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?

Question

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

Answer 1

Many raptors (large birds of prey) like eagles have a special adaptation called a “convexiclivate” fovea. Like ourselves, they have a location where receptors are at their highest density,and where overlying material is also moved aside, making a pit or depression, what “fovea” means. Then, the raptors go a step further, filling the pit with a medium (the clear jelly stuff inside the eye, “the vitreous”, which means glasslike) that has a greater refractive index just in the pit than the rest of the eye. This takes the light coming in through the top of the pit and spreads it out, a built in mini-telescope. Better geometry for distant vision!