Otherwise titled: Your mouse sounds JUST like his dad!

Hoffman et al. "Spectrographic analyses reveal signals of individuality and kinship in the ultrasonic courtship vocalizations of wild house mice" Physiology and Behavior, 2012.


Obviously, we've known about mice "squeaking" for ages. Some of them even HOWL. But mice also communicate with sounds that are too high pitched for humans to hear. These ultrasonic vocalizations (USVs) are used primarily by male mice, and the male mice make them when they scent or are near a likely lady. Female mice apparently like being serenaded, they respond to male's USVs, and can even distinguish between the USVs of their close kin vs the USVs of unrelated mice.

So we know that females can discriminate between close kin USVs and non-kin USVs. Is this because they simply memorize the ones closest to them and look for ones that are different? Or is there something addition, say that male mice USVs can reveal kinships between mice?

To test this, the authors of this study captured a bunch of wild house mice (laboratory mice won't work here, you wouldn't be able to really determine kinship vs non, each strain is inbred to have the same DNA, so unless you compared strains...). They cross bred the wild house mice together in the lab to make sure everyone had the same social background and age, and recorded the mice calling. They pulled apart the recordings and classified them by the types of sounds, and the similarities between the calls in related and non-related mice. And it turns out that, when translated into tones that human ears can hear, mouse USVs sound a lot like bird chirps.

Mouse Serenade

And they have things in common with bird chirps as well: kinship and individuality.

This is what a mouse USV "looks" like. You can see that mice can emit these sounds at two levels at the same time, with a high ultrasonic pitch (at the bottom of the graphs), and a higher harmonic (at the top, which is a multiple of the first pitch). The harmonic is optional, many just contain the top pitch and are more "whistles". And they clearly emit them in different patterns as well. When they compared previous vocalizations between mice that were related or not, they found that closely related mice 'sound' like each other, with similarity between 93% of the lower harmonics and 89% of the higher ultrasonic pitch.

Here you can see two sibling male mice. Their vocal calls "look" extremely similar. But it turns out that related males don't just sing the SAME song. Their USVs have their own original variations as well. While the USVs show high relationships with kin, each mouse also has his own special chirp.

This graph depicts the USVs of their tested mice. You can see that there is overlap between some individuals, but that each individual is also somewhat distinct.

Of course this leaves us with more questions. How do male mice "learn" their USVs? Is it innate or do they pick it up from closely related mice? Do the calls contain any indications of the "quality" of the male (is it related to higher hormone levels or dominance, for example) and will females choose a male for specific aspects of their calls?

And what about the silent males? In their studies, three of the male mice never called at all, and this apparently takes place in both the laboratory and the wild. What about these 'silent' mice? Are there other more effective mechanisms for attracting mates?

But until we can answer these questions, we can imagine our little furry friends twittering soft little love songs. And know that female mice know the difference.

Hoffmann, F., Musolf, K., & Penn, D. (2012). Spectrographic analyses reveal signals of individuality and kinship in the ultrasonic courtship vocalizations of wild house mice Physiology & Behavior, 105 (3), 766-771 DOI: 10.1016/j.physbeh.2011.10.011