Eagle Eye
The Bald Eagle, our national symbol, is truly an all-American bird. It is the only eagle unique to North America.
Bald Eagle
Few of us have an opportunity to get close enough to appreciate the size of these birds.
The length of a Bald Eagle’s body ranges 28 to nearly 38 inches with a wingspan of up to 80.3 inches. That’s almost 6’ 7”; about the same as the average height of a NBA player. They weigh roughly 6 to 14 pounds.
Bald Eagle
One of the most impressive facts about the Bald Eagle is its eyesight. That is the main topic of this photo blog post.
The Bald Eagle is known for its excellent eyesight. In fact, the eagle eye is one of the strongest in the animal kingdom.
To begin, I want to remind everyone that I am not an Ornithologist, so the following facts were obtained from various reliable sources.
An eagle’s eyes are almost as large as a humans but their eyesight is four times sharper than a human with 20/20 vision. That would put them at about 20/5 using a scale everyone is aware of.
In the middle of the retina is a small dimple called the fovea. It is the center of the eye’s sharpest vision. The eagle differs from humans in that they have a much deeper and convex shaped fovea. Some people believe this convex pit allows their eyes to act like a telephoto lens, providing extra magnification. That means, if an eagle is soaring 1000 feet over open country, it could spot prey over an area of three square miles. To put this in perspective, if you had eagle eyes, you would be able to count ants on the ground while standing on a 10 story building.
To continue describing the amazing abilities of eagle eyes, an eagle has two centers of focus that allow them to see forward and sideways at the same time. They see colors more vivid than we do and can distinguish more shades than humans. This outstanding ability makes it possible to spot the dark top of a fish in the water, while soaring, gliding, or flapping in flight several hundred feet in the air. They can even see ultraviolet light, helping to detect the UV-reflecting urine trails of small prey.
This female eagle just finished her dinner indicated by the blood remaining on her beak.
Eagles have three eyelids. They blink up because the lower eyelid is larger than the upper eyelid. Those eyelids close during sleep. The third eyelid is known as the nictitating membrane; it grows in the inner corner of the eye, near the tear duct, and is used for blinking. Every three or four seconds, the nictitating membrane slides across the eye from front to back, wiping dirt and dust from the cornea. Because the membrane is translucent, the eagle can see even while it is over the eye. This translucency also allows the nictitating membrane to be drawn across the eye for protection and to moisten it while maintaining sight.
This series of photos were made while a male Bald Eagle adjusted branches on the nest. The leftmost photo shows the full, uncovered eye of the eagle. The middle photo was made when the nictitating membrane was partially across the eye. The rightmost photo shows the eye completely covered by the membrane but its translucency allows him to see. His pupil is still visible in the photo.
Bald EagleIllustrating use of the Nictitating Membrane
I'll wrap up this blog post with a little Native American folklore.
Native American Indians were a deeply spiritual people and they communicated their ideas and dreams from generation to generation through symbols such as the eagle.
The meaning of the Eagle symbol was to signify courage, wisdom and strength and its purpose was as the messenger to the Creator. The eagle was believed to carry prayers to the Great Spirit in the Spirit World.
Last spring, my wife, Elena, and I met a Native American fellow from the Potawatomi tribe. We met while watching eagle activity at an active nest. He explained a ritual performed by their spiritual people. They believe the eagles and hawks, because they fly the highest of all birds, are communicators to the Creator.
During their ritual, which he performed in song and dance for us, they would sing, drum, and dance around a fire. The smoke from the fire rose to the sky, carrying with it, prayers to the Creator. The Creator would deliver his message to the eagles and hawks to carry back to the ground. I cannot give the story the justice it deserves but it was very emotional and uplifting.
May you have the strength
Of eagles' wings,
The faith and courage to
Fly to new heights,
And the wisdom
Of the universe
To carry you there.
-- A Native American Prayer
Thanks for looking,
Dan
