How Did Crows Learn Which Human Face Was Dangerous?

Researchers at the University of Washington wanted to know whether wild crows could recognize an individual human. To make the test reliable, they did not use their own faces. They wore realistic masks.

A person wearing one particular mask trapped, banded, and released several crows. The experience was unpleasant but did not physically harm the birds. Other researchers wore a different mask while walking through the same area without capturing anything. Later, people wearing both faces followed identical routes through the university campus.

The crows reacted strongly to the trapping mask. They scolded its wearer with harsh calls, followed the person, and sometimes gathered other crows nearby. They largely ignored the neutral mask. Because different people could wear each disguise, the birds were responding to the face rather than the researcher’s body, clothing, or walking style.

The response did not quickly disappear. Crows continued identifying the threatening face years later. Even more strikingly, birds that had never been trapped began joining the alarm calls. Knowledge of the dangerous face spread socially through the local crow population. Young crows could learn from their parents, while nearby adults learned by watching the reactions of others.

The experiment revealed that a crow moving through a city does not necessarily see humans as one interchangeable species. It can remember a particular face, connect that face with an earlier event, and pass the warning to other birds. A human may forget an encounter with a crow, while the neighborhood’s crows continue remembering the human.