Other examples of specialized eyesight abound in the animal kingdom. The lowly frog would starve to death in a field of dead bugs, but if something moving should happen by, a highly developed set of cells in the frog's eye responds, the tongue whips out, and dinner is served. Because of this peculiarity of a frog's vision, it perceives things about it only as a constant motion picture, and blocks out anything stationary. With this type of vision, it sees the sun as only a single point of reference which it uses in navigation. In addition, the bee's eye provides a measure of flight speed so accurate that aeronautical engineers have designed a system based on it.
Animals can have multi-purpose eyes.
For instance, humans may see perfectly well in the air, but they are far-sighted underwater. The kingfisher is a bird that needs acuity in both environments for scanning the water below in search of fish and for pursuing its prey once it has dived below the surface. The kingfisher is endowed with two foveae, areas of the eye which permit this visual distinction. Still, there is much to be said for human sight. Although it may lack some niceties such as the bee's capability of seeing ultraviolet light, of all the mammals, only man and a few primates enjoy the pleasures of color vision.