My friend went out and checked on her ducks one night, and the next morning one of the ducks could not walk, he wasn't walking, his head was moving uncontrollably, it looked like it was actually dizzy, it can't stand nothing. It's feet are turning black. I have read articals about mareks but see no symptoms. Now the duck has stopped drinking, and eating. She is getting ready to cull the duck, but we are just wondering what could have possibly caused this. None of the other ducks are sick like this.