In a typical spring, nesting seabirds – and human seabirds – flock to Stora Karlsö, an island off the coast of Sweden.
But in 2020, the Covid-19 pandemic canceled the tourist season, reducing human presence on the island by more than 90 percent. With people out of the picture, bald eagles came in and became much more abundant than usual, researchers found.
That may seem like a neat parable about how nature recovers when people disappear from the landscape – if it’s not that ecosystems are complex. The newly numerous eagles flew repeatedly along the cliffs where a protected population of guillemots laid their eggs and washed the smaller birds off their ledges.
In the commotion, some eggs tumbled off the cliffs; others were grabbed by predators while the guillemots were gone. The breeding performance of the guillemots dropped by 26 percent, Jonas Hentati-Sundberg, a marine ecologist at the Swedish University of Agricultural Sciences, found. “They flew away in panic and lost their eggs,” he said.
The pandemic was and remains a global human tragedy. But for ecologists, it was also an unparalleled opportunity to learn more about how humans affect the natural world by documenting what happened when we abruptly parted ways with it.
A growing body of literature paints a complex portrait of the slowdown in human activity that has come to be known as the ‘anthropause’. Some species have clearly benefited from our absence, in line with early media stories that nature was finally healing, with no humans around. But other species struggled without human protection or resources.
“Humans play this dual role,” said Amanda Bates, an ocean conservation scientist at the University of Victoria in Canada. We are, she said, “threats to wildlife, but we are also guardians of our environment.”
The research has useful lessons for conservation, scientists say, suggesting that even modest changes in human behavior could have disproportionate benefits for other species. Those shifts may be especially important to consider as the human world comes back to life and summer travel increases, potentially generating an “anthropule” of intense activity.
“A lot of people will feel like they want to catch up on vacation trips, work trips, and life,” says Christian Rutz, a behavioral ecologist at the University of St Andrews who introduced the concept of an “antropulse” in a recent paper. (He and Dr. Bates were also part of the team that came up with “anthropause.”)
“People will and should travel and enjoy nature,” he added. “But I think it could be very subtle adjustments to how we do things that can still have a huge impact.”
When the pandemic hit, many human routines came to a sudden halt. As of April 5, 2020 — the peak of pandemic lockdowns — 4.4 billion people, or 57 percent of the planet, were under some sort of movement restriction, scientists estimate. Driving decreased by more than 40 percent, while air traffic decreased by 75 percent.
These sudden shifts have allowed researchers to distinguish the effects of human travel from the many other ways we shape the lives of other species.
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“We know that humans affect ecosystems by changing the climate. We know that they have dramatic consequences from changing land use, such as demolishing habitats and building shopping malls,” said Christopher Wilmers, a wildlife ecologist at the University of California. Santa Cruz. “But this kind of stripping all that away, saying, ‘Oh, well, what are the effects of human mobility itself?'”
With people holed up in their homes — cars stuck in garages, planes in hangars, ships in docks — air and water quality improved in some places, scientists found. Noise pollution has decreased on land and under sea. Human-disturbed habitats began to recover.
In March 2020, Hawaii’s Hanauma Bay Nature Preserve, a popular snorkeling destination, was closed and closed for nearly nine months. “The pandemic has zeroed in on visitor impact,” said Ku’ulei Rodgers, a coral reef ecologist at the Hawai’i Institute of Marine Biology.
Without swimmers kicking up sediment, water clarity improved by 56 percent, Dr. Rodgers and her colleagues. Fish density, biomass and diversity increased in waters previously thick with snorkelers.
Indeed, scientists found that many species had moved to new habitats as pandemic lockdowns changed what ecologists have sometimes called “the landscape of fear.”
“All animals, you know, try not to die,” said Kaitlyn Gaynor, an ecologist at the University of British Columbia. That survival instinct drives them to keep their distance from potential predators, including humans. “We’re noisy and new and like their predators — and in many cases, that’s their predators,” said Dr. gaynor.
For example, the mountain lions that live in California’s Santa Cruz Mountains tend to stay away from cities. But after local ordinances went into effect in 2020, the animals were more likely to select habitats on the outskirts of the city, Dr. Wilmers and his colleagues.
dr. Wilmers speculated that the cougars were responding to changes in the urban soundscape, which could usually be filled with human chatter and the rumble of passing cars. “But once those audio stimuli are gone, the animals say, ‘Well, we might as well go and see if there’s anything to eat here,'” he said.
Just north, in a newly hushed San Francisco, white-crowned sparrows began to sing more quietly, but the distance they could communicate “more than doubled,” researchers found.
The birds also began to sing at lower frequencies, a shift associated with better performance — and an improved ability to defend territory and chase mates. “Their songs were much ‘sexy,'” said Elizabeth Derryberry, a behavioral ecologist at the University of Tennessee, Knoxville and author of the study.
“And it was at night,” she added. “That gives you hope that if you reduce the noise level in an area, you can have a positive impact right away.”
But the effects of human absence were nuanced, varying by species, location and time.
Multiple studies have shown that as traffic decreased in the spring of 2020, the number of wild animals hit and killed by cars decreased. But the number of collisions between wildlife quickly rose again, even as traffic remained below normal levels, a team of researchers reported.
“There were more accidents per mile driven during the pandemic, which we interpreted as changes in animals’ use of space,” said Joel Abraham, an ecology graduate student at Princeton University and an author of the study. “Animals started using roads. And it was hard for them to stop, even when the traffic started to pick up.”
The fences appeared to encourage some invasive species, increasing the diurnal activity of eastern cottontail rabbits in Italy, where their rapid expansion could threaten native hares, while disrupting efforts to control others. For example, the pandemic delayed a long-planned project to kill giant, predatory mice off Gough Island, a critical habitat for endangered seabirds in the South Atlantic.
The mice, which probably arrived with 19th-century sailors, attack and feed on live bird chicks, often leaving large open wounds. “I nicknamed them ‘vampire mice,'” said Stephanie Martin, environmental and conservation policy officer for Tristan da Cunha, the archipelago of which Gough Island is a part. Many chicks succumb to their injuries.
When the pandemic hit, scientists would embark on an ambitious attempt to eradicate mice, delaying the project by a year. In the intervening breeding season, with the vampire mice still rampant, not a single MacGillivray’s prion chick — an endangered bird that breeds almost exclusively on Gough — has survived. “We’ve lost a very different breeding season,” said Ms. Martin. “It meant another year without a boy.”
It’s another illustration of humanity’s dual role: the mice are only on Gough because humans brought them there. “But now we definitely need people to get them out,” said Dr. Bates.
These kinds of effects piled up around the world, she said, as local conservation, education and monitoring programs were disrupted or failed to fund. Peaks in wildlife poaching and persecution, as well as illegal logging and mining, have been reported in multiple countries.
Economic uncertainty may have caused some of this activity, but experts believe it was also made possible by deficiencies in human protection, including fewer staff in parks and nature reserves and even the absence of tourists, whose presence would typically discourage illegal activity. .
“We’re not quite the bad guys,” said Mitra Nikoo, a research assistant at the University of Victoria. “We actually do a lot more good than we give ourselves credit for.”
As people resume their normal routines, researchers will continue to monitor nature and ecosystems. If an ecosystem that seemed to benefit from the disappearance of humanity suffers when humans come back, that will provide stronger evidence of our impact.
“It is this reversal of the experimental or semi-experimental intervention that enables scientifically really robust insights into how environmental processes work,” said Dr. rutz.
Understanding these mechanisms can help experts design programs and policies that channel our influence in a more thoughtful way.
“If we then strengthen the role of custodians and then continue to regulate the pressure, we can really tilt the role of humans in the environment to an overwhelmingly positive one,” said Carlos Duarte, a marine ecologist at King Abdullah. University of Science and Technology. in Saudi Arabia.
For example, a team of researchers found that with vacationers not traveling to the Greek island of Zakynthos in the summer of 2020, the loggerhead turtles nesting there spent more time close to shore in the warmer waters optimal for female egg development. than they had in previous years.
The results suggest that tourists herd sea turtles in cooler waters, delaying egg development and possibly reducing the number of clutches or batches of eggs the animals lay during the short breeding season, said Gail Schofield, a conservation ecologist at Queen Mary University of London and a study author.
“It’s a very small chance,” she said.
Stopping all tourism is not possible, she acknowledged. But designating a stretch of coastline as protected habitat for turtles and banning swimming there in early summer could provide an important sanctuary for the animals, she said.
When the Hanauma Bay Nature Preserve reopened in December 2020, it instituted a strict new limit for daily visitors. It’s now closed two days a week, more than one before the pandemic, said Dr. Rodgers.
Other changes could also pay off, experts said: Building wildlife crossings over highways could prevent some wildlife from being killed on the road, while mandating quieter car engines and boat propellers could curb noise pollution on land and at sea .
“No one can say anymore that we can’t change the whole world in a year because we can,” said Dr. Bates. “We did.”