Oakwood Cemetery should not be so noisy at night, but the thousands of crows encamped here this evening will not shut up.

The graveyard, perched near downtown Rochester, Minn., is alive with the creatures yelling from the trees, cutting sharp silhouettes against the gray, late fall sky.

Left to themselves, the crows will eventually make their way to downtown where — intentionally or not — they will rain down poop, creating a slimy mess for city residents as well as staff and patients at the sprawling Mayo Clinic campus.

Standing in the way of that chaos is Sally Vehrenkamp, part of a band of city employees who each winter take on the job of chasing away the birds. They're known as the Crow Patrol, and they are ready for the fight.

"We have the laser, we have the distress crow call ... and our blank pistol," Vehrenkamp said as she readied her tools on a conference table in the Rochester parks department before heading out for the night.

Each winter, a murder of crows — yes, that's the term for a flock of these highly intelligent birds — make their home in downtown Rochester. It's the Crow Patrol's job to keep them from getting too comfortable.

'Very disgusting'

Mayo's presence downtown, which attracts patients from all over the world, is the main reason they work so hard to keep crows away, Vehrenkamp said as she and her colleagues fanned out at dusk in pick-up trucks.

"It's very disgusting for them to walk in," she noted. "They, you know, have to walk through all the crow poop."

Parks employees gear up daily in the late afternoon and usually stay out until 11 p.m., training the birds to stay away from downtown. The city spends up to $40,000 annually on the efforts, depending on how long it takes for the crows to figure out they should perch elsewhere.

Averaging about 17 inches long with a wingspan of roughly 3 feet, crows are considered to be among the most intelligent birds in the world. They like grassy, open areas where they can forage for grains, nuts and even small animals.

In mid-November, just as they do every year, the beasts arrive for the season. This year, they appear to be gathering in Oakwood Cemetery.

"It's a very convenient coincidence," Kaeli Swift, a lecturer at the University of Washington who studies crow death rituals, said of the cemetery's location to downtown.

Big, loud crow gatherings happen right before the birds head to their roosts to sleep. The convocations likely serve a social purpose, she added.

"Maybe it is a way for crows to meet potential mates, for example, or reconnect with individuals that they haven't seen for a long time," she said.

Also a mystery is why crows are attracted to urban centers in the winter. Swift says a likely reason is that they provide warmth.

But with those crowds of crows comes a lot of feces, which leads many cities to use creative, non-lethal means to keep them at bay.

Rochester's annual epic crow battles draw chuckles from some residents who think the city is trying too hard to polish up its image.

That includes Rochester filmmaker Tyler Aug, who spent years making "The Crows," a mockumentary about Rochester's crows and the city's outsized efforts to keep them at bay.

"With the alarms and the lasers. All together it's just funny," he said. "It's all about curb appeal."

Aug, whose film is screening Thursday night at the Gray Duck Theater in Rochester, says it's not just about these fascinating birds that he finds in his own downtown neighborhood, but about what he perceives to be Rochester's quest for perfection.

He questions whether it's worth the effort to teach the birds to stay away.

"Generationally, when they come back every year, are they going to remember that?" he asked. "And know that? I think it's this endless lesson they keep teaching."

'A hot spot last night'

Back on the Crow Patrol, parks employee Don Yust drives slowly down a street of popular restaurants and bars.

He spots a tree filled with crows.

"This was a hot spot last night," he says before blasting a cacophony of crow calls from the back of his truck.

It doesn't work, so he shines a laser at them. Only a few fly off.

Finally, Yust whips out the starter gun. A couple of bangs cleared the crowd — except for one bird.

"You'll get that stubborn one that will not leave no matter what you do," he says. "It's like, 'I found my home for the night. Leave me alone.'"

The crows will eventually learn to stay away, he says — at least for this winter.

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