kirkl-

If you gave your dog a bone, could you take it back without any growling? Classic case of dominance .. you have a dog that wants to be an alpha, and is showing you by taking "your" things and claiming them as it's own. I have never seen a case where birds were the only thing a dog exerted this type of behavior with. Food, toys and a spot on the couch are other types of things that a dog may show this kind of behavior.

I'll give the classic response, and mention read and follow a training guide. I would also stress obedience drills with your dog, specifically the down command. Strong willed dogs normally HATE to be told "down" followed by "stay" .. but when you get complete control, these types of behavior aren't as typical. Other things you can do to insure your dog knows you are the top dog, have the dog sit and stay while you walk through a door first. Have the dog sit and stay when you put their food down, then give the command "ok" when it is allowed to eat, Pick up the dog's food when they are eating ... but NOT if they snap!!! ... you'll need more control before trying that .. all of these things are designed to show your dog you are the pack's alpha.

If you are serious about having a good retriever, it may be time to take the game out of fetch and train the desired behavior. Remember, the "bird" isn't the reward, it is the praise you give for retrieving the bird that your dog should be retrieving for.