I have inherited a very large duck from our wildlife rehab centre that I believe is a Rouen. Don't know what else he/she could be as it looks like a female Mallard on steroids. We know nothing about it beside the fact that when it came in , was totally imprinted. Unsure as to the age and my question is as follows. If this duck is about 2/3 the size of my full grown Pekin male, can we assume that it is full grown? If so, would you have expected it to be displaying it's final feather pattern? Please say yes. The LAST thing I need is another drake. One thing that concerns me is that it doesn't quack. Rather, it sounds more like a tundra swan. More like a whistle. Not a mutter like my other drakes.