An animal’s eyes have the capacity of a great language.
—Martin Buber, I and Thou 
These owl eyes speak the language of the night, where owls live and move and have their being. In the morning, under this owl’s winter perch, I find the small gray pellets that are the story of the previous night’s successful hunt: tiny jaw fragments interlaced with fur, a femur, a scapula. Silently sailing through the dark forest, scanning for signs of prey, owls read a visual language lost to us in our diurnal speech.
Can imaginative presence help us glimpse the owl’s language? Let’s look at a scene from the forest at night, first through our own eyes, then through the eyes of the owl. Here’s the human image.
Not a lot of information here that we can use, right? Here’s how an owl might see the scene.
Like other animals that are fluent in night-language, owls have eyes that are beautifully equipped to read light and shadows. How do they do this? Eyes have two different ways of interpreting light: rods are the cells in eyes that are activated just by receiving photons, and cones are tickled by specific wavelength ranges. In owl eyes, the rods are much more densely packed than those of diurnal creatures. Since color isn’t that important at night, evolution has benefitted owls by allocating more retina real estate to those cells (rods) that give them helpful night information.
Here’s another way that owls’ eyes are adapted to help them read better at night. Look at the shape of this young Barred Owl’s cornea:
His eyes’ dramatically curved shape, in combination with the widely expandable pupils you can see in the first photo, helps him gather light from many directions. When all those photons get to the very large retinas at the back of his eyes, they provide lots of information to his brain to help him read the forest to find food.
Given how important they are, it’s not surprising that the owl’s eyes take up so much space in his head that there’s only a thin divider between them—so thin that light from one eye can filter through into the other. Jerry Waldvogel has pointed out that if our eyes were proportionally the same size as the owl’s, they’d be as big as tennis balls in our heads! 
Finally, our owl is unusual even among birds in that the place on his retina with the sharpest vision (the fovea) is packed with rods, not cones, giving him enhanced sight where he focuses. So when the owl’s amazing hearing helps him focus on a movement in the forest scene above, he might see something like this:
And once his attention becomes riveted:
While it is the owl’s exquisite hearing that lets him finally decide where to pounce, his remarkable night vision helps him read the forest, so that he can navigate his way through and hone in on his prey’s location.
* * * * *
We used to be creatures of the night, too. Our earliest mammal ancestors lived their lives in the Mesozoic darkness—and our eyes tell that history.
As I’ve noted previously, most humans’ eyes contain three different types of color-sensing cells. Each type is most sensitive to a particular light wavelength (medium blue, green-yellow, or orange), and our brains interpret the combination of signals sent by all types to yield our sense of color. This gives us a wonderful visual dimension beyond what many mammals can perceive; for instance, dogs and cats have just two types of color sensors.
But most birds have four-color vision, generally including a separate kind of cell that is sensitive to ultraviolet. They inherited this rich way of seeing their world from their dinosaur ancestors, who probably also could see a much more colorful world than we can. Although there’s currently no way we can truly envision or simulate how it would be to see this way, I imagine that the forest scene in daylight might look something like this to such a bird (right), compared to human vision (left):
These birds’ eyes speak a syntax of saturation, words of hues: the ultimate “colorful language” of which we can only dream. Why did we mammals lose some of our ability to sense colors?
Because we were scared of dinosaurs.
Back in the Mesozoic when they first appeared, little mammals would have made a nice snack for a hungry dinosaur—most of whom hunted during the day.
So our ancestors scuttled into hiding places during the day and waited until darkness to emerge (tiptoeing carefully around snoring dinos), learning to hunt by night. Because our little fuzzy forebears’ fancy color vision wasn’t much use at night, space in their retinas was much more valuable for rods that could help them see in the dark, and they eventually lost two of the four types of cones they’d started with. We began our own mammalian history with vision shaped by dinosaur appetites.
Once that handy meteor winnowed out a lot of those big pesky predators and turned the rest into birds, though, mammals could creep out of the darkness and relearn how to live in light. Genetic mutations in many primates and some marsupials recreated a third type of cone, and we humans got lucky and evolved from those lines.
But our history, our dawn in Mesozoic roots, is still told by the stories in our dinosaur-shaped eyes, eyes that once spoke the “great language” of the night. As we encounter the deep gaze of the owl, we can see traces of a shared history, echoes of an ancient intimacy—an eye-Thou relationship of epochal duration.
 Buber, Martin, and Walter Arnold Kaufmann. I and Thou by Martin Buber; a new translation with a prologue and notes by Walter Kaufmann. Simon & Schuster, 1970, p. 144.
 Waldvogel, Jerry A. “The bird’s eye view.” American Scientist 78, no. 4 (1990): 342-353.
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