Researchers Hear Mouse 'Songs'
Everyone knows that mice squeak and squeal, but few realize that mice also communicate in the ultrasound range, at frequencies far higher than the human ear can detect.
Now scientists conducting the first detailed analyses of those vocalizations have concluded that these sounds are much more than a high-pitched version of the simple hisses and grunts produced by many other animals. Rather they are complex patterns of chirplike syllables that meet the scientific definition of "song."
Indeed, conclude Timothy Holy and Zhongsheng Guo of Washington University School of Medicine in St. Louis, reporting in the December issue of the journal PLoS Biology: "The richness and complexity of mouse song appear to approach that of many songbirds."
If confirmed, the work means mice are members of an elite club that includes only three other mammals: humans, whales and bats.
The two researchers recorded the inaudible sounds with a high-frequency microphone. After filtering out unwanted noises -- including persistent squeaks and gnawing sounds -- they used a computer program to bring the calls down to the range of human hearing.
The syllables and sweeping arcs of pitch, which sound very much like bird songs, fulfill commonly accepted definitions of "song," which require that multiple syllable types be strung into phrases of recognizable sequences or motifs.
Comparative studies indicated that -- as with birds, which develop personal styles close to those of the mentors who taught them -- individual mice sing their own versions of songs. But it remains unclear whether mice learn to sing or are born with the talent.
The team also found preliminary evidence that mice can produce two sounds simultaneously from separate parts of the larynx, perhaps explaining how they produce overlapping tonal transitions.
So far, only the mice know why they are singing. Ongoing experiments aim to see whether males sing differently around the scent of females, which might point to courtship as a motivation.
The team speculates that generations of inbreeding and captivity may have reduced the richness of mouse song. If so, they write, wild mice may have even more interesting repertoires.