Crows gang up in urban roosts

Posted Dec. 24, 2010, at 9:34 a.m.
Last modified Jan. 29, 2011, at 12:26 p.m.

EDITOR’S NOTE: This column was first published Saturday, February 9, 2008, in the Bangor Daily News

One winter evening a few years back, I glanced into the sky while walking across the office parking lot and was amazed at what I saw … and what, apparently, I’d been missing.

The sky was full of crows. Thousands of them flew in the same direction, toward the Penobscot River and Brewer. (Cue the creepy Alfred Hitchcock music).

For the next 10 minutes, I watched the crows fly past, curious about a few things.

Where are they all going?

Do they always do that?

And if they do, why hadn’t I noticed before?

In the ensuing years, many people have mentioned the phenomenon to me and assumed, since I write about the outdoors, that I’d know exactly what possesses the big black birds to group up at certain times of the year and act like they’re heading to a convention.

I didn’t.

But now (after hearing the question one time too many and finally asking the right person the right question), I do.

On Wednesday, I stopped by the office of Brad Allen, the Department of Inland Fisheries & Wildlife’s bird group leader, and we talked about crows. Allen said he’d done a bit of advance research on the matter and was happy to share the info.

“It appears that during the fall and winter, when [ crows] aren’t territorial around nest sites, they congregate in staging areas,” Allen explained. “These staging areas are all over the landscape — there might be one in this town, one in that town – they stage there during the day, and then at night they appear to fly to one common roost.”

That’s what I’ve seen. The question, however, remained. Why?

As it turns out, there are many reasons.

“They think crows get information from other crows about where there’s good food,” Allen said. “You’ve got one skinny little crow sitting there, very attracted to other crows coming in that look like they’re eating well. And they share information.”

But not the way you might think.

“It’s not like they talk and say, ‘Hey, I found a dead thing. Come with me tomorrow [and we’ll eat it],’” Allen said. “But they borrow from that information of others about good places to feed the next day.”

Allen said there’s a communal roosting area in Brewer near City Hall and said cemeteries often serve the same purpose.

“There are some neat theories as to why they roost [together in huge groups],” Allen said. “One is, they like to be in big trees in cities. A lot of cities have cemeteries and woodlots that are big, mature trees that out on the landscape don’t kind of exist. Mount Hope Cemetery would be a good example.”

Allen said cities tend to be marginally warmer than the surrounding areas, and crows may seek out that warmth in the winter. City lights, in turn, create a safer environment for crows.

Allen explained that there are really only two primary predators that target crows: humans (through hunting) and great horned owls.

Humans can’t hunt in cities, and owls prefer to do their hunting under cover of darkness in the forests, he said. That makes cities safer.

And then there’s an even simpler explanation: If predators do arrive, it’s much safer to have several hundred — or several thousand — eyes peeled for danger.

Allen said that in some parts of the country, hundreds of thousands of crows have been known to gather for the evening roosting ritual.

Then, in the morning, they disperse to forage for another day.

Some go off on their own … and others have company.

“Some of the skinnier ones that didn’t forage very well [the day before] will probably try to follow some of the fat ones in their direction,” Allen said.

When spring arrives, Allen said the communal roosting will break down as crows become more territorial and defend their nest and forage area from other birds.

Over the years, some readers have told me that the birds I’ve been identifying as crows are, in fact, ravens. Crows, one man asserted, are migratory, and don’t stick around Bangor during the winter.

Not so fast, Allen said.

“There are crows and ravens that live here year-round,” Allen said, pointing out that crows do migrate, but that doesn’t mean they seek out truly warm climes during the winter.

“There are crows from the Bangor area that probably migrate to southern New England, and there are crows from Quebec that probably think they’re in Key West when they’re in Bangor,” Allen said. “They’re protected as a migratory bird, but they’re not famous for long-distance migrations like a lot of critters are. They only go as far as they have to go. It’s food that drives migration, not cold.”

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