Birds can accurately judge distances when flying, landing, and looking for food. Bird eyes can resolve fine detail at considerable distances -an eagle can spot food while flying a mile above the earth. Large eyes mean a large, sharp image. In proportion to head weight, a starling eye is 15 times the weight of a human eye. Cone cells in the eyes provide color vision and acuity.
Some hawk eyes have five times more cones per square inch than human eyes.
Eyes of owls and other nocturnal birds are especially densely packed with rod cells to see better in low light. Cats are another animal that need terrific eye sight. Select this text to learn how cats in general see the world. Many birds show remarkable, specialized hearing abilities. So fine-tuned is the hearing of guinea fowl and water fowl that they have been used as watchdogs throughout history.