Consider this a friendly reminder not to antagonize crows: According to a 2011 study in Proceedings of the Royal Society B, American crows remember the faces of people who wrong them, and enlist other birds to attack the offenders.

When it comes to intelligence, birds get no respect. For a long time, scientists assumed birds were stupid because their brains had significant differences from ours. But recent studies on bird brains and abilities are putting those fallacies in their place. Researchers have found sophisticated behavior in birds from finches and pigeons to Antarctic gulls. But there’s one group of birds that consistently amazes: crows and ravens.

Within the last 10 years we’ve learned that crows can make, store, and care for tools. They can count and exercise self-restraint. They can use bait to catch fish. They can certainly play. And, the authors of the Royal Proceedings study say, they can nurse some serious grudges.

Researchers at the University of Washington’s School of Forest Resources bought two masks that looked like human faces. A caveman-looking mask was designated the “dangerous” mask, while a Dick Cheney mask was “neutral.” They then visited wild crows at five sites around Seattle. At each site, the person wearing the caveman mask would approach the crows, trapped a few, banded their legs, and set them free—an experience the birds did not enjoy. As soon as the researcher let them go, the birds began yelling at their captor with a harsh, aggressive cry called “scolding.”

The sounds of conflict attracted more birds, which joined in scolding and attacking the researcher, even though they’d never met. “The mob of two to 15 birds hounds us, sometimes diving from the sky to within a few meters or less. This pursuit lasts about 100 meters (328 feet) as we walk away,” crow expert John Marzluff told Discovery News.

The Dick Cheney mask did not elicit a response.

Marzluff and his colleagues then traveled to other crow territories. The sight of the caveman mask caused an immediate ruckus among these crows—even though none of them had ever been caught or banded. Crows up to a mile away from the original site had heard about this no-good caveman guy, and they knew he was trouble when he walked in.

The grudge didn’t wear off, either. Marzluff said return trips in the caveman mask provoked the same hostile response, even five years later. He told Discovery News, "Individual crows that are adults can live 15-40 years in the wild (most die when young, but those that make it to adulthood can live a long time) and they probably remember important associations they have formed for much of their lives."

These associations aren't all negative. An 8-year-old girl, also in Seattle, made news last year when her family revealed that local crows had pretty much made her their queen.