On average, birds can see
Two or three times more
Sharply than humans – David Allen Sibley
I always wondered why birds always seem to notice me before I see them.
I would be birding and just when I spotted them, in a flash they would fly away. A person can never sneak up on a bird – they see you first!
I saw my first Colorado Bullock’s Oriole years ago while birding on County Road 24. He was sitting on a branch of a cottonwood tree, so I thought I would walk slowly, closer to him. After my second step, the bird flew to me. I was wearing a light-orange colored shirt, and I believe he thought it might be a tasty orange. When he discovered I was not food, he immediately flew away.
After that incident I began to think of birds’ vision and why they have such keen, unique eyes.
Like human eyes, they have a cornea, lens, iris and retina, but they are much larger in relation to the size of their heads.
Humans have three color-detecting cones in their eyes, allowing them to see red, green and blue shades. But birds have a fourth cone that enables them to see ultraviolet (UV) light. This permits birds to see a broader spectrum of colors than humans. Birds also have a filtering oil in their cone color receptors. This oil helps to filter lighter for them to see many subtle variations in shades of color.
Scientists believe ultraviolet colors help birds forage, identify species, select partners and effectively deal with orientation, especially during migration.
Some birds also have incredible adaptations for their eyes. I saw my first American Dipper, previously called a Water Ouzel, at Box Canyon in Ouray. I was amazed to see him go under the water. I later learned this bird has a third eyelid called a “nictitating membrane.” This transparent film slides horizontally across the eye, which lubricates, cleanses and protects it. There are also other diving birds that have this protection.
All birds see well, but the birds of prey probably see better than any other living creature. Scientists claim they see as much as eight times better than humans. The raptors of North America include hawks, vultures, falcons, osprey, condors, owls and eagles. Eagles, particularly bald and golden eagles, have superior vision. The bald eagle has astonishing distance vision – it can see a rabbit move from more than a mile away.
Owls have binocular vision, which means both eyes focus on the same object at the same time to determine the size of an object and its distance. This supports owls’ ability to hunt while flying in the dark. Though they have a narrower field of vision than some other birds, they also have the ability to swivel their necks nearly 340 degrees.
Other birds have monocular vision, allowing them to scan large areas with their left and right eyes. The American Robin is a good example of a bird with monocular vision and you can witness some of its behavior using this vision – you can see them foraging for bugs and worms in a grassy area, cocking their heads to one side to turn their eyes toward movement, pinpointing prey.
Some birds are also adept at detecting colors. Hummingbirds can do this with flowers, plants and insects, as well as the red bird feeders providing high-energy sugar water. This helps them with substantial energy to survive and migrate.
The next time you are outside birding, hiking or just enjoying being outdoors, remember these remarkable birds will see you before you see them. What a marvel!
