An eagle can see fish swimming in water while soaring at a height of several hundred feet (quite a feat considering fish have dark backs that help them blend into surrounding water). An eagle soaring over land can probably see a rabbit at a distance of nearly a mile.
“Eagle eye” is more than just an expression.
If people say you have an “eagle eye,” thank them: They’ve equated your sight to a bird that has some of the best vision found in nature. Bald eagles have several admirable characteristics, but vision definitely ranks in the “most impressive” category.
Thanks to an annual influx of visiting eagles from the north that usually swells the state’s bald eagle numbers to more than 2,000, winter is the best time to see bald eagles in the Ozarks. While you’re watching them, you can be rest assured they’re seeing you, too.
All eagle species are known for excellent vision and bald eagles are no exception. A bald eagle’s eyeball is nearly as large as a human’s, but the quality of an eagle’s vision is about more than eye size. Let’s start with a part of the eye called the fovea. In a highly cliff-notes version of optometry; the fovea is the part of the eye that provides strong, centrally concentrated vision. Humans have one fovea per eyeball; bald eagles have two. Because of this, an eagle’s eyeball is equipped to simultaneously focus on objects in front of it and to the side.
The extra fovea adds more than a wide range of vision for eagles, though. The fovea is where an eye’s cones are located. In a nutshell (once again, with apologies to optometrists for broad-brushing this), cones help discern characteristics and details of an item being looked at. Because of the additional fovea, an eagle’s eye has more cones than a human eye.
In an eagle’s world, this increased enhancement of perception and detail recognition allows eagles to see prey (and threats) at remarkable distances. An eagle can see fish swimming in water while soaring at a height of several hundred feet (quite a feat considering fish have dark backs that help them blend into surrounding water). An eagle soaring over land can probably see a rabbit at a distance of nearly a mile.
Also assisting an eagle’s vision is the bony shield that projects over each eye. This shield protects an eagle’s eye from brush and other vegetation during a chase and also shades the eye from the sun’s glare.
One visual trait we have over eagles is eye movement. Eagles cannot move their eyeballs from side to side: Each eye is fixed in its socket. However, to compensate for this, a bald eagle has a great range of head motion than a human.
Great vision is just one of several characteristics that make bald eagles fascinating creatures. Area residents will have an opportunity to learn about bald eagles at the Missouri Department of Conservation’s “Eagle Days” event at the Springfield Conservation Nature Center in Springfield. This program will be 9 a.m. to 4 p.m. on January 19 and 12:30 p.m. to 4:30 p.m. on January 20. Included in the indoors portion of the event is a chance to view a live captive bald eagle furnished by Springfield’s Dickerson Park Zoo. Outside, spotting scopes will be set up at the Springfield-Greene County Park Board’s Lake Springfield Boathouse and Marina in the hopes of providing people a view of the eagles that winter at Lake Springfield. For more information about Eagle Days, call 417-888-4237. Eagle information can also be found at mdc.mo.gov.
Francis Skalicky is the media specialist for the Missouri Department of Conservation’s Southwest Region. For more information about conservation issues, call 417-895-6880.