COVID-19 lockdowns have been hard on us all. But not on the birds, a new study finds. From March to May 2020, common species such as the ruby-throated hummingbird and bald eagle became more abundant in cities and suburbs across North America. With major roads and airports unusually quiet, they apparently enjoyed the respite from human commotion.
“The results point out how much of an impact noise and human activity can have on what habitats are usable by birds, both during breeding and migration,” says Jennifer Phillips, a behavioral ecologist at Texas A&M University, San Antonio, who was not involved in the study. The new work, she says, suggests many bird species would benefit from less noise pollution and fewer human disturbances.
The COVID-19 lockdown in the United States—when offices and schools were shuttered in many cities—led to declines in vehicle traffic and other human activity. The drop was so pronounced that scientists dubbed spring 2020 the “anthropause.” Around the world, it became a kind of natural experiment, an opportunity to study how nature might respond if human disturbances were reduced even after the pandemic. Researchers have already shown the quality of birds’ songs improved when they didn’t have to compete with the noise of traffic. But the larger patterns of impact—for many species over vast areas—wasn’t known.
Michael Schrimpf, a conservation biologist at the University of Manitoba, and colleagues now report how the lockdown changed habitat use by bird species across Canada and the United States. To study bird populations at this scale, they turned to data from eBird, a citizen science project run by Cornell University’s Lab of Ornithology that collects and analyzes observations by mostly amateur birders. The scientists studied 4.3 million sightings of birds in counties that have both major roads and an international airport. They focused on 82 relatively common species, like robins and blackbirds. As a proxy for traffic, they examined pooled data sets of cellphone locations that showed where drivers were going.
When the researchers compared records from March to May 2020—when the lockdown was at its height—with those from the same period in 2017, 2018, and 2019, they found that 80% of bird species had changed their whereabouts. Overall, many species were more likely to be observed in cities and urban areas than before the lockdown, the team reports today in Science Advances.
Bald eagles were about one-third more likely to be seen in cities where traffic had declined by 17% or so, for example. Some species increased their abundance by 50% as far as 10 kilometers from airports. And ruby-throated hummingbirds became three times more likely to be observed within 1 kilometer of airports, which means they might have expanded their habitat.
“These are really, really large changes,” says Nicola Koper, a conservation biologist at Manitoba who led the research. “These are probably the strongest impacts I’ve ever seen.”
It’s not easy to translate bird spottings to the abundance of a species in a particular location. But the scientists, including experts at the Lab of Ornithology, carefully scrubbed the data to remove possible biases, such as observations from beginner birders. They also concluded through statistical tests that increased sightings probably didn’t happen simply because birds were easier to see or hear during the lockdown. “They did a really good job of exhaustively analyzing [the patterns],” says Scott Loss, a conservation ecologist at Oklahoma State University, Stillwater.
The lockdown had a particularly large impact for migratory birds, the authors say. Species migrating during this period showed up in urban areas in greater numbers than in previous years. That could mean birds had more choices for their migratory “rest stops,” which are important to surviving long journeys.
Most species increased their use of human landscapes during the lockdowns, a net positive, Koper says. However, some animals responded to the lockdown in complex ways. Red-tailed hawks, for example, were seen more frequently in cities, but they weren’t seen as often near major roads. That might be due to less road-killed wildlife to feed on, Koper says.
It will take more research to determine whether the changes were driven by less noise, fewer collisions with vehicles, or other factors, Koper says. For some species that became less common near roads, such as red-winged blackbirds, it’s possible that lighter traffic might have enabled their predators easier access to them and their nests, Koper says. And one familiar city dweller—the rock pigeon—showed no apparent change in abundance during the lockdown.
A key lesson from the work, Koper says, is that even though the species in the study may appear to be well adapted to human landscapes, they have been displaced from many suitable habitats. That’s clear because they expanded their range during the lockdown. Endangered species could be even more sensitive to human activity, but the team did not have enough data to study them.
The researchers plan to adapt their methods to look at the effect of the lockdown on at-risk species with fewer observations in eBird. Meanwhile, Koper says that although habitat protection remains the most vital task for protecting birds, the new findings suggest reducing human disturbance can help, too. Telecommuting can lower the amount of vehicle traffic, and noise can be reduced by sound barriers along highways. Phillips says this could help increase bird diversity and abundance in urban areas. “We as a society just have to be willing to change and not just go back to ‘normal.’”