Many birds flocked to cities during COVID-19 lockdowns

While viral posts about dolphins returning to the canals of Venice during the 2020 lockdowns were fake news, the “nature is healing” memes weren’t altogether wrong. Reduced human activity in spring 2020, following the outbreak of COVID-19, led to considerable changes in migratory patterns and habitat use for birds across the United States and Canada, according to a study published today in Science Advances.

In general, many birds seemed to have benefited from these lockdowns, spending more time within and around urban areas, according to the research. Some species which seemed to have most enjoyed the reprieve from human activity—or at least shifted closer to civilization—were warblers and native sparrows; osprey and bald eagles; and several species of ducks and geese.

The “anthropause,” as scientists have dubbed the abrupt slowdown of human movement during the first wave of lockdowns, has allowed researchers an unprecedented opportunity to see how animals behave with less interference from us.

“The pandemic created a unique—hopefully—opportunity to understand the effects of traffic separated from the effects of the human-altered landscape at a scale that would be impossible under any other circumstances,” says study author Nicola Koper, a professor of conservation biology at the University of Manitoba.

The results suggest many species respond quickly to even modest changes in human traffic—with important implications for conservation.  

Citizen science 

To gather enough data to draw meaningful conclusions, a team of researchers from the Cornell Lab of Ornithology and various Canadian universities needed boots on the ground across the continent. The researchers pulled data from the popular app eBird, a citizen science initiative led by the Cornell Ornithological Institute that allows birdwatchers to log what they see in a format that’s easy for educators, scientists, and other birders to access and analyze. 

The eBird app guides users through a checklist of birds they might see or hear in their area and how to gather data on time and location through the phone’s GPS. (As some Twitter users have observed, the eBird app is an ornithologist’s answer to a Pokédex, a database of Pokémon.) As the novelty of endless online streaming wore off and people turned from their screens to their windows, the spring lockdowns saw an explosion of fledgling birders—eBird’s survey collection soared 29 percent between January and September of 2020.   

But since the researchers needed to be sure their citizen scientists knew their grackles from their sapsuckers, the study only included surveys from people who had also logged springtime observations with eBird in the previous three years.

The researchers assessed data from every county in the United States and every census division in Canada that had three attributes: an international airport, a municipality of at least 50,000 residents, and at least 200 eBird checklists between March and May 2020. Even with those stringent requirements, nearly 89,000 eBird checklists—and 4.3 million observations of individual birds—qualified for the study from 2017 to 2020.  

Then, our avian friends’ movements were cross-referenced against our own, in the form of aggregate movement data provided by Google’s COVID-19 Community Mobility program, which tracked how much human activity was actually reduced in each county.

City bird, country bird 

Of the 82 bird species tracked in the study, 66 changed their behavior during the spring of 2020 compared to previous years.

The biggest “winners” of the pandemic—or, couched differently, the biggest losers under the status quo of typical human activity—were warblers and native sparrows. These species increased their use of human-altered habitats across the board, venturing closer to airports and major roads as flights were cancelled, and cars stayed home.

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That’s intriguing because “those two groups together represent a huge percent in the decline in the bird population,” Koper explains—nearly 50 percent of the 3 billion birds lost in North America since the 1970s. Anything we learn about making habitat hospitable for them is “inspiring for conservation management,” says Freda Fengyi Guo, a graduate student at Princeton who studies the stopover ecology of migratory birds and was not involved in the study.

At the opposite end of the spectrum, city birds like the rock pigeon and house sparrow didn’t seem to give a hoot about the reduction in human activity due to the pandemic. “They just didn’t seem to care one way or another,” Koper says. “They’re obviously perfectly happy in our cities.”

Two iconic birds of prey—osprey and bald eagles—seem to have intentionally sought out areas with less human hubbub. “They actually moved from counties where they would have been historically more abundant to the counties that had stronger lockdowns,” Koper says. “They sort of traveled up the whole U.S. through these routes, these potentially safer counties…hundreds or thousands of kilometers away from where they maybe normally were.”

As for red-tailed hawks, another common raptor, the study found these birds ventured into urban areas more often during lockdowns, but were less frequently spotted near major roads. One of the most dramatic changes was in observations of the ruby-throated hummingbird, which became three times more likely to be observed in proximity to airports. Koper theorizes the hummers may have been taking advantage of the opportunity to sip nectar from nearby residential gardens without the nuisance of planes overhead.  

Several species of ducks and geese also seemed to benefit considerably from the shutdowns, particularly when they coincided with the peak of their migrations. “We wouldn’t necessarily have expected that,” Koper says. “I think we see geese and ducks around human landscapes all the time, so we tend to think they’re very robust and resilient to humans.”

Bird Band-Aids and sustainable solutions 

Koper said she found the results of the study encouraging from a conservation and management perspective. “It took a very short period of time for birds to change their behavior,” she explains. “Within a couple weeks, you can see these trends.”

And while it certainly felt like a dramatic difference at the time, traffic was only reduced by an average of eight to 20 percent at the peak of lockdown—a relatively modest reduction in movement. “If, as a society, we decided to change our behavior to reduce our disturbance of birds in the landscape, we can have an effect and benefit them almost right away,” Koper says.

John Swaddle, a professor of biology and director of the Institute for Integrative Conservation at the College of William and Mary, describes the study as a “nice large-scale example” of the impacts of human activity on land use by birds. But he cautions, “shutdowns and large-scale exclusions of humans from the landscape are not sustainable solutions for the extinction crisis we are inflicting on the planet.” And efforts to mitigate noise or improve technology are “Band-Aids…treating symptoms rather than causes,” he says. 

Amber Roth, an assistant professor at the University of Maine who researches conservation solutions, adds that while it was lovely to spot a yellow warbler on campus during the 2020 lockdowns, “the noise and hustle and bustle of people in cities may warn away birds from risky situations that may put their lives at risk.”

The study authors agree that it’s too early to tell if the “anthropause” resulted in any substantive conservation gains for birds in general. In fact, the sudden return to normal human activity levels as lockdowns ended may have created “ecological traps” for birds that had chosen to nest in temporarily hospitable areas for the spring breeding season.

“Collisions with building windows, outdoor cats, elevated abundance of bird predators, and other factors may mean decreases in survival for birds venturing into the urban landscape and that likely remained as threats throughout the COVID-19 pandemic,” Roth explains. “More research is needed to understand the consequences of our urban human activities and to understand if attracting more birds to cities is a good thing or not.”