How Man-Made Noise May Be Altering Earth's Ecology

"Bernie Krause listens to nature for a living. The 69-year-old is a field recording scientist: He heads into the wilderness to document the noises made by native fauna — crickets chirping in the Amazon rain forest, frogs croaking in the Australian outback.

But Krause has noticed something alarming. The natural sound of the world is vanishing. He'll be deep inside the Amazon, recording that cricket, but when he listens carefully he also hears machinery: The distant howl of a 747 or the dull roar of a Hummer miles way.

Krause has a word for the pristine acoustics of nature: biophony. It's what the world sounds like in the absence of humans. But in 40 percent of the locations where Krause has recorded over the past 40 years, human-generated noise has infiltrated the wilderness. 'It's getting harder and harder to find places that aren't contaminated,' he says.

This isn't just a matter of aesthetics. The contamination of biophony may soon become a serious environmental issue — Krause says that man-made sounds are already wreaking havoc with animal communication. We worry about the carbon emissions from SUVs and airplanes; maybe we should be equally concerned about the racket they cause.

Krause's argument is simple. In a biophony, animals divide up the acoustic spectrum so they don't interfere with one another's voices. He shows me a spectrogram of a wilderness recording, in which all the component noises are mapped according to pitch. It looks like the musical score for an orchestra, with each instrument in its place. No two species are using the same frequency. 'That's part of how they coexist so well,' Krause says. When they issue mating calls or all-important warning cries, they aren't masked by the noises of other animals."