Bats Sing Louder Than a Rock Band

Sept. 2, 2009— -- If you had the ears of a bat, what would you hear if you walked into a crowded bat cave? Music, it turns out, but not your basic string ensemble.

The noise would be louder than a rock concert, and it would be "so loud it would blow your ears out," according to a bat lover at Texas A&M University who has been studying the creatures for 13 years.

And what would the music be all about? Love, or at least procreation, said Kirsten Bohn, lead author of a study in the current issue of PloS One.

Bohn and several other researchers at three institutions, including the University of Texas, are turning up astounding facts about the only mammal on the planet that is capable of flying.

Some glide, actually, but they don't fly. And it just may be that this much-maligned animal that rids the world of billions of insects every night may play a key role in the years ahead in the fight against diseases that afflict millions of people.

That's because the lowly bat is more like us than we had imagined, and in some areas it may be more suitable for research than the furry friend of humankind, the rat.

Male Bats Sing to Win Females' Affection

The latest discovery to come from Bohn and her colleagues is that male bats sing complex, sophisticated love songs to the females in their neighborhood in hopes of winning their affection, and simultaneously warning other males to back off.

We've always known that birds can sing, and even dolphins and whales use sounds to communicate with others in their group, but now it appears that bats may be the only mammals -- except humans -- that communicate through multi-syllable, tightly structured, patterns of phrases.

That's surprising, because if you've ever heard a bat sing, it doesn't sound like much. But that's because humans can only hear a tiny part of the bat's song, most of which reaches frequencies far above human hearing.

Bohn began studying bats while working on her doctorate at the University of Maryland, where she discovered that bats are highly social and very cooperative, at least with their own kind. That set her on her current course, studying social and vocal evolution. She linked up with another researcher, Barbara French, known among her friends as the "bat whisperer."

Does Music Come Naturally to Bats?

French had noticed that bats start making "buzzing sounds" at about the same time every year, and she joined the research team of neurobiologist George Pollock at the University of Texas. Bohn also joined the Texas team, and for three years the researchers recorded the sounds of bats. There are about a million bats near the Austin campus, and to the researchers it seemed like the bats were, well, singing.

Fortuitously, another researcher, biologist Mike Smotherman at Texas A&M, had also discovered that bats in his neighborhood were singing. Bohn joined forces with Smotherman, and all the researchers began pooling their data. Not only did the evidence show the bats were indeed singing complex songs, they were singing the same song.

"We were stunned to find almost identical songs in College Station and in Austin," although the two campuses are about 200 miles apart, Bohn said in a telephone interview.

That raised an interesting question. Does music just come naturally to bats, or do they learn it from some other bat? No one knows for sure yet, but that will be a major focus of Bohn's future research.

Bats Process Vocal Information Similar to How Humans Do It

But of possibly far more importance, bats appear to process vocal information in a way that is similar to how humans do it. We process vocal information through a major motor control center in the brain, called the basal ganglia.

That center is also involved in a number of crippling human health problems, including Parkinson's disease and various speech disorders. Research in Smotherman's lab indicates that bats process audio information through the same nerve center as humans, and that's extraordinarily rare, Bohn said.

That finding suggests that bats may be very useful to medical researchers who are trying to understand, and resolve, a number of human health problems. They may, for example, use bats to study the effect of pharmaceuticals on speech disorders, because in that case bats are more similar to us than rats.

"That's why I've been trying to get these little guys to sing in the lab for us," Bohn said. "Birds have highly structured vocalizations, but they aren't mammals. We also use rodents, but they do not have the structure we are finding in these vocalizations."

Bats Don't Always Cooperate With Research

So bats may fill a void in research labs, but getting them to cooperate isn't always easy. It's not hard to get a bird in captivity to sing, even if there's no other bird around, Bohn said. But a bat "is harder to fool." It needs a female to woo, and other males to threaten, or it will just shut up.

And to really test some of these ideas, the research needs to be done in the field, not just in a lab. When Bohn first started her research it was really tough to study the sounds of bats in the wild. She had to lug around a huge two-reeled recorder that could pick up ultra high frequencies, but noise was so loud at those frequencies that the bats kept blowing out the microphones.

It has gotten a lot easier recently because she can capture the desired frequencies with a mini-cam and a laptop computer, but "it's almost impossible for me to not have my system overloaded."

Researchers in Denmark and Germany have measured the sound intensity of bats at 140 decibels, the highest level for any animal. A rock concert is about 115 decibels, and the threshold of pain is around 120 decibels.

When Bohn plays back the songs at one-eighth the speed of the recordings the frequency drops to a level that humans can hear it. Not much of a song to a non-bat lover. It sounds like any number of nondescript birds -- chirps, buzzes, an occasional trill.

It's a brief song, with each syllable lasting for 10 to 30 milliseconds, but the complexity and structure is clear even to an untrained ear.

And to Bohn and her colleagues, no symphony orchestra ever sounded sweeter.