I have been putting my male Pekin duck in a dog pen/kennel in the day and shutting him in a little shed at night to keep him from mating with my chickens. About a week ago he started snapping at me when I'm taking him to the kennel. Well, today, he has started charging. He is usually very unfriendly and runs away as soon as i put him down, but today he was right at my heels with his head down. he has done this several times today. How can I stop this behavior?