I got a couple of ducklings the other day and am starting to wonder if one of them might be blind. When I handfeed them, he comes for my hand, but it's as if he can't see where the food is, because he nibbles all over my hand until he finds the food. He also doesn't react if I wave my hand in front of his face, but our other duckling--who I have seen track ants and can definitely see--doesn't react much either. Do you have any suggestions for how I can figure out if he is vision impaired or blind?