Crows can remember dangerous human faces for years.

A bird remembering a specific human face sounds like folklore until the mask experiments make it concrete. University of Washington researchers trapped and released wild crows while wearing distinctive masks, then tracked later reactions. Crows scolded and mobbed people wearing the dangerous mask long after the original encounter, and other crows could learn the warning socially. The finding is not that crows hold human-style grudges with human motives. It is that they can store a very specific threat identity and spread that information through a group. That is a lot of social memory in a city bird.

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