SHORT: What We’re Listening To: How Sound Inventories Can Contribute to Understanding Change

What We’re Listening To: How Sound Inventories Can Contribute to Understanding Change

by Jennifer Jerrett

Do you want to get off the beaten track and experience Yellowstone in an entirely new way?

If you answered “yes,” visit Black Sand Pool and turn an ear to the ground. The giant, imploding bubbles in Black Sand Pool make a low-frequency sound that you’ll feel through your whole body. It’s undeniably an Earth sound—a planetary sound. And listening to a hot spring is an entirely different experience than looking at a hot spring.

Or instead of wolf watching, try howl hunting in the dark. It’s difficult to describe the experience of being outside with millions of twinkling stars for company and listening to the haunting sound of wolf howls bouncing off the hills around you. It’s an experience like no other. Or visit this place in the winter and seek out the utter absence of sound. A silence so complete, what you’ll hear mostly is the sound of your own heartbeat. You can still find such tranquility in Yellowstone.

And that’s just the point. For a truly rich and unique experience, it’s not always where in the park you should go, but rather what senses you let guide you. And experiencing the park through your ears is another way to enjoy a thrill.
Our sense of hearing is switched on while we are still in the womb. In fact hearing is about as fully developed for us in utero as it is for us as adults. At the same time, our other senses are either not yet turned on or are nascent and largely undeveloped.

And so that primacy—that early emergence of our sense of hearing in human development—has to be significant in terms of the role that hearing plays in our lives and how profoundly sounds contribute to learning and understanding. To think that our very unfolding of consciousness happens (for those of us who are hearing) largely through sound. And though we can choose to close our eyes, we cannot close our ears. That’s a very big deal from an evolutionary biology perspective, showing that we depend on our ears—maybe even more than our eyes—for survival.

Easy to forget in this age of the selfie, we’ve always been creatures of sound. And we’re not alone. Most organisms use sound to communicate, find food, avoid predators, or find mates. When we cover these sounds with human-caused noise, we affect those processes and alter not only the natural soundscape but modify vital elements of wild ecosystems.

Soundscapes are categorized as a vital sign in the Greater Yellowstone Inventory and Monitoring Network (GRYN) (Jean et. al. 2005). The National Park Service (NPS) Natural Sounds Program has collected acoustic data in over 100 parks. The GYRN, however, is one of the few networks that acquired sound data from park staff, Yellowstone National Park has been monitoring soundscapes for over two decades, and these efforts have cataloged an amazing diversity of sounds.

The Yellowstone National Park (YNP) soundscape monitoring program was launched in the late 1990s and early 2000s, primarily as a component of winter use planning. At the time, managers from Yellowstone and Grand Teton national parks were interested in quantifying the potential noise impacts from vehicles that travel over snow (snowmobiles and snowcoaches): where, when, and how loud was the noise? How did that compare to the ambient baseline condition of the natural soundscape? And how should park managers deal with the noise? They worked with Skip Ambrose from the then-newly-formed NPS Natural Sounds Program and Shan Burson, who was working as an acoustic ecologist in Denali National Park at the time, to develop a soundscape monitoring program for the ecosystem. Shan came on as the full-time bioacoustic ecologist for Grand Teton and Yellowstone in 2003 (Shan retired in December 2017 and recently received a Director’s Natural Resource Stewardship and Science award for his outstanding work over the years. As a testament to the importance of his work, the program lives on in Yellowstone).

It’s difficult to overstate how successful this program has been. One of the most notable outcomes was a comprehensive reframing of how we establish vehicular noise thresholds during the winter use season. Initially to mitigate the increasing noise impacts from oversnow vehicles (OSVs), thresholds regulated the number of snowcoaches and the number of snowmobiles that were allowed in the park. This understandably created some tension among groups of users that preferred access either by snowcoach or snowmobile. Scientists discerned that groups of snowmobiles had a similar acoustic “footprint” to individual snowcoaches. This created a perceptual shift for park managers: instead of visitation thresholds based on the number of vehicles allowed, managers were able to quantify things in terms of the number of transportation events allowed. Not only did this set the stage for the best possible visitation scenario with the least impact, but it let commercial outfitters make their own decisions about the types of vehicles they wanted to use and how to structure their tours. It also eliminated some of the conflict among user groups: since all OSVs were treated more or less the same, outfitters and visitors didn’t feel penalized for choosing one type over the other.

The YNP soundscape monitoring program is one of the longest running environmental acoustic monitoring programs ever. In fact it might surprise you to learn that Old Faithful may be the longest running acoustic data collection site on the planet (that’s not an airport)! The winter use monitoring continues to provide the foundation for acoustic monitoring in the ecosystem today. In addition, the monitoring program has collected thousands of hours of sounds representing numerous species and rarely heard a natural laboratory known as YNP. These resources awe visitors from around the world and serve as reference points for future comparisons.

Currently scientists such as Ann Rodman, who coordinates with the Climate Change Response Program in YNP, and Jacob Job, from the Listening Lab at Colorado State University, are exploring how acoustic monitoring in YNP and the region can be used as a tool to address other scientific questions and how acoustic monitoring can be linked with other ongoing vital signs monitoring activities. Specifically, acoustic information will be leveraged to consider what it can tell us, for example about climate change, the timing of important biological events (e.g., phenology), how species composition varies through time and spatial distribution, or how to define the acoustic “signature” of a site. New tools are on the horizon and have the potential to revolutionize how scientists use and interpret acoustic data (Buxon et al. 2018, Mennitt et al. 2012) and how acoustic techniques alone or in combination with other tools can be used as part of a broadscale monitoring framework to measure and monitor ecosystem health (Ross et al. 2018). As one example, YNP is pairing continuous autonomous recorders with climate monitoring stations across an elevational gradient to investigate both the potential and the limitations of acoustic monitoring. This pioneering work will inform how acoustic monitoring can also be used to measure and monitor acoustic variation across YNP and throughout the Greater Yellowstone Ecosystem (GYE) and support soundscape monitoring across other gradients of ecosystem drivers such as land use and human use that are rapidly changing in the GYE. Taken together acoustic monitoring in YNP and across the GYE has already revealed unexpected findings that continue to inform management actions and decision making as well as support opportunities for sharing and interpreting discoveries with park visitors.

Natural sounds are fundamental components of our ecosystems and of YNP—these sounds have a lot to tell us. We just have to listen.

Literature Cited

Buxon, R.T., M.F. McKenna, M. Clapp, E. Meyer, E. Stabenau, L.M. Angeloni, K. Crooks, and G. Wittemyer. 2018. Efficacy of extracting indices from large-scale acoustic recordings to monitor biodiversity. Conservation Biology 32:1174-1184.

Mennitt, D., K. Fristrup, and K. Sherrill. 2012. A geospatial model of ambient sound pressure levels in the continental United States. The Journal of the Acoustical Society of America 132:1926.

Ross, S.R.P.J., N.R. Friedman, K.L. Dudley, M. Yoshimura, T. Yoshida, E.P. Economo. 2018. Listening to ecosystems: data-rich acoustic monitoring through landscape-scale sensor networks. Ecological Research 33:135-147.

Jennifer Jerrett is an editor, audio producer, and natural sound recordist for Yellowstone National Park. She is the creator and producer of "Telemetry," Yellowstone's science and issues audio podcast. Find it at or wherever you get your podcasts.

Last updated: September 16, 2019