Crows remember your face, and they tell their friends.
Researchers at the University of Washington wore a distinctive mask while trapping and ringing crows. For years afterwards, crows scolded and mobbed anyone wearing that mask, including birds that had never been caught. Harmless masks got no reaction. The grudge had spread through the flock.
In 2006, the wildlife biologist John Marzluff and his team at the University of Washington in Seattle began an experiment. While trapping and ringing wild American crows on campus, they wore a particular rubber mask, a 'dangerous' face. Afterwards, they walked the campus wearing either that mask or a 'neutral' one, and recorded the crows' reactions.
The crows remembered. When a person wore the dangerous mask, crows scolded loudly and dive-bombed, even though the wearer was doing nothing threatening. The neutral mask drew little response. It did not matter who wore the mask; the crows were responding to the face.
More remarkably, the reaction spread. Over the following years, the number of crows scolding the dangerous mask grew, including young birds that had never been trapped and had not been born when the experiment began. They seem to have learned from watching other crows' reactions. The response persisted for years after the trapping stopped.
Later brain-imaging studies by the same group showed crows' brains respond differently to the faces of threatening and caring people. Crows and their relatives, the corvids, are famously clever: New Caledonian crows make hook-shaped tools, and ravens can plan for the future. Crows are very good at telling people apart, and it seems they hold on to what they learn.
Source: Marzluff et al. (2010), Animal Behaviour
