Just put the chickens to bed and found one dead, frozen stiff in a nest box. All were acting normally the last few days, went out and milled around even in the bitter cold today. No signs of trauma but she's missing most of the feathers on her butt. Don't know if they were pulled off by a predator or fell out due to some disease. They're in an insulated room in the barn with a heat lamp and they are not all huddling up underneath it so I don't think they're too cold. They have free choice lay ration and a supplement of scratch and corn oil on cold days. Any ideas? She's an 8 mo old Wyandotte and should be in her prime.