Birds Fall For The Same Optical Illusions We Do, And This Experiment Proves It


Dr. Katie Spalding

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer

Hehehe, stoopid birbs. CLICKMANIS/Shutterstock

If there's anything the recent spate of viral illusions has shown us, it's that humans just aren't that great at understanding color. And now, a new study has shown that a certain species of bird might fall into the same traps we do when it comes to sorting their coquelicot from their vermillion.

To find out how zebra finches discriminate between colors, researchers from Duke University conducted an experiment that involved showing female finches a set of small discs in various shades of red and orange. While some were colored a solid red or orange, others were two-toned – the finches were taught to flip over the two-toned discs and leave the solid ones. So, when the birds failed to flip a two-tone disc, it meant they couldn't see that the colors were different. The findings are published in Nature


So why did the researchers choose orange and red for this experiment, as opposed to, say, purple and blue? As with so many things, it all comes down to sex.

You see, zebra finch beaks come in both red and orange shades – a red beak is a sign of good health, so, basically, female finches find red-beaked males sexier. But the study's most interesting finding was bad news for Pantone-challenged males: as senior author Stephen Nowicki explained in a statement, "he’s either red enough or not."

"Females had no difficulty discriminating the most dissimilar pairings. What was interesting was how they treated the various hues in between," reports the statement. "The findings suggest a threshold effect at work – a sharp perceptual boundary where orange turns to red."

Despite a wide range of hues being used, it seems the finches lumped them all into either "red" or "orange" – to the extent that a difference in shade would be noticed if it went over the red/orange boundary but appeared invisible if not. This is unlikely to be because of visual shortcomings, say the researchers – instead, it's the birds' minds that are making the distinction.


"What hits the retina is not always what we see," explained study author Eleanor Caves in the statement.

The phenomenon behind the strange result is "categorical perception" – and humans are no better at it than the bird-brained test subjects. Here, for instance, you'll hear a clear point at which "ba" becomes "pa" – even though no such discrete distinction really exists.

Although it's perhaps frustrating that we're once again at the mercy of our brain's bizarre idiosyncrasies, the researchers say it's actually a crucial cognitive ability – helping animals make important decisions despite having limited or ambiguous information.

"Categorical perception... is perhaps one strategy the brain has for reducing this ambiguity," Caves said. "Categories make it less crucial that you precisely interpret a stimulus; rather, you just need to interpret the category that it’s in."


  • tag
  • birds,

  • color,

  • vision,

  • zebra finches