Most birds, like most mammals, have a single area within the eye of perfect vision, called the fovea, where cone cells, which detect sharp contrast and detail, are most concentrated. A raptor’s eye has two foveae. One is for lateral vision, the other for forward vision. A human eye has two hundred thousand cones to each square millimeter of fovea. Sparrows have twice that. Raptors have more than a million.
