The crow stared at the screen, as it had many times before. Six shapes appeared. Five were neat, balanced, regular; one was not. The crow tilted its head, paused, and tapped the odd one out. A chime sounded and worm dropped. Another test was over, demonstrating something profound about crow intelligence.

That crow, without ever studying mathematics, had seen a key geometrical property. It had grasped something many scientists once believed only humans could truly understand: the intuitive logic of shapes.

Crow geometry

We humans are seemingly born with geometry. From toddlerhood, we favor symmetrical faces, build with blocks, and draw rectangles even before we write letters. We don’t have to learn what “regular” geometry looks like, we just know. And we’ve long thought that this intuitive geometry — our sense for straight lines, right angles, parallel edges — was part of our special cognitive heritage.

Turns out, it’s not.

The experiment, led by Philipp Schmidbauer and Andreas Nieder at the University of Tübingen, started with two carrion crows. The crows were aged 10 and 11, respectively. They were trained to spot the “intruder” in a group of visual stimuli — a shape that didn’t match the rest. Initially, the intruders were easy to spot: a red blob among green ones, a spiky pattern among smooth.

Then the crows were shown six quadrilaterals — four-sided shapes. Five shared a regular structure: squares, rectangles, symmetrical trapezoids. The sixth was off. A corner poked out too far, or an angle was wrong.

The crows had never been trained to care about angles or symmetry. But they picked out the intruder far more often than chance would allow. They were seeing the geometry.

“Claiming that it is specific to us humans, that only humans can detect geometric regularity, is now falsified,” says Nieder for NPR. “Because we have at least the crow.”

Brilliant bird brain

Geometry, like language, was long thought to be uniquely human. Sure, animals navigate spaces. They remember routes and recognize places. But most scientists didn’t think they recognize geometric rules. Which begs the question, why do they have this ability?

Corvids — crows, ravens, jays — are notorious for being brainy birds. They recognize themselves in mirrors, plan for the future and use tools with such sophistication that some researchers compare them to chimpanzees. But their brains don’t resemble ours. They don’t even have a neocortex, the six-layered sheet where mammals store most of their abstract thoughts. But they have a pallium, and that pallium somehow produces what looks a lot like abstract thought.

They are also highly visual, flight-dependent animals. They must quickly assess the shapes and spatial relationships of branches, gaps, and tools to navigate, land, and forage safely. Recognizing symmetry and detecting subtle irregularities in shapes could help them judge whether a perch is stable or a twig is usable.

Back in 2021, a similar experiment was done with baboons, and they really struggled. Despite extensive training, they didn’t show any consistent ability to pick out the geometrically odd shape. What this crow study suggests is that some forms of reasoning — especially those useful for navigating complex environments — may not require mammalian hardware. Evolution found another way.

Crows are breaking human monopoly

For decades, the narrative in cognitive science has been that certain abilities — language, logic, mathematics — are uniquely human. Time and time again, we’ve seen these boundaries fall.

Bees can count. Parrots can mimic human speech in ways that suggest understanding. Dolphins recognize themselves in mirrors. And now, we know crows can also pick out geometric irregularities without help.

This doesn’t mean crows are doing geometry homework in their nests. But they have the raw perceptual building blocks that form the basis of geometry — and this is enough to challenge what we think about geometry.

Nieder believes there are other species that have this ability as well that bear researching. But he also calls for more study into the brains of crows. It’s important to understand why we share such fundamental skills with creatures that are so different from us and how such skills evolved.