That is odd.
I wonder if it could possibly be a human thief???? (Not to accuse the neighbors or anything, but there are a lot of homeless people in some areas. A human would want to stop the squawking as quickly as possible and obviously want the body to eat....but why leave evidence then???)
I agree. Dogs generally attack the whole flock, maiming and killing. You might have a few with a head off, but the bodies beside.
Coons will eat the heads off, leaving the body for later.
Hawks eviscerate. Sometimes taking the heads, other times not.
Coyotes carry off the whole thing, so will a hungry mongrel, and I think so will fox.
But I've not dealt with minks, bobcat, or cougar to know their habits.
What kind of predators do you have in your area? Are you located far out or in suburbia?
In America or elsewhere?
I agree with Junebugenna, a photo of your set up would help.
So sorry for your losses. A webcam may definitely be in order tonight.
LofMc