Hummingbirds Can See Colors Invisible to Humans, Study Finds
It turns out that hummingbirds are even more magical than previously thought.
According to a new study, the tiny birds can see colors that humans can neither detect, nor even imagine.
Unlike human eyes, which have three types of color-sensitive cones, bird eyes are tetrachromatic, meaning they have four color cones. While humans are able to see spectral hues (the seven colors of the rainbow) as well as one nonspectral color (purple), birds are able to discriminate a much broader range of colors, including the ultraviolet spectrum, which includes colors such as UV-green and UV-red. At least that's the theory. Up until recently, researchers have made few investigations into what birds can actually see.
That's where Mary Stoddard, a Princeton University evolutionary biologist, and her colleagues come in. They carried out a series of field experiments with wild broad-tailed hummingbirds near the Rocky Mountain Biological Laboratory in Colorado. The results, published this week in the journal Proceedings of National Academy of Sciences, revealed the birds could discern spectral-colored feeders from feeders in nonspectral colors.
In layman's terms, hummingbirds can see colors outside the rainbow.
For the study, Stoddard and her team set up several feeders outfitted with LED devices. They programmed the LED devices to turn two different colors, depending upon whether the feeder held either a small amount of sugary water (the hummingbird's food of choice) or plain water.
The hummingbirds quickly learned to associate one color with a rewarding sweet sip, and the other color with unrewarding plain water.
By tracking the birds' visits to the feeders over three field sessions, the scientists showed that broad-tailed hummingbirds consistently chose the feeder with the sweet taste, regardless of whether it had a nonspectral or spectral hue.
"Even when the colors looked the same to us—for example, when the birds had to choose from a feeder colored UV-green and one that was simply green—they could see the difference," Stoddard told National Geographic.
Scientists believe that this amped-up vision helps hummingbirds locate a diverse variety of plants and their nectar. Bees have a similar ability, allowing them to see ultraviolet bull's-eye patterns in yellow flowers that directs them to the nectar.