By KIM TINGLEY

Setting off in the predawn gloaming of central Alaska, we were the sounds of swishing snow pants, crunching boots and cold puffs of breath. As sunrise gradually lightened the late November sky, we took visible shape: a single-file parade on a narrow white trail traveling west, deeper into Denali National Park and Preserve. It was three degrees and so still that when we pulled up to rest, I heard no wind, no sibilant leaves, just a barely perceptible ringing in my ears. Tundra swans, kestrels and warblers had all flown south. Grizzlies were asleep in their dens. We tramped over frozen streams and paused to discover water still trickling faintly in hollows below. To the north, a morning blast of pink and orange brightened snow-shrouded Mount Healy at the edge of the Alaska Range; to the south — where the sun is always rising or setting during winter at a latitude just three degrees shy of the Arctic Circle — an alpine ridge remained covered in shadow and alder.

We saw a beaver hut on a frozen pond and moose tracks in snow. Ice frosted the nettles of black spruce and the beard of our leader, Davyd Betchkal, the park’s physical-science technician. Betchkal’s beard recalled that of his hero, the naturalist Henry David Thoreau, at the start of the Civil War. Otherwise he was a 25-year-old Wisconsinite wearing a lime green hat knit by his mother. He and I shouldered backpacks each weighted with 30 pounds of recording equipment. Far up ahead, a park ranger on skis towed more gear by sled.

Our destination was a ridge above Hines Creek, where Betchkal planned to assemble a station to collect a month’s worth of continuous acoustic data documenting an intangible, invisible and — increasingly — endangered resource: natural sound. Our mission was not only to trap the ephemeral but also to experience it ourselves, which at the moment was impossible for three reasons: 1) the chafing of our nylon outfits; 2) the chunking of our military-issue Bunny Boots on ice; and 3) planes.

“If you’re on foot and you choose to focus on the natural quality of the landscape, you’re completely immersed in nature; nothing else exists,” Betchkal said to the back of my head, letting me set the pace as we traipsed steadily uphill. “Then a jet will go over, and it kind of breaks that flow of consciousness, that ecstatic moment.” Meditating on our surroundings, I became a little curious how much farther we had to go. “Don’t think about that — that’s my answer,” Betchkal called ahead cheerfully. “Another answer is that I don’t know.”

An undeveloped swath of land nearly the size of Vermont, Denali should be a haven for natural sound. Enormous stretches of wild country abut the park in every direction save east, where Route 3 connects Fairbanks to Anchorage. One dead-end and mostly unpaved road penetrates the park itself. Yet since 2006, when scientists at Denali began a decade-long effort to collect a month’s worth of acoustic data from more than 60 sites across the park — including a 14,000-foot-high spot on Mount McKinley — Betchkal and his colleagues have recorded only 36 complete days in which the sounds of an internal combustion engine of some sort were absent. Planes are the most common source. Once, in the course of 24 hours, a single recording station captured the buzzing of 78 low-altitude props — the kind used for sightseeing tours; other areas have logged daily averages as high as one sky- or street-traffic sound every 17 minutes. The loudest stretch of the year is summer, when hundreds of thousands of tourists flock to Denali, embarking on helicopter or fixed-wing rides. Snowmobiles are popular with locals, and noise from the highway, the park road and daily passenger trains can travel for miles. That sort of human din, studies are beginning to suggest, is imperiling habitat — in Denali as well as wilderness areas around the world — as surely as a bulldozer or oil spill. But scientists have so little information about what landscapes should sound like without human interference that trying to correct the problem would be like a surgeon’s wielding a scalpel without knowing the parts of the body, let alone his patient’s symptoms. To restore ecosystems to acoustic health, researchers must determine, to the last raindrop, what compositions nature would play without us.

For more than 40 years, scientists have used radio telescopes to probe starry regions trillions of miles away for sounds of alien life. But only in the past five years or so have they been able to reliably record monthslong stretches of audio in the wildernesses of Earth. Last March, a group of ecologists and engineers taking advantage of advances in collecting, storing and analyzing vast quantities of digital data declared a new field of science: soundscape ecology. Other disciplines have long observed how various sounds affect people and individual animal species, but no one, they argued in the journal Bioscience, has yet studied the interconnected sounds of whole ecosystems. Soundscapes — composed of biological utterances like birdcalls, geophysical commotions like wind and running water and anthropogenic noises like motors — are “an acoustic reflection of the patterns and processes of the landscape,” the paper’s lead author, Bryan Pijanowski, an ecologist at Purdue University, told me. “And if we can take sound samples and develop appropriate metrics, we might be able to say, ‘Hey, this is a healthy landscape and this is an unhealthy landscape.’ ”

Indeed, though soundscape ecology has hardly begun, natural soundscapes already face a crisis. Humans have irrevocably altered the acoustics of the entire globe — and our racket continues to spread. Missing or altered voices in a soundscape tend to indicate broader environmental problems. For instance, at least one invasive species, the red-billed leiothrix of East Asia, appears to use its clamorous chatter to drown out the native European blackbird in Northern Italy. Noise can mask mating calls, cause stress and prevent animals from hearing alarms, the stirrings of prey and other useful survival cues. And as climate change prompts a shift in creatures’ migration schedules, circadian rhythms and preferred habitats — reshuffling the where and when of their calls — soundscapes are altered, too. Soundscape ecologists hope they can save some ecosystems, but they also realize they will bear witness to many finales. “There may be some very unique soundscapes around the world that — just through normal human activities — would be lost forever,” Pijanowski says — unless he and colleagues can record them before they disappear. An even more critical task, he thinks, is alerting people to the way “soundscapes provide us with a sense of place” and an emotional bond with the natural world that is unraveling. As children, our grandparents could hope to swim in a lake or lie in a meadow for whole afternoons without hearing a motorboat, car or plane; today the engineless hour is all but extinct, and we’ve grown accustomed to constant, mild auditory intrusions. “Humans are becoming an increasingly more urban species, and so we’re surrounding ourselves with concrete and buildings” and “the low hum of the urban landscape,” Pijanowski says. “We’re kind of severing the acoustic link that humans have with nature.”

In Denali, silence and solitude define the winter. Fall, Betchkal says, is the departure of the sandhill cranes — an urgent, lonely trilling of flocks taking flight. Spring returns with wood frogs, the park’s only amphibian. “They’re a riotous little chorus of fellows,” Betchkal told me the day before our expedition, as I watched him assemble and test, in an empty library across from his office building, the station he planned to deploy. Outfitted in a flannel shirt and jeans, he could have been a woodsman readying his traps if not for the headphones he wore. “It’s like a really organic, biological sounding rasping, but it’s really nice, like krrrup, krrrup,” he continued, pausing amid a tangle of wire to roll his R’s. In high school, Betchkal’s band teacher told him that before he could play a note on his trumpet, in order to appreciate how the instrument produced the syllable, he needed to articulate the sound himself. Betchkal thinks the same is true of wildlife sounds: “To understand what they’re all about, you have to make them,” he said. “You’ve got to. People think it’s goofy, but it isn’t. It’s studying.”

Sounds are remarkably difficult to describe without onomatopoeia. Defining the resource he wants to protect — in words and numbers, to scientists and policy makers — is a fundamental challenge for Betchkal and other soundscape researchers. Betchkal, though, is well suited to his role. As a boy, he went camping in Wisconsin’s Devil’s Lake State Park with his father, an amateur ornithologist who taught him the pleasures of lying in a sleeping bag listening to birdcalls. At the University of Wisconsin, Madison, he majored in biochemistry and botany while running soundboards for indie bands at the King Club downtown. For Betchkal, whose office bookshelf holds titles as various as “An Introduction to the Psychology of Hearing,” “Statistical Treatment of Experimental Data” and “Glacier Travel and Crevasse Rescue,” perhaps the greatest appeal of soundscape ecology is the way it intersects other fields of study. “It’s almost like going back to old-school naturalism,” Betchkal said, “where you paid attention to anything and everything that was fascinating. That’s totally what I’m into — interdisciplinary science.”

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.”

In the library across from his office building, Betchkal crawled among cables, politely probing each instrument with a voltmeter like a plaid-clad doctor with a stethoscope. The park has been able to take continuous recordings since only 2010 (previous setups recorded five seconds of audio every five minutes), and the scale and quality of its efforts in the wilderness are among the most advanced in the world. Though each station costs about $12,000, glitches are common: the instruments still aren’t designed to work together, or in outdoor conditions. Wind has toppled them; rivers have flooded them; grizzlies have mangled microphones. Betchkal fiddled much of the morning before he felt satisfied that the station was running properly and began to break it down, packing it methodically away and carrying it to his office. Pulling a checklist from his desk, he started filling bags with tools he might need the next day: blue crystal desiccants in vials to keep the air in the equipment boxes dry, wire strippers, extra cable. He’d never set up a station in November and December before. Part of the point was to add to baseline measurements of the park’s overall soundscape — another was to measure just how quiet the winter could be and preserve that sensation for posterity. “I suspect that it gets down below the threshold of human hearing,” Betchkal said, adding duck seal, Gaffer’s tape and an Exacto knife to the bag. “Below zero decibels.” If he did manage to capture a stretch of quiet that extreme, I wondered, what would it reveal?

“Openness!” Betchkal exclaimed. He paused to chase his thought. “Quiet is related to openness in the sense that the quieter it gets — as your listening area increases — your ability to hear reflections from farther away increases. The implication of that is that you get an immense sense of openness, of the landscape reflecting back to you, right? You can go out there, and you stand on a mountaintop, and it’s so quiet that you get this sense of space that’s unbelievable. The reflections are coming to you from afar. All of a sudden your perception is being affected by a larger area. Which is different from when you’re in your car. Why, when you’re in your car, do you feel like you are your car? It’s ’cause the car envelops you, it wraps you up in that sound of itself. Sound has everything to do with place. What is beautiful about this place? What is interesting or iconic about Alaska? Anyway,” he bowed apologetically at the waist, “that’s a lot of words. What I’m really measuring is the potential — the potential to hear natural sounds. If you’re choosing to listen, what are you actually going to hear?”

Around noon, nearing Hines Creek, we halted on the trail. The afternoon was windless. We were warm from walking but rapidly started to freeze; feeling left our fingers and noses first. Betchkal pointed off the path to the south, across a field of tangled willows, to a steep, snowy ridge, atop which he wanted to put the station. We shook up chemical hand warmers so they’d be hot when we reached the summit and charged into the thicket after Jeff Duckett, the ranger. Branches crashed against jackets and backpacks. We tripped on roots and fell. The sled proved too awkward to carry, and after retrieving two solar panels and a box of gear, Duckett and Betchkal abandoned it. At the foot of the hill, we began switchbacking upward through knee-high snow drifts. A Piper Cub skirted low over our heads, the roar of the engine momentarily blotting out the sounds of our breathing. Reaching the top, we dumped the audio equipment and threw on extra jackets. Betchkal got to work quickly, arranging tripods and running Arctic cable designed not to snap in subzero weather. Below, miles of black spruce spanned the valley separating us from Mount Healy.

Ostensibly, Betchkal’s stations capture exactly what we would hear if we could stand invisibly in the wilderness for a month. The recordings can reveal the sonic relationships that play out in our absence — and help us to modify our acoustic footprint. But our understanding of sound will always be limited by our perception of it. We will never experience the ultrasonic cries of insects, lizards or bats without distorting them. Decibels are self-deception. Bell Telephone Laboratories conjured them to measure loudness in the 1920s (the “bel” honors the company’s eponymous founder), but they represent volume as our ears register it, and the louder a sound is, the less of it we actually take in.

Hearing arguably fixes us in time, space and our own bodies more than the other senses do. Our vitals are audible: sighing lungs, a pounding pulse, a burbling gut. John Cage, the composer, once tried to observe complete silence in a soundproof room, but he still heard distinct noises — made, it turned out, by the nerves and blood of his own body. “Until I die,” he concluded, “there will be sounds.” We can shut our eyes at will, but not our ears, and what we hear is penetrating and physical — a wave entering our head. Even the deaf perceive internal jangling and external sonic feedback. The tactile nature of sound — the way it bounces back to us from other surfaces — helps us locate ourselves in relation to our surroundings and to know what’s behind us or around a corner. Fast asleep, our heartbeats quicken at a loud noise. In the womb, before we are aware, we hear the cacophonous exertions of our mother’s body. Returning from a field trip to the Potomac River refuge in Northern Virginia last year, a fourth grader wrote — in a passage that eventually reached a biologist in Soldotna, Alaska — that “the best thing about this place is that it has such nice noises you don’t feel alone when you are alone.”

In a series of gloveless maneuvers, Betchkal screwed together a weather station that would measure temperature, wind speed and direction, plus humidity. He arranged the solar panels, connected them to a box of batteries and sent power to the instruments: a sound level meter that continuously logs decibels at specific frequencies and an audio recorder. The meter powered on. The recorder did not. “Come on, you little stinker!” Betchkal said. Thinking it might be frozen, he slipped the device under his long johns, yelping when it met his thigh.

The next day, Betchkal showed me on his computer how he uses a program called Splat to analyze the data he gets. “Like in farming,” he said, “you’ve made the harvest, and now we’re going to take that raw thing and cook it or refine it down into something that can be used for different products.” Splat takes the data from the sound-level meter and arranges it on a spectrogram: a blue field of time on which sounds appear as orange shapes, their height representing their frequency, their brightness showing loudness, their length duration. Scrolling through the month, Betchkal labels many sounds by sight. Once he’s done tagging, the data can take on meaning, morphing into a graph of the circadian rhythms of wood-frog calls, say, or a park map of helicopter audibility.

Betchkal also listens to a subsample of the recordings. “I love this clip,” he said, pressing play on his computer. We heard a snuffling at the microphone and, nearby, the bellowing of babies that were actually bear cubs. “Part of my job is to go around and document these rare sounds,” he said, “to better understand the resource that needs to be protected — are there really important sounds out there that are disappearing?” He clicked again, and the tinny gurgle of an ice cave filled the speakers. “There’s thousands of little bubbles,” he said in narration. “I imagine like a big cave, and each room of the cave probably has different ways of reflecting sound. We can share sounds with people who might not be able to walk up to that ice cave and go hang around inside of it. Maybe even better, it excites them enough that they’re like, All right, let’s go on a hike! We’re going to check out an ice cave! Or whatever.”

Listening to Betchkal’s recordings of people passing his stations in the course of their travels can be unexpectedly elegiac. Tents flap, camp stoves hiss, people laugh, sniffle, adjust their packs. Once, trolling through audio from a mountain site, Betchkal happened upon a two-man concert, climbers duetting on guitar and mandolin. Another time, he discovered a rocky summer avalanche, an escalating rumble so deep it shook his desk.

On the ridge top, Betchkal’s body heat and hand warmers failed to revive the recorder. After more than an hour of troubleshooting, a spare pair of AA batteries succeeded in getting the device to work — but that meant, unlike the rest of the solar-powered equipment, it would run for only about a week. “It’s disappointing to me — really disappointing,” Betchkal said. “But that can happen — that does happen. If things go wrong, I’ll come back, and I can fix them.” He wrestled the instrument case closed and sealed it against the snow and wind of the coming month. The weather had begun to seep through our Polartec defenses, numbing our joints; water and pen ink were solids; cheese sticks gonged against canteens. “One last thing we need to do,” Betchkal said, shaking off defeat. “I know everyone’s probably cold and tired, but we’re going to listen. Get comfortable, be sure you’re not needing to fidget with stuff — ” A zipper zipped. Two magpies chirped. I lifted my arms from my sides to shush my sleeves and closed my eyes.

Night fell as we retraced our steps along the trail. The sky turned from lavender to indigo while the snow on the ground and the mountains glowed even when the last of the sun was gone. We headed for Jupiter, hanging low above the trees, and as we walked, I pictured the station back on the ridge, wrapped in the same darkness. When Betchkal harvests the audio, he will find us repacking our packs, exclaiming over our frozen apparatuses and sliding down the hillside into the willow field below. He will also, for three minutes, witness us still our movements and attune our ears to one of the quietest places left on Earth. In that window, I could hear the vastness of the valley — no sound marks materialized, like buoys bobbing on an empty ocean, to segment the sense of infinity. The landscape enveloped me, as Betchkal said it would, and I felt I was the landscape, where mountains and glaciers rose and shifted eons before the first heartbeats came to life.

“Standing in that place right there,” Betchkal told me later, “I had a complete sense that I was standing in that place right there and not drawn or distracted from it at all.” I felt located, too, but I could also imagine that if I hollered, my voice might not ever bounce back — that where I was, precisely, was a ridge top in a wide wilderness on a spinning rock in outer space. Ahead of me on the trail, as we neared our destination, Betchkal’s figure blurred in the darkness. The trees around us disappeared. There were, at last, only our footsteps. Then, barely audible, an inevitable airborne murmur — a sign from the civilized world.