I have a pair of 3 yr old male Magpies. One lately has developed a slight limp, he's always thirsty and tonight I noticed his vision is not so great. They are fed the same dog food that our dog gets (I know, I know). It's protein content is 24% and they love to eat a piece of cheese each morning. They also get mixed greens. They are mainly house ducks, but do forage or play in the lake for a few hours a day. My only other thought is Niacin deficiency, because of the wobbly legs, but everything I have read about that doesn't mention thirst or vision. His brother has the exact same diet and has zero issues. I'm asking here before we go to the vet. Thanks in advance!