The All-New Book of Amazing Facts, Volume 1

12 Among the most unusual of birds, bald eagles primarily eat fish and live up to forty years in the wild. Furthermore, they are monogamous, remaining faithful to their mate until death. But these amazing birds are especially known for their keen eyesight. Eagles have two foveae, or centers of focus, in the retina of each eye that allow them to see both forward and to the side at the same time. (Human retinas have only one.) Depending on which way the eagle looks, the lens of its eye focuses an image on one fovea or the other. The rear fovea is for forward stereoscopic vision, and the other is for looking sideways. Both foveae are more densely lined with rods and cones than those of human eyes, giving them much greater resolving power. They also have eyelids that close during sleep. For blinking, they have an inner eyelid called a nictitating membrane. Every three or four seconds, the nictitating membrane slides across the eye from front to back, wiping dirt and dust from the cornea. Because the membrane is translucent, the eagle can see even while the membrane covers the eye. Eagles have color vision, and while their eyes are not as large as a human’s, their sharpness is at least four times that of an individual with perfect vision. While soaring, gliding, or flapping, they are capable of seeing fish in the water from several hundred feet above. An eagle flying in a fixed position at an altitude of 1,000 feet could spot prey as small as a rabbit over an area of almost three square miles! An eagle’s eyes are impressive, but the Creator’s eyes see every detail of our lives. “The L ORD is in His holy temple, the L ORD ’ S throne is in heaven; His eyes behold, His eyelids test the sons of men” (Psalm 11:4). Bald Eagles Unmatched Eye Sight Animals & Biology