What does it mean when scientists say “an eagle can see a rabbit in a field from a mile away”. Is their vision automatically more zoomed in? Do they have better than 20/20 vision? Is their vision just clearer?
In: Biology
They have better than 20/20 vision. In fact they have 20/5 vision.
I can’t find a figure for their field of view (how “zoomed” their eyes are) but it sounds like they have good peripheral vision so it’s probably no more zoomed than our eyes, just sharper.
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They have 20/5 vision. Meaning that they can see things as clearly at 20 feet as you can see them at 5.
Bird eyes tend to be better than those of mammals. More detector cells in any given surface area* (at the spot where we can focus best we have the equivalent of a 56 megapixel camera. For an eagle, where the largest eagles have eyes as large as ours, this resolution is about 200 megapixels), larger eyes compared to the size of their head (so ostriches have the largest eyes of any land animal), no bloodvessels on the inside of the retina, They also have multiple muscle rings that helps the lens in your eye to focus (which helps with viewing things very close up or very far away) plus a scleral ring (a ring made from cartilege and/or bone) that helps support the eye and the muscles that helps the eye focus.
The drawback to bird vision is that their eyeballs can’t move. Many species don’t have the muscles for it (and the scleral ring inhibits movement on the birds that do), so they need to move their heads to focus on something (which leads to the weird headmovements you see in for example pidgeons and chickens).
*And a 4th colour receptor cell that allows them to see intro the ultraviolet spectrum.
It’s not necessarily more “zoomed in”. Rather, think of it as being able to better discern small detail. When you’re at the optometrist and you look at that chart of progressively smaller letters, they get blurry and less distinct the smaller they are. But an eagle would be able to discern much smaller letters (and would see them as much less blurry) if they could read. This helps them tell the difference between little grey mice and little grey stones from way high in the air.
their eyes process light in a more focused way that enhances their perception of space.
think of how a different lenses on an optical zoom camera affects the image. or a telescope lens. your eyes similarly take in light and focus it onto what’s called “photoreceptors”, then your brain processes the information provided by photoreceptors.
the eye of an eagle is heavily focused, at the cost of their field of vision being narrower, but they can percieve smaller changes in light (provided by the movement of a rabbit) in their eyes, sending a “better” signal to the photoreceptors.
They track motion so once something moves in their field of vision their eyes can process the information in that area to tell them what the motion is, the eyes of birds of prey take up most of the skull and a lot of the brain left in the remaining part of the skull is an image processor.
Imagine you and an eagle are looking at the same field. The rabbit is far away. You will see a blurry speck.The eagle sees a clear rabbit, like it’s much closer than it really is.Eagles have super powerful eyes, not zoom lenses! They have more parts to see details and even see colors we can’t!
After lasik surgery, I had 20/10 vision in both eyes.
That means I can resolve images at 20 feet what you need to stand 10 feet from to figure out.
I don’t see zoomed in. It’s just more detailed. Like a higher resolution display.
My Caique parrots can spot almost anything in the sky. If they are looking up I’ll follow their gaze and there is always an airplane that I can just barely see. They make a growling noise when they see them too. Their night vision is a lot worse and they are afraid of the dark lol
Like others have said it’s not that they are zooming in (that would be cool!) but more so that they almost have higher resolution retinas. So they see things sharper where we couldn’t at all or would be blurry.
Eagles have much better than 20/20 vision.
Your eyes are like looking at an old 800×600 monitor. The eagle’s eyes are like 4K HD. They have so many more pixels in the image that they can see the details even if the camera is much farther away.
That’s because birds of prey have 2-5x more cells that respond to light in their eyes relative to our eyes, and those cells have fewer interruptions than in our eyes. Their brain is specialized in processing those signals to see prey.
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