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.
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