Why Mice Sing: Sex, and to Protect Habitat

PHOTO: U of Texas scientists find that mice in Costa Rica and Panama sing to attract mates, and even guard their territory.
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If a mouse could sing, what would its song say? Most likely either come here sweetie, or get out of my territory.

High in the mountains of Costa Rica two species of mice have attracted the attention of scientists in recent years because, apparently, no one really thought mice could sing.

But biologist Bret Pasch has spent three years capturing, recording and releasing hundreds of mice just to figure out what they have to sing about.

He published his first paper on mice a couple years ago while he was a graduate student at the University of Florida in Gainesville. The paper showed that male mice fill the air with trills so high-pitched that most humans can't even hear them.

Why Would a Mouse Sing?

But if the song is right, and the melody is sweet enough, at least to the ears of a female mouse, the vocalist soon finds himself with a companion.

OK, mice aren't the only animals that sing to win the favors of a beautiful girl. Birds do it. Even whales do it. But is that all there is to the story? No way.

Pasch is now with the University of Texas, and he and his colleagues are out with another paper, published in The American Naturalist. The singing mice of Costa Rica and Panama don't just sing to get the girl. They also sing to warn other mice to stay away.

That might not seem all that important, but to biologists interested in the distribution and diversity of wildlife, how animals decide where to make their homes is an ongoing concern. Generally, those decisions are purely biological.

They live where the living is good. But these tiny mice have complicated the equation. Verbal communications, not just biology, play a role, at least for these mice.

In the lush hills of Central America, the Alston's singing mouse (scotinomys teguina) and the Chiriqui singing mouse (S. xerampelinus) have similar diets, and like living in the forest, so there's plenty of room for conflict. The Alston's is smaller, and more timid, than the Chiriqui, and they both open their mouths about 15 times per second as they sing, Pasch said.

Both species cherish the same territory, but when the Alston's hears the voice of the Chiriqui, it stops singing and flees the area. In other words, it's obeying a vocal command. But are the mice really singing?

Most biologist believe a sound isn't a song unless it comes from an animal with certain physiological features, like those shared among humans and birds, and mice were not thought to have those features.

Most songbirds aren't born singers. They have to learn how to sing. And learning to sing requires an ability to hear someone else, called auditory feedback.

If mice don't have that, they can't learn how to sing. So scientists at the Howard Hughes Medical Institute, Duke University and Tulane University, have spent several years experimenting with mice to see how well equipped they are to sing.

One of several experiments seems to answer that. Male mice from another species of singers thought they were opera stars when they found themselves sharing a room with a female. Or as the scientists put it, the smell of a female "enhanced their subsequent singing responses to the female."

But these guys, sadly, later had surgery that left them deaf. The result: "Striking differences" in their songs. They no longer had that essential "auditory feedback," and their melodies were reduced to "squawks and screams," according to that study, which was also published in PLoS One.

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