Rommy, my untufted roman, has started grabbing one of my ducks by the neck and putting her head under water. He isn't trying to mate her (I don't think) He'll grab her from the side of the pond or in the pond. He doesn't try to mount her anything, he just holds her head under water. I'm very worried about this behavior. Should I be? And if so, is there anything I can do to get him to stop?