You’ve probably heard the high-pitched squeak of a house mouse, but did you know mice also make ultrasonic calls during courtship? A new PLOS ONE study finds that mice produce these complex, birdsong-like vocalizations at higher rates and at higher frequencies when targeting a member of the opposite sex than when calling to a same-sex mouse.
Study author Sarah Zala, a behavioral biologist at the Konrad Lorenz Institute of Ethology of the University of Veterinary Medicine, Vienna, knows more about mice than most. She has always been curious about animal behavior, an interest kindled by an “exceptional” professor who also taught her proper experimental design. “Once I had the tools necessary to solve the mysteries of animal behavior,” she says, “I never looked back and I pursued science as a career.”
I interviewed Zala via email to learn more about her investigation of mouse behavior.
Most of us are unaware that house mice make any sounds at all. Can you tell us about their vocalizations?
SZ: Humans can only hear frequencies between 20 hertz and 20 kilohertz. We can hear mouse squeaks, but we can’t hear their courtship vocalizations, which are at ultrasonic frequencies of above 20 kilohertz. Mouse ultrasonic vocalizations are complex, and when recordings are played back at lower, audible frequencies, they sound amazingly like birdsong.
What do mouse vocalizations have in common with birdsong?
SZ: Like birdsong, mouse ultrasonic vocalizations consist of several types of calls or “syllables,” which they emit in bouts or “phrases” of repeated sequences, which may contain a single repeated syllable or a combination of different syllables. Like many birds, mice emit these songs during courtship, though their function is unclear.
You found that house mouse vocalizations varied depending on the sex of the caller and receiver – how?
SZ: Mice vocalized at higher rates and at higher frequencies when presented with another mouse of the opposite sex, compared to same-sex interactions. So females called at higher frequencies when presented with a male than when presented with a female mouse, and the reverse was true for males. Mice of both sexes therefore appear to modulate their vocalizations depending upon the sex of the intended receiver.
What might be the function of this variation in vocalization?
SZ: Modulation of calls depending on the sex of the receiver may function to attract opposite-sex and repel same-sex individuals. Interestingly, some studies on humans suggest that men alter the frequencies of their voices depending upon the sex of the receiver, and that women’s trust in men can depend upon the frequency of their voice.
What did you find particularly interesting about your results?
SZ: We were interested that our results confirmed previous findings in our lab, which showed that calling rates are highly variable between individuals. Some mice emitted few or no calls, whereas others emitted more than 200 calls per minute. The mice acted according to what behavioral scientists like to call the Harvard Law of Animal Behavior: “Under carefully controlled experimental conditions, the animal reacts as it pleases!”
Why are some mice so chatty, and others so quiet?
SZ: We have no idea! Most studies screen the mice and only investigate highly vocal individuals, so the variation in individuals’ propensity to vocalize has not received much attention.
What are the next steps for your research?
SZ: Our next aim is to determine the contexts and functions of these ultrasonic calls. We are currently investigating the vocal behavior of wild mice under naturalistic social conditions and are recording mice living in populations and freely interacting with each other. We are also conducting playback experiments to test the reactions of wild mice to different call recordings.
Research Article: Zala SM, Reitschmidt D, Noll A, Balazs P, Penn DJ (2017) Sex-dependent modulation of ultrasonic vocalizations in house mice (Mus musculus musculus). PLoS ONE 12(12): e0188647. https://doi.org/10.1371/journal.pone.0188647
Images Credits: Bettina Wernisch; Sarah Zala