Do Crows Remember Faces? The Famous Mask Experiments Explained

The caveman mask experiment

The best-known study began in 2006 in Seattle. Wildlife biologist John Marzluff and his colleagues needed to trap and band crows on the university campus, and they noticed that the birds seemed to remember the people who had caught them. To test this properly, they used masks.

While trapping and banding seven crows, the researchers wore a rubber “caveman” mask, which became the “dangerous” face. A different mask was worn only while walking calmly around campus, never during trapping, as a neutral control. Afterward, volunteers walked set routes wearing one mask or the other and recorded how the crows behaved.

The results were clear. Crows scolded and mobbed people wearing the caveman mask, diving and giving harsh alarm calls, but mostly ignored the neutral mask. It did not matter who was under the mask, how tall they were or what they wore. Even when the dangerous mask was worn upside down, the crows twisted their heads to look and still scolded.

The grudge spread to other crows

The most surprising result was how the reaction grew. Soon after the trapping, about a quarter of the crows met on the walks scolded the dangerous mask. Over the next few years that share rose to around two-thirds, even though only seven birds had ever been caught and no more trapping took place.

A follow-up study published in 2012 explained why. Young crows learned to fear the mask from their parents, and adult crows learned from neighbors that joined in a mobbing. Knowledge about the dangerous face spread through the crow population and across the campus, a clear example of social learning in wild birds. Marzluff has said the scolding went on for well over a decade before finally fading away.

What happens in a crow’s brain

In 2012 the same team scanned the brains of captive crows while showing them the face of a person who had captured them, and a familiar face of a person who had fed them. The threatening face activated brain regions linked to fear and learning, including an area similar to the mammalian amygdala, while the caretaker’s face activated areas linked to motivation and reward.

This suggests that crows process faces in ways broadly similar to mammals, even though bird and mammal brains are organized very differently. For more about corvid brains, see How smart are crows and ravens?

Why would crows need to recognize people?

American crows are long-lived, territorial and live in family groups, often in towns and cities where they meet the same people every day. Telling a harmless neighbor from someone who throws stones, shoots or raids nests saves time and energy, because the crow can relax around most people and save its alarm for the few who matter.

Sharing that knowledge also helps the whole family. A young crow does not have to be attacked to learn who is dangerous; it simply copies the scolding of older birds. Crows learn about predators such as hawks and owls in the same way, by mobbing them together.

Do crows remember kind people too?

Many people who feed crows report that the birds recognize them, follow them down the street or wait for them at the same time each day. This fits what is known about crow memory, but most of these accounts are anecdotes rather than controlled experiments. Stories of crows leaving “gifts” for people who feed them are popular, but they have not been studied scientifically.

The brain-scan study does show that crows treat a familiar, food-giving person differently from a threatening one, so friendly recognition is very likely real.

Other animals that recognize people

Crows are not alone. Researchers in Florida found that northern mockingbirds quickly learned to flee from a person who had approached their nest, while ignoring other passers-by. Black-billed magpies in South Korea recognized researchers who had climbed to their nests, and feral pigeons in Paris learned to avoid a person who chased them. Among mammals, dogs, horses, sheep and elephants recognize individual people.

What makes crows special is how long they remember and how quickly the knowledge spreads to birds that were never involved.

What to do if crows scold you

If crows dive and scold, it is usually spring and there are fledglings nearby, sitting on low branches or on the ground. The adults are warning you away rather than trying to hurt you. Give the area a wide berth for a few days until the young can fly well. Never pick up or handle a fledgling crow; in the United States it is protected by law, and its parents are almost always nearby.