I am new to ducks. I have two khaki campbells that are about 4 weeks old now. I keep noticing that one of them has really quivery legs. Not all the time, and it seems to walk fine. When it is just standing though it's legs shake really bad. The other duckling doesn't seem to have this problem. They are on a flock starter food. Is it possible that just one of them has a niacin deficiency? Or could it have bigger problems? Or is this a normal behavior?