Today, laser surgery can correct, and in some cases even improve, naturally impaired vision in humans. But no laser or corrective lens will allow us to see as well as some raptors, a group that includes many birds of prey that boast superior sight thanks to special anatomical features of their eyes.
Twice the Foveae
The eyes of some species, like the Wedge-tailed Eagle, are nearly the same size as our own—yet these birds can see prey from heights as great as 5,900 feet. Compared to the size of its relatively small head, this bird’s large eyes give it a wide field of vision. And where the human eye has one fovea—a depression in the retina where vision is sharpest—many raptors have two.
Their foveae are also distinctly shaped, deep and convex, as opposed to the rounded and shallow single fovea of our own eye. In a 1978 article for the scientific journal Nature, Allan W. Snyder and William H. Miller proposed that the unique shape of foveae found in some birds of prey may act like a telephoto lens, magnifying their vision, which is perhaps why these feathered predators can spot food from over a mile away.
Vivid Vision
The human eye contains, on average, around 200,000 light-sensitive cone cells—receptors that detect changes in color. Meanwhile, a Golden Eagle’s eye, for example, has close to 1 million such cells. Bird eyes also have four different types of cone cells, versus our three, allowing birds to see a broader color spectrum than humans and other mammals.
Do They See UV?
For years, some raptors have also been thought to have the ability to detect ultraviolet (UV) light. For an airborne predator scanning the ground for a meal from above, that would offer a big benefit: a rodent’s urine trail, which absorbs UV light, might appear bright through the dense brush. Some research, including studies of kestrels and the diurnal Pygmy owl, has suggested that these birds may in fact be able to detect UV. But for others, like the Golden Eagle, UV may not be visible, after all: a 2014 study of the Golden Eagle's genome didn't find evidence for an ultraviolet vision system—and put into question conservation strategies that relied on UV signals, such as using ultraviolet-reflective paint to mark wind turbines to prevent collisions.
Learn more about the senses of different species in our new exhibition Our Senses: An Immersive Environment.