Caws and effect: Penn State wildlife scientists study urban crows

Melissa Beattie-Moss
May 19, 2010

“I think of them as flying monkeys, because they’re so smart,” Grant Stokke tells me, as we zip along the back roads of Lancaster County, Pennsylvania on a March afternoon, our eyes scanning the skies.

The flying monkeys in question? Those famously adaptable, inventive black birds that inspired the Reverend Henry Ward Beecher to once quip, "If men had wings and bore black feathers, few of them would be clever enough to be crows.”

In 2006, Stokke, a graduate student in the School of Forest Resources, and his adviser Margaret Brittingham, professor of wildlife resources, were tapped by the Pennsylvania Department of Agriculture to help develop a multifaceted approach to reducing Lancaster’s crow problem. They joined forces with Michael Avery and other biologists from the USDA’s Wildlife Services National Wildlife Research Center and local Wildlife Services biologists who were developing and testing techniques to move crows to more suitable roosting sites. Brittingham and Stokke spearheaded a crow behavior study titled “Ecology and Management of Urban Crows in Pennsylvania” that has brought Stokke to suburban Lancaster County for the past two winters to trap, tag, and track crows.

The cleverness of these familiar birds may have contributed to “the crow problem” Brittingham and Stokke are researching. North American crows are partially migratory, meaning that birds born north of New York State generally head south each winter. Pennsylvania is the year-round home to a resident crow population and the winter destination for migrant crows from Canada.

Twenty years ago, huge wintertime crow roosts—evening gatherings in the tens of thousands—would typically be found on the outskirts of agricultural cities, such as Lancaster. Over the years, explains Brittingham, as shopping centers and housing developments sprawled outwards, what was once the edge of town “is now the roof of a shopping mall.” Adds Stokke, “Once the crows got into the city, they realized ‘Hey, these are pretty good places to be.’ By roosting in urban areas at night, they’re protected from their main predator, the great horned owl; they’re well-lit so they can see each other and chat and move around at night; it’s warmer. The crows know a good thing when they’ve got one. Natural selection favors the city dwellers.”

Human city dwellers, on the other hand, favor being able to conduct holiday shopping without confronting the noise and droppings of twenty thousand crows roosting above their heads, as was the case in Lancaster’s Park City Mall a couple years ago. When store owners blamed a slow shopping season and damage to roofs on the birds, that was the final straw for Lancaster city officials who had put up with the crows’ raucous caucus for years.

But quick fixes to this complex issue are hard to come by. Harassment techniques such as noisemakers, shooting blanks, and distress calls only scared the birds away temporarily. Poisoning the birds didn’t work very well and angered some community members who formed the Lancaster County Crow Coalition to advocate for “non-lethal and environmentally sound solutions” to the crow problem.

Understanding the birds’ behavior is key to finding workable solutions, say Brittingham and Stokke. “Where are they coming from? How long do they stay? How are they responding to different management practices? What roost site characteristics do they prefer? The more we know about them, the better we’ll get at figuring out how to co-exist with them.”

Stokke and Brittingham use radio telemetry and regular monitoring of roosts to gather data on the crows’ movements and survival. To date, they’ve trapped fifty crows and equipped each with “a little backpack” holding an antenna and radio with a distinct frequency which allows the researchers to track them over wide areas of southeast Pennsylvania. Stokke and Brittingham also gather data by conducting pre-dawn roost counts, with the help of volunteers.

“This is an example of science and communities working together to help a species,” says Brittingham. “This is as much of a people issue as a wildlife issue.”

“Or more so,” adds Stokke. “People ask me all the time ‘Why are you bothering to tag and count these crows? Why don’t you just trap ‘em and get rid of ‘em?’”

“We’re never going to completely solve ‘the crow problem,’” concludes Brittingham. “But do we really want to? These birds are a native North American species and in their role as scavengers they’re cleaning up the environment. They’re part of our ecosystem, cycling nutrients and controlling insect problems in farmers’ fields. These huge roosts have caused some problems, and that’s a real concern to address. But crow roosts are also a natural phenomenon that’s pretty incredible.”

“Remember,” she cautions, “The passenger pigeon went from being the most abundant bird ever on earth to being extinct. The last one died in captivity in 1914. If we put our minds to it, sure, we can get rid of the crows, but is that what we really want to do?”

Margaret Brittingham, Ph.D. is a professor of Wildlife Resources and Extension Wildlife Specialist. She can be reached at

Grant Stokke is a Master's candidate in Wildlife and Fisheries Sciences in the School of Forest Resources. He can be reached at

Last Updated May 19, 2010