I just came across this post and haven't gotten through the whole thing yet. I know it's a few months old at this point and hopefully your dog is getting along with your duck by now. But I just wanted to say, the growling over food is completely normal. And is good actually. That is the dogs warning, saying to back off. It is the only way they have to communicate. Never punish something like that. Its when they don't give warning and go right to snapping or biting that you have an issue. Also keep an eye on them. I had a gosling many years ago, and also had a dog that was a big scaredy cat too. One time I had my bad turned for just a second, the gosling was right next to me and my dogs were eating. I turned to see how everyone was doing and the gosling was next to my dog, on the ground. He died a few seconds later. It was only a snap, he had no marks on him. Vegas (my dog) didn't mean to kill him, it was my fault. He was never aggressive with the gosling, but did always keep his distance. I'm sure you have things worked out by now. Just a warning to anyone that may find themselves in a similar situation.