In a typical spring, breeding seabirds — and human seabird- watchers — flock to Stora Karlso, 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%. With people out of the picture, white-tailed eagles moved in, becoming much more abundant than usual, researchers found.

That might seem like a tidy parable about how nature recovers when people disappear from the landscape — if not for the fact that ecosystems are complex. The newly numerous eagles repeatedly soared past the cliffs where a protected population of common murres laid its eggs, flushing the smaller birds from their ledges.

In the commotion, some eggs tumbled from the cliffs; others were snatched by predators while the murres were away. The murres’ breeding performance dropped 26%, Jonas Hentati- Sundberg, a marine ecologist at the Swedish University of Agricultural Sciences, found. “They were flying out in panic, and they lost their eggs,” he said.

The pandemic was, and remains, a global human tragedy. But for ecologists it has also been an unparalleled opportunity to learn more about how people affect the natural world by documenting what happened when we abruptly stepped back from it.

A growing body of literature paints a complex portrait of the slowdown of human activity that has become known as the “anthropause.” Some species clearly benefited from our absence, consistent with early media narratives that nature, without people bumbling about, was finally healing. But other species struggled without human protection or resources.

“Human beings are playing this dual role,” said Amanda Bates, an ocean conservation scientist at the University of Victoria in Canada. We are, she said, acting as “threats to wildlife but also being custodians for our environment.”

The research has actionable lessons for conservation, scientists say, suggesting that even modest changes in human behavior can have outsize benefits for other species. Those shifts could be especially important to consider as the human world roars back to life and summer travel surges, potentially generating an “anthropulse” of intense activity.

With humans holed up in their homes — cars stuck in garages, airplanes in hangars, ships in docks — air and water quality improved in some places, scientists found. Noise pollution abated on land and under the sea. Human-disturbed habitats began to recover.

In March 2020, Hawaii’s Ha­nauma Bay Nature Preserve, a popular snorkeling destination, closed and remained shuttered for nearly nine months. “The pandemic reset the visitor impacts to zero,” 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%, Rodgers and her colleagues found. Fish density, biomass and diversity increased in waters that had previously been thick with snorkelers.

Indeed, scientists found that many species had moved into new habitats as pandemic lockdowns changed what ecologists have sometimes called “the landscape of fear.”

As people resume their normal routines, researchers will continue monitoring wildlife and ecosystems. If an ecosystem that appeared to benefit from humanity’s disappearance suffers when people come flooding back, that will provide stronger evidence of our impact.

Understanding these mechanisms can help experts design programs and policies that channel our influence more thoughtfully.

When the Hanauma Bay Nature Preserve reopened in December 2020, it instituted a strict new cap on daily visitors. It is now closed two days a week, up from one before the pandemic, Rodgers said.