Duck ripping out feathers

I have two almost 6 week old ducks, a Rouen named Darkwing, and a Pekin named Scrooge. Darkwing has started pulling feathers out of Scrooge's wings, leaving small patches on either side featherless and bloody. I noticed this two days ago and have since separated them. Does anyone know why Darkwing would suddenly start doing this? And how can I get him to stop? Right now they are living in the guest bathroom. I was going to wait until it gets a little warmer out to move them outside, but should I consider moving them out sooner? Any advice would be greatly appreciated!