Drake is raping chickens?

I know this sounds odd, but my mother doesn't know what to do. We have 9 chickens (Rhode Island reds), and 3 female ducks and one drake. One of our ducks has recently starting sittin on eggs, soon after we noticed some chickens missing many feathers on their bottom? like pink exposed skin?it's not a disease, we've had them checked out, and some local famer told us that the drake is raping them, in turn, pulling out the feathers? other day we found one chicken, missing feathers, floating in the duck pond, drowned..The what do we do?? why is he doing this???