They might not huddle round a marvellous mechanical mouse organ or live with an old cloth cat called Bagpuss, but scientists have discovered that mice are more musical than their simple squeaks suggest.
Research by a team of neuroscientists has revealed that male mice construct complex songs and sing them for minutes at a time when they come across sex pheromones produced by potential mates. The songs are not audible to the human ear because they are too high frequency and although scientists knew mice emitted ultrasonic chirps, recordings of the noises had never been fully analysed.
Tim Holy and Zhongsheng Guo at Washington University School of Medicine in Missouri discovered the murine melodies by accident. In experiments to test how male mice responded to sex pheromones - chemicals which are found in the urine of female mice - they recorded males as they sniffed cotton swabs dunked in urine from females, males and a mixture of the two.
“We were trying to find out the brain mechanisms they used to detect and recognise pheromones, but we noticed the sounds they made on encountering swabs were interesting in their own right,” said Dr Holy, whose study appears in the open access journal, Public Library of Science, Biology.
Instead of turning up their snouts, within seconds of encountering the scent of female mouse urine, the males broke into ultrasonic song. Dr Holy and his team processed the sound recordings on a computer and made them audible to the human ear, first by slowing down the entire audio track, and then by keeping the tempo but significantly lowering the pitch. “The first moment I heard them I thought they sounded like songs, and they really do,” said Dr Holy.
If the researchers are right, it will elevate mice to an exclusive musical club until now populated mostly by birds, whales, dolphins and gibbons.
The mice used in the experiment were genetically identical and the same age, but still the songs varied widely from mouse to mouse. Some showed a preference for certain syllables over others while others varied how long they spent on different syllables. There is no universal definition of song, but variations in the sounds made and a structure that gives the utterances rhythm make for more convincing songs, said Dr Holy. “Instead of making sounds randomly, mice tend to repeat certain syllables a number of times, then shift to a different syllable. It sounds a lot like the twittering of a bird,” he said.
In many bird species, song helps in mate selection, with females choosing males with the most impressive melodies.
“We don’t know for sure why mice sing, but it probably plays a part in courtship. But whether a male gains an advantage when it comes to mating by singing well is something nobody has yet looked at,” said Dr Holy.
Because mice can easily be genetically modified to test the importance of different genes, the discovery could have a huge impact on research as diverse as the origins of speech, the causes of speech defects and the role of song.
Peter Slater, head of the bird and mammal sound communication group at St Andrews University, said: “With birds it’s really only the males that sing, so it would be good to see if that’s true of mice too. It would confirm it’s a sexual thing.
Listen to audio clips of singing mice:
· In the first clip, the sound has been shifted down 4 octaves (16-fold), but the timing has not been altered - it reflects the real rate and cadence at which these songs occur.
· You can hear some of the differences between the syllables better if you instead slow the song down. This version has been slowed 16-fold, which has the effect of also dropping the pitch by the same factor.