Some friend that is. She stole those ducks, gave you stolen property, and then ratted you out immediately. Watch your back around that one.
The mother had no right to give away ducks that weren't hers. So your friend took ducks that weren't hers without permission. That's theft.
They aren't your ducks. They weren't your friend's ducks. They weren't the mother's ducks. If the owner of the ducks knows you have them, (and he does, thanks to your "friend" ) you must give them back if he asks for them.
If he decides to press charges for theft of livestock, the judge isn't going to buy it if you claim that you won't give them back because he won't take care of them. Legal avenues were not followed. You don't get to take the law into your own hands.
Sorry for you, sorry for the ducks. Hope he doesn't call you, or at least will agree to give them to you, or sell them to you for a small price.