How Smart Are Crows and Ravens? What Experiments Show

Tool makers: New Caledonian crows

The most striking evidence comes from the New Caledonian crow (Corvus moneduloides) of the South Pacific. In the wild these crows strip and shape twigs into hooked tools and cut stepped probes from the barbed edges of pandanus leaves, then use them to fish beetle larvae out of dead wood. Young crows take many months to learn the skill, partly by watching their parents.

In 2002, researchers at the University of Oxford reported that a captive female called Betty had bent a straight piece of wire into a hook to lift a small bucket of food out of a tube. She had never been trained to do it. Later work showed that bending tools is something New Caledonian crows also do with natural materials, but the experiment made Betty world famous.

Other studies have shown these crows solving puzzles in sequence, using a short tool to reach a longer tool and then using that to reach food.

The Aesop’s fable experiments

In Aesop’s fable, a thirsty crow drops pebbles into a pitcher until the water rises high enough to drink. Researchers turned the story into a test. In 2009, captive rooks dropped stones into a tube of water to raise a floating worm within reach, and they chose larger stones, which raise the water faster.

New Caledonian crows solved similar tasks in 2014. They preferred to drop objects into water rather than sand and chose solid objects over hollow ones, performing about as well as children aged five to seven. That comparison is the source of the popular claim that a crow is “as smart as a 7-year-old,” but it applies only to this one kind of task.

Ravens that plan ahead

Planning for the future was long thought to be uniquely human, with perhaps a little in great apes. In 2017, Swedish researchers Can Kabadayi and Mathias Osvath tested captive common ravens. The ravens learned to use a stone to open a puzzle box, then were offered a choice of objects when the box was out of sight. They picked the right tool and kept it, and used it later, even when the box only returned the next day. They also learned to save a token they could trade with a person for food.

Ravens have shown other clever behavior too. In classic tests by biologist Bernd Heinrich, wild-caught ravens pulled up meat hanging on a long string, using bill and foot in turn, with little trial and error. Wild ravens follow wolves to their kills and hide surplus food out of sight of other ravens that might steal it.

Memory, faces and social learning

Corvids have excellent memories. Scrub-jays and nutcrackers hide thousands of seeds and recover many of them months later. Western scrub-jays that were watched by another jay while hiding food often moved it again later when alone, as if they understood that the watcher might steal it.

American crows remember individual people. In long-running studies at the University of Washington, crows learned to scold a mask worn by researchers who had trapped them, and the habit spread to crows that had never been caught. Read the full story in Do crows remember faces?

Mirror self-recognition

In 2008, German researchers reported that Eurasian magpies passed the mirror mark test: when a colored sticker was placed on their throat, where they could only see it in a mirror, some birds tried to remove it. This was the first time a non-mammal had passed. A later attempt to repeat the experiment with magpies did not find the same result, so this finding is still debated.

How does a crow brain work?

A crow’s brain is small in absolute terms, but relative to body size it is about as large as a chimpanzee’s. Birds lack the layered neocortex of mammals. Instead, a region called the pallium, especially an area named the nidopallium caudolaterale, does similar work in decision-making and memory.

Bird brains are also densely packed. A 2016 study found that songbirds and parrots have far more neurons per gram of brain than mammals, so a raven’s small brain holds as many forebrain neurons as the much larger brains of some monkeys.

Scientists describe corvids and great apes as an example of convergent evolution: the two groups evolved similar mental abilities independently, because both are long-lived, social animals that must find varied food in a changing world.

How do crows compare with other smart animals?

There is no single intelligence score, and each species is tested in ways that suit its body. On tool use, planning and problem solving, crows and ravens rival chimpanzees; on self-recognition and social learning they compare well with dolphins and elephants. For a wider ranking, see our list of the smartest animals.