Humans are not the only species to hold grudges, according to a new study. Turns out, wild crows can recognize human faces and can hold a grudge for years against anyone who tried to harm them.

For years, field biologists have sensed that crows recognize them, and some have gone as far as wearing masks when capturing birds to avoid being identified later on, according to a report in New Scientist. But it was unclear whether the crows recognized the scientists' faces or other details, such as clothing or gait.

To find out, a team of researchers from the University of Washington wore rubber caveman masks while capturing and tagging wild American crows. When a person wearing the caveman mask approached the crows later, the birds attacked, or “scolded” them loudly. If the same person approached the birds wearing a mask of former Vice President Dick Cheney — whom they had not seen before — the birds didn’t bat an eye.

“Most of the time you walk right up to them and they don't care at all,” said John Marzluff, who led the research team.

According to their research, published in the journal Animal Behaviour, the crows also held a grudge. Three years after the birds saw the caveman mask, they still had an aversion to it.

Upping the ante in a second experiment, Marzluff and his team made six masks from casts of people’s faces. They wore the masks to capture crows in four locations. In each case, they found the crows recognized and “scolded” the masks they recognized from when they were captured. They ignored the others.

Based on that finding, it is safe to say that crows pay attention to humans — particularly noting those who may be a threat to them, said a scientist not affiliated with the experiment, Doug Levey of the University of Florida in Gainesville. “We may think they are just bystanders minding their own business — but we are their business,” Levey said.

The research could also indicate that other wild animals may have the same perceptiveness. But certainly, it sheds light on the crows’ ability to recognize faces in their environment. “It’s likely that they’re incredibly perceptive of the dog and cat components of their environment, as well,” Levey said.