If you're having trouble sleeping, maybe it's because you live on the East Coast: whether you have neighbors or not, America east of the Mississippi is the noisier half of the continent.

Audio levels across the United States - (NPS Photo)

This amazing acoustical heatmap was generated by researchers from the National Park Service and Colorado State University to show the average summer soundscape of the United States. Blue areas are quieter, and pale yellow the loudest. Predictably, major cities around the country show in yellow, trailing streaks of bright color off along major highway and rail networks branching away from them. The mountains, prairies and particularly deserts of the country fall into various shades of cool to icy blue.

The researchers did not, of course, park microphones to cover every square inch of the country. Instead, they put up microphones in parks around the country, collecting around 1.5 million hours worth of audio samples. They then fed the samples into a computer program which analyzed the audio and a host of other data. That data includes such generic noise-generating events as rainfall totals and airplane overflights, and some very location-specific data such as the sound generated by snow coaches in Yellowstone or crickets in Zion National Park. Attenuation factors such as terrain shielding, foliage, and atmospheric effects are factored in. The program then extrapolates the known data to fill in the blanks and produce the map.

A microphone recording sounds in Great Sand Dunes National Park and Preserver - (NPS Photo)

The Park Service has a mandate for preservation, but few people realize that it extends beyond drawing lines around chunks of dirt and restricting development. The sounds and sights of America's National Parks are frequently impacted by events and factors outside the parks themselves. Monitoring and mitigating these impacts is enough work that the Park Service has a whole branch dedicated to it: the Natural Sounds and Night Skies Division. Among other things, the division works with park tour operators to reduce sound generated while conducting tours of the parks.

To illustrate the problem with noise pollution:

Studies have found that hummingbirds prefer sites that are noisy. Scientists speculate that this is because their primary predators,  western scrub jays, flee from high noise areas. This often results in hummingbirds vacating natural environments to live in man-made towns and cities. This, in turn, significantly decreases pollination in more wooded areas. This is also bad news for the  western scrub jays, who rely on the hummingbirds for food.

It might not seem any great revelation that the parts of the country populated by humans, and all the machinery and infrastructure that we tend to collect around us, are more noisy than the parts that are not so populated. Concurrently, the more populous eastern parts of the country could be presumed to generate more decibels per square meter than the less populous west.

The truly intriguing output from the project, however, comes instead in the form of this map:

(NPS Photo)

That map shows the same summer soundscape as the first, with one crucial difference: only natural noise sources are included. All human-generated audio was excluded. Fascinatingly, the eastern part of the country, now devoid of humans, though quieter than with their presence, remains noisier than the west.

The difference, biologists told Science News, is largely due to water. The louder areas on that map tend to frame the great river valleys of the East and swamps of the south. Of course, water in motion tends to generate noise in and of itself, but more importantly, water in abundance also feeds life. The moist, verdant surroundings have foliage that rustles in the wind, and shelters more animals per square mile and the sounds that come along with them.

Share This Article