“I’m telling on you!” (Image: Amy White and Al Petteway/National Geographic/Getty)

If you’ve ever wondered what crows are saying when they caw at a perceived threat from the treetops, here is a sample: “I’m telling on you!” By watching who their neighbours and parents scold, one group of crows has learned to recognise and scold a dubious human.

John Marzluff of the University of Washington in Seattle discovered five years ago that crows can recognise individual humans who posed a threat. He briefly trapped American crows (Corvus brachyrhynchos) on his university’s campus while wearing a distinctive “caveman” mask. Afterwards, crows that had been trapped scolded anyone they spotted wearing the caveman mask, following them around and cawing harshly, but studiously ignored people wearing a neutral mask.

Since then Marzluff has been monitoring the birds’ response to the masks. Tests in which researchers toured the campus wearing masks showed that more and more crows had taken to scolding people sporting the caveman mask.


Two weeks after the trapping, 26 per cent of crows scolded people wearing the offending mask, but 2.7 years later a remarkable 66 per cent did so. In the fifth year of the study, Marzluff barely got 50 metres out of his office in the caveman mask before a mob of crows started scolding him. The behaviour also gradually spread outwards from the original trapping site.

Copycat crows

Even young crows, who were not born when the original trapping happened, learned to scold people wearing the caveman mask by copying their parents. “The young are very receptive to what their parents are doing,” says Marzluff.

The crows have two different ways of learning, Marzluff says. They can learn through their own experience and by watching others, making them quick to learn about new threats.

While it’s difficult to definitively prove social learning in nature, “I’m convinced,” says Doug Levey of the University of Florida in Gainesville, who has shown that mockingbirds can also recognise individual humans.

“Crows are much more observant of each other, and of humans, than we thought,” Levey says.

Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2011.0957