I'm new to chicken raising. I have 11 hens and they're 8 months old. Pretty much all of them give me an egg per day, but I've noticed lately that 2 of them are quite bare of feathers on their bellies and their bottoms. It doesn't appear that the missing feathers are due to pecking, in fact they look quite healthy. Is this perhaps due to molting? Or do I need to be worried that something sinister is going on? Thanks for any advice.