We all know the meaning of that phrase but the marvels of bird vision go far beyond the capabilities of the Eagle. All raptors, hawks in particular have a keen vision. It is far better than that of any human, I guess you could say it is sharper, better focus and much better distance evaluation. It is kind of hard to imagine if you think about it. Since we don’t have the capability I find it hard to see sharper than sharp. Can they zoom in? Zooming would make sense, but how could they do it?
Well, in fact it is a little bit like zooming, you see it is all about the size of the eye just like the size of the sensors light gathering cells on a digital camera. The larger the cell the bigger the palate. It is like comparing a 12″ television to a 50″ big screen, everything is bigger. This is born out by birds that are most active when light is low like at sunrise and set, they usually have very large eyes. In general birds have the largest optical sensors of any animal. Looks can be deceiving too, because often we can only see the pupil of many birds eye and compare it to ours thinking it is the entire eye when in fact it is only a small portion of the eye, making the entire eye enormous. None of this is specific to Raptors either, the larger the birds eyes the better the vision. Another thing that has been thought but not proven until relatively recently is that many birds sleep with one eye open and control eyes independently with the two sides of the brain. Eyes that can move independently increase the context or field of view which may explain the origin of the phrase “birds eye view”.
As humans we have three color receptors in our eyes. That is the Red, Green, and Blue color channels, commonly known RGB and those three colors make up the millions of color combinations we see. In the animal world it is among the best but as you might have guessed birds can do better. They have 4 channels as it were, the additional being the UV spectrum. Once again it is a little bit abstract and hard to imagine exactly how this can change vision. Does it allow birds to see some color we can’t? Does it mean they have better definition? Could be, problem is they are not saying. The one thing that we can safely assume though, is that the chances of you getting the drop on any bird are pretty remote. If you are truly interested in getting close to birds to photograph you are far better off to concentrate on being quiet and unthreatening. Be very slow, approach on the diagonal, and use the 30 minute rule to establish your presence and hopefully the bird will tolerate you.
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