Boy, they can be so catty lol. We're done with major breeding and egg-laying since we're going into fall/winter and mine have been picking on each other. Just like kids. 

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That's just it. They're only a couple of weeks older, not an adult duck yet.I would definitely keep the adults away from the ducklings until they can fend for themselves. At least you figured out what was going on and the culprit.
Thank you for all your advice and help.I'd definitely keep an eye on the wing chewer. That's pretty excessive. But, maybe once the feed issue is sorted out, some of this will simmer down as well. Of course opportunity is key too, that duck had the opportunity to do that and took advantage of the situation.