London: Crows have an excellent memory and can remember your face for over five years if you mess with them, scientists have found.

Researchers at the University of Washington found that birds have such a memory power that they can tell the difference between a friendly face and a dangerous one, and can warn each other which is which.

"Our findings add to the evolving view of large-brained, social and long-lived birds like crows being on a cognitive par with our closest relatives," lead researcher Dr John Marzluff was quoted as saying by a newspaper.

For their study, the scientists exposed crows in Seattle to a "dangerous face" by wearing a mask while trapping, banding and releasing birds at five sites.

Over a five-year period after the trapping had stopped, they found that the mask received an increasingly hostile response from birds in the area, suggesting that the captured birds had been able to warn others.

Dr Marzluff said: "Because human actions often threaten animals, learning socially about individual people's habits would be advantageous. The number of crows scolding the dangerous mask continued to increase for five years after trapping, as expected if social learning or social stimulation were present.”

"As we conducted trials, walking with the dangerous mask along the route, our actions presented opportunities for crows to observe or be stimulated by scolding. The number of crows encountered was consistent across trials, but the number that scolded the dangerous mask increased steadily,” he added.

The new study was published in the journal Proceedings of the Royal Society B.

(Agencies)