Mice are known for their squeaks, but scientists have just discovered how these diminutive rodents are also capable of making ultrasonic vocalizations far beyond the human capacity to hear. And the secret songs they sing usually take the form of love ballads for their mates.
Though researchers have known for a while that a fair amount of mouse communication happens at ultrasonic frequencies, they've only just figured out how the rodents do it. Using ultra-high-speed video recording at a whopping 100,000 frames per second, the team was able to see that a mouse is capable of pointing a small air jet, which comes from the windpipe, to blow against the inner wall of the larynx. This causes a resonance and produces an ultrasonic whistle.
“Mice make ultrasound in a way never found before in any animal,” said study lead author Elena Mahrt, from Washington State University, in a press release.
The mechanism is so bizarre that its closest analogue might be in human technology. Namely, what's happening in the throats of mice is akin to a jet engine.
“This mechanism is known only to produce sound in supersonic flow applications, such as vertical takeoff and landing with jet engines, or high-speed subsonic flows, such as jets for rapid cooling of electrical components and turbines,” said study co-author Dr. Anurag Agarwal. “Mice seem to be doing something very complicated and clever to make ultrasound.”
Humans can't hear these sounds, and maybe that's the point. Singing in ultrasound allows mice to communicate at frequencies that many other animals can't hear. That's a boon when you're often on the menu for most other larger predators.
Scientists think that the ultrasound whistles are actually mating calls, often sung by males to attract females; a mouse version of a "cat call," perhaps. The sounds are also likely used for signaling territorial boundaries to rivals, though the full extent and use of the songs is still being studied. It's even possible that this ultrasound mechanism was a prerequisite for the echolocation abilities seen in bats.
“Even though mice have been studied so intensely, they still have some cool tricks up their sleeves,” said senior author Dr. Coen Elemans.