So it is not vigorously, just often. Does seem to be more when he’s drinking and around the pool. Our female duck had similar symptoms two weeks after we collected her from a farm from new born. But her head shaking was vigorous, she also had a temperature and diarrhoea. I have been putting out layers mash for our female duck, which he doesn’t like, but he is still eating his normal growers pellets which he loves. They are mating lots but he shakes his head when hes cleaning, eating, etc not so much when hes doing his other mating behaviors. I noticed a little bit of runny poop but all others looked normal