What does a hoot look like? What about a croak? Or a howl?
Vivid images used by scientists capture sounds that soothe and nurture us — and some that jar the natural soundscape
Listen to a dawn chorus from Mungwezi Ranch in Zimbabwe. Make a mental note of the sounds you’re hearing and how they make you feel.
You might be able to pick out a rising birdcall or buzzing insects from the recording below, but a new world reveals itself when you visualize sound via the colorful image below, also known as a spectrogram.
Soundscape researchers use spectrograms to visually identify species and scan through hours of audio data. Using machine learning and neural networks, they pick out specific audio signals from animals and their surroundings that give a sense of that ecosystem’s health. This way, scientists can monitor biodiversity and answer more specific questions about the behavior of a species.
“If you look at a spectrogram of a healthy ecosystem that’s full of lots of biodiversity, you’ll see that spectrogram fairly full of different sounds from different species,” said Rachel Buxton, a professor at Carleton University who studies how natural sounds affect human health.
Mungwezi Ranch, Zimbabwe
Here, birds, insects and bats greet the new day. Fuzzy horizontal red bands near the bottom of the image represent the drone of insects, and the ascending thin red pillars just below the bands show birdcalls, including those of the Natal francolin and the chinspot batis, pictured below.
Natal francolin
Chinspot batis
Simply listening to natural sounds has been shown to decrease mortality rates and stress and improve mental health, cognitive performance and even birth outcomes. Even though some birds’ calls exceed 70 decibels — the same volume as a vacuum cleaner — a dawn chorus is a soothing sound, not a jarring one.
“We’ve evolved as a species in these environments that are full of different natural sounds,” Buxton said. So, “an environment that’s full of natural sounds is a fairly good indicator of a safe environment.”
Spectrograms present an image of frequencies over time and convey a sound’s volume. They are created by feeding an audio signal into a Fourier transform, a mathematical model for translating sounds into another format.
Intense lines register loud moments, soft blurred patches are quiet hums, and a stack of bars sloping upward might represent the bugling of an elk or the howling of a coyote. Adding colors — as we’ve done in the spectrograms included in this article — helps to distinguish sounds within an image.
In a dawn chorus, “you’ll see lots of color, lots of higher-decibel sounds,” Buxton said.
“Some [birdsongs] might have sort of a sweeping call,” Buxton said, sliding her finger down, miming a comma in the air. “The summer cicadas are more buzzy,” she continued, “so they’re going to spread across the whole upper frequency range.”
Tensas River National Wildlife Refuge, Louisiana
Frog calls fill the bumpy, cloudlike lower bands. Insect and amphibian noises dominate the image, but tiny, thin rising and falling lines in lighter blue at the bottom of the picture show a barred owl hooting.
Tensas River National Wildlife Refuge, Louisiana
Barred owl
Gray tree frog
Smith Oaks Sanctuary, Texas
This is a soundscape of wading birds in Texas. The piglike calls of neotropic cormorants are represented in the blue sandpaper-like ribbon at the bottom. Light blue sloping streaks, lower left and lower middle, rising above the cormorants’ calls depict the calls of the great-tailed grackle.
Smith Oaks Sanctuary, Texas
Neotropic cormorant
Great-tailed grackle
In a 2021 review paper, Buxton found that birdsong was best at relieving stress in human participants, while water sounds resulted in the largest positive effects to our nervous system.
One reason for water sounds’ benefits may lie in their masking of other, more jarring stimuli.
Water sounds have louder ripples peaking in the lower frequencies, with the quieter water flows softly combining up through the frequencies, blanketing and often masking other sounds. Spectrogram images of water bear this out with Rothko-like washes of color — no jagged peaks or intensely blurred lines but rather a soothing canvas.
Glacier National Park, Montana
A scrim-like wall of color reveals the sounds of a glacially fed creek in Glacier National Park. Small light red slashes at the bottom are splashes and bubbles.
Glacier National Park, Montana
The idea that natural sounds benefit our health dates to the Middle Ages, when infirmaries incorporated restorative gardens to help patients recover. Scientists today refer to the biophilia hypothesis, in which we are — as the name suggests — drawn to nature through deeply evolved attractions to favorable landscapes.
Researchers have documented nature’s many health benefits and its ability to help people relax reflexively. Being in nature can replenish our focus or diminish our stress within minutes, science indicates.
“I always try to encourage people to just get outside and just experience the real thing,” Buxton said.
“You know, nature really is the best medicine,” she said. “It’s not just about hearing nature. It’s also about all the other senses that go along with being in nature.”
Rocky Mountain National Park, Colorado
The jagged rising slashes at the bottom of this image represent coyotes raising and lowering the pitch of their howls. Birdcalls look like thin bright quills sticking out of the coyote signals.
Rocky Mountain National Park, Colorado
Coyote
Red-winged blackbird
Jacob Job is a soundscape researcher, an evolutionary biologist and the associate director of the Bird Genoscape Project. Most of the recordings you’ve heard and seen here are his. Job sometimes sets up multiple recording spots, dons scent-block camouflage and disappears into nature.
“The only time I’m truly mindful, in the moment, not thinking about the rest of the world are moments like that,” Job said. “And so it’s like a freedom. I’m in nature. I’m with it.”
A large part of Job’s recording work is simply finding places where there is no noise pollution or people. “It’s nearly impossible,” Job said.
Researchers find that animals are adapting by shifting their calls to be heard above the human-made thrum.
Rocky Mountain National Park, Colorado
The thick blur at the very bottom shows the sound of a passing car. Low-frequency road noise muddies the lower range of birdcalls. A pine siskin appears to react to the car noise by blasting out a call — see the thick red vertical smear about three-quarters of the way across the image — spanning many frequencies.
Rocky Mountain National Park, Colorado
Pine siskin
The National Park Service has experimented with its messaging to parkgoers about noise. For example, signs at the entrance to Cathedral Grove in California’s Muir Woods National Monument remind visitors that they are in a “quiet zone.” The signs decreased the sound levels by almost three decibels.
Gentle guidance such as that, Job said, sends a good message.
“You’re not telling people how to behave,” he said, “but you’re holding them responsible for their actions and letting them know other ways of engaging that could be more meaningful and more beneficial.”
Protecting natural sounds has implications for human health — and for the health of all the creatures in the audio clips above, as well as for the planet overall, researchers say. Spectrograms offer a way to understand and promote that message.
“We are a loud culture for reasons that are complicated and many,” Job said. “And until we start seeing some changes about the root causes of those, I don’t know that we can handle some of the more nuanced and critical things surrounding conservation and protecting our access to clean air, water, places to grow healthy food and recreate and recover in.”