Intruder detection task. Two carrion crows were trained to detect an intruder stimulus in an array of six simultaneously presented stimuli. The crows initiated the trial by moving their head in front of the screen whenever a go-stimulus appeared. After a prestimulus period of 200 ms, an array of six stimuli was displayed. The crows responded by pecking on the intruder. In 50% of the trials, the crows were tested with non-quadrilateral background stimuli (top); in this example, the crescent is the intruder among stars. In the other 50% of the trials, the crows were tested with quadrilateral probe stimuli (bottom); in this example, a nonsymmetric quadrilateral is the intruder among symmetric quadrilaterals. Credit: Science Advances (2025). DOI: 10.1126/sciadv.adt3718
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Intruder detection task. Two carrion crows were trained to detect an intruder stimulus in an array of six simultaneously presented stimuli. The crows initiated the trial by moving their head in front of the screen whenever a go-stimulus appeared. After a prestimulus period of 200 ms, an array of six stimuli was displayed. The crows responded by pecking on the intruder. In 50% of the trials, the crows were tested with non-quadrilateral background stimuli (top); in this example, the crescent is the intruder among stars. In the other 50% of the trials, the crows were tested with quadrilateral probe stimuli (bottom); in this example, a nonsymmetric quadrilateral is the intruder among symmetric quadrilaterals. Credit: Science Advances (2025). DOI: 10.1126/sciadv.adt3718
A trio of animal physiologists at the University of Tübingen, in Germany, has found that at least one species of crow has the ability to recognize geometric regularity. In their published in the journal Science Advances, Philipp Schmidbauer, Madita Hahn and Andreas Nieder conducted several experiments that involved testing crows on their ability to recognize geometric shapes.
Recognizing regularity in geometric shapes means being able to pick out one shape that is different from others in a group—picking out a plastic star, for example, when it is placed among several plastic moons. Testing for the ability to recognize geometric regularity has been done with many animals, including chimps and bonobos. Until now, this ability has never been observed in any creature except for humans.
Because of that, the team started with a bit of skepticism when they began testing carrion crows. In their work, the testing was done using computer screens—the birds were asked to peck the outlier in a group; if they chose correctly, they got a food treat. The team chose to test carrion crows because prior experiments have shown them to have exceptional intelligence and mathematical capabilities.
All the birds tested caught on right away. Each could pick out a star if it was placed within a group of rectangles, for example. To determine their level of skill, the researchers started showing them objects that were only slightly different: one box that was tilted slightly, for example, among others that were not. Their accuracy went down, but it was still much higher than chance.
Example of a canonical probe stimulus layout. Here, a deviant shape (in the top-left position) was placed amid five right hinge reference shapes and had to be recognized as the intruder. Credit: Science Advances (2025). DOI: 10.1126/sciadv.adt3718
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Example of a canonical probe stimulus layout. Here, a deviant shape (in the top-left position) was placed amid five right hinge reference shapes and had to be recognized as the intruder. Credit: Science Advances (2025). DOI: 10.1126/sciadv.adt3718
Continued testing showed that the birds had some understanding of right angles, parallel lines and even some degree of symmetry.
The research team suggests their experiments were quite convincing—the crows were very obviously able to recognize geometric regularity. They note that the experiments also showed that the birds could do so with no prior learning. The findings strongly suggest that the ability exists in other animals as well.
(A) Test stimulus set. The crows were tested with a stimulus set consisting of five pairs of nonquadrilateral shapes used as familiar background stimuli that had been used during training (left) and five pairs of quadrilateral shapes used as probe stimuli (right). (B) The five quadrilateral reference shapes used to test deviation from geometric regularity. From left to right, the quadrilaterals increasingly differed in geometric properties (parallelism, symmetry, perpendicularity, equal sides, and equal angles). Here, they are ordered from left to right by decreasing regularity. Credit: Science Advances (2025). DOI: 10.1126/sciadv.adt3718
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(A) Test stimulus set. The crows were tested with a stimulus set consisting of five pairs of nonquadrilateral shapes used as familiar background stimuli that had been used during training (left) and five pairs of quadrilateral shapes used as probe stimuli (right). (B) The five quadrilateral reference shapes used to test deviation from geometric regularity. From left to right, the quadrilaterals increasingly differed in geometric properties (parallelism, symmetry, perpendicularity, equal sides, and equal angles). Here, they are ordered from left to right by decreasing regularity. Credit: Science Advances (2025). DOI: 10.1126/sciadv.adt3718
More information:
Philipp Schmidbauer et al, Crows recognize geometric regularity, Science Advances (2025).
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Crows have demonstrated the ability to recognize geometric regularity, a skill previously observed only in humans. Experiments showed that carrion crows could identify outlier shapes among groups, such as a star among rectangles, using computer screens. Their accuracy remained high even with subtle differences, indicating an understanding of right angles, parallel lines, and symmetry. This suggests that such cognitive abilities may exist in other animals as well.
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