Ultra-high pitched mouse squeaks have something in common with the roar of a jet engine. New research finds that the rodents make ultrasound bleeps by creating a small air jet in their windpipes, employing a mechanism previously seen only in jet engines and high-speed subsonic flows.
The ultrasonic whistles are important because rodents use them to sing mating songs and make announcements about their territory. The sounds are too high in frequency to be detected by the human ear.
Until now, though, no one knew exactly how these whistles were produced. Researchers led by biologist Coen Elemans of the University of Southern Denmark used high-speed camera scopes to capture images of the larynxes, or voice boxes, of mice as the animals made their vocalizations. The cameras captured 100,000 frames per second for analysis.
Two competing hypotheses had been put forward to explain how the ultrasonic vocalizations are made. The first suggested that the sounds are the result of superficial vocal-cord vibrations; essentially, air moves through the vocal cords as it would for any typical vocalization. However, the videos showed that the vocal cords weren't vibrating, even superficially.