That's a good theory. In my opinion ducks are emotionally complicated animals. Do they head bob at him, or make other mating request behaviors like laying/sitting down with their backs flat soon before the fighting begins?Is there a possibility that our females are frustrated that he isn't mating with them? Before all this fighting started, they kept trying to get him to mate with them but with him molting, he isn't interested.
I don't have a drake, but my females mate each other everyday. They always make very specific body language requests moments before.