| Re: Kestrels
For one-eyed raptors, I think a lot will depend on how old the raptor was when it lost the eye.
I only recently developed binocular vision; before that, I had no depth perception. Most people never knew - while I occasionally misjudged where something was, I didn't have too much trouble because I compensated. The biggest problem for me was playing tennis and other ball games, but I was an excellent shot with rifle or bow, and good at sports such as fencing.
I judged distance by size - people-shaped targets were much easier than round ones, because I know how big people are and thus how far away they are - and at melee range I never had a problem while on the offensive. Plants, buildings and other known-size things were also easy for me, it was only objects I didn't know well that I'd undershoot or overshoot with the bow. Badminton was easier for me than tennis, and not just because the shuttle moves slower - the shuttle is an object of a known size and flight pattern, rather than something with no distinguishing features.
I can only guess that a raptor can learn to judge these things the way I did, and like every other raptor, will only waste the energy on a kill it thinks it can make. Given the reported miss rates of a two-eyed bird, if a one-eyed raptor takes fewer chances (as I did, I never crossed a road if I wasn't absolutely sure about the cars on it) and doesn't go for the targets it considers marginal, it's not wasting the same amount of energy and thus may survive because while it isn't catching as much, it hasn't worn itself out trying.  |