You can hear them before you see them. As the sun begins to sink below the horizon, ghostly caws and flapping wings echo through the air. Then, they come in droves. Hundreds, if not thousands, of huge, black birds darken the sky, swooping through buildings and swarming like giant gnats.

This Hitchcockian scene is a typical Tuesday in North Rosslyn for tech consultant David Allen. After working in Rosslyn for four years, he’s become accustomed to the eerie nightly ritual. That wasn’t the case the first time he witnessed it.

“It was a little bit surreal,” he says. “You always hear that nature knows when some kind of natural disaster is going to happen before humans can sense it, so my first thought was “is there a fire somewhere?””

It might look like a harbingering of the end of days, but Smithsonian Research Wildlife Biologist Scott Sillett says this flocking is fairly normal bird behavior. He ID’ed the birds as American and Fish Crows, both native species of the region. The massive numbers can be attributed to the end of the crows’ breeding seasons, he says, as the young born in the spring have matured to join their parents in darkening the sky.

Sillett says this massive “murder” of crows isn’t circling for the kill. Rather, they’re just looking for a place to roost for the night, grouping in large numbers to defend themselves against predators. He posits Rosslyn is attractive to the crowfolk due to its messy residents: any trash left in the open is a buffet for the omnivorous birds.

Once the breeding season starts in early spring, the crows will become territorial and dissipate, Sillett says. For now, though, Rosslynians can continue to look forward to the nightly visits from the world’s smartest bird species. Crows have demonstrated higher functioning skills like hiding food and retrieving it later, manipulating metal wires to get into glass bottles and containers, and using sticks as mini shovels.

So, should Northern Virginia should be concerned about an eventual crow takeover à la Planet of the Apes?

“That’s unlikely unless crows start to evolve opposable thumbs,” Sillet says. “Despite Alfred Hitchcock’s movie, I don’t think we have to worry about a ‘crowpocalypse,’ and them trying to jimmy open our windows, and steal our food, or take our car keys.”

Sillett adds that — as long as their nests are left alone — crows don’t show aggression towards people. Other than the occasional inadvertent poop bomb, the only thing people have to worry about is the crows’ proclivity for stealing shiny objects for their nests.

And, according to Allen, the noise.

“Rosslyn is under the flight path for Reagan airport, so that’s usually the loudest thing you’re going to hear,” he says. “But the crows are a close second.”

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