including humans, make it between three and four. The frequency spectrum of bats ranges from about 1 to 120 kilohertz. The low-frequency pitches are not used for hunting, but for communication with conspecifics.
In order to find out how bats create this impressive spectrum, the researchers have to Coen Elemans from the University of Southern Denmark the vocal apparatus of water bat examined more closely. The larynxes of five adult animals were examined in the air tunnel and filmed with high-speed cameras. Machine learning methods were used to capture the movements of the invisible parts as well.
Rough throat singing
Like the team now in the specialist magazine PLOS ONE reports, the high- and low-frequency sounds come about in different ways. At the higher frequencies above ten kilohertz, the thin ends of the vocal cords are set in self-sustaining vibrations. For the frequencies between one and three kilohertz, however, the thicker pocket folds above the vocal cords are used.
Audio samples for social calls
As the study authors write, this is similar to the human throat singing practiced in some cultures (guttural Gesang). The vocal folds are used, among other things, when clearing the throat. In this way, people can expand their normal vocal range and produce a special harsh and throaty sound. This technique is also popular, for example, in “death metal” to produce a kind of growl (“growling”) with the voice.
According to the study, these two types of sound production were probably a result of evolutionary adaptation in bats. The high frequencies are much more accurate for echolocation, and the broad audibility is more useful for social communication.