Compared to hummingbirds, we humans are practically colorblind. This is according to research done with wild broad-tailed hummingbirds, with a team led by evolutionary biologist Mary Caswell Stoddard from Princeton University. Humans are pretty amazing (at least we think we are!), but it turns out that certain members of the animal kingdom have us beat where the eyesight thing is concerned. The difference is in the ability to distinguish non-spectral colors. which include ultraviolet wavelengths. The way that color is perceived by these hummingbirds, and most birds, may inform many of their basic activities of daily living, including mating, feeding, and even escaping the grip of predators. (1)
How Hummingbirds See Color Differently
Human eyes have three kinds of color-sensitive cone cells in our eyes, but many birds have four. This allows them to not only perceive the different colors that we can see but to perceive different kinds of colors too. Where we just see variations and mixes of reds, yellows, and blues, birds see into the ultraviolet ranges.
For example, our human brains can perceive the color purple. It’s just a mix of red and blue, no big deal. But with the extra cone, birds become sensitive to more kinds of light wavelengths that are present. Where we just see the purple, they can pick up on ultraviolet and red, or ultraviolet and yellow for example. It is believed that with their extra cone cell, birds may be able to perceive as many as five non-spectral colors: purple, ultraviolet+red, ultraviolet+green, ultraviolet+yellow, and ultraviolet+purple. (1)
Bird Vision: Testing For What We Can’t See
As you might imagine, it’s a little hard to know what hummingbirds see. We can’t possibly see what they’re seeing. You see? So you might be wondering what the testing looked like.
Caswell and her research team fitted hummingbird feeders with LED lights. These were programmed to display a wide range of colors, including non-spectral colors that humans cannot perceive. For the feeders themselves, half of them had sugar water in them and the other half offered plain water. Then they would swap out the location of the feeders, testing whether the birds could use the color they were seeing to accurately distinguish which feeder was which.
This experiment was done thousands of times over the course of more than three years. They were able to repeatedly confirm that hummingbirds show a preference for the water stations that display the ultraviolet color. In this way, the findings support that hummingbirds can indeed perceive the ultraviolet color that humans cannot.
The study’s co-author and Ph.D. student Harold Eyster from the University of British Columbia had this to say: “It was amazing to watch. The ultraviolet+green light and green light looked identical to us, but the hummingbirds kept correctly choosing the ultraviolet+green light associated with sugar water. Our experiments enabled us to get a sneak peek into what the world looks like to a hummingbird.” (1)
Findings like these are so fascinating because they imply just how much there is out there that we don’t know. With experiments like this, we are able to test for what we know we don’t know, or can’t see. But it also reminds us there are likely whole realms of existence that we don’t even know yet that we don’t know about. That’s pretty awe-inspiring.
