I'm new to raising chickens and got 7 pullets and one rooster (by accident) barred rocks that are now 4 weeks old. One pullet has 2 symmetrical circles on the the top of her head that are "hairless". It's been that way since the day we got her. The spots are just larger now as she's growing. None of the others are pecking at her. She seems perfectly fine otherwise. Does anyone know what this is? I can't post a photo since I just joined the forum. Thanks!