A scientific study provides evidence that crows are capable of recognizing threatening people and can even pass their concerns on to other crows  Researchers wearing rubber caveman masks trapped wild crows and then released them in the same area
Years later, people wearing the same masks near where the crows had been trapped were shrieked at and dive-bombed by crows
some of the crows that shrieked at and dive-bombed people wearing the masks were not among the crows that had been trapped