If you love the color red, you're in good company. Zebra finches love red, or at least, the males of the species have red beaks and female zebra finches love them. But if you have a specific favorite shade of red, such as lava red or scarlet, while you can determine which is your favorite, the birds might have a much harder time.

Researchers found that zebra finches categorize hues from light orange to dark red into two distinct groups--either orange or red. In an experiment, researchers picked eight hues that represented typical male beak colors.

A Boundary Line Between Orange And Red

They showed female finches a set of quarter-sized paper discs, some of which had two tones, and some of which had one solid color. The researchers taught the birds that if they flipped over the bicolor discs first, they received a treat. Then, they tested whether the finches would flip over the bicolor disc first even if the bicolored discs featured colors close together on the color spectrum.

Interestingly, the finches seemed to perceive a boundary line between orange and red. They were better at distinguishing between two colors that were on opposite sides of the boundary line than two colors on the same side, even if the colors in the pairs were equally far apart on the spectrum.

Humans categorize colors like that too, which implies that our perception of color has deep biological roots.

Thank you to Innes Cuthill of the University of Bristol for reviewing this episode's script.

Sources And Further Reading:

• Caves, Eleanor M. Green, Patrick A. Zipple, Matthew N. Peters, Susan. Johnsen, Sönke. Nowicki, Stephen. Categorical perception of colour signals in a songbird. Nature: volume 560, pages 365–367 (2018). Accessed November 12, 2018.
• Duke University. "Birds categorize colors just like humans do: Zebra finches perceive only red or orange, even when the truth falls somewhere in between." ScienceDaily. August 1, 2018. Accessed November 12, 2018.