Which will sometimes mean something with claws, but that's odd unless you've already put the ducks inside the screened porch? It doesn't cancel out raptors, believe me. We've owned Cockatoos. They ate our dining room chairs. Can you at least post a pic of the tear?
It sounds like a raptor, which could mean many breeds of large predatory birds. I don't know what's in your region, but I don't think it was a mammal unless it was a multiple predator attack, which is always possible. How long had it been since you'd seen the drake?
@Tinque had a great...
I agree with the others that this was probably some type of raptor. An animal that is able to carry the duck away, e.g., a dog, will typically take it away. You also wouldn't normally see the type of thing you describe with a mammal, whereas raptors will be able to pick the bones completely...