As a species, we humans are quite taken with our intelligence and supposedly expanded awareness compared to other living creatures. In reality, we don’t see nearly as much.
Hummingbirds, for instance, can see four dimensions of color, as opposed to humans’ three, new research has shown. In addition to the three types of color-sensitive cones that human eyes have, hummingbirds have a fourth, and that one is sensitive to ultraviolet light.
“Humans are color-blind compared to birds and many other animals,” said Mary Caswell Stoddard, an assistant professor in the Princeton University Department of Ecology and Evolutionary Biology, in a statement from Princeton about the study, published in Proceedings of the National Academy of Sciences earlier this month. “Not only does having a fourth color cone type extend the range of bird-visible colors into the UV, but it also potentially allows birds to perceive combination colors like ultraviolet plus green and ultraviolet plus red _ but this has been hard to test.”
Human eyes are attuned to red, green and blue light, and some mixtures of those, but that’s it, the researchers explained. People see mostly spectral colors, which are made up of just one sliver of the visible light spectrum, ranging from red to violet, as Inside Science explained. We see some non-spectral colors that do not show up in the rainbow, such as purple, which we perceive when light rays activate the red and blue cones in our eyes without activating the green.
The researchers tested whether, for instance, birds would see a mixture of ultraviolet and red as a separate color, given that humans would simply see red, Inside Science said.
To find out what birds see, the researchers planted themselves in an alpine meadow for three summers running. The team from Princeton, the University of British Columbia, Harvard, the University of Maryland and the Rocky Mountain Biological Laboratory (RMBL) built feeding stations equipped with special tubes displaying a broad range of colors, including those humans can’t see.
“Most detailed perceptual experiments on birds are performed in the lab, but we risk missing the bigger picture of how birds really use color vision in their daily lives,” Stoddard said in a statement from UBC. “Hummingbirds are perfect for studying color vision in the wild. These sugar fiends have evolved to respond to flower colors that advertise a nectar reward, so they can learn color associations rapidly and with little training.”
“It was amazing to watch,” said Harold N. Eyster, a Ph.D. student at UBC and a co-author of the study. “The ultraviolet plus green light and green light looked identical to us, but the hummingbirds kept correctly choosing the ultraviolet plus green light associated with sugar water.”
Watching another creature perceive something that humans cannot was tantalizing.
“The colors that we see in the fields of wildflowers at our study site, the wildflower capital of Colorado, are stunning to us,” said co-author David Inouye, with the University of Maryland and RMBL. “But just imagine what those flowers look like to birds with that extra sensory dimension.”