My muscovy ducks (born on St Patrick's Day) are having a problem with feather picking. It's mostly one, but when I remove that one I see that another starts. Then when I remove that one there is another (there are 9 total). It is getting bad to the point of drawing blood at the tail and wing areas. I have let them out to free roam the backyard and it is still going on. They are fed a duck feed crumble and have plenty of water. Does anyone have any suggestions?