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.