What started as a lone blip on a map in the Far East nearly three years ago mired into a world overcome with red dots. The novel coronavirus was suddenly everywhere, a reflection of the kindred creatures and delicate symbioses that exist across Earth’s ecosystems.

It was only a matter of time before COVID-19 would shut off the music through its quarantines and lockdowns, pressing pause on the soundtrack to bustling economic activity. While many retreated in their homes, nature’s menagerie of life seemed to occupy new — or perhaps pre-anthropogenic — spaces.

Even if just temporarily.

“Animals are pretty plastic when it comes to changes in human activity,” said Christopher Schell, an assistant professor of environmental science, policy and management, or ESPM, at UC Berkeley. “Their behavior is wholly dependent on how we operate and how predictable we are.”

As the volume was lowered on energy-intensive sectors, greenhouse gas emissions waned. The campus Renewable & Appropriate Energy Laboratory, or RAEL, reported a 5.4% global reduction in carbon dioxide emissions in 2020 compared to 2019, which is five times larger than the annual emissions decline that occurred at the peak of the 2008 Financial Crisis.

With people confined to their homes, changes in the ground transportation sector contributed most to the decrease in emissions, followed most significantly by international aviation and power generation, according to a RAEL study.

The United States contributed most to the global decline, experiencing an estimated 9.4% reduction in greenhouse gas emissions from the pandemic. Since then, emissions have returned to normal, according to campus energy professor and founding director of RAEL Daniel Kammen.

Though the pandemic’s lull in industrial activity amounts to mere seconds in ecological time, it provided a dress rehearsal of the potential glimmers of life amid more stringent climate legislation.

At the very least, it showed what the world stands to lose if emissions continue unabated.

“COVID-19 has been a lesson in the need for collective action. No one country can solve COVID, and no country can isolate itself forever from these global pandemics, or threats,” Kammen said in an email. “We are only as secure as the most vulnerable globally — to COVID-19 and to climate change.”

The pandemic’s avian opera 

Over the hum of human chatter and rumble of ceaseless traffic in the Bay Area, white-crowned sparrows are trilling overhead.

Ranging from low frequencies of about 2,000 hertz up to 6,000 hertz — a range audible to humans — the birds’ songs are complex, warbling implausible melodies to defend territories or attract mates, according to Jennifer Phillips, assistant professor of biology at Texas A&M University San Antonio.

Amid the backdrop of constant background music from human life, the birds have had to adjust their singing to a higher pitch, producing “less sexy” songs, Phillips said. Rather than invest energy into conveying information about their vocal performance ability to potential mates and neighbors, white-crowned sparrows have had to triage, compromising their low, seductive register to simply be heard at all.

But during the world’s intermission from commuting and polluting, white-crowned sparrows filled the silence with low frequency and evermore complex trills, producing higher-performance songs, according to Phillips.

It was as though the pandemic muted the Bay Area as noise in 2020 decreased to a level that hadn’t been heard since the 1950s, Phillips noted. The Golden Gate Bridge, often flocked with tourists and notorious to Phillips as one of her loudest research sites, decreased to the same noise level as Point Reyes National Seashore, a remote expanse of protected coastline 50 miles north.

Armed with her digital recorder, Phillips frolicked through scrub habitat across the Bay in search of white-crowned sparrows to assess how the birds were responding to the soundscape reversion.

In collaboration with an array of ecologists, she found that the birds quickly filled the newly emptied acoustic space, illustrating the plasticity of behavioral traits. Beyond singing more softly, the birds produced more effective songs because the frequency of noise from human traffic occurs in a range that interferes with the highest performance bird songs, according to a 2020 study published in Science.

As door crevices spun cobwebs and car keys collected dust, male sparrows began singing in a wider range of pitches, according to the study. This increased frequency bandwidth conveys more information to females and males alike.

“All of a sudden, the birds could now have a much greater communication distance and get the attention to hopefully attract more females or kick out more guys from their territory because they could actually be heard,” Phillips said.

In her flurry of discoveries, Phillips was surprised to learn that the birds performed more optimally in 2020.

As close-ended learners, white-crowned sparrows are only able to learn and practice songs during their first year of life. After this window of time, their song is crystallized and the birds can no longer adjust their repertoire of mastered trills, Phillips said.

“So the question is, did these higher performing birds adapt on the fly?” Phillips posited. “Or was it that now that it was quiet, the tougher, stronger males could outcompete the males with higher pitch songs and kick them out to take over their newly quieted territories?”

Like most inquiries into nature, the answer remains buried in the environment’s treasure trove of secrets unbeknownst to humans. What this means for now is that white-crowned sparrows may not be as close-ended as previously thought, Phillips said.

In the pandemic’s twilight, noise has crescendoed, but it’s not nearly as loud as it was prior to the public health crisis, Phillips remarked. She still frequents the Bay Area with her microphone, collecting song recordings to monitor the long term change in performance.

In an evolutionary context, if unfettered anthropogenic noise returns and white-crowned sparrows can’t be heard, natural selection may favor birds that are louder but not necessarily better performers, Phillips said. It would take a reprise of generations to see any population-level effect, but if songs are completely drowned out by humans and birds reach their energetic limits, certain species face permanent erasure from noisy habitats.

“The greatest lesson from the pandemic is that if we try, we can actually reduce our impact on nature quite a bit. If we take action on noise and fossil fuel pollution, we can make a difference in having urban spaces be suitable for wildlife,” Phillips said. “You can enjoy nature even in the city.”

The Bay’s symphony of the sea

In a region awash with new arrivals and permanent residents, the San Francisco Bay is bubbling with seasonal whales and longer faring dolphins and porpoises.

Over the past few decades, cleanup efforts in the Bay have led to an influx of visits by gray and humpback whales along their yearly migrations. The clearer water has also become a home to harbor porpoises and bottlenose dolphins, according to Samantha Cope, a researcher at the Anthropocene Institute.

As a highly urbanized estuary, however, the Bay is an active site for commercial shipping, ferry service and recreational traffic.

“The San Francisco Bay is a complex place compared to the open ocean; we have a whole entire spectrum of boat types,” Cope said. “Having a kayaker within a mile of a large tanker carrying oil is something that you don’t see in a lot of other places.”

This surface activity contributes significant noise that drowns out marine animals’ underwater orchestra, according to a 2021 study led by Cope.

Traveling farther than light and quicker than sound in the air, sound underwater is an essential sensory signal for marine animals. From dolphin whistles and porpoise clicks to the more intricate songs of baleen whales, marine mammals use sound to communicate, navigate, forage, find mates, defend territories and warn each other of predators.

But as fishing, shipping and infrastructure development have increased, the oceanic soundscape has been filled by the sounds of human activity, placing marine animals in peril as they may struggle to find food, reproduce and sense oncoming danger.

“If the overall sound is loud, they might have more difficulty detecting a vessel coming toward them,” Cope said. “Especially in the San Francisco Bay, all of the sound is really a concern for masking and making it more difficult for them to hear their surroundings.”

Large commercial ships are required by law to broadcast vessel and voyage information via the Automatic Identification System, or AIS, which is then used to create models assessing noise pollution in cetacean habitats, according to the study. However, with a minimum vessel size requirement for AIS data transmission, smaller recreational boats often go ignored — though not unheard.

As the number of registered vessels continues to grow, so does the risk of underestimations of the volume of anthropogenic noise in urbanized areas.

To present a more instrumental account of the Bay’s soundscape, capturing the cello of human voices and calliope of ship horns, Cope and her colleagues used the Marine Monitor (M2), a system that uses radar to autonomously track vessels of all sizes.

As expected, the largest ships in the bay were the loudest, but Cope was surprised to learn that high-speed ferries were the biggest noise polluters by area. On average, large vessels made 11 transits throughout the study area per day compared to 58 transits by ferries, according to the study.

“When we looked at sound over time, because there are so many ferries that criss-cross the Bay, they actually contributed the most sound over time,” Cope said. “That’s directly related to human activity because those are everyday humans riding the ferries.”

Though the ferries make many journeys across the bay, small recreational boats use the area more dynamically as they’re going in all different directions, Cope said.

The level of noise exposure from recreational boats, primarily tracked by radar as opposed to AIS, covered about twice as much area as that from larger commercial ships that have well-defined transit pathways.

“Those small recreational boats, they don’t have any restrictions,” Cope said. “They’re going everywhere.”

The study, relying on vessel data from 2018, predated the pandemic, but Cope noted that stay-at-home orders and the accompanying suspension of ferry service turned down the volume knob on the Bay’s human radio.

When San Francisco’s humming cable cars remained parked and boat engines no longer buzzed, the quiet rolling through the Bay’s foggy hills prompted Cope to recall a study from a decade past on whale stress following the 9/11 terrorist attacks. Conducted in Canada’s Bay of Fundy, the researchers found that the lull in ship noise after 9/11 eased right whales’ stress-hormone levels.

Time will tell if the months of lockdown yielded any similar results linking noise pollution to animal stress. One silver lining from the world’s recent dormancy, Cope said, is that scientists can look back at data to assess what things look like — and sound like — when humans are not present.

“Situations like the pandemic provide interesting opportunities to observe changes in animal behavior,” Cope said. “It’s really difficult to say we’re going to stop ferry service for three months, it’s just not something that happens in the status quo type of world.”

To protect the world’s marine fauna from their noisy cohabitants, management measures must be adaptive, Cope said. In the age of climate change, animal ranges and distributions are changing, rendering noise quotas fixed by location less effective as animals may be moving out of those unsuitable habitats.

The pandemic was a reminder that life is not static, Cope added. As new insights are uncovered and situations change, mandates and quarantines must evolve.

With climate change still in its verse and building to a chorus, Cope hopes humans can remain nimble in adapting management legislation.

Rewriting the music 

After people’s doors creaked closed and locks clicked tight as they prepared for quarantining, nature seemed to beckon humans. Local park visitation rose as green spaces were perceived to be “beacons of freedom,” Schell said.

In this wave of people discovering their neighborhood’s secluded edens, researchers like Schell became interested in teasing apart the effects on wildlife. What they’ve found is that in some instances, species will shorten their hours of activity or become more nocturnal to avoid humans.

Beyond behavioral changes, the city itself can cause genetic changes in animals, Schell said, favoring traits that confer greater survival in dealing with the omnipresence of humans.

“Everything is connected, nothing is siloed and if we think it isn’t, we’re sadly mistaken,” Schell said.

As people press play on their post-lockdown playlists and waste no time in booking their next vacation, the opportunity for nature to recover without humans is becoming ever more elusive. Some may forget the toll of their actions; how every chord they strike adds to the melody of climate change.

As COVID-19’s virulence reached new octaves and inflation rates soared, people started shelving their climate worries, said Christopher Jones, a lecturer at the Haas School of Business and director of CoolClimate Network, a university-government-industry partnership at UC Berkeley. But the pandemic and economic crisis are temporary forces, while climate change continues simmering in the background, he noted.

“I have a bit of a fear that the new generation is going to think that the world in which we’re starting to live in is normal,” Jones said. “It may be normal for Californians to have a long fire season and smoke and power outages, but that’s not normal and it’s just getting worse.”

In the long run, any pulse or pause in human activity isn’t going to significantly affect the climate, so the focus should be on creating economic and policy incentives to change people’s behaviors and facilitate mass change, Jones said.

Every person can harp on their own creative potential to make a meaningful contribution to address climate change, but there must be a change in people’s perception of the climate, Jones noted. Many just throw their hands up and claim nothing can be done, but if everyone used their fingers to tickle the world’s ivories, Jones said people could rewrite the song of climate change.

A singer on their own can only carry a note so far, but a choir has the ability to drive demand for the technologies that reduce emissions, thus making those cheaper, he added.

“Any individual change really doesn’t add up to very much, but if we do it collectively it does make a big difference and it also increases people’s belief in their ability to create meaningful change,” Jones said. “Ultimately, that’s what’s needed in order to address climate change at scale.”