Lately I have been finding small fluffy feathers in the nesting box. Quite a few of them. Yesterday as my son was picking up a chicken I realized that at least 2 of my chickens are missing a LOT of feathers on their bellies. They look like a plucked chicken under there. There is no sign of pecking. The skin is not under distress or bloodied. What could be causing this? Will they grow back?