What does it mean when wildlife biologists say that “an eagle can see a rabbit in a field from miles away”? Does this imply that their vision is automatically more zoomed in? Do they have better than 20/20 vision, or is their vision simply clearer?
In: Biology
Their vision is much, much better than 20/20. 20/20 means you can see at 20 feet what a normal person with clear visual acuity sees at 20 feet. (20/40 means you see at 20 what a normal eye sees at 40; 20/10 means you can see at 20 what a normal human eye sees at 10 feet – good for you.) Hawks and eagles are probably around 20/4 or 20/5, meaning they can see from 20 feet what a healthy human eye sees from 4 feet.
They’re not more zoomed in, they can just perceive and process many more details in their field of vision than we can.
Yes they have better than 20/20 vision. Because of how their eyes are arranged they actually have a wider field of view than us, so their eyes are both sharper but also more zoomed *out* than ours.
Imagine our vision as a 480p YouTube video while Eagles’ is in 4k.
Eagles are said to have 20/5, compared to human 20/20. Meaning they can see things 4 times further. This is due to higher number of rod and cone cells per mm squared and having 2 fovea, humans have 1. If I remember right, fovea is responsible for high acuity vision (details at distance)
Eagles have about five times more cells in their retinas than humans.. You can think of it as eagles having a higher resolution, while humans see in HD, eagles experience vision that surpasses 4K.
I recall hearing that birds of prey can detect movement from far away, but their aim is terrible when diving to capture it. Hawks miss a lot of their targets – persistence is key
20/10 crew checking in.
Tho I’m >40 now and sometimes my vision gets a little blurry and i have to rub my eyes a little to get them to “reset”
Hmmm. Now that i wrote that out it sounds kind of bad. Welp, to the doctor for me!
They have better than 20/20 vision. 20/20 does not mean “perfect” vision. 20/20 means “average” vision. You can see at 20 feet what the average person can see at 20 feet. Some people actually have better than 20/20 vision. Eagles have much better than 20/20 vision.
Not necessarily that it is “zoomed in.” Just that they can pick out smaller details. They have a higher “resolution”. More pixels
So theoretically I could get eagle eyes transplanted and have insane vision?
When elder gamers were young, video games came in resolutions like “480×240”. They played on monitors that were only a few hundred pixels wide, so a game character’s “head” was a tan square. A game screen today has easily some 4,000 pixels across, and can draw a game character’s head with enough pixels that the eyes and hairline are still visible when the head is across a sizable room. An eagle’s vision is so sharp, it’s like them playing on a monitor with 20,000 pixels, so that a mouse in a field 100 yds away is still drawn clearly enough to see its eyes, ears, and which direction it’s facing if you zoom in on it with a microscope. And an eagle’s eyes have the zoom feature built in. Things you and I see as a dot, they see as a face with a nose and whiskers. It’d be easier to explain if you wore eyeglasses. Humans need eyeglasses to read. Eagles don’t need glasses, but they also don’t need binoculars to read a 100 yds away.
One way to visualize this is to think about staring at a computer monitor and thinking about the smallest amount of movement it can represent.
Imagine the whole screen is white and there are 100 black dots exactly 1 pixel in size representing blips a radar is picking up. For fun, let’s say this is an AWFUL monitor and 1 pixel is 1 square centimeter.
So what should happen if, in terms of the position of the dots, 2 of them are only 0.5 cm apart? Ignoring some fancy tricks we could do, our monitor has to fudge it a little. Either it incorrectly displays the two dots on the same pixel or it has to incorrectly display them side-by-side. Makes sense. It can’t light up a pixel “in between” two pixels.
Now imagine there’s a dot that, from the radar data, has moved 0.5cm. Again, the monitor has a choice: incorrectly leave the pixel alone or incorrectly move the pixel.
What we’re learning here is with this monitor, we can’t do a good job seeing things smaller than 1cm square.
If that is how human eyes see the world, eagle eyes are like if we replaced the monitor with one that has pixels 0.01 cm square. They are much smaller! So now if a dot moves 0.5cm, the movement is visible. Or if two dots are even 0.1cm apart, you can tell.
Now, our eyes don’t really see in “pixels”. But what happens is if two things get close together beyond the extent of where our eyes can focus, they blur together. If we try to look at a rabbit a mile away, and there is grass near it, we have a VERY hard time because our eyes only see blurry stuff that’s about the same color. The rabbit has to move for us to start to sense something’s up. If the same rabbit and the same grass were only 100 feet away, we’d be a lot more likely to be able to tell the details.
When the eagle is looking at the rabbit a mile away, it can still see the grass *and* the rabbit. Both its eyes and its brain are set up to look at things that far away with more detail than we can. It’s *like* they have binoculars, but technically that’s a bad comparison because when we zoom in with binoculars we see more details but also a smaller field of vision. Eagle eyes see both more details AND a wider field of vision.
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