Ask Marilyn

Birds with eyes on the sides of their heads lack 3-D vision. How can they avoid hitting obstacles when they fly? —Gerald C., Manhattan Beach, Calif. Predatory animals, such as primates, dogs and cats, need binocular vision to accurately assess the location of their prey. But birds are more in need of the broad panoramic vision that their laterally placed eyes provide, to avoid becoming prey themselves. Yet they do have a small field of 3-D vision, just enough to easily avoid flying into trees. Even a narrow 5-degree visual overlap is sufficient for some birds. Mostly, they use their limited binocular vision for grabbing food and feeding their young.