One of my 5 week old runner ducks legs are pretty shaky at times. The legs don't shake all of the time but sometimes when the group is all standing around the one's legs just shake. It looks like it is shivering but I'm in Florida and its not cold out. Any ideas as to what could be causing this? This particular duck does seem to lay down more often than the rest but is not always lying down, just tends to plop down first. She (I think) keeps up with the rest, swims, eats etc. I have been adding Niacin to their water since their arrival. They are eating TSC chick/duck starter/grower 20% protein. I just started mixing their current food with grower/finisher to get a 17% protein mix as suggested by Metzer. Should I be concerned about the shaking? It is not constant just seems to occur at times. Any ideas would be appreciated.