Crows and geometry

Do you think understanding geometry is an exclusive human faculty? Think again. Crows, too, have a knack for geometry, says a new study.

Researchers at the University of Tubingen have demonstrated that carrion crows can detect geometric regularity in shapes and can distinguish between different geometric forms, opening up a new window to look at animal intelligence.

Even without schooling, humans can recognise simple geometric rules. They know about symmetry, parallel lines, and can identify odd geometric shapes. The carrion crows—known for their advanced cognitive and arithmetic skills—do the same, and the success rate is way beyond mere chance.

Researchers showed sets of six shapes to two crows and tasked them with spotting the odd one out. The birds aced simple tests like picking a crescent moon from a group of stars with little trouble.

Even on more difficult tasks—identifying a slightly distorted quadrilateral from a group of otherwise very similar regular shapes—the crows still performed well, even when the shapes were randomly rotated and scaled.

Lead researcher Andreas Niedar, who has been working with two male carrion crows for a few years, trained the birds to interact with a touch screen. These birds had previously shown the ability to count, and now they faced a new kind of challenge.

They were presented with an array of six shapes. Five were similar, one was not, and their task was to pick the odd one out. Initially, the birds were given easier tasks—five stars and a crescent moon—to pick up the odd one. The reward was a tasty food: mealworms.

After they consistently succeeded with simple patterns, researchers introduced more complex ones. The new shapes were all quadrilaterals, carefully adjusted to vary in geometric regularity. These shapes weren’t easy to distinguish, as the scientists made only subtle changes like shifting a single corner to distort the shape’s symmetry or right angles.

The birds had never seen these quadrilateral comparisons before, and yet, when tested, they performed far above chance. On their very first try with the quadrilateral shapes, the crows performed strikingly well. Crow 1 correctly picked the outlier in 50% of the trials, while Crow 2 managed 60%. Since there were six options, random guessing would result in a success rate of just 16.7%.

The shapes were randomly rotated and scaled. The irregular shape, called the “intruder,” changed position every trial. Yet both crows maintained impressive accuracy. Their detection rate remained well above chance across 60 initial tests. Even with more complex tasks, the crows performed well above the average.

“Our findings suggest that geometric intuitions are not specific to humans but are deeply rooted in biological evolution,” the researchers reported in Science Advances.