My fifteen 5-week-old Araucana chicks were getting too big for their brooder box in the basement, so this morning I moved them to a sectioned-off area of the barn. As I was transferring them from the brooder to the barn, I took the opportunity to do a quick physical inspection on each one. They were all fine. When I got home from work today, at least half of the chicks had all the feathers missing from their backs! I observed them for 15 minutes and didn't see any bullying, feather-picking, or self-picking behavior. There's no blood, scratches or bite marks (like you would see if a predator had been after them or an older bird got into their pen and beat them up). On each bird the feathers are all missing from the exact same area on the back (from the shoulders to the base of the tail. Has this ever happened to anyone else? Does anyone have any idea what might be going on? Thanks in advance for any help or ideas.