Researchers have identified an invisible threat posing an increasing challenge for national parks such as Rocky Mountain National Park, Yosemite and others across the country.

Anthropogenic noise is defined as noise due to human activity. Noise made by machines and people is heard in 37% of recordings collected from Park Service lands around the country.

The noise pollution is problematic, disturbing the peace for people visiting the parks, as well as the animals who live there. For many animals, being able to hear their surroundings and determine their safety is key to their survival. Some species even rely on listening for the song of a potential mate.

To tackle the problem, a team of scientists from Colorado State University and the Park Service has spent the past decade studying the effects of anthropogenic noise on national parks. The team found that recreational watercraft and trains create the loudest noise, but the sources of the greatest noise are vehicles and aircraft.

Researchers analyzed 46,789 hours of audio from 66 parks, producing a firm understanding of the frequency of noise, the types of noises heard, and how loud the noises were. The sounds were analyzed in CSU’s listening lab.

“Listening lab is where undergraduate students listen to the data in detail and identify these sources of noise,” explained Emma Brown, who works in the Natural Sounds and Night Skies Division of the Parks Service and worked on the study.

“Without the laboratory, I don’t think this research could have been possible. All that undergrad time invested really allows a paper of this magnitude to come together.”

The study was led by Rachel Buxton, a postdoctoral fellow doing research with CSU and the U.S. National Parks Service.

When discussing why the research was important to her, Buxton said, “It’s a really good example of science being done to inform management and inform how we can make things better. We know noise pollution is an issue in our parks, but we don’t know where it is, and we don’t know what is causing it. We need to know those things because we have the technology to tackle these issues.”

A leading cause of anthropogenic noise is human voices. Quiet zones have been suggested as a solution to the noise issue. These zones require people to speak in conversational level voices and to turn their cellphones off.

The Park Service continuously works to improve parks’ sound environments and find innovative solutions to noise, scientists said.

George Wittemyer of the Department of Fish, Wildlife and Conservation Biology at CSU wrote in an email, “There are a surprising variety of attempts to manage noise at national parks. This includes trying to require busing in sensitive areas (to reduce traffic), encourage aviation to be focused in limited areas of park and specific times, managing the amount of snow machines in areas based on noise exposure, and encouraging quiet voices in spectacular locations.”

When it comes to the future, Buxton hopes people will begin appreciating the national parks for their acoustic properties and be mindful of their audio footprints.