Corvus brachyrhynchos, better known as the common crow, as pictured in a Berkeley backyard.  Dan Brekke/KQED
Corvus brachyrhynchos, better known as the common crow, as pictured in a Berkeley backyard.  (Dan Brekke/KQED)

Crows Are Crowding Your Bay Area Skies. Why?

Crows Are Crowding Your Bay Area Skies. Why?

Q

uick: What's the one bird you see and hear most every day, day in and day out, without fail?

We're willing to bet that for most of us in the Bay Area, there's one avian species that predominates in our daily bird experience: Corvus brachyrhynchos, better known to most of us as "the crow."

"I see 'em in the morning, I see 'em in the afternoon, I see 'em up in trees, I see 'em on top of buildings," said San Mateo native Kevin Branch. "They’re everywhere. I kind of feel like the crow has taken over — big time."

Branch has a lot of questions for Bay Curious about crows in the Bay Area: Why are there so many? Are crows replacing other familiar birds, such as mockingbirds, blue jays and red-winged blackbirds? Is there a plan to reduce crow populations?

Yes, There Are More Crows

T

he most persuasive evidence comes from the Audubon Society and its Christmas Bird Count. The count is conducted by more than 2,500 local chapters across the Americas, the Caribbean and Hawaii, each with volunteer observers tallying birds in a predefined 15-mile-diameter circle over a 24-hour period.

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The Audubon Society's Golden Gate chapter conducts two counts each December: one in a circle centered in Oakland, covering a big slice of the East Bay Hills and the bay shore from El Cerrito to San Leandro, and the second in a circle centered on San Francisco's Oceanview neighborhood, which covers the entire city and most of the Peninsula.

The number of crows in the Oakland circle has grown from 167 in 2000 to nearly 2,500 in 2018 — an increase of nearly 15 times in fewer than 20 years. The numbers for San Francisco are impressive, if not as dramatic. The 2000 count recorded 122 crows, with more recent counts in the 700 to 900 range.

So what's behind the increase? People who watch the birds point to an equation with two major parts.

Crows Not Welcome

"One argument, which may be true, is that crows are smart birds, and crows have historically inhabited the countryside," Lewis said. "Farmers put up scarecrows and crows eat corn. We have that kind of feeling about them. But in the country, crows get shot, too, and crows have perhaps discovered in the cities and towns that it’s a much safer place to be."

Crows have been on the receiving end of our hostility for a long time — a creature viewed by many as a voracious destroyer of crops and inveterate opportunist preying on the young of smaller, more valuable, and let's face it, better-liked birds.

Some, including E.R. Kalmbach, the author of a U.S. Department of Agriculture bulletin published in 1918, acknowledged that crows sometimes did have a negative impact on crops. But based on an intensive study of what crows actually ate — the stomachs of 2,118 crows were examined for evidence — Kalmbach argued the birds played an essential role in controlling harmful insects, a service that "can ill be spared."

"The attitude of the individual farmer toward the crow should be one of toleration when no serious losses are suffered, rather than one of uncompromising antagonism resulting in the unwarranted destruction of these birds which at times are most valuable aids to man,” Kalmbach concluded.

That appeal for reason apparently didn't resonate too widely. The very next year, 1919, the DuPont chemical company launched a National Crow Shoot. DuPont declared "it is certain that some concerted action on the part of farmers and sportsmen" was needed to ensure a bountiful grain harvest. The company promoted another benefit to hardware retailers, who at the time sold firearms — it would help them sell more ammunition.

An ad for DuPont's 1919 National Crow Shoot, a yearlong event the company promoted as a way to help farmers and sell ammunition. (Internet Archive)

Attempts to eliminate crows weren't, and aren't, limited to the countryside. In the early 20th century, San Francisco’s Golden Gate Park employed a hunter — usually a city cop — to shoot crows and other unwanted animals, like jays and coyotes.

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And it may come as news to city dwellers, but California has a hunting season for crows from Dec. 1 through the beginning of April every year in most of the state's rural areas. State law allows landowners to kill crows out of season, too, if they "are committing or about to commit depredations upon ornamental or shade trees, agricultural crops, livestock, or wildlife, or when concentrated in such numbers and manner as to constitute a health hazard or other nuisance."

In 2015, the most recent year for which the Department of Fish and Wildlife has numbers, hunters here reported killing about 35,000 crows.

More Food Means More Crows

But unfriendly humans are just one major factor that has led to more crows joining us in our cities and suburbs. The other?

"I think it’s kind of simple myself," said University of Washington wildlife biologist John Marzluff, who has studied crows and other corvids for decades. "Basically, we’ve provided more food for them. Now, the reasons for that may be more complex because it includes things like garbage, like fast-food restaurant waste, like roadkill. So there are a lot of ways we provide them food. But that’s the bottom line. That’s why they’re more abundant."

There's a sort of common-sense objection to that idea: City dwellers have always been pretty messy. Look at the giant open garbage dumps that used to be on the edge of every big city. If garbage is attracting crows, where were they before?

Marzluff says it actually works better for crows to spread out their food sources.

"You don’t have to have a dump," he says. "I think actually in terms of territoriality and increasing the breeding population, it’s better to have food more uniformly distributed."

Ready availability of food in cities — in this case, meant for some backyard chickens — is a major factor driving crows' urban population increase, biologists say. (Dan Brekke/KQED)

Marzluff also says crows have no problem crowding in among us.

"They only defend enough space that’s necessary to get enough food to raise their young and survive," he says. "So as more food is available, they can live in tighter and tighter quarters and you can fit more of them into the place."

Adrian Cotter, a web developer for the Sierra Club who is also a citizen scientist and corvid enthusiast, points out that some of the very things we do to make cities more livable for us are also attractive to crows.

"We're sort of 'crow-forming' our cities — terraforming, but for crows," Cotter says. "We plant trees they like to nest in. We plant trees that other birds nest in, and that becomes a source of food. So we're presenting this sort of lovely banquet for them."

Are Crows Replacing or Killing Off Other Species of Birds?

Kaeli Swift, another University of Washington biologist who has spent years studying crows and their ways, says research has found that the crow's reputation for reducing the population of other songbirds is largely undeserved.

"Most people that contact me feeling like crows wiped away all of the birds in their neighborhood just have this perception that if you see a flock of crows, it means none of your songbirds are going to reproduce, that everything is doomed," Swift says. "The science just does not back that up."

The research she's pointing to is a 2014 compilation of 42 studies that looked at the impact of corvids on dozens of songbirds that were their potential prey. In four out of five cases, the analysis found, corvids had no negative impact on either the reproduction — nesting success and rearing of young — or the abundance of other birds.

A crow battles with a white-tailed kite at Cesar Chavez Park on the Berkeley waterfront. (Courtesy of Bob Lewis)

Crows did have a larger impact than some other corvids on how successful other birds were in reproducing, the study found, but not on their overall numbers.

Swift says the explanation for this finding — in essence, that even though crows and other corvids do prey upon other birds, the overall impact is small — is "compensatory mortality." In plain English: It's a hard world for little things. There are lots of things out there that kill birds and reduce their populations.

"It can be easy for us to think, 'If this predator was gone, then all of the babies they would have eaten will survive,'" Swift says. "That's really not how it generally works. ... The other predators in the system will just come in and take their place."

What kinds of other predators? Hawks. Owls. Jays. Snakes. Foxes. Raccoons. Cats. And, Swift, notes, some animals we might not think of as a menace.

"A lot of people don't realize squirrels and chipmunks are huge nest predators, much more impactful than crows," Swift says.

Is There a Plan to Reduce the Crow Population?

Well, no. Crow hunts continue in California and across the United States, and there's lots of video evidence of that on YouTube. But scientists like Swift and Marzluff argue that the best way to deal with crows is to try to understand who they are and what they're doing here — an echo of biologist E.R. Kalmbach's long-ago call for crow tolerance.

"There’s a lot of qualities that I don’t think you can help but find really attractive in crows — like their ability to learn our faces and be pretty excited to see us when you’ve built up a positive relationship with them by feeding them," Swift says.

"They play, so you can watch them play games, particularly the young birds. And they’re just kind of charismatic and goofy in the way that a dog with a really strong personality is. For me, crows have the same sort of quality where, if you watch them, you just see them do all these things that are so interesting that you just kind of can’t help falling in love with them if you just open yourself up to that."

Swift says many of our problems with crows may stem from how much we share in common with them.

"They’re clever, so they’re able to outsmart some of the ways we try to keep them out of our garbage or out of our property," she says. "They are social, so they are really noisy. They are protective parents, so they can be aggressive around their babies when they feel like they’re being a threat."

Marzluff says it's important to remember crows are “sentient beings” like us and that we ought to learn to use our big human brains to discover and address the problems we have with a growing crow population.

"I do end every one of my talks about crows with a slide that’s like, ‘OK, these things can get under our skin. Why? And what should we do?’ " he says. "And my take-home is that we should celebrate them for being successful, and if we need to control them in places, we need to think hard about it. Like they think about how to live with us, we need to think about how to live with them and come up with strategies that will have meaningful effects on their populations — not just kill a bunch of them."

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