To find the best food and the best mates, chickens and other birds must be able to see color reliably under any lighting conditions, according to findings published in Proceedings of the Royal Society B last month.
Over the course of a day, the illumination spectrum changes. An open field, for example, would bask in more sunshine than a shady forest. And that means the spectrum of light that strikes the eyes from the same object also changes. To us, a banana appears yellow in different kinds of lighting. This happens despite the fact that information about the banana that actually reaches the eyes in red illumination is closer to that of an orange color in white illumination. This ability to keep color perception constant despite changes in the spectrum is known as “color constancy”. Without it, color wouldn’t provide reliable information since the perceived color would change depending on the lighting.
While this phenomenon is present in a variety of animals, it’s only been tested in humans, goldfish, and honey bees. Now, to test this in chickens (Gallus gallus), a trio led by Lund University’s Peter Olsson trained six mixed-breed chickens and 16 Lohman White chickens to discriminate colors, and then tested their performance in different illuminations.
During training, the birds were kept in a space with white light fluorescent tubes and food containers that were red, yellow, or orange. The birds were rewarded with crumbs if they selected the orange container. When training was over, the team watched the chickens make their choices as the light in the room was switched to varying shades of red. The chickens continued to pick out the orange container.
"We studied many different lighting conditions to find out how big the changes in light could be without the chickens losing their color constancy,” Olsson said in a statement. Not only can chickens maintain their color constancy in lab settlings that have far more exaggerated shifts in light than those they’d find in nature, chickens can compensate for larger illumination changes than both goldfish and honeybees.
C. Schubert/Lund University