Thanks to Q for the link.

http://www.nytimes.com/2008/08/26/science/26crow.html?_r=1&oref=slogin

Friend or Foe? Crows Never Forget a Face, It Seems

Crows and their relatives — among them ravens, magpies and jays — are renowned for their intelligence and for their ability to flourish in human-dominated landscapes. That ability may have to do with cross-species social skills. In the Seattle area, where rapid suburban growth has attracted a thriving crow population, researchers have found that the birds can recognize individual human faces.

John M. Marzluff, a wildlife biologist at the University of Washington, has studied crows and ravens for more than 20 years and has long wondered if the birds could identify individual researchers. Previously trapped birds seemed more wary of particular scientists, and often were harder to catch. "I thought, 'Well, it's an annoyance, but it's not really hampering our work,' " Dr. Marzluff said. "But then I thought we should test it directly."

To test the birds' recognition of faces separately from that of clothing, gait and other individual human characteristics, Dr. Marzluff and two students wore rubber masks. He designated a caveman mask as "dangerous" and, in a deliberate gesture of civic generosity, a Dick Cheney mask as "neutral." Researchers in the dangerous mask then trapped and banded seven crows on the university's campus in Seattle.

In the months that followed, the researchers and volunteers donned the masks on campus, this time walking prescribed routes and not bothering crows.

The crows had not forgotten. They scolded people in the dangerous mask significantly more than they did before they were trapped, even when the mask was disguised with a hat or worn upside down. The neutral mask provoked little reaction. The effect has not only persisted, but also multiplied over the past two years. Wearing the dangerous mask on one recent walk through campus, Dr. Marzluff said, he was scolded by 47 of the 53 crows he encountered, many more than had experienced or witnessed the initial trapping. The researchers hypothesize that crows learn to recognize threatening humans from both parents and others in their flock.

After their experiments on campus, Dr. Marzluff and his students tested the effect with more realistic masks. Using a half-dozen students as models, they enlisted a professional mask maker, then wore the new masks while trapping crows at several sites in and around Seattle. The researchers then gave a mix of neutral and dangerous masks to volunteer observers who, unaware of the masks' histories, wore them at the trapping sites and recorded the crows' responses.

The reaction to one of the dangerous masks was "quite spectacular," said one volunteer, Bill Pochmerski, a retired telephone company manager who lives near Snohomish, Wash. "The birds were really raucous, screaming persistently," he said, "and it was clear they weren't upset about something in general. They were upset with me."

Again, crows were significantly more likely to scold observers who wore a dangerous mask, and when confronted simultaneously by observers in dangerous and neutral masks, the birds almost unerringly chose to persecute the dangerous face. In downtown Seattle, where most passersby ignore crows, angry birds nearly touched their human foes. In rural areas, where crows are more likely to be viewed as noisy "flying rats" and shot, the birds expressed their displeasure from a distance.

Though Dr. Marzluff's is the first formal study of human face recognition in wild birds, his preliminary findings confirm the suspicions of many other researchers who have observed similar abilities in crows, ravens, gulls and other species. The pioneering animal behaviorist Konrad Lorenz was so convinced of the perceptive capacities of crows and their relatives that he wore a devil costume when handling jackdaws. Stacia Backensto, a master's student at the University of Alaska Fairbanks who studies ravens in the oil fields on Alaska's North Slope, has assembled an elaborate costume — including a fake beard and a potbelly made of pillows — because she believes her face and body are familiar to previously captured birds.

Kevin J. McGowan, an ornithologist at the Cornell Laboratory of Ornithology who has trapped and banded crows in upstate New York for 20 years, said he was regularly followed by birds who have benefited from his handouts of peanuts — and harassed by others he has trapped in the past.

Why crows and similar species are so closely attuned to humans is a matter of debate. Bernd Heinrich, a professor emeritus at the University of Vermont known for his books on raven behavior, suggested that crows' apparent ability to distinguish among human faces is a "byproduct of their acuity," an outgrowth of their unusually keen ability to recognize one another, even after many months of separation.

Dr. McGowan and Dr. Marzluff believe that this ability gives crows and their brethren an evolutionary edge. "If you can learn who to avoid and who to seek out, that's a lot easier than continually getting hurt," Dr. Marzluff said. "I think it allows these animals to survive with us — and take advantage of us — in a much safer, more effective way."