I’m sorry to hear that you lost a duck also. Sounds like a good idea keeping the gander, ducks, and rats in one safe building until you can get rid of the predators. As long as all entry points are covered, they will hopefully be safe while you do away with the culprits. Fortifying and watching one building right now will be much easier on you, as you come up with a new game plan. I’ve never had a wild rat actually attack one of my animals (and, I know they will), but I’ve seen a few on my property. I’ve found the most effective way to deal with them is poison bait chunks. I don’t feel good about using them, but I also know that a pair of wild rats can become dozens and dozens very quickly… especially if there’s no black snakes, etc, to deal with them for me.