How Smart Are Crows? Toolmakers, Face Readers and Planners of the Bird World

“Bird brain” is meant as an insult. Yet the crow on the streetlight outside your window may be one of the cleverest animals you will ever meet. Crows and their relatives, a family called corvids that also includes ravens, jays, magpies and rooks, can make tools, solve multi-step puzzles, recognise individual humans and even plan for the future. Some scientists call them “feathered apes”.

A family of clever birds

Corvids are found on every continent except Antarctica and South America’s far south. They thrive in cities as easily as in forests, which itself says something about their flexibility. They live long, often in family groups, and spend a long time learning from their parents, all traits associated with intelligence in other animals.

Toolmakers of New Caledonia

On the Pacific island of New Caledonia lives a crow that has become a celebrity in animal research. In 1996, biologist Gavin Hunt reported in Nature that wild New Caledonian crows make two kinds of tools: hooked twigs and stepped tools cut from the stiff, barbed leaves of the pandanus plant. They use them to pull insect larvae out of holes in dead wood.

Making a hooked tool is not simple. The crow must choose a suitable forked twig, snap it off just below the fork, strip off leaves and bark and then shape the stub of the fork into a hook with its beak. Young crows take months to master the technique, learning partly by watching adults.

In 2002, scientists at Oxford described a crow called Betty. Offered a straight piece of wire and a little bucket of food at the bottom of a tube, she bent the wire into a hook and used it to lift the bucket out. Later research showed that New Caledonian crows bend materials into hooks more often than first thought, but Betty’s flexible problem-solving remains a classic example.

The Aesop’s fable test

In one of Aesop’s ancient fables, a thirsty crow drops pebbles into a pitcher until the water rises high enough to drink. Scientists turned this story into an experiment. A treat floats on water in a narrow tube, too low for the crow to reach. Stones and other objects are placed nearby.

In a 2014 study, Sarah Jelbert and colleagues found that New Caledonian crows quickly learned to drop stones into the tube. They preferred heavy objects that sink over ones that float, and solid objects over hollow ones, and they chose tubes with water over tubes filled with sand. Their understanding had limits, though: in some trickier versions they performed no better than young children, showing that they learn the task step by step rather than fully understanding the physics.

They never forget a face

In Seattle, researchers led by John Marzluff trapped and released a few wild American crows while wearing a particular rubber mask. Afterwards, people wearing that “dangerous” mask were scolded and mobbed by crows on the campus, while a different, neutral mask was ignored. According to the 2010 study in Animal Behaviour, this recognition lasted for years, and the number of crows scolding the mask actually grew. Many of those crows had never been caught themselves. They seem to have learned who was dangerous by watching other crows.

Planning for tomorrow

For a long time, planning for future needs was thought to be uniquely human, perhaps shared with great apes. In 2017, Can Kabadayi and Mathias Osvath tested ravens. The birds learned to use a tool to open a box containing food. Later, they were offered a choice of objects, including the right tool, but the box was not available until the next day. The ravens chose and kept the tool, and used it successfully later. They also learned to save a token that could be traded with a human for food later. The researchers concluded that ravens’ planning skills were comparable to those of great apes.

A small brain packed with neurons

How can a brain the size of a walnut do all this? Part of the answer came in 2016, when Seweryna Olkowicz and colleagues counted neurons in the brains of 28 bird species. They found that the forebrains of corvids and parrots contain primate-like numbers of neurons, because their neurons are much smaller and more densely packed. Some corvids have as many forebrain neurons as some monkeys with much larger brains.

Why did crows become so smart?

Crows and great apes are only very distantly related; their last common ancestor lived over 300 million years ago. Their intelligence evolved independently, an example of convergent evolution. Scientists suggest that similar pressures shaped both: a varied diet that requires flexibility, long lives, complex social groups and a long period of learning when young.

Living with clever neighbours

Crows’ intelligence explains much of what we see in cities: birds that learn rubbish collection schedules, drop nuts onto roads for cars to crack, or remember which neighbour feeds them and which one chases them away. If you treat crows well, they may well remember you.

In short

• Crows and ravens belong to the corvids, some of the cleverest animals known.
• New Caledonian crows make hooked tools from twigs and leaves.
• Crows drop stones to raise water levels, much like the crow in Aesop’s fable.
• American crows remember threatening faces for years and teach others.
• Ravens can plan ahead, saving tools for the next day.
• Corvid brains are small but packed with primate-like numbers of neurons.