Counting Crows: Why are there So Many?

by on April 04, 2014

 
Crows staging in a tree after sunset. Photo: Elaine Miller Bond.
 

 

“Why are there so many darn crows in Berkeley these days?”

We get that question a lot at Golden Gate Audubon, and the Berkeleyside editors get it too.

It’s not just Berkeley. Crows are on the increase throughout the Bay Area, as are their larger and deeper-voiced cousins, ravens.

Back in the 1980s, Golden Gate Audubon members typically found between 30 and 90 American Crows each year in our Oakland Christmas Bird Count, which includes Berkeley. We typically found fewer than ten Common Ravens.

Since 2010, however, the count has turned up over 1,100 crows and 170 to 300 ravens each year.

“Crows have gone from being very uncommon to common to abundant,” said Rusty Scalf,  a Golden Gate Audubon birding instructor who lives in Berkeley. “Ravens used to be unheard of in the city, but now they’re all over the place.

Photo: Elaine Miller Bond

Photo: Elaine Miller Bond

If you’ve seen hundreds of crows flapping and cawing in a single tree — a murder of crows in fact — you might think that 1,100 crows is an understatement, and Berkeley is on the verge of being taken over à la Hitchcock by these bold, loud creatures. You might join the many bird lovers who accuse crows of driving down local songbird populations by stealing and eating their eggs.

But on both these counts, crows get a bum rap. The real crow story is more complicated.

Crows are intensely social and intelligent birds that, like humans, maintain both a family life and a community life.

During breeding season – spring and summer – they spend time with their family, building a nest and raising young on a defined territory. Adult crows usually mate for life. Juvenile crows stick around for several years and help their parents feed the nestlings. (Don’t you wish your teenagers would do that?)

In the winter, on the other hand, crows often come together for the night in huge colonies. Around sunset, they gather at a staging area such as a big tree, calling and flapping and chasing each other. Then they fly together to another tree to roost for the night.

A raven: the larger, deeper voiced cousin of the crow, also on the increase locally. Photo: Elaine Miller Bond

A raven: the larger, deeper voiced cousin of the crow, also on the increase locally. Photo: Elaine Miller Bond

If you’ve had one of those jaw-dropping “is this Hitchcock?” moments, you may have been glimpsing one of these winter evening roosts. But if you think 50 or 100 birds in one tree is a lot, consider this: Auburn, New York had groups of 25,000 crows in a single roost as far back as the 1930s.

And Fort Cobb, Oklahoma, had one crow roost in 1972 with more than 2 million birds – enough to rival the Passenger Pigeon flocks that used to darken midwestern skies before they went extinct a century ago.

“They do a lot of chasing and calling and preening in these groups, the function of which is not readily apparent,” said Kevin McGowan, a crow expert at the Cornell Laboratory of Ornithology. “I think of them potentially as singles bars, crows going in and trying to find a mate.”

According to McGowan, crows’ negative reputation as nest predators is largely undeserved.

Yes, crows do feed on songbird eggs. But studies have shown that crows play a relatively small role in nest predation.

“There are studies that put cameras into nests and watch for predators,” McGowan said.  “The main nest predator is almost always squirrels and snakes. Then come mammals like raccoons and possums, then jays, raptors, cowbirds and mice. Crows are way down on the list.”

According to McGowan, the spread of crows and ravens into urban areas like Berkeley probably has a variety of roots:

  • Crows happily devour many kinds of human debris, such as French fries and other fast food scraps.
  • Their main predator, the Great Horned Owl, is relatively scarce in cities. Plus city street lights help crows spot and evade owls at night.
  • Cities tend to be 5 to 10 degrees warmer than the surrounding countryside since sidewalks and buildings absorb heat. That’s a boon for birds in winter.
  • On top of this, crows and ravens were added in 1972 to the list of species protected under the Migratory Bird Treaty Act of 1918. That meant farmers could no longer shoot them as pests – and so the birds gradually learned to be less leery of people.

And while West Nile virus took a heavy toll on crow populations back east over the past 15 years, it doesn’t seem to have significantly hit Bay Area birds.

Crows’ and ravens’ adaptability has been aided by the fact that they are some of the smartest birds around. Crows recognize individual human faces, and will respond with hostility to someone who has threatened their nest on past occasions. They make and use tools – for instance, pulling off a sliver of wood to poke a yummy spider out of a crevice.

(And don’t forget that viral YouTube video of a Russian crow making a plastic lid into a rooftop sled. Although, really, couldn’t the crow just be trying to peck crumbs from the lid and sliding by accident?)

Right now, we’re entering the start of nesting season. So for the next few months, you’ll be less likely to see giant crow gatherings in large trees at dusk. Instead, you may find a group of five or six crows hanging out in your yard. John Marzluff, a crow researcher at the University of Washington, found that suburban nesting pairs tend to defend territory stretching across two backyards – that’s one crow family for every other house.

Photo: Elaine Miller Bond

Photo: Elaine Miller Bond

Don’t want crows in your yard?  You can try banging pots to scare them away, but you’ll need to do this consistently. And it’s probably not worth making a scarecrow: Crows are too smart to be deceived for more than a day or so.

“The best thing is to change your attitude,” McGowan said. “Those crows in your yard aren’t a mob. They’re not a gang. They’re probably a family. And they’re very beautiful if you look at them.”

Some Corvid facts:

Crows and ravens are members of the corvid family, along with jays and magpies. Our local species are American Crows and Common Ravens.

Ravens are larger than crows, but that won’t help you identify them unless a crow has helpfully chosen to sit right next to a raven. Instead, look for the larger, heavier beak on the raven and the shaggy “beard” of feathers on its throat. The raven’s voice is deep and croaky, while the crow has a higher-pitched caw. In flight, a crow’s tail has a flat or slightly rounded end while a raven’s tail ends with a v-shaped wedge.   Easy memory aid: Raven is spelled with a “v,” and has a v-shaped tail.

Learn more:

Learn about Bay Area birds: come on one of Golden Gate Audubon’s free bird walks.

This article was originally published on Golden Gate Birder. Ilana DeBare is Communications Director for Golden Gate Audubon Society. She is working on a novel.

Elaine Miller Bond is the author/illustrator of Affimals: Affirmations + Animals and the newly published Dream Affimals, from Sunstone Press. She is also the photographer for the upcoming book, The Utah Prairie Dog.

Editor’s Note: Berkeleyside, the online news site serving the city of Berkeley, recently asked us about the increase in crows there. Here’s the article we wrote for them.

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4 comments:

Cindy Roessler on April 4th, 2014 at 1:19 pm

I frequently see ravens in the rural areas of the Santa Cruz Mountains. Their dark shiny bodies slice the foggy skies as they fly about in pairs most of the year (often in threes at end of summer) on regular routes with daily patterns. The local pair call back when I squawk at them and sometimes peel out a playful barrel roll. If I see more than a few in a grassland, it usual means either a hatching of grasshoppers or they are cleaning up a mammal carcass. One day I’ll figure out what that funny bubbly sound they make means. Ravens certainly seem like intelligent and useful critters in the natural areas around here, maybe we should just get better about cleaning up our human trash.

Green Bean on April 5th, 2014 at 8:54 am

I appreciate insight as to predators of song birds and such but crow populations must have an impact on hawks? Every time I see a hawk in our suburban area, it is being attacked by between 2-20 crows. Any information on this?

kathy on April 11th, 2014 at 11:05 am

I work at a school and crows are common, waiting in the trees to pick up litter from the kids. Occasionally they’ll steal a lunch. What is unbearably unnerving is the sound made by the seagulls as they’re being pecked to death by a swarm of crows. No, I don’t like the nasty little buggers.

Nancy Reyering on April 14th, 2014 at 10:08 am

Our local crows have become as abundant as the article suggests. Where we used to hear a variety of songbirds in the morning, we now hear only crows. Last summer I observed crows repeatedly harassing our local nesting hawk and finally taking a just hatched hawklet from the nest. It was horrific. I don’t care any longer for descriptions of how intelligent they are. Their larger numbers are indeed contributing to the decline of other species and it is our great loss.

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