Angry Birds

IT TURNS OUT A CROW CAN HOLD A SERIOUS GRUDGE. If you annoy one, it won’t forget your face anytime soon. The next time you cross paths, it’ll squawk angrily. That’s the crow’s way of saying, “I know you, and I don’t like you. Get lost!”

In the mid-2000s, wildlife ecologist John Marzluff of the University of Washington was studying how the growth of towns and cities affects crows, and how crow populations affect other birds. As part of his research, Marzluff and his students captured crows, put identification bands on their legs, and then released them. As the team worked, Marzluff noticed that nearby crows watched him closely—and they didn’t like seeing friends and mates get caught.

Crows are intelligent animals. They can solve puzzles, use tools, and have excellent memories—as Marzluff would come to find out. He was curious about the birds’ reaction to members of their flock being trapped and released by his team. That led to a nearly two-decade-long investigation into how well crows recognize people.

A CROW CAN HOLD A SERIOUS GRUDGE. Annoy one, and it won’t forget your face anytime soon. The next time you cross paths, it’ll squawk angrily. That means “I know you, and I don’t like you. Get lost!”

In the mid-2000s, John Marzluff was studying crows. Marzluff is a wildlife ecologist at the University of Washington. He examined how the growth of towns and cities affects crows, and how crow populations affect other birds. For his research, Marzluff and his students captured crows. They put identification bands on their legs and then released them. As Marzluff’s team worked, nearby crows watched closely. Their friends and mates were getting caught, and the crows didn’t like it.

Crows are intelligent animals. They can solve puzzles and use tools. They also have excellent memories, as Marzluff would find out. He saw the birds’ reaction when his team trapped and released members of their flock. Marzluff was curious. How well did crows recognize people? So he began an investigation. It lasted nearly two decades.

Marzluff’s team repeated the walks several times to replicate their results. The crows’ responses to the masks stayed consistent. But over time, the proportion of crows mobbing and scolding the researcher in the caveman mask increased. Word seemed to be spreading among the birds that the mask wearer was a threat.

“When crows hear scolding and join a mob, they learn that something is potentially dangerous,” Marzluff explains. “Next time they see it, those crows scold and warn others. It’s a way they share learned behavior. In this case, they learned to hate the masked guy on campus!”

Marzluff’s team needed to replicate their results. So they repeated the walks several times. The crows’ responses to the masks stayed the same. But over time, more crows began mobbing and scolding the researcher in the caveman mask. The birds saw the mask wearer as a threat. And they seemed to be spreading the word.

“When crows hear scolding and join a mob, they learn that something is potentially dangerous,” Marzluff explains. “Next time they see it, those crows scold and warn others. It’s a way they share learned behavior. In this case, they learned to hate the masked guy on campus!”

Marzluff’s results suggested crows hold a grudge. But the investigation had some limitations—aspects of the design that can affect its outcome. Maybe crows at a college responded differently from crows elsewhere. Or maybe they reacted to the caveman mask because they didn’t like it, not because someone wore it while trapping crows.

To find out, Marzluff and his team repeated their experiment at four other locations around Seattle, Washington, over the next few years. They used several human masks. And they mixed up the roles of the masks: A mask designated “dangerous” (worn while trapping crows) at one site would be the control mask (worn without bothering crows) at another. No matter which masks were used, crows scolded the mask worn during catch and release.

Back on campus, Marzluff continued his masked walks once a year. Scolding by crows increased for several years. After that, it slowly lessened, perhaps as crows from the 2006 capture gradually died of old age. By 2024, 18 years later, only an occasional bird scolded him.

Marzluff’s findings show that crows have a long memory. Such intense grudge-holding may protect the birds from threats. “The American crow has lived closely with people for millennia,” he says. “Their world is basically the human world, so it’s important for them to be able to recognize potentially dangerous people.”

Marzluff’s results suggested crows hold a grudge. But the investigation had some limitations. Parts of the design could have affected its outcome. Crows at a college might react differently from crows elsewhere. Or maybe they just didn’t like the caveman mask. Maybe their reaction wasn’t because it was worn during trapping.

Marzluff and his team decided to find out. Over the next few years, they repeated their experiment at four other locations around Seattle, Washington. They used several human masks. And they mixed up the masks’ roles. At one site, a mask was “dangerous” (worn while trapping crows). At another site, that same mask was the control mask (worn without bothering crows). The crows always scolded the mask worn during catch and release. It didn’t matter which mask it was.

Marzluff continued his masked walks on campus once a year. The crows’ scolding increased for several years. After that, it slowly lessened. Maybe the crows from the 2006 capture were dying of old age. Eighteen years passed. By 2024, he heard only a little scolding here and there. 

Marzluff showed that crows have a long memory. Such strong grudges may protect them from threats. “The American crow has lived closely with people for millennia,” he says. “Their world is basically the human world, so it’s important for them to be able to recognize potentially dangerous people.”