I have two relatively young Pekin ducks (~4lbs). The one is very healthy with clean feathers. The other one seems very unstable on his feet, and constantly has dirty feathers, particularly around one eye. He will try to walk and sit down almost immediately. If he loses his balance, he sometimes flips over on his back and can not seem to get up, almost like a turtle. Any ideas what is causing this? No broken bones - His legs seem slightly larger than the other ducks, but nothing out of the ordinary. Not a vitamin/mineral deficiency - He is fed Nutrena feed. Eats and drinks well. Thanks in advance for anyones help as this is perplexing me.