Even after a year, a slighted crow may gang up with buddies to
By Stephanie Pappas, LiveScience Senior Writer
The common crow knows when you're out to get him -- 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
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 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."
Holding a grudge
Crows are savvy birds: They not only use tools, but can
use common sense to come up with ways to make unfamiliar tools work.
They also hold a grudge. A study published in May in the journal Animal
Cognition found that crows' close relatives, magpies,
recognize researcher's faces regardless of what the scientists wear. And
just this month, police in Everett, Wash., about 25 miles north of Seattle,
found themselves on the wrong side of a flock (or "murder") of crows. The
birds dive-bombed the officers as they walked across their station's parking
lot. State Department of Fish and Wildlife officials blamed fledgling
season, when adult birds become extremely protective of the young that are
just leaving the nest. ("Umbrellas may be used as a defense tactic" against
reported the Everett Herald newspaper.)
Marzluff and his
colleagues similarly noticed that when they trapped and banded crows for
research, mobs of angry birds would fly overhead, scolding them. When the
researchers returned to the area later, the birds immediately recognized
them and started scolding.
"The more we messed with them, the more
we thought they were really paying attention to us," Marzluff told
The researchers launched a five-year study to find out
how much data their research subjects had been gathering on them. To ensure
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.
To find out, the researchers tested a "dangerous" mask and a neutral
mask on fledgling crows while their parents were in the nest and also while
their parents were away. They found that the presence of a grudge-holding
leader wasn't necessary: If the baby birds had ever seen their parents scold
the mask, they started scolding it even when mom and dad weren't around.
"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.
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