Bats are known for their high-pitched speech, which they use for echolocation. But bats are also capable of making very low growling sounds.
Bats reach these low frequencies with what are called false vocal cords, says Jonas Håkansson, a PhD researcher studying bat vocalization at the University of Southern Denmark at Odense and the University of Colorado.
“What helps him growl is the ventricular folds, also called the false vocal cords, which lie over the true vocal cords,” he said. False vocal folds are thick mucosal folds that appear in the larynx in most mammals; “These vibrations vibrate at a relatively low frequency and therefore produce an audible growl,” Hakansson explained.
Researchers recently investigated this unusual vocal ability in Dubenton’s bats (Myotis daubentonii), which live in Europe and Asia and have a wingspan of about 9.8 inches (25 centimeters), according to Animal Diversity Web. The scientists reported their findings November 29 in the journal PLOS Biology.
To understand the vocal range of these tiny bats, the researchers captured the first footage of bat vocal cords in action, using extracted bat larynxes that they swirled with air to mimic bronchial pressure. They then imaged the larynx at up to 250,000 frames per second. High-speed filming showed that the sounds produced by the false vocal cords were very low, ranging from 1 to 5 kHz.
The research team also found that the bats’ vocal range was wider than they expected, up to seven octaves. In comparison, humans – and most other mammals – can only manage three or four octaves. (Singers like Prince, Mariah Carey, and Freddie Mercury, whose vocal range spans four to five octaves, are rare exceptions.) What gives bats their high-pitched momentum is the membranes that extend from the vocal cords and aren’t taller. . And it’s just over 0.0004 inches (10 micrometers) thick, a feature that humans lack.
Some primates have these laryngeal membranes, according to the study, but humans are thought to have never developed them or lost them at some point in our evolutionary past.
“The high-frequency communication used for echolocation is produced by the vocal membranes. These are thin membranes located at the ends of the vocal cords. Due to their low mass, they can oscillate at very high frequencies, thus creating a high-frequency coupling. which the scientists measured at frequencies between 10 and 20 kHz. He said that the combination of these thin membranes and thick folds allows bats to exhibit such a remarkable range of vocalizations.
Hakansson and his colleagues noticed that bats growl when they get together, perhaps to express aggression or annoyance.
“If you handle bats, for example when setting up nets or when you watch them in groups, they will make these sounds,” Hakansson said, although the exact reason remains a mystery.
Source: Living Science