Mice Serenade Mates With Complex Tunes, Study Suggests

Brian Handwerk
for National Geographic News

November 1, 2005

The stereotypically silent mouse may be one of nature's best singers,
according to new research.

The male rodents sing ultrasonic songs that are inaudible to humans—but quite possibly sweet music to the opposite sex.

Scientists have known for decades that male mice vocalize when they encounter females or female urine pheromones.

"[This new] study, however, was a more careful examination of the sounds, looking for patterns that had not been previously documented—or even perhaps expected," said Timothy E. Holy, a neurobiologist at the Washington University in St. Louis School of Medicine.

Holy and colleague Zhongsheng Guo recorded and manipulated the ultrasonic vocalizations to unveil a surprising complexity. The researchers also found that individual male mice sing their own distinct songs.

"The richness and diversity of mouse song appear to approach that of many songbirds," the authors write in the current edition of the open-access journal PLoS Biology.

Nature's Chorus

Definitions of what constitutes "song" aren't always hard and fast. But the mice appear to share characteristics with birds and other natural crooners.

"The existence of several [musical] syllable types, and the fact that those syllables are arranged over time in regular and interesting ways, are sort of the two most striking characteristics of bird song and whale song," Holy said. He notes that mice sing in similar ways.

Some birdsong experts who reviewed the research were impressed by the rodents' virtuosity.

In fact mouse songs may be more complex than those of some birds, though the best bird singers produce tones that are more obviously varied than those displayed by the study mice.

"The best singers in the bird family also tend to have a more stereotypical structure to their songs," Holy said. "They learn them over a period of months and then sing the same themes and sequences of themes over and over again.

"Whether it's an attribute or a deficiency, the mouse song differs [from birds']," he said. "It seems a bit more experimental and not as stereotyped."

Singing for Sex

Male mice may be inspired to sing by the same drive that biologists believe fuels many birds' crooning—sex.

"Birdsong is used for any number of functions, but generally it is related to breeding," said Christopher Sturdy, an animal behavior expert at the University of Alberta in Edmonton. "Song is used mainly to attract and maintain females, to keep other males away, and to propagate the genes"

Holy, the study co-author, said, "I'd guess that these songs play a role in courtship, but studies would have to be done to acquire any degree of certainty."

Jill Soha, curator of the Borror Laboratory of Bioacoustics at the Ohio State University Museum of Biological Diversity, says that mouse songs are intriguingly complex.

"This discovery is striking, because it shows that mice might communicate using complex vocalizations previously unknown in this species," she said. "Finding out how these sounds are used will be an exciting next step."

One future test could involve playing recorded male songs to female mice and observing any behavioral changes. Manipulating those songs could provide a key to understanding which aspects of song trigger a reaction, if any, in the opposite sex. It's also not known if female mice sing.

Schooled in Song?

Many researchers will be keen to learn if mice display definitive evidence of an ability called "vocal learning," which allows some species to imitate and replicate sounds.

"What sets songbirds—[as well as bats and some marine mammals]—apart from many other animals is that they seem to acquire their learned vocal signals in a way that is similar to how humans acquire theirs," Sturdy, the University of Alberta biologist, explained.

"It's dependent on them being exposed to a tutor, like their parent or another animal. It has to happen at the right period in life—[humans] can learn second languages later in life, but we're not nearly as good at it."

The process of vocal learning is important for humans and songbirds. Isolated young of both species will not vocalize normally as adults.

Other species, including nonhuman primates, do not seem to learn vocalization in this way but have their various barks and growls hard-wired from birth.

If mice are vocal learners, they could become an exciting tool for studying the genetic codes that grant the ability to some species.

"One thing it could really do is give us a handle on the genetic underpinnings of language," Sturdy speculated.

"If you had a mammal that showed vocal learning, then you could do genetic manipulations and compare them with human genetic abnormalities to study the effects that they have on human language."

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