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Is That a Caveman or Dick Cheney? Crows Know the Difference
23 February 2010 3:28 pm
In a creative experiment that relied on rubber masks of former Vice President Dick Cheney and other distinctive mugs, researchers have shown that American crows have an uncanny ability to pick a familiar human face out of a crowd. The study confirms some long-standing folklore about the acuity of one of North America's most familiar birds—and offers new insight into how some wild animals may cope with living alongside people.
The study "really points the finger-or the wing, if you will—at the idea that there's a benefit to being able to identify your human neighbors, especially the ones that might pose a threat," says Douglas Levey, a biologist at the University of Florida, Gainesville.
Farmers have long told tales about wily American crows that learned to flee from hunters bent on shooting the birds, which are still considered pests in many areas. And researchers have long known that crows-like many other animals-can quickly learn to recognize people who feed them. In Bellevue, Washington, for instance, a bus driver who routinely fed crows at home nearly lost her job because the flock started following her to work. But researchers had never rigorously tested a wild crow's ability to recognize people until John Marzluff got interested.
In 2006, Marzluff, an ecologist at the University of Washington, Seattle, was using nets to capture local crows as part of a study on how expanding crow populations were affecting other birds. His research team, however, soon learned that the crows weren't easily fooled twice. "We'd go back to recapture birds, and it seemed obvious that they had learned to recognize and fear us," he recalls.
Marzluff began three decidedly theatrical experiments designed to reveal just how much attention crows paid to human faces. Working at five different sites in and around Seattle with resident flocks, Marzluff first had researchers record how the birds reacted when they walked by wearing several rubber masks-including one of Cheney and another craggy visage they dubbed the "caveman." Some weeks later, a trapper wearing one selected mask—the caveman, for instance—moved in with a net launcher and captured and marked seven to 15 crows. Then, for nearly three more years, masked researchers periodically revisited the sites--often mixing with large crowds of other pedestrians—and again recorded how the crows reacted.
The results were stark, the researchers report in the current issue of Animal Behaviour: Crows don't forget the face of the person who trapped them. Prior to trapping, for instance, less than 5% of the crows scolded the person wearing the "dangerous" caveman mask used in some experiments. After trapping, however, up to two-thirds of the birds would become upset when they saw the dangerous mask and start scolding, mobbing, and dive-bombing the wearer. And it didn't matter who wore the mask; the birds appeared to ignore differences in age, height, gender, ethnicity and walking gait-they just focused on the faces. In contrast, the birds essentially ignored researchers wearing "neutral" masks not associated with trapping-such as Dick Cheney's rubber double. "For once, Dick Cheney got to play the nice guy," Marzluff jokes about the controversial former vice president. "We decided to give [him] a break."
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Credit: Susan Flemming, producer; Keith Brust, photographer
The crow's ability to recognize human friends and foes may help explain how it has adapted so ably to life alongside people, Marzluff says. And the fact that, over time, a growing number of the crows reacted to the "dangerous" masks suggests that flock mates learn from each other. "Parents may teach their kids," he says, adding that his group will soon publish another paper examining this facet of the study.
In the meantime, Marzluff's students have once more donned masks to see if the crows still remember their tormentors. "It's remarkable; ... it's been 4 years now, but they see that mask and still go crazy," he says.
Other researchers aren't surprised. Florida's Levey, for instance, has shown that Northern Mockingbirds also develop keen memories of people who touch their nests. And "crows are very observant birds," adds Kevin McGowan, an ecologist at the Cornell Laboratory of Ornithology who has studied crows for decades. One irony, he notes, is that the study shows that whereas "crows can recognize people as individuals, we still see crows as just crows."