Soundscapes? Krause explained that this is the term Canadian composer and writer R. Murray Schafer invented in the 1960s when he was exploring how industrialization affects our relationship with the natural environment. “Schafer really started this field,” said Krause. “The idea of recording whole landscapes is only 40 years old, and already we’re losing these natural soundscapes faster than we can record them.” Krause estimates that one-third of the 3,500 ecosystems he has captured are aurally extinct. They’ve been lost to development, or invaded by mechanized noise to such a degree that they’re impossible to duplicate.

Between questions, we sat quietly at a picnic table under a spreading oak near the stream, listening to the ever-expanding chorus. It reached a crescendo with the piping calls of ruby-crowned kinglets, the rougher, brassy notes of scrub jays, the wheezes and twees of nuthatches, and finally the trumpet-like salutation of a California quail. By 5:30, sunshine was sweeping over the mountaintops, burning off the last of the fog, and Krause said the birds would soon call it a wrap.

They sing like this at dawn to protect their territories and mates from other males, scientists think, and they stop singing once the sun has risen, perhaps because there is enough light for foraging. (Insects, a preferred prey for many birds, also start moving in the sun’s warmth and light.) We’d listened for nearly an hour, and Krause pointed out that during that time we hadn’t heard anything other than the birds, the wind, and the trickling stream. “A full hour of natural quiet uninterrupted by motors. Try finding that in your town, or anywhere you travel,” he dared.

Krause’s words and the headphones had their effect: Already I was listening in a new way. I was paying closer attention to sounds—the lilting creek, the wind’s rustle and oomph as it moved through grasses and tree limbs, the tiny peeps of the kinglets—that I usually think of as background noise. I was about to comment on this when our quiet spell came to an abrupt end. Somewhere—Krause estimated about 15 miles away—a motorcyclist revved his engine and ripped down the highway. Seconds later, the first jet of the day lifted off from San Francisco International Airport, and its thunder tore away what remained of our quiet. In its wake, the birds stopped singing.

“That’s the way it usually ends,” Krause said, tapping the table. “Can you imagine what sounds like that do to the calls of other species? The sound of one jet disrupts the whole fabric of the birds’ chorus; it destroys their communication. Many of them can’t compete with it, so they move farther and farther away from us and our noise.”

Although often overlooked, noise pollution is increasing across the world, as highways, jet routes, cities, and suburbs expand. Since the 1970s, scientists have known that urban environments can cause health problems for their denizens: Blood pressure and stress-hormone levels rise, as does the incidence of heart disease and sleep disorders, and a child’s ability to learn drops precipitously. But documenting the effects of our cacophony on the natural world has proved more difficult, due largely to the lack of funding. “It’s an orphan issue,” said Robert Dooling, a bioacoustician at the University of Maryland, Baltimore. “All of the decisions about such things as sound barriers on highways and noise limitations on aircraft are based on how these affect humans. There’s no comparable animal research.”

But because human noise is increasing in frequency, intensity, and spread, biologists feel an urgency to find out what it is doing to our fellow creatures, and noise-pollution studies are finally getting under way—thanks in part to a 2003 study by Hans Slabbekoorn, a behavioral biologist in the Netherlands. His research showed definitively that a bird common to European cities—the greater tit—has changed its song in response to its noisy urban environs: The creature now sings higher-pitched and shorter tunes than do its forest counterparts. Another research team has shown that robins living near cities now sing at night instead of during the day, presumably to avoid competing with our peak-hour ruckus.