Crows remembered a mask worn by the researchers who trapped and banded them, and scolded walkers who wore it later. But I think the more interesting point is that the group of banded crows apparently taught other crows to recognise the mask too: "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." (via robertogreco, FriendFeed) - Deirdre