Like many rodents, male mice (Mus musculus) produce ultrasonic vocalizations (USVs) when they encounter females or the scent of females. The squeaks are attractive to female mice, which can discriminate between calls of siblings and those of unrelated males. These characteristics suggest that the 'songs' play a part in courtship and mating, but their content and function have remained something of a mystery.

To find out what all the squeaking is about, Frauke Hoffmann and colleagues Kerstin Musolf and Dustin J. Penn at the Konrad Lorenz Institute of Ethology, Veterinary University of Vienna (Austria) decided to listen in on the USVs of wild mice. They recorded the vocalizations of 15 adult male offspring of wild-caught mice after exposing them to the scent of female mice. Three of the males did not produce any vocalizations at all, but the recordings from the remaining 12 mice were slowed down and analyzed spectrographically.

The analysis showed that the USVs had several features resembling a song. USVs could be classified by both duration and frequency (J. Ethol. 30, 173–180; 2012), with frequency being the clearest distinguishing characteristic. The vocalizations included four main types of syllables: high-frequency, low-frequency, one-frequency step and two-frequency step. Males emitted more high-frequency syllables, which were shorter and higher in pitch, than low-frequency syllables when exposed to the scent of females. Furthermore, the wild males seemed to produce more high-frequency syllables than previously reported for lab mice, a difference that may be related to domestication.

Hoffmann's group also found that the USVs included signals of kinship and of individuality (Physiol. Behav. 105, 766–771; 2012). The 12 vocalizing mice belonged to five sibling groups, and the spectrographic analyses showed that calls could be classified according to kinship. The average rate of correct sibling group classification was 98.6% for low-frequency syllables and 89.0% for high-frequency syllables. Calls could also be reliably classified according to individual: the average rate of correct individual classification was 64.3% for low-frequency syllables and 63.9% for high-frequency syllables.

“It seems as though house mice might provide a new model organism for the study of song in animals,” said Penn in a statement from the Veterinary University of Vienna. “Who would have thought that?”

Further studies may investigate the consistency of individual USVs over time and in different contexts, the factors underlying the similarity of USVs among related males and the reasons why some males do not produce USVs at all.