For several months of the Covid-19 pandemic, bustling streets around the world cleared, and traffic jams became a memory. As humans went into lockdowns and quarantines, the Earth vibrated less. The “anthropause,” as some researchers are calling it, provided an unexpected opportunity to study some of the subtler ways that we alter the world around us.
During the pandemic, the world got quieter. So much quieter, in fact, that scientists were able to put numbers to it. When stay-at-home orders began taking effect around the world, the reduction in noise was so drastic that seismologists saw a decrease in rumblings deep in the earth’s crust. The decline lasted for months and could be measured 1,300 feet underground. In some areas, the ground noise fell by up to 50%—the equivalent of going from a conversation to a quiet whisper.
Scientists were not the only ones to notice this shift. Animals across the globe changed their behavior in response to the newfound quiet. Locally, researchers saw shifts in everything from mountain lions to songbirds to whales.
One of the most noticeable changes was that silent streets encouraged animals to venture closer.
“Since things were quieter, wildlife was able to encroach more into our territory—which, you know, is sort of their territory—but into human territory,” says Amy Red Feather, a wildlife technician at Native Animal Rescue of Santa Cruz County. The rescue and rehabilitation center received an influx of calls from residents during the stay-at-home orders.
“A lot of that, I think, is because more people are home,” says Red Feather of locals’ alarm at seeing raccoons, coyotes, opossums, bobcats, hawks and owls near their homes. “A lot of people are surprised to know that they do live here, that it’s completely natural to see them in the wild during the day and at night.”
The timing of lockdowns also meant people saw more babies and young animals.
“We had coyote pups getting born right on school properties,” she says. “A lot of dens are being occupied where normally it just would have been too noisy for the animals to safely be there.”
As wildlife interactions increased, so did the number of people trying to keep animals illegally.
“We got a lot of animals that grew up, started biting people, and they needed to find a place for, which is terrible,” says Red Feather. “The animal, if it becomes imprinted, can never live in the wild. It will start biting you once its hormones kick in, and once it matures, it’s not going to be happy with you and it won’t be able to live in the wild. A lot of these animals end up having to be euthanized.”
Mountain lions also ventured closer during the shelter-in-place orders. Scientists at the Santa Cruz Puma Project have been studying mountain lions and the way they respond to human-made noise since 2008. Using speakers in the forest and GPS tracking collars, the group studies how adding sound to habitat scares away mountain lions. During the shutdowns, the scientists could study the opposite.
“Mountain lions have always responded negatively to houses on the landscape, and they still continue to do so through Covid,” says Chris Wilmers, a professor at UCSC and the lead scientist on the Santa Cruz Puma Project. “But before Covid, mountain lions had the additional fear of cities, and that additional fear completely disappeared with the shutdown.”
Without the noise of traffic and daily life, the pumas quickly adjusted their ranges to include previously busy areas. It happened within weeks—and in some cases, days—of the shutdown.
“Animals like mountain lions make their decisions based on what they hear,” says Wilmers. “And so if, all of a sudden, they’re not hearing people in a particular place, then it makes sense they might respond quite quickly.”
As things started opening back up and traffic resumed, the group saw the mountain lions recede just as quickly.
“What this study shows is that even human mobility itself can have influences on the environment and animal behavior that are sustained, in addition to all the other ways that humans influence ecosystems,” says Wilmers.
Changing Their Tune
While some animals changed their geographic range during the shutdown, others changed their vocal range. One group of scientists found that birds in the Bay Area altered their songs in response to the newfound quiet.
The team has recorded the effects of noise pollution in white-crowned sparrows—a small, native songbird—since 2012. Once the shelter-in-place orders began, they expected to hear a change.
But, “we were surprised to find that it was quite a large shift,” says Elizabeth Derryberry, an ecology and evolutionary biology associate professor at the University of Tennessee, Knoxville and main author on the study.
“In fact, in some of the areas in San Francisco, we saw—or we heard—songs that hadn’t been heard since the ‘70s… those songs have changed in ways where they now sounded like they did when they were recorded back during the summer of love.”
The birds sang softer than normal, but the notes reached more than four times as far. Before the pandemic, their songs could only be heard from about 15 feet away. During the shutdowns, they could communicate with birds more than 65 feet away.
“Because noise went away, they don’t have to shout to be heard,” says Derryberry.In addition to singing more softly, the songbirds also changed their pitch. Lots of human-generated sounds are loud at low frequencies, so birds in urban areas tend to sing higher-pitched songs in order to cut through the noise.
Without the din of traffic, the birds sang lower and increased the overall pitch range of their songs. Songs with more variation do a better job attracting mates.
“So not only could they be heard further, but they also essentially sounded sexier,” says Derryberry. “We can imagine that reducing that noise pollution would allow their population set to do better and for other native species, which have been excluded from more urban areas, to maybe come back in.”
Within the Pod
The extent of our noise reaches far beyond what we might expect. In the ocean, noise pollution travels for miles and disrupts normal life.
“Sound travels really well in water—far and fast,” says John Ryan, a biological oceanographer at the Monterey Bay Aquarium Research Institute (MBARI). “So nature has evolved to take advantage of that transparency of the ocean to sound.”
Marine animals tend to rely on sound more than other senses. Noise pollution from boats, military activity and oil exploration limits their communication, navigation and hunting.
“It can shrink their world,” says Ryan.
He and collaborators from around Monterey Bay monitor an underwater microphone placed almost 3,000 feet below the surface of the Monterey Bay National Marine Sanctuary. They noticed a significant drop in low-frequency noise during the pandemic compared to other years—likely due to reduced shipping.
“We’re in the middle of a sanctuary, and these ships never get very close to our recorder. But we heard the changes crystal clear,” says Ryan.
As the world re-opens, the researchers are watching the clamor ramp back up. This past spring, shipping noise was even louder than pre-pandemic levels.
“Things tend to oscillate before they settle back into typical,” says Ryan. “We had the drop, we had the rise, we’ve had the overshoot—and theoretically, it will settle into typical.”
These recordings are helping scientists study how noise pollution affects the stress levels of whales. Through the pandemic, researchers at UCSC took small blubber samples from humpback whales in Monterey Bay to test their stress hormones. The samples are about the size of a pen cap and don’t harm the whales.
The scientists will collect the same information over the next year and compare hormone levels. They expect to see the drop in noise pollution corresponding to less stress. In quieter oceans, animals don’t have to work as hard.
“It may be that with more noise in the environment, the amount of information that gets exchanged between you and other animals gets diminished,” says Ari Friedlaender, an ecologist at the Institute for Marine Sciences at UCSC who leads the project. “And that might mean that your social interactions might change.”
The ruckus we make usually doesn’t kill animals directly. “But if it means that you don’t reproduce as frequently or you’re not as healthy, then your population may suffer as a consequence,” says Friedlaender.
Both Ryan and Friedlaender hope for quieter solutions that won’t push people out of the water.
“What I don’t want our research to ever sound like it’s doing is putting blame on people and telling people how to change what they’re doing,” says Friedlaender. “What I’d rather have come out of this is showing that if we can do things that make the ocean a quieter place, it can be a positive for the animals that are out there.”
Healthier marine ecosystems means more opportunities for people to interact with ocean life, he explains.
“It doesn’t necessarily mean less people on the water and fewer boats. It might just mean, ‘Let’s come up with a quieter way to be on the ocean,’” he says. He uses electric cars as an example of quieter transportation.
Ryan offers a few other ideas: “Slow down ships. Change ship design. Move to fewer, larger ships, maybe that put out even lower frequency sound—below the communication channel of the animals.”
Many of the solutions for reducing our noise footprint already exist. And in addition to helping wildlife, these changes could also benefit people.
“Biodiversity enriches our lives in so many ways that we can see, and in some ways we cannot see immediately unless we look more deeply,” says Ryan.
During the anthropause, many people rediscovered the life in their own neighborhoods.
“With reduction of noise levels, it wasn’t just the animals that were benefiting,” says Derryberry. Noise pollution drives up stress and anxiety in humans, too. Quieter streets, skies and seas could lead to better sleep and better mental health.
“There’s a lot of things about the anthropause that were horrible,” says Derryberry. “But I think we also learned a lot about how we can change some of the ways that we operate.”