I am reading through all of these as I was thinking......wow, I can definitely add to this.
We have a rare type of possum here that are so stinking smart. I've lost over 30 birds in our enclosed pins......... The possums work it until they find an opening. Raccoons have been responsible for 4 kills. I've had a lot question us on it. One........the game camera catches most of it and two, by the 2nd nights kill, we have been able to hear the chickens screaming and get them. The possums go in, if there isn't any eggs or birds on the ground, they go up and find them. they typcially start eating on top of the bird, top of head, then they eat the backs out. if we leave the carcass in there, they come back the next night to clean it up.
Racoons, they take the head off, then breast it out. They come back for the rest as well. If its a small chicken, they try to take it out. Both the raccoon kills were from a hole in the center of the pen where the roof covering (basically bird mesh) has slipped away from the tree. We now have metal over the lower 3 foot, so when they come down, they can't get back out.
A possum is like a rat, if its head can fit through the hole, the rest of the body can to. It took me a week to catch one possum and to figure out where he was coming in and out at. He had worked a corner of the pen at the top open just enough to get that head through. The possums do eat them right there.