Or is it really too much sugar aka refined carbs?? Most sites blame it on too much protein, but that doesn't make sense. A duck in nature is going to get tons of protein by eating bugs, worms, frogs, etc... This site does mention commercial feed being the cause, but commercial feed is mostly carbohydrates... http://www.domestic-waterfowl.co.uk/page10.htm This site mentions there are two competing theories...one being too much protein and the other being excessive sugars/carbs.... http://www.petsgator.com/pets-health-care/bird-diseases.html True, I have a natural bias against refined carbohydrates, but I was curious about anyone else's thoughts. It looks like the sugar theory fits more with a duck's ancestral diet.