Crows Are Taking Over American Cities

Every night as dusk falls in Portland, Oregon, the sky fills with birds. While workers make their way from the city center toward their homes, crows leave the suburban lawns where they’ve spent the day picking for grubs to fly downtown. They swirl across the river in large groups, cawing as they go. A community science project recently recorded 22,370 crows spread out downtown—about twice as many as the number of people who lay their heads in that neighborhood.

Across North America, crow populations have been declining for decades. But crows appear to be flocking to cities more than ever before. Cities from Sunnyvale, California, to Danville, Illinois, to Poughkeepsie, New York, host thousands of crows each winter. Some popular urban roosts host more than 100,000 crows each night.

Crows are territorial during the spring and summer breeding season, but during the rest of the year, they sleep in large groups known as roosts. Sometimes a roost occupies a single tree; sometimes it’s spread over multiple perching sites—usually flat roofs or treetops—in a consistent area. Roosting has clear advantages for crows, especially during winter. “They’re better off being in a big group, where they get the benefit of all those eyes looking out for danger. It’s also warmer,” John Marzluff, the author of Gifts of the Crow, told me.

[From the June 2020 issue: Why birds do what they do]

City roosts offer even more advantages. The very features of urban life that harm other species—fragmented landscapes, bright lights at night, and open stretches of grass in parks—benefit crows. Lights make it easier to spot predators, such as owls. Grass doesn’t offer much in the way of food or shelter for many animals, but crows will happily dig through it for beetle larvae and other snacks. Also, Marzluff told me, crows like that we humans often plant grass close to clusters of trees, where they can sleep or nest, and other food sources, such as our trash. Fragmented habitats, such as a group of trees in a park surrounded by asphalt, harm other species because they aren’t big enough to foster genetic diversity. But they are ideal for crows, who can fly between pockets of greenery and like to have a variety of options for their nesting areas and foraging sites.

Crows, in other words, move to urban areas for the same reason humans do: Cities offer just about everything they need within flapping distance. During the breeding season, Marzluff said, crows even decamp to the suburbs to raise their families, just like humans. And once even small roosts are established, many of them grow year after year, from perhaps a few hundred birds to a few hundred thousand. News spreads fast through the crow community, Marzluff said: Crows share information with one another and develop traditions and culture within populations, including roosting habits, though scientists still don’t know exactly how they do it.

The bigger the roost, the bigger the mayhem it leaves behind come morning. Walking around any urban crow roost, it’s easy to see where the birds perched the night before: White droppings dot the ground, benches, parking meters, and cars whose owners were foolish enough to park them overnight under a group of sleeping crows. (At least the birds are relatively quiet while they’re sleeping, saving the loud caws for twilight.) “The crows are exciting. Their messes are not,” says Sydney Mead, the director of downtown programs for Downtown Portland Clean & Safe, the organization that cleans up the neighborhood after urban wildlife such as crows.

[Read: Crows are doing the best they can]

When the Portland roost was smaller, Mead’s organization kept the sidewalks clean with a combination of power-washing and a scrubbing device called the Poopmaster 6000. But the local businesses Clean & Safe represents don’t think that’s enough anymore. For seven years, the group has employed a team of falconers to “haze” the crows with Harris’s hawks. The raptors chase crows away from the downtown core and toward green spaces where, as Mead puts it, “their interaction with humans and our infrastructure is more tolerable and manageable.”

Hazing is one of the more humane methods used to control urban crow populations, John Griffin, an urban-wildlife expert for the Humane Society of the United States, told me. But it’s still controversial among some bird advocates because it interrupts the birds’ natural activities and causes them to use unnecessary energy fleeing the raptors. Griffin told me that some cities still rely on bird pesticides such as Avitrol to control crows. The chemical acts on crows’ central nervous system and sends the birds into convulsions, scaring the rest of the flock. (Although the company that makes it insists that Avitrol’s purpose isn’t to kill birds, it can be deadly and its use has resulted in reports of numerous dead birds falling out of the sky.) Other cities have had luck dotting their downtowns with effigies—sometimes already-dead crows provided by wildlife services, but usually an upside-down, crow-shaped object—that make crows want to spend their time elsewhere. “You can get a pretty good Halloween crow on Amazon,” Griffin said.

Effigies or the death of a flock member can keep crows away from an area for the same reason that crows come together to roost at all: They are social and highly intelligent creatures. In a study Marzluff co-authored at the University of Washington, where he is a professor emeritus, crows even recognized people who had been unkind to them in the past. They shared this information with other crows (adult and fledglings alike), which resulted in large groups of the birds congregating in trees to “scold” unsavory humans.

[Read: A journey into the animal mind]

Crows may also change their behavior in response to our kindness. Kevin McGowan, a crow expert at the Cornell Lab of Ornithology, told me that crows might be flocking to urban and suburban areas because humans have, in recent decades, been unusually tolerant of them. Before an amendment to the Migratory Bird Treaty Act passed in the early 1970s, people across the country regularly shot crows that appeared in locations where they weren’t wanted. (Some states still allow crow hunting during a short season.) Scaring them with hawks is certainly more polite than shooting them.

Some crow advocates would rather city dwellers stopped trying to rid themselves of crows at all, and simply embraced them. Gary Granger, one of the birders who tracks the size and location of the Portland crow roost, has been in talks with a local wildlife group to make viewing the crows’ nightly flight an educational event. Portland would join the University of Washington at Bothell, which holds an annual Crow Watch that invites the community to see as many as 16,000 crows meet and roost for the night. And around the country, many suburbanites, whose summer crows are territorial and tend to stay in one area, become attached to “their” birds. Marzluff noted that he’s heard from an increasing number of people who have close relationships with their neighborhood crows—for example, feeding them in the hopes of developing a bond or getting gifts in exchange.

As more and more animals lose their habitats and are forced into urban environments, cities are finding that urban wildlife can be not only a nuisance but also a draw. When Austin’s Congress Avenue Bridge was renovated in the 1980s and bats began roosting underneath it, people were scared of the mammals and worried that they would spread disease. Thanks to education and advocacy from bat lovers, they were allowed to stay. Today, watching a cloud of 1.5 million bats wake up and leave to go hunting at dusk is a major tourist attraction for the city.

[Read: TikTok told me to adopt a pigeon]

A few weeks ago, I met Granger in downtown Portland to watch the crows swirl in. As the birds cawed and rattled and cooed overhead, our conversation kept turning to all the things we still didn’t know about them. Why did they like the trees on certain blocks more than others? Why did they meet in a large group near the waterfront before sleeping in the city a few blocks away? We traded questions as the subjects of our inquiry headed downtown to the place they called home—at least for the night.