Changes in Nature’s Symphony Can Reflect Climate Impacts

Shifts in sound across ecosystems could offer an early warning system for environmental changes, researchers say.

If a tree falls in a forest and no one is around to hear it, does it make a sound? 

The answer is a resounding yes—and we know this for certain because of the vast network of audio recorders that researchers have set up in recent decades to eavesdrop on nature’s symphony, from chirping birds to singing whales. Studying environmental acoustics has enabled us to uncover some of the secrets of the natural world, from elephants’ names for each other to the uncanny parallels between birdsong and human-made music. 

But through these soundscapes, scientists have also discovered the cascading impacts of climate change and human activity on ecosystems and wildlife. Experts say tracking these haunting sonic shifts could help serve as early warning systems of climate consequences. 

Ears in the Sky: Among nature’s most famous and ubiquitous musicians are birds. (In fact, a group of them is providing background music outside my window as I am writing this.) 

Scientists depend on these avian concerts to help monitor global bird populations, and changes in these tunes can help reflect threats they may be facing. That’s largely because audio recording can capture ecosystem dynamics at a much broader scale than visual data alone can, which is crucial for an “incomprehensibly vast problem” like climate change, bioacoustic researcher Connor Wood told me. 

“To understand what’s happening with climate change in the context of, say, wildlife conservation … you need to have data from across the landscape or, really, across an entire ecosystem,” said Wood, a scientist at the K. Lisa Yang Center for Conservation Bioacoustics, part of the Cornell Lab of Ornithology in Ithaca, New York. “That is something that bioacoustics makes uniquely possible.” 

And as bird populations decline in the face of habitat loss and warming temperatures, their soundtracks are changing too, according to a 2021 study. By analyzing soundscapes from more than 200,000 sites across North America and Europe over the past 25 years, researchers found “a pervasive loss of acoustic diversity and intensity of soundscapes.” This widespread noise dampening was a direct reflection of changes in species abundance and richness. 

Other animals across the world are also showing climate-driven shifts in their tunes. For example, shorter winters and early springtime warming are altering the timing of wood frog calls in Alaska. Meanwhile, during a particularly smoky bout of intense fires in Indonesia in 2015, researchers documented changes in the pitch and harshness of orangutan calls, which project lead Wendy Erb said sounded “a little like humans who smoke a lot.” 

Detecting these acoustic cues early can sometimes help researchers stop or slow changes wrought by environmental degradation, Wood said. Each year, he and a team of ornithologists deploy more than 1,500 audio recorders across the forests of the Sierra Nevada range in the western U.S. While recording millions of hours of audio, these devices catch the hoots, barks and whistles of the California spotted owl. Between 2017 and 2018, the researchers noticed a stark uptick in calls across more areas from a different bird: the barred owl. This invasive species is a top threat to California spotted owls due to overcompetition for limited resources. 

With this audio evidence in mind, a coalition of academic, agency and industry partners developed a program to remove the barred owls, and successfully eradicated most of them from the Sierra Nevada at the time before they could further threaten the spotted owls. 

Under the Sea: Just like animals in the sky or on land, marine life below the surface is constantly hosting its own natural concert. Using waterproof microphones known as hydrophones, scientists can record the vast array of songs, chirps, clicks and other sounds in seascapes, even in remote parts of the Antarctic Ocean, as my colleague Teresa Tomassoni reported in April. 

Humans aren’t just doing the listening. We also generate an exceptional level of noise at sea from shipping and drilling, which can drown out the ocean’s natural song—a trend I pointed out last year. Meanwhile, ocean temperature changes are also altering the sounds of the sea, according to a growing body of research. 

Take “The Blob,” a severe marine heatwave that settled over the northeast Pacific Ocean from 2013 to 2016. In some areas, ocean temperatures climbed more than 4.5 degrees Fahrenheit above average, triggering a record outbreak of toxic algae and widespread die-offs of marine creatures and seabirds on the West Coast. Recently, scientists uncovered other, more subtle shifts happening underwater as the Blob engulfed the region. 

A study published in February found both blue and humpback whales in the central California Current Ecosystem sang less than average during the peak of the marine heatwave in 2015, when the animals’ main diet sources—fish and krill—were meager. This is likely because the whales had to focus more of their energy on finding food than vocalizing, according to study co-author John Ryan, a biological oceanographer at the Monterey Bay Aquarium Research Institute. 

He told me that a combination of visual, chemical and sound data is crucial to help create a “fairly complete understanding of what the ecosystem is doing in order to understand the whales’ behavior.”

Warming oceans may amplify the sounds of other creatures, such as the snapping shrimp, which can create popping sounds so loud and wide-reaching that they interfere with ship sonar. Scientists can even use bioacoustic tools to listen in on geological changes brought by global warming, including babbling pops of a melting iceberg. 

In recent years, musicians and conservationists have also tapped into nature’s noises to bring attention to environmental issues. But as habitat loss and climate change decimate biodiversity around the world, some ecosystems could face a different acoustic fate altogether: silence. 

Cover photo: 

Humpback whales communicate through intricate songs and vocalizations. Credit: Reinhard Dirscherl/ullstein bild via Getty Images