Hi, my name is Steve.
Today we're talking about bird eyes and all the adaptations that make bird eyes different
than human eyes.
Vision is very, very important to birds.
For almost all bird species, it's the way they find food, avoid predators, and avoid
crashing during flight.
So their eyes are also very important!
Eyes are important to humans as well, but our eyes are only 1% of the contents of our
head.
In European Starlings, their giant eyes are 15% of their head!
And speaking of giant eyes, the largest eye of any land animal belongs to the ostrich.
Each of its eyes is almost the size of a tennis ball.
For species of birds that hunt for prey, their eyes are on the front of their head for maximum
clarity and depth perception.
For species that are prey, their eyes are on the sides of their head for maximum field
of vision, so they can see a predator coming from any angle.
For birds with lateral eyes like a dove, you can see it's focusing on you if it turns sideways.
Their eyesight is better in the middle of each side than it is in front.
Birds' eyes have some big differences to human eyes.
For one thing, they have three eyelids.
Two are normal eyelids that work the way you expect.
The third is a transparent membrane that sweeps in from the side.
Kind of different, huh?
They also have a sclerotic ring, a circle of bone that anchors their eye muscles.
Yes, bird have bones in their eyes.
The sclerotic ring provides support for their eye, also eye muscles attach to the eye bone.
Those muscles are striated tissue, so most bird have voluntary control over their iris,
meaning they can make their pupil big or small as they choose.
One final adaptation is the pecten.
In humans, blood brings oxygen and food to retinal cells in a series of vessels.
It works pretty well, but there are cases where we see our own blood vessels.
The pecten avoids this problem by extending into the center of the eye like a broadcast
tower.
Imagine this bowl is a bird eye.
We remove the lens and sclerotic ring so that only the retina is left.
The pecten extends out from the retina, showering food and oxygen on the retinal cells below
without blocking their ability to see.
Speaking of the retina, there's a lot to be said about the bird retina.
Falcons have more visual cells in their retina than you do.
Like, way more visual cells.
It's hard to describe how much better a hawk can see than you, but this might help.
See this video of a parrot in a tree?
This is 240p, low-resolution video.
Pretend that this represents your clearest vision.
Now let's see how the hawk compares.
Here's what a hawk would see in the same scene.
This is 720p, high-definition video.
Hawks can see individual feathers, leaf details, where the eye is looking.
All in the same scene.
Here's another video to show the same thing.
Here's your vision...
And here's falcon vision.
Hawks have about 8 times as many visual cells, so they can see 8 times sharper than you can.
And like we covered in a different video, birds can see colors that you cannot.
Click the link in the description for a more complete explanation.
Thanks for stopping by to learn about birds.
If you'd like to know more, check out my channel page for more videos.
If there's something you'd like me to cover in the future, leave a comment below.