We have a sad mystery to resolve in our chicken coop. We have lost four hens in the past several weeks. Here's the situation - we started with ten hens that we raised together since last spring. Three died about 3-4 weeks ago, with two apparently pecked to death by a mean hen that was bullying the other hens in our coop. The third had a hole in her side and all of her intestines pulled out and eaten, but no pecking other than that. We pulled the mean hen out, bought a rooster and three more hens from a breeder - full grown - and transitioned the new hens to the coop with the rooster. We took out three more hens that were severely pecked and put them in a separate area to heal. We left the mean hen in solitary confinement (in our brooder pen.) One week ago, my husband put the mean hen back with the six other hens and the rooster. So three of the original hens, three of the new hens and the rooster. She was not happy at first, but the rooster put her in her place and they started cuddling up together every night and sleeping. It was pretty cute. We thought all was well in the chicken coop. Until today. My husband found another hen - one of the new ones and completely unpecked and healthy except for a hole in her side and all of her intestines eaten. We're now wondering if it's a rat getting into the coop doing the damage or some other predator. Our coop has a one-foot deep concrete footing all the way around the base to keep predators from digging under, but there are burrows in the dirt floor of the pen that look like they could be dug by rats or moles. Can anyone help us out? Any suggestions? Here is a photo of our pen if that gives any indication of anything. It's a secure pen with no way in other than digging down a foot and then back up into the pen.