Bird sense is a bizarre thing. Different species of avians have different ways of working their sensations: Penguins can only recognize salty and sour tastes, ducks use touch sensors in their bills to find food, and certain seabirds depend on smells to navigate. But one thing that all birds do share is a type of super vision that makes their world look way more psychedelic than yours or mine.
In a post for the Nature Conservancy’s Cool Green Science blog, ornithologist Joe Smith explains that birds have the ability to see a whole spectrum of colors that are invisible to people. Smith cites a 2007 study that, using a spectrophotometer, analyzed the colors of 166 North American songbird species with no apparent physical variance between the sexes. From a human’s perspective, 92 percent of species have males and females that appear identical, including Blue Jays, Black-capped Chickadees, Red-eyed Vireos, Wood Thrushes, and Carolina Wrens. However, the study revealed that these birds sport colors undetectable by the human eye that differentiate their genders.
When we look at a male Yellow-breasted Chat, for example, we see, well, a yellow breast. But when potential avian mates (or rivals) look at him, they also see ultraviolet feathers on his chest—a hue that sets him apart from the females of his species. (You can imagine why this might be important.) This theory was proven in another study in which taxidermied male and female chats were set up in the wild to see how their living equivalents would react. The males, staying true to their territorial nature, attacked the stuffed male chats and tried winning over the fake females. Clearly, they were seeing something that the researchers couldn't when determining who to court and who to challenge.
But how is it possible for birds to see ultraviolet? The human retina contains three types of photoreceptors, also known as cones, which allow us to distinguish red, yellow, and blue, and all their different combinations. Birds have these three types of cones as well, plus one more cone type that allows them to see ultraviolet. They also have colored oil droplets in their cones that act like special Instagram filters, allowing them to discern even more colors.
So beauty is indeed in the eye of the beholder, and when birds look at each other, they see even more beauty than we do. But just because we can’t access the full spectrum of colors that birds can, that shouldn’t stop us from enjoying what we do see. (You can always pretend that you didn't read this story, and go back to being blissfully unaware.)
For more on how bird sight differs from human sight, read Smith’s story.