Owls have many interesting features, however probably the most interesting of these features are their eyes. An owl’s eyes are unlike the eyes of other birds which usually are located on the side of the head. In fact an owl’s eyes may account for one to five percent of their body weight depending on the species and are large, round, and facing forward. This forward facing position gives the bird a binocular vision, able to see an object with both eyes at the same time. Furthermore what this means is that the owl is able to see objects in three dimensions. (height, width, and depth) this also gives them the ability to judge distances in a similar way that humans can. An owl’s field of vision is about 110 degrees, with about 70% of that accounting for binocular vision.
An owl’s eyes are so well developed that they are able to see quite efficiently in low lighting conditions. However interestingly enough, their eyes are not really “eyeballs” rather than they are elongated tubes that are held in place by bony structures in the skull known as Sclerotic rings. It is for this reason that owls are unable to roll or move their eyes, instead it can only look straight ahead.
However, to the owl’s advantage is its flexible head which is able to turn around and almost upside down as well. This is more than enough to help compensate for not being able to move its eyes. An owl’s neck is very long, flexible and hidden by feathers. Their necks consist of fourteen vertebrae, which is twice as many as humans have. This allows for these amazing creatures to turn their heads through a range of 270 degrees measured from a facing forward position.
Since owls are nocturnal animals that hunt their prey during the night, their eyes are well equipped at collecting and processing light. This all starts with the large cornea (the transparent outer coating of the eye) and the pupil (the opening at the center of the eye). The pupil’s size is controlled by the iris (the colored membrane that is suspended between the cornea and the lens) When the owl’s pupil becomes larger it allows more light to pass through the lens and onto the large retina (the light sensitive tissue on which an image is formed). An owl’s retina has an abundance of rod cells (light sensitive rod shaped cells) that are very sensitive to light and movement but do not react well to color. Cells that do not react well to color are known as cone cells. Owls possess a few of these cones. These cone shaped cells are what cause most owls to see in limited color, or in monochrome. However, to say that owls have trouble seeing well in strong lighting is not true.
Owl’s have a wide range of adjustment in their pupils which allow the right amount of light to strike the retina thus allowing some species of owls to see even better than humans do in bright light. To help protect their eyes, owl’s eyes are equipped with not one, but three eyelids each. They have a normal upper and lower eyelid like most animals with the upper eyelid closing when the creature blinks, and the lower lid closing up when the owl sleeps. However the third eyelid is referred to as the nictitating membrane and it is a thin layer of tissue that closes diagonally across the eye, from the inside to the outside, helping to protect the surface of the owl’s eye.