Mission Statement

          Birds and people are "sight animals." For both, the eyes are the dominant sense organs, vastly more important than their inferior sense of smell. The reasons for our sensory similarity to birds can be found in human evolutionary history. At one point the ancestors of Homo sapiens were small, tree-dwelling primates. When leaping from limb to limb and snatching of insect prey with the hands, sharp, binocular vision was very handy; those of our forebears that tried instead to smell the location of a branch on which to land were unlikely to survive to reproduce. And since in the breezy treetops odors quickly dissipate, they do not provide good cues for detecting food, enemies, or mates. Birds, flying higher and faster than primates leap, naturally also evolved sight as their major device for orienting to the world.
​          Most birds have binocular vision. It is especially well developed in predators that must precisely estimate ever-changing distances to moving prey. Their eyes tend to be rotated toward the front of the head, so that the visual fields of each eye overlap to some degree. This trend is most pronounced in owls, whose eyes are almost as completely overlapping in field as ours. Small birds that are likely to be prey for raptors tend to have their eyes set on the sides of the head, permitting them to watch for danger in all directions. At the opposite extreme from the owls are the woodcocks, mud probers with eyes set high and back on the head, out of the way of vegetation and splattering mud and in a position to look out for predators. In fact, the woodcock has better binocular vision to the rear than to the front!
          The term "hawk-eyed" accurately describes many birds. For example, both raptors that must see prey at great distances and seed eaters that must pick tiny objects off the ground have eyes designed for high "visual acuity" -- the capacity to make fine discriminations. There is, in fact, evidence that hawks can distinguish their prey at something like two or three times the distance that a human being can detect the same creature. Interestingly, even with such visual acuity, Cooper's Hawks are known to hunt quail by their calls.
          One way that birds have attained such a high degree of acuity is by having relatively large eyes. A human eye weighs less than I percent of the weight of the head, whereas a starling's eye accounts for some 15 percent of its head weight. But more than size alone appears to account for the astonishing performance of the eyes of hawks. Evolution has arranged the structure of their eyes so that each eye functions very much like a telescope. The eye has a somewhat flattened lens placed rather far from the retina, giving it a long "focal length," which produces a large image. A large pupil and highly curved cornea admit plenty of light to keep the image on the retina bright.