This is Artie. He’s an educational ambassador at Treasure Coast Wildlife Center. He can only stare straight ahead. No, I mean it. Like all owls, his eyes cannot move. He turns his head when he wants to look in a different direction.
Great Horned Owls like Artie have the largest eyes of all North American birds – they are almost the size of a human eye.
The size as well as the position of the eye is perfect for hunting at night. The bigger lens means that the owl can absorb as much light as possible. That is how the bird manages to see things even in low-light conditions.
More on owl eyeballs (actually eye tubes!)
Bald Eagles also have large, fixed eyes, like owls. So weird, right? In fact, it’s true that ALL BIRDS have very limited eye movement in the socket.
Birds have the largest eyes relative to their size in the animal kingdom, and movement is consequently limited within the eye’s bony socket.
Eagles use both monocular and binocular vision, meaning they can use they eyes independently or together depending on what they are looking at.
An eagle eye has two focal points (called “fovea” [singular] or “foveae” [plural]) one of which looks forward and the other to the side at about a 45 degree angle. These two foveae allow eagles to see straight ahead and to the side simultaneously. The fovea at 45 degrees is used to view things at long distances. An eagle can see something the size of a rabbit at more than three miles away.
Eagles can distinguish more colors than humans. They can also see in the UV range of light, allowing them to see the urine trail of prey.
Like most birds, eagles have upper and lower eyelids plus a “third eyelid” called a nictitating membrane.
The nictitating membrane closes horizontally across the eye and provides moisture, protection and cleans the eye.
This eagle is Golfball. He is a permanent resident on display at TCWC. He was hit by a golf ball while perched on a tree branch at a golf course and it broke his wing. He has a partial wing amputation. When I clean his enclosure, he chirps at me.
More on eagle vision…
If you swapped your eyes for an eagle’s, you could see an ant crawling on the ground from the roof of a 10-story building. You could make out the expressions on basketball players’ faces from the worst seats in the arena. Objects directly in your line of sight would appear magnified, and everything would be brilliantly colored, rendered in an inconceivable array of shades.
That sounds amazing!
Herc is a fine specimen of a Red-tailed Hawk. (Note the reddish brown tail.) He is an educational bird at TCWC. He has a partial wing injury.
Herc too has very large eyes compared to the size of the head.
The visual ability of birds of prey is legendary, and the keenness of their eyesight is due to a variety of factors. Raptors have large eyes for their size, 1.4 times greater than the average for birds of the same weight, and the eye is tube-shaped to produce a larger retinal image.
In most raptors, a prominent eye ridge and its feathers extend above and in front of the eye. This “eyebrow” gives birds of prey their distinctive stare. The ridge physically protects the eye from wind, dust, and debris and shields it from excessive glare.
My, what big eyes you have too!
Ali’i is a female Red-tailed Hawk at TCWC. She has a broken wing at one shoulder and is blind in one eye after being hit by a truck on King’s Highway in Martin County. She’s a big bird, but pretty easy to get up on the falconer’s glove. She’s a pro!
Another big-eyed raptor: Phoenix the Short-tailed Hawk.
Phoenix was brought to TCWC recently with a severe wing injury that eventually required amputation. She is young and adaptable, around 2 years old, and that’s part of the reason she made a good candidate for an educational bird. (You can visit Phoenix and the other educational and display birds Thursday through Sunday from 11 a.m. to 3 p.m. Group tours are available with reservations.)
Short-tailed Hawks are a tropical species ranging from Florida south into Central and South America. They are fairly uncommon in Florida (maybe only 500 of them).
Phoenix is the first one I’ve ever seen (#227 on blog sidebar), and now I get to see her every day I volunteer.
A Short-tailed Hawk “seldom perches in the open; when hunting, it regularly soars very high, where it may go unnoticed by the observer on the ground. Unlike most of the Buteo hawks, the Short-tail feeds mostly on small birds, dropping from the sky to take them by surprise.”
For size comparison, check out the eye on this Brown Pelican in the pelican enclosure at TCWC.
And perched on the top of the pelican enclosure, a wild Black Vulture keeping an eye out for any clean up opportunities.
More on Bird vision.