Consider the common starling, a bird that, to human eyes, appears at a distance to be plain black, known for massive flocks that irritate homeowners when in a nearby tree. Up close, the plain coloration shows more depth and texture, with flecks of lighter colors and hints of iridescence at certain angles, but still, nothing like fancier peacocks or tropical parrots. Or is it?
In recent decades, bird biologists have discovered that many bird species have coloration in the invisible (to humans) ultraviolet (UV) spectrum, beyond the human capacity to perceive. In addition, bird eyes are significantly different from human eyes, allowing birds to see details and colors we can’t even imagine.
All animals detect and perceive colors using small cells in the back of the eye called rods. These are embedded in the retina, and when light a certain wavelength, which determines the color, hits that cell, we see that color. Humans and most other mammals have three different kinds of cones, sensitive to light roughly corresponding to violet, green, and yellow-green, and the combination of these gives us the palette of colors we perceive.
Birds, on the other hand, have four different kinds of cones, with an additional one sensitive to light in the UV range. In addition, bird retinas have other structures, such as small oil droplets that act as wavelength filters, and the arrangement of the cells in the retina that give them significantly improved resolution and range of color detection.
In UV light, the plain starling lights up with additional markings and a rainbow of colors. Many other bird species exhibit this characteristic, and researchers now know that the ability to see UV impacts hunting, breeding, competition for resources, and habitat selection.
As the descendants of the dinosaurs that once dominated the Earth hundreds of millions of years ago, presumably this trait was one shared by most animals of that era. We know the younger atmosphere blocked less UV back then, and we see similar UV coloration in insects. More ancient lineages of plants also have adaptations to UV. These features have been around for a very, very long time, right under our noses, and we’re only now just beginning to appreciate how important they are for birds, insects, and plants.
Why this blind spot, so to speak, about bird vision? Part of it is due to availability of tools and technology for studying it, which only recently became cheap and accessible enough for widespread use by researchers. Part of it is lack of communication between biologists in other fields, but part also is due to a lack of imagination. It’s very difficult to formulate theories about problems you can’t perceive, until you have data right under your nose proving they exist, especially when they challenge preconceived notions.
What does all this mean for us today? First thing that’s clear is that there’s a lot going on around us in the world that we have no clue about. The human nervous system, for all we can do and achieve, is still a very crude tool for perceiving and understanding the infinite complexity of the universe.
That’s not to say that these things are unknowable; they are. That knowledge can be discovered and acquired through science, not common sense. Collecting reliable data, analyzing it, formulating new theories, collecting more data: the pursuit of more and better evidence and the reexamination of what it means never ends. Science extends our senses, our perceptions, and thereby our understanding.
Another lesson is that progress is not linear, or even guaranteed. Complex, wonderful things can be lost, but they can also be regained. Biologists resist judgments like “the bird eye is better than a human eye” but it’s pretty clear they, and their dinosaur ancestors, see a lot more of what’s going on in the natural world than we do.
Other important, wonderful things can be lost if we don’t look past our personal biases, emotions, and tribal instincts and see the world as it is, not as we want it to be, no matter how strong those feelings are. Otherwise, we risk joining the dinosaurs.
Robert Wack writes from Westminster. He can be reached at Robert.firstname.lastname@example.org.