That's what I meant with non-predatory birds but scavengers birds...But did not want to say :'(But you saw the weasel grab hold of one of your ducks this evening right? Chickens may have peck the eyes they are cannibals.
I do not about every breed of chickens; but yeah.. they do that more then ducks.. they have the bills for it.. =/ (and ducks do not)
You can get dead-pecking less by providing a lot of room, actvities and a (big) safe social circle with the right amount of hens etc... but you will never get rid of it. They stay unique individual characters. And some will always keep doing that. And noone knows why. They have more deep things going on then we can grasp.
It's not a pleasent site to find a beloved animal like that; extra eaten by other beloved pets.
But there is clearly another killer on the loose; I hope you will manage to keep that one away to never see it again