One fovea birds have the fovea located near the place where the optic nerve enters the eye- a central fovea. Most birds have a one-fovea eye that functions similarly to ours, but many birds are bifoveal. Overlapping of the visual fields of the two eyes produces binocular vision and depth perception. Humans have a fovea when you focus directly on an object the image falls on the fovea- that’s why peripheral vision is weak. Not only are the cells denser in that area but the pit shape serves to refract the light so that a larger image is formed. One such area of densely packed cells is called a fovea. Hummingbirds, like insects, can see ultraviolet light.Īny part of the retina that has a denser concentration of receptor cells perceives sharper images. Many hawks and owls have more sensory cells in the upper half of the eye that receives more light when the birds look down.Color vision varies among birds some, but not all, see color.
Diurnal birds have retinas dominated by cones while nocturnal birds have mostly rods. The distribution and density and proportion of rods to cones varies with the species of bird. Cones are for color and rods are for black and white and dim light. The entire retina is thicker than that of mammals and the rods and cones are more abundant. The retina is the sensitive layer of the eye that absorbs the incoming light, senses it, integrates the information in it, and sends this information to the brain. The entire eye also varies in shape form flat to round to tubular (hawks and owl) the shape is maintained by a ring of overlapping bony plates. The lens is very flexible in most birds and can change shape readily – birds need to focus near and far and change rapidly. The eyes of a bird are able to adjust to the light about 2x as well as that of a 20 year old human. In most aspects, the avian eye structure resembles that of mammals. In the Starling, the eyes comprise 15% of the head weight in humans it is only about 1%. In some owls, the eyes comprise up to 1/3 of the total weight of the head.
The eyes of the ostrich, at 50 mm in diameter are the largest of any land vertebrate. Some hawks and owls have eyes as large as human eyes. The importance of birds’ eyes is implied by their size – they are the largest relative to the body of all animals. But their cerebellum, the center of mechanical coordination, is well developed for flight.īirds are highly visual animals they have to be to be able to fly. In addition, the cerebrum, the “thinking ” part of the brain is not as well developed because birds are more instinctive than learners. A bird’s brain is similar to that of mammal’s but there are difference in the acuity of the senses, especially sight.