Human hearing is pretty good. In fact, as mammals we have some of the best hearing among animals on Earth. But some frequencies, such as ultrasound, are outside the range of our hearing. And as it turns out, other mammals, such as mice, rats, and other rodents, regularly communicate in ultrasonic frequencies.
Mouse Songs
Mice emit ultrasonic vocalizations, most frequently as pups, and when they’re distressed—for example, when separated from the nest or feeling cold.
But as adults, mice use complex calls to get a different sort of attention: from potential mates. Adult male mice produce complex calls around females, or when they detect female pheromones, as a 2005 study published in the journal PLoS ONE, analyzed. Researchers Timothy E. Holy and Zhongsheng Guo found that not only did calls vary widely by individual, but that they could identify within each mouse’s call distinct sounds (syllables), sequences (phrases), and repetitions (motifs).
And when researchers recorded the calls and played the sounds back at lower frequencies and slower speeds, they found that the vocalizations had a lot in common with birdsong. These “singing mice” used jumps and dips in pitch, rapid chirping sounds, and had a tendency to sing using unique syllable types—just as one person might emphasize certain words or speak with a regional accent.
Ticklish Rats
Rats, too, produce ultrasonic vocalizations. But, unlike mice—which mostly vocalize during mating or in other nonaggressive situations—the noises a rat produces can indicate a specific emotional response. When an adult rat senses a predator, feels threatened, or is in pain, it will emit calls at a frequency of 22 kilohertz. In response to a positive stimulus, such as play or mating, the frequency of its calls jumps to 50 kilohertz.
And then there’s tickling: adult rats produce ultrasonic calls around 50 kilohertz in response to tickling—a behavior that’s been tested in the lab, using what the researchers called “manual tickling sessions”—and some suspect there may be a correlation to human laughter. A study published in the journal Behavioral Brain Research in 2000 tested this hypothesis, and found that not only did young rats exhibit a strong vocal response to tickling that was similar to “youthful human laughter that typically occurs during play,” but that rats that were isolated and kept away from others actively sought out tickling more frequently. In other words, laughter might just be the best medicine.
Learn more about the senses of different species in our new exhibition Our Senses: An Immersive Experience.