Hitchcockian Crows Spread the Word About Unkind Humans
June 28, 2011
Crows are savvy birds: They not only use tools, but can use common senseÂ to come up with ways to make unfamiliar tools work. They also hold a grudge.
The common crow knows when you're out to get him â€” and he's likely to teach his friends and family to watch out for you, a new study finds.
In results that can only be described as Hitchcockian, researchers in Seattle who trapped and banded crows for five years found that those birds don't forget a face. Even after going for a year without seeing the threatening human, the crows would scold the person on sight, cackling, swooping and dive-bombing in mobs [ a "murder ofÂ crows" is the usual term for a group] of 30 or more.
"Most of the birds that are scolding us are not the ones we captured," said study researcher John Marzluff, a professor of wildlife science at the University of Washington and an occasional victim of crow attacks. "It's likely that they're learning from their parents and their peers that this dangerous person is still out there."
The researchers launched a five-year study to find out how much data their research subjects had been gathering on them. To ensure that crows were responding to their faces and not to their clothes, binoculars or some other ornithologist cue, the scientists wore different masks while trapping birds at each site. The masks included a caveman, Dick Cheney and several custom-made realistic faces.
The birds quickly learned that the masked bird-trapper was bad news and proceeded to scold the mask-wearer anytime they saw him or her. But over the years, the researchers found, the mobbing became more and more widespread. In February, Marzluff said, he ventured out of his office in a mask he'd worn five years earlier while trapping seven birds."I got about 50 meters [165 feet] out of my office and I had about 50 birds on me, scolding me," he said. "I hadn't worn that mask on campus for a year."
It was clear the birds that had never seen the trapping were joining the angry murders. The question, Marzluff said, was whether those birds were simply following the lead of a single bird that had seen the trapping, or had learned from their flockmates that this was a face to watch out for.
"A lot of laboratory studies will show that [crows] can learn by observation, but not in the field," Marzluff said. "That combination of learning firsthand and learning through these observations, that's what's unique about our study."
The researchers reported their results June 28 in the journal Proceedings of the Royal Society B. They are now using brain-scanning techniques on captured birds to find out what's happening in the crows' brains when they see a dangerous face.