many times a weasel will try to drag his kill away.. when it gets it that far through a fence or hole it quits trying. an owl will not drag it through a small hole, neither will a hawk. they are in the pen with the chicken, why would they poke it's head through a hole??
a coon will reach through a fence and grab a bird.. but then ,usually,
there is s sign of struggle and a lot of feathers missing or roughed up .. and if a coon did eat the chicken which he dragged through the hole , everything he could chew away through the hole would be gone, not just the head..
I have been fighting with these critters for 40 years..
do not rule out rat for this one..