Picking out the faint notes of Die Fleder-Mouse
Researchers hear the silent serenades that male rodents use to woo
mates

By ANNE MCILROY

Tuesday, November 1, 2005 Page A3

SCIENCE REPORTER

Mice can sing.

Humans can't hear it, but researchers say the ultrasonic songs of male
mice trying to woo females are comparable to the musical trills
produced by songbirds.

That mice make noise is nothing new to those who have had them in their
houses, and scientists have known for decades that male mice will make
sounds when they are near females, or exposed to female pheromones. Now
they say that those utterances are love songs.

"The richness and diversity of mouse song appear to approach that of
many songbirds," said Timothy Holy, an assistant professor of
neurobiology and anatomy at the Washington University school of
medicine in St. Louis, Mo.

First, the researchers let male mice sniff cotton swabs dipped in
female mouse urine, which contains chemical compounds known as
pheromones that can signal sexual status. Then the researchers recorded
the reactions of the mice.

As expected, the males produced noises that were beyond the upper limit
of human hearing. But when the researchers slowed the recordings to
one-16th the normal speed, they heard calls that sounded like low,
intermittent whistles. They also dropped the pitch to an audible level,
and heard shrill chirps that sounded remarkably like bird songs.

"It was very surprising. The real moment of discovery came when I first
wrote the software to transpose the songs into our hearing waves. I
said, 'My gosh, these things sound like songs,' " Dr. Holy said.

A computer analysis showed the sounds meet key definitions of songs, he
said. There are distinct categories of sound, instead of just one note
repeated over and over again. There are also recurring themes, such as
the melodic hook in a catchy tune, he said.

Dr. Holy and his colleague, Zhongsheng Guo, tested 45 mice and, like
songbirds, they all sang their own tune.

"You can sometimes recognize an individual male from his song," Dr.
Holy said. He and his colleague's findings are published in today's
edition of the journal PLoS Biology.

He's not sure why the mice sing in the ultrasonic range rather than
using the kind of squeaks humans can hear.

The range means mice vocalizations are difficult to record and analyze,
which is why researchers have not noticed singing mice before now. The
scientists said new computer technology made their discovery possible.

They were initially interested in how and why male mice respond to
female pheromones, but became intrigued by the sounds and decided to
study them instead.

Female mice may also sing, although they weren't part of this
experiment. The female mice can hear the males singing, but the
researchers don't know yet whether the serenades translate into more
sexual activity for the males.

"We don't know what the female reaction is to these songs," Dr. Holy
said.

The researchers aren't sure whether wild mice sing different songs from
lab mice, or whether mice learn to sing from "tutors," as many birds
do.

Mice now join the ranks of other animals -- including birds, insects,
frogs, whales and bats -- that make music to woo the opposite sex. Mice
songs are more complex than those produced by insects and amphibians,
but less diverse and less complicated than bird songs.

"Perhaps the best analogy for mouse song would be the song of juvenile
birds, who put forth what you might call proto-motifs and themes," Dr.
Holy said.

The tunes also appear to be less complicated than whale songs. Earlier
research found that the undersea songs of humpback whales are so
similar to human songs that the marine mammals are true composers,
following rules similar to those used by musicians.

The research on singing mice may open the door to a better
understanding of the biological basis for song-making, and perhaps for
music in general. It is much easier to investigate the genes related to
a specific behaviour -- such as singing -- in a mouse than in a whale,
for example. Scientists have already completed the mouse genome.

Some researchers believe that in humans, music is instinctual, and that
the capacity to make it is innate. If this is true, similar genes may
be involved in humans and other animals.

Others aren't so sure. It may be that the songs produced by mice are
more comparable to language than to music, Dr. Holy said.

To hear mice sing, go to: mednews.wustl.edu/news/page/normal/6040.html