From hummingbirds to eagles, birds across North America flocked to once frenetic urban areas that had locked down in response to the Covid-19 pandemic, according to a new study based on millions of observations by amateur bird-watchers.
Populations of dozens of bird species rose significantly around city centers, major roads and airports apparently in response to the lull in human activity, a research team led by scientists at the University of Manitoba in Winnipeg found. Some species were as much as 14 times more numerous during the lockdowns than before pandemic restrictions were imposed.
“I am shocked at the fact we saw so many changes in bird behavior,” said Nicola Koper, a conservation scientist at the university and senior author of the study. “All birds are way more sensitive to human disturbance than we had really realized. Once we reduced traffic, we got almost immediate movement of birds into these landscapes.”
The findings were based on more than 4.3 million observations by thousands of birders in the U.S. and Canada, gathered through a citizen-science program managed by the Cornell University Lab of Ornithology called eBird. The sightings covered 82 species during the 2020 spring migration season, which coincided with large declines in human activity tied to the lockdowns. The researchers compared those observations with reports of bird populations before and after the lockdowns.
The research was published Wednesday in the journal Science Advances.
Pigeons appeared unaffected by the lockdowns, the scientists said. But American robins quickly moved into crowded urban areas and along roads they had previously shunned, and the number of ruby-throated hummingbirds seen near airports tripled, the researchers found.
Populations of bald eagles increased more in counties with strict lockdowns than in those with looser restrictions. The numbers of red-tailed hawks rose in city centers but fell slightly near roads, perhaps as a result of the reduced availability of roadkills for scavenging as road traffic eased.
Species of New World warblers and sparrows were observed in higher numbers, a finding the researchers called “particularly notable, as these two families account for nearly 50% of the 3 billion birds lost in North America since 1970.”
Ken Rosenberg, an ornithologist at Cornell who studies bird populations, said, “They are very responsive to positive change and that is a hopeful sign.” He wasn’t part of the project. “For nature, it has been a little bit of a reprieve. A population response by birds makes a lot of sense,” he said.
The 20 billion birds living or migrating in North America every year face a gantlet of human-related hazards, from nesting grounds and food sources lost to commercial or residential development to pet cats and pesticide use. Cats kill 2.4 billion birds annually, according to the Migratory Bird Center at the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service.
About 600 million birds die in the U.S. each year in collisions with buildings, especially glass-covered or illuminated skyscrapers, according to a 2019 study published in Frontiers in Ecology and Environment.
The new research suggests that minor changes to control road noise or residential lighting could bring immediate benefits to wildlife. “It’s clear that it would have very rapid effects,” Dr. Koper said. “We could have immediate benefits to many wildlife species, including the birds that we enjoy.”
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