I have to agree with everyone else, this just has a racoon 'feel' to it. And yes, it will definitely be back for more. 

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I bet you had a perpetrator that killed and ate, plus someone else that wanted to steal carcass and could not get in by digging.
There was no blood anywhere on the wire or the ground, only on the bird. The wire is confirmed live I don't remember the voltage but it high!Any blood on the chicken wire?
Is that hot wire good and hot?
Yes, we do have bears. 3 years ago in mid November, before the electric fence, we had a bear raid the coop. Since that time there haven't been any around that I have seen.X2
Kill looks like a coon.......except for daytime kill.
Scrape looks like a bear trying for the carcass but frustrated by hot fence.
Do you have bears?
I know we have them here! I've seen their little footprints, along with raccoon footprints, in the mud in the past.another possibility would be a weasel. they are known to kill by biting the neck and sometimes not eat any of the bird, reportedly sometimes only to eat the blood. if this is a least weasel he will only be about the size of a chipmunk and can climb and dig easily and fit through a pretty small hole.
please make sure your birds are locked in a secure coop at night as this is when coons and weasels are most actively hunting for food.