We have 4 ducks - 1 elderly female campbell, 2 female runners and 1 male runner. They have all lived happily together for 3+ years, but in the last few days the runner drake has started attacking one of the female runners! It is nothing to do with mating and he chases her and grabs hold of any part, including pulling out feathers. She is now scared of him and avoiding the rest of them. They free-range during the day and I separated him off in their overnight pen last night to give her a break. They were all best of friends up until a few days ago. The only change I can see is that the runners have just finished a moult. Any thoughts or ideas would be appreciated. Thank you.