Wild crows can recognise individual human faces and hold a grudge for years against people who have treated them badly. This ability – which may also exist in other wild animals – highlights how carefully some animals monitor the humans with whom they share living space.
Field biologists have observed that crows seem to recognise them, and a few researchers have even gone to the extreme of wearing masks when capturing birds to band (or “ring”) them, so that they could later observe the birds without upsetting them. John Marzluff at the University of Washington in Seattle and colleagues donned a rubber caveman mask and then captured and banded wild American crows.
Whenever a person wearing the same mask approached those crows later, the birds scolded them loudly. In contrast, they ignored the same person wearing a mask of former US Vice-President Dick Cheney, which had never been worn during banding. “Most of the time you walk right up to them and they don’t care at all,” says Marzluff.
The birds’ antipathy to the caveman mask has lasted more than three years, even though the crows have had no further bad experiences with people wearing it.