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
It’s not just that an eagle has better magnification in their eyeball than you do, they also have millions of years of focusing on all animals they fly over, and knowing exactly which ones can’t put up enough of a fight.
So past the millions of years of developing a super-strong kneejerk reaction to “THAT thing I can eat”, they also have eyes [that are literally telescopes, cylindrical.](https://chestofbooks.com/animals/zoology/Anatomy/images/Eye-of-the-Owl.jpg) To get the distance and depth perception they need.
So yes, on the topic of pattern recognition and target acquisition, they shit all over you.
And movement of the ciliary muscles contracting and dilating the pupil are not involuntary like in mammals. As a vet: I can shine a light into their eye trying to check response to light and the birds go “no, dunno if I feel like it”.
Think about it as a higher resolution display. You can see more detail in the same image at 4K vs 1080P.
They definitely have much better than 20/20 vision. 20/20 is the baseline for humans. It means you can read something 20 feet away that an average person should be able read 20 feet away. If you have 20/60 it means you have to be 20 feet away to read something that you should be able to read from 60 feet away. 20/10 means the opposite. You can read something from further away than a person with average vision. An Eagles vision would be off the scale for a vision metric that’s designed for humans. Like far less than 20/1. Basically their lenses can bend way more than ours and focus images that are further away.
I also think animals see movement more easily that we do. If a rabbit is stone still, I don’t know that it would be noticed. Once it moves around, it gives the predator something to focus in on and *then* they can more easily see the rabbit
The ELI5 is our eyes see in standard definition, and theirs see in 4k UHD.
I noticed this effect when I got laser eye surgery and came out of it seeing 20/10. Everything in the middle distance looked like it was in HD; I could see mortar joints in brick buildings that had previously just been a brick-colored wall at that distance.
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