Research Takes Aim at Urban-Roosting Crows

Every year in early November, tens of thousands of crows descend upon the southeastern Pennsylvania city of Lancaster, gathering each night in colossal, raucous communal roosts.

The noisy hordes of big, black birds—which aggravate residents nightly over four months or so before abruptly disappearing in early March—damage property, deposit their droppings over cars and sidewalks, and create a huge racket. The problem got so bad a few years ago that Pennsylvania Department of Agriculture officials enlisted the help of avian researchers in Penn State’s College of Agricultural Sciences.

“Most of the birds in the communal roosts are migrating crows from Canada,” explains Margaret Brittingham, professor of wildlife resources, who is spearheading a crow-behavior study titled “Ecology and Management of Urban Crows in Pennsylvania.”

The research is aimed at discovering what these migrant crows are seeking when they move into cities and using this information to make urban roost sites—where people and crows come into conflict—less hospitable while still providing a place for crows to roost.

“There are some resident crows there, but it turns out that they are mostly not part of the problem, and there doesn’t seem to be a lot of mingling between migrant crows and resident birds,” Brittingham says. “Resident crows have well-defined territories where they remain throughout the year.”

All of the birds spend much of their days foraging for insects, seeds, and other foods among the rich agricultural fields that have made Lancaster County famous as one of the richest farming areas in the country, according to Brittingham. But late in the afternoons, the crows—known to be among the most intelligent birds—head back to the city of 50,000, where they have worn out their welcome.

“The phenomenon of huge, urban crow roosts is fairly new,” says Brittingham. “Our study was precipitated by what was going on in Lancaster, but there are many other mid-sized cities adjacent to agricultural fields where they have similar problems, such as Auburn, N.Y., Bethlehem, and Harrisburg.

“We believe crows cluster in urban areas because they are attracted to lights and perhaps the warmth of the city,” she adds. “Why they do that, nobody is sure. But the lighted urban areas may make them feel safe from great horned owls, which are their greatest predator.”

After putting up with these bothersome crow conventions for years, Lancaster city officials finally lost their patience with the crows when a huge group of them roosted at the Park City Mall, damaging the roof and making a mess of shoppers’ cars.

“The city first sought help from the Wildlife Services people at USDA and then from the Pennsylvania Department of Agriculture,” Brittingham says. “They used a variety of harassment techniques, including exploders, distress calls, effigies, and lasers. Although they were able to move the roost short distances, they were not able to solve the problem. They even tried a toxic chemical to kill the birds that ingested it. But that didn’t really work, and there was a backlash in the community against using the toxicant and killing crows.”

It became evident that this problem is very complicated, and solving it is going to take a combination of research, management, and education, Brittingham points out. “We have worked collaboratively with local citizens groups and government officials, USDA Wildlife Services personnel at both the state and federal level, and colleagues at Franklin and Marshall College to develop a multifaceted approach to reducing the crow problem,” she says. “We have been studying the crows’ behavior, trying to understand why they act the way they do and roost where they do.”

Penn State graduate student Grant Stokke of Port Angeles, Wash.—who Brittingham notes “has put his heart and soul into this research project”—probably knows more about crow behavior in Pennsylvania than anyone. For about a year, Stokke, who is pursuing a master’s degree in wildlife and fisheries science, has been capturing dozens of crows, fitting them with radios, and following their movements with telemetry equipment.
“If we can understand why the crows congregate where they do, then we will be able to predict where problems are likely to occur,” he says. “We are looking at whether we might create a place to attract these crows where they won’t be so much of a problem.

“We tried a park on the south end of town, but we didn’t have a lot of success with that,” Stokke adds. “Certainly it is easy to move crows from one place to another, but we have seen that they just fly a few miles and come back. It may also be that the public has to become more tolerant of the crows.”

According to Stokke, researchers are collecting data about crow-roost characteristics, such as temperature, amount of lighting, landscape type, and building exteriors that the birds seem to prefer. “We need to know where they are coming from, how long they stay, why they like certain kinds of roost sites, and how they behave when they get here,” he explains. “We even collected feather samples and did a hydrogen ion test that shows us where they were when they grew the feathers. That’s how we know they primarily come from Canada.”

After a year of the study, Brittingham has seen enough to be pretty sure that researchers won’t be able to solve Lancaster’s problem—not completely anyway. “Nobody anywhere in the country has been able to solve this problem with urban roosts, and moving the birds will be a continual, ongoing process,” she says. “We are making progress, though. There were many fewer crow complaints this year than last, and we are learning a lot of new information that we will use to develop an action plan before the crows return next year. The work that has gone into this is a great example of the collaboration between citizens, researchers, and managers working together to help wildlife and people coexist in a rapidly urbanizing world.”

—Jeff Mulhollem