If somebody does you wrong, you’ll probably remember their face. But what if the offender was a cat, or a fish? Recognizing individuals from other species is not easy, but it's not impossible—at least, not for skuas. A new study published in the journal Animal Cognition shows that the Antarctic birds identified and attacked any researcher who had previously touched their nests.

In recent years, scientists have learned that other birds can recognize individual people. Crows, magpies, and mockingbirds have all been shown to attack people who have bothered them before. But crows, magpies, and mockingbirds spend a lot of time around people, and so it makes sense that they’d develop these specialized defensive talents.

But the brown skua (Stercorarius antarcticus) lives in Antarctica—a place that’s been fairly human-free for a long time. Only in the last half-century or so have humans really made their presence in Antarctica known. So when a team of South Korean researchers set out to study the skuas’ habitats, they were not expecting to become the (very reasonable) objects of bird grudge.

The scientists had originally intended to examine the birds’ nests once a week and record their observations. But soon after they started their weekly checkups, the attacks by skua adults began—and, the researchers realized, it seemed personal. Skuas are big birds, with wingspans that can reach more than 5 feet, so these attacks were not trivial.

To make the most of this unexpected behavior, the team incorporated the attack patterns into their research, taking notes each time the birds became aggressive.

They found that a single researcher only had to visit a nest three to five times before they ended up on the birds’ hit list. To test whether the attacks really were personalized, the team began sending two researchers on nest visits: one who had bothered the birds before, and a neutral person who the birds had never seen. Sure enough, the neutral person could approach and walk away safely, but the known nest-invaders were always attacked, with yelling, aggressive flying, and kicks to the head.

This was true even when the researchers wore identical clothing, and even in crowds. The birds still only attacked the offenders and not the innocent bystanders.

“Even when I changed my field clothes, they followed me,” researcher Yeong-Deok Han said in a press statement. "The birds seemed to know me no matter what I wear." The researchers think the birds were using facial features and posture to tell the people apart.

Skuas are not the only birds in the area, but they are the only ones that seem to be able to spot people they don’t like. The researchers say that’s probably because they’re smarter than their neighbors; scientists had previously seen skuas swiping food from even bigger birds, and they’ve even been known to barge in on nursing seals to steal their breast milk.