Never scaring a crow is a rule that everyone should follow. And not just because animals must be respected. If one of these birds identifies you as his enemy, you may soon find yourself in the crosshairs of a flock of croaking crows. Thanks to an efficient word-of-mouth system, as researchers at the University of Washington in Seattle have discovered.

Researcher John Marzluff had already discovered five years ago that these crows had discovered that crows learn to recognize a "dangerous" human being in their eyes. Marzluff had tried to briefly trap some American crows (Corvus brachyrhynchos) wearing a caveman mask. Later, the birds involved in the experiment showed aggressive behavior towards anyone wearing the same mask, chasing him and croaking harshly, while ignoring those wearing a neutral mask.

Since then, Marzluff has continued to monitor the reactions to the masks of crows that populated his university campus. Together with his team he discovered that more and more birds reacted negatively to the sight of fake "cave men". Two weeks after the experiment, only 26% of the entire crow population was crackling brightly at the sight of the masks; 2.7 years later, the percentage of specimens conscious of the "danger" was 66%. Today, five years after the experiment, the researcher cannot even complete 50 meters wearing the mask that is immediately surrounded by a flock of defensive animals.

Even the youngest crows, which at the time of the "foul deed" were not yet born, know how to identify the human being considered threatening. According to the researchers, these birds would have two ways of learning: that of direct experience and what happens when observing the behavior of the companions. The crows, in essence, "are observed and observed much more than we thought", the ethologists concluded.