Why crows gather in trees at dusk

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It’s that time of year again, when trees are decorated with lights, ornaments and crows. Lots of crows.
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It’s that time of year again, when trees are decorated with lights, ornaments and crows. Lots of crows. I was recently asked to explain why so many crows gather on the banks of the Kenduskeag Stream in Bangor every evening. Actually, I get asked that question every year, because crows have been doing this since time immemorial.

All birds are primarily interested in three things: eat, don’t be eaten and who wants to make babies? When crows come together at night, all three of those interests come into play, especially the second one.

[Read more Good Birding here]

Look, it’s not all just fun and games up there in the treetops. Many birds dislike each other. Crows hate ravens, hawks and eagles, and they thoroughly despise owls, particularly great horned owls. In daylight, crows can elude or gang up on most predators. At night, they are almost defenseless, so they gather in large flocks to roost in a spot where they have good visibility and reasonable shelter.

Although crows congregate in rural areas, if there is a town nearby, they’ll take advantage of it. Cities offer benefits. There are fewer predators willing to be near people. There is more ambient light from houses and street lamps, so crows have a better chance of seeing trouble coming. It’s even a little bit warmer on a cold winter night. Oh, and you can’t shoot them in town.

There is another big advantage. When you’re one crow among a thousand, the odds of being the unlucky crow grabbed by a nocturnal owl are a thousand to one. Although it’s hard to be sure, since all crows look alike, there is plenty of observational evidence that crows even jockey for position in the treetops, trying hard not to be the vulnerable crow on the exposed edge of the flock. Crows often seem to return to the roost simultaneously, perhaps because no crow wants to arrive after all the good spots are taken.

It’s also likely that crows use the gathering to exchange information. Although we don’t know specifically what they’re saying to each other during that caw-cophony at dusk, we do observe that birds roosting close together often leave together in the morning and head in the same direction. We know that crows will sometimes solicit support from fellow crows to dominate a food source. We know that crows are highly intelligent. They can tell human faces apart, so it’s a near certainty they can tell which crow among them seems to be well fed and ought to be followed the next morning.

Plus, a lot of the daytime feeding takes place in big flocks anyway. In snow-covered Maine, wind-blown fields, plow-scoured roadsides and even landfills are big banquet tables for crows. And if manure is freshly spread on an agricultural field, look out! It’ll be crow-covered before the spreader stops moving. There’s a lot of undigested seed in that composted poop, and the birds know it.

[Related: A mass murder of crows?]

Later in winter, love blooms up in those branches, as pairs begin to match up. Crows are less social around nesting season but are quite gregarious at all other times. You can watch the seasons change by observing their behavior. Mated pairs go off together in spring, breaking up the big flocks. After the nestlings fledge in June, it’s typical to see noisy family groups of four to five foraging roadsides and fields. Come winter, the big twilight flocking begins again and lasts until courtship renews in the spring.

Even in winter, when adults are no longer protecting young, some lingering resentment exists between traditional enemies. As I took a walk this morning, I heard an approaching raven croaking a guttural call about a quarter mile away. When it was half again closer, two nearby crows started calling the alarm, though half-heartedly.

Rather than veering away to avoid trouble, the raven flew right at them and circled around, apparently just to annoy them, or possibly to see if they had anything worth stealing. The crows flew up to intercept but took only a few mild swipes at the intruder. Undaunted, the raven circled them again, now just taunting them for fun. One crow made another pass at the raven, an even weaker effort than the first. Then they all went on their merry way.

By March, when crows are thinking about nesting, expect this type of encounter to be much fiercer.

Crows flock at nightly roosts all over Maine. There’s probably one near you, just a few miles away … as the crow flies.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.


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