If it’s gone for the necks, it’ll be a rat or a stoat. We had chickens once (no ducks) and the rats ended up killing them all. They were just in a small coop and didn’t roost very high off the floor. My neighbor had ducks which rats ended up killing off as they couldn’t fly
Hi, try looking up ‘dropped tongue’. There’s a bit about it in a book I have called ‘Keeping Geese. Breeds and management’ by Chris Ashton
It’s when the lower mandible becomes full of food waste and grit.
Hope this helps