Bats are known for making high-pitched calls that they use for echolocation. But bats are also capable of producing very low growling sounds much like the snarling sounds of metal singers — and now, scientists know how bats do it.
like metal singers, bat These lower frequencies are achieved using what are known as false vocal folds Jonas Hackansson (Opens in a new tab)a postdoctoral researcher studying bat vocalization at the University of Southern Denmark in Odense and the University of Colorado in Colorado Springs.
“What helps them growl are the ventral folds, also called the false vocal folds, which lie above the true vocal folds,” he told Live Science. False vocal folds are thick folds of mucous membrane that appear in the larynx of most mammals; “These vibrations vibrate at a relatively low frequency and therefore produce audible sounds (growls),” explained Häkansson. These sounds are rarely uttered by humans—except for trained Mongolian throat-singers and, of course, heavy metal singers.
And now, Bats can be added to the roster of ring performers.
Researchers recently examined this unusual vocal ability in Dubenton bats (Myotis daubentonii), which lives throughout Europe and Asia and has a wingspan of about 9.8 inches (25 centimeters), according to Animal Diversity on the Web (Opens in a new tab). The scientists announced their findings November 29 in the journal Nature Biology PLUS (Opens in a new tab).
To understand the vocal range of these tiny bats, the researchers captured the first footage of the bat’s vocal cords in action, using extracted bat larynxes that they animated with flowing air to simulate bronchial pressure. Then they imaged the larynx at rates of up to 250,000 frames per second. High-speed footage revealed that sounds from the false vocal folds were very low, in the range of 1 to 5 kHz.
Related: Bats tell predators to “go off” — literally
The research team also learned that the bats’ vocal range was wider than they expected, extending to seven octaves. For comparison, humans—and most other mammals—can only manage three or four octaves. (Singers like Prince, Mariah Carey and the legendary Queen Freddie Mercury, who have ranges of four to five octaves, are rare exceptions.) What gives the bass a high-frequency boost are the diaphragms that extend from the vocal cords and measure no further than that. It is over 0.0004 inch (10 micrometers) thick – a feature humans lack.
According to the study, some primates have these laryngeal membranes, but it is believed that humans never developed them or lost them at some point in our evolutionary past.
“The high-frequency calls used for echolocation are produced by the vocal membranes,” Hakansson said. “These are thin membranes located at the end of the vocal folds. Because of their low mass, they can oscillate at very high frequencies, thus producing high-frequency calls,” which the scientists measured at frequencies from 10 to 20 kHz. He said the combination of these thin membranes and thick folds is what allows bats to display such a remarkable range in their vocalizations.
Scientists report that the reason bats make death metal noises is not yet understood. However, Häkansson and his colleagues note that the bats will begin to growl when they are crowded together, perhaps to express aggression or annoyance.
“If you handle bats, like when setting up nets, or when you observe them in groups, they will make these kinds of sounds,” Häkansson said, though the exact reason remains a mystery.
However, it is still a beautiful mineral.
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