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. {The New Scientist}
