I'm so sorry to hear about your duck.
I would never have thought any bird would be capable of such horror but then it happened to us....crows attacked one of our pregnant ewes three months ago - it was so badly wounded, it had to be put down by the vet.
I too now have a hatred of these birds and would happily torture any to death that I find near any of my animals. They are monsters! Their purpose in life is what?
Pebbles