Crows scolded a 'dangerous' mask for years after a single bad encounter

Researchers trapped and banded wild crows on a Seattle campus while wearing a caveman mask. Months and even years later, crows that had never been trapped still mobbed and scolded anyone wearing that mask, but ignored a different, neutral mask, suggesting the birds had learned the threat and passed it on to others.

— John Marzluff, Crows Hold Grudges in Humanlike Fashion — University of Washington research, begun 2008