Surprisingly, soundscape ecology, with its focus on the natural, got its start in the streets. An M.I.T. city planner first applied the word “soundscape” to habitat analysis in 1969 for a study he did on the “informativeness” and “delightfulness” of various sonic environments around Boston. Pushing volunteers about in wheelchairs, first blindfolded, then ear-muffled, then without sensory checks, he discovered that the sounds of seaports and civic centers were just as important as their appearance in influencing how much people enjoyed being there. This was a novel notion, even though objections to undesirable sounds date back to the invention of neighbors. In his influential 1977 work, “The Tuning of the World,” the Canadian composer R. Murray Schafer charts man’s relationship with noise. As long ago as 3000 B.C., he notes, the Epic of Gilgamesh discussed “the uproar of mankind,” which aggravated the god Enlil. “Sleep is no longer possible,” he complains to the other gods. In the second century A.D., wagon traffic “sufficient to wake the dead” ruined the Roman poet Juvenal’s ability to rest between Satires. Many English towns were sequestering their blacksmiths by the 13th century, and Bern, Switzerland, passed its first law “against singing and shouting in streets or houses on festival days” in 1628. Over the next 300 years, it also legislated against “barking dogs,” “singing at Christmas and New Year’s parties,” “carpet-beating” and “noisy children.” In 1972, the U.S. Environmental Protection Agency declared noise a pollutant.

Only recently, however, have governments from Japan to the European Union begun to recognize natural sounds as a resource requiring protection. When Woodrow Wilson created the National Park Service in 1916, it was to “conserve the scenery”; not until 2000 did a Park Service director issue systemwide instructions for addressing “soundscape preservation.” In 1986, a midair plane crash above the Grand Canyon National Park — where sightseeing tours had operated virtually unchecked for almost 70 years — prompted Congress to pass the National Parks Overflights Act, requiring the Park Service to work with the Federal Aviation Administration in remedying the “significant adverse effect on the natural quiet” that aircraft there appeared to be having. The act also called for studying the impacts of overflight noise on other parks.

Initial research returned alarming results. In Yosemite, planes were heard 30 to 60 percent of the day. In the Haleakala volcano crater in Maui, 8 to 10 helicopters passed overhead per hour. What’s more, other experiments showed, much as the M.I.T. study did, that noise affected the way visitors saw landscapes: when volunteers viewed photos of natural vistas while listening to helicopters on tape, they rated the scenes less picturesque than they did under quieter conditions. By 2000, the National Park Service had staffed a division to gather data on park soundscapes nationwide and create, with the F.A.A., air-tour management plans at 100-plus locations. More than a decade since — partly because of disagreements between aviation and conservation interests — no such plan is in place, though many parks have begun looking for ways to trim other noise, turning off idling shuttle buses, curbing car traffic and investing in less uproarious maintenance tools. Grand Canyon managers, after nearly 25 years of laboring, last year proposed amendments to the timing and routes of sightseeing flights that would make the park somewhat more serene.

When Denali fielded its first sound station in April 2001, far earlier than nearly every other park in the country, the primary concern was determining the level of annoyance caused by planes and snowmobiles. But scientists were about to realize the damage society’s widening sonic footprint could do to natural ecosystems. In 2003, a Dutch team studying a common songbird, the great tit, reported in Nature that males of the species shifted their calls to a higher frequency in cities, where low-frequency human noise masked their normal song range. Further proof that urban sounds cause wild creatures to adjust their vocal styles quickly followed. Nightingales sing louder in louder environments. Robins — usually diurnal singers — switch to nighttime in areas that are chaotic by day. Subjected to constant mechanical whirring, certain primates, bats, whales, squirrels and frogs all change their cries. Many other animals, it seems, lack the physical equipment to adapt, and perish or move away. Not only are individuals editing their tunes in real time — as the great tits did — but natural selection is also rewarding louder, higher-frequency singers, redirecting the course of evolution.

Species can fight for airtime in a limited bandwidth by changing their volume or frequency, or by rescheduling the timing of their calls. But there’s no way animals can alter their ability to listen — for their very survival — if human noise conceals, for example, the twig-snap of a prowler or the skittering of prey. In the United States, where more than 80 percent of land is within two-thirds of a mile of a road, the listening area available to most creatures is rapidly shrinking. Beyond hunting and hiding, even invertebrates use the gabbing of unwitting cohabitants for navigation. Sightless, earless and adrift in the open ocean, coral larvae seek to settle on tropical reefs by swimming toward the throbs of muttering fish and snapping-shrimp claws. Eurasian reed warblers en route to southern Africa at night flutter blind over pine forests, sand dunes and the Baltic Sea until, hundreds of feet below, the cheeping of other warblers signals the presence of sustaining wetlands. If those aural cues disappear, the species that heed them may be floating and flying without a compass.

Explosive human sounds can have catastrophic impacts, especially underwater, where they travel faster and farther than they do in the air. Porpoises and whales have beached themselves fleeing the high-pitched shrieks of U.S. Navy sonar, researchers believe; they also blame the low-frequency booms ships use to search for oil and gas for fatally ripping through the organs that cephalopods like squid use to detect vibrations. Fewer studies have examined the health impacts of more mundane, chronic noises on terrestrial species, but proof is emerging that the droning of freeway traffic and the 24/7 rumbling of natural-gas-pipeline compressors directly harm the ability of birds nesting nearby to reproduce. Jesse Barber, a biologist at Boise State University who is the co-author of two recent papers about the impacts of noise on land-dwelling animals, writes that “it is clear that the acoustical environment is not a collection of private conversations between signaler and receiver” but a network of broadcasts reaching both intended and invisible listeners. Like pulling Jenga blocks from a teetering tower, removing sounds from soundscapes — or adding them — he warns, “could have volatile and unpredictable consequences.”