This is our first time raising chickens. We purchased a dozen cornish cross birds from our local fleet supply store. I assumed they were just a few days old when we got them, but I didn't ask. We kept them under a heat lamp in a kid's swimming pool inside our chicken tractor in the garage for the first several weeks. They were on pine shavings which my husband changed usually two or three times daily, as needed. At about 3-4 weeks of age, we started putting them out in the grass in their chicken tractor for a few hours a day when it was warm. Gradually we increased the time they were out as their age and the outdoor temps increased. By mid week last week, the weather was consistently warm and we figured they were old enough to be outdoors all the time. They have been gradually loosing their downy feathers and getting what appears to be their "real" feathers. During this process they have had nearly bald spots here and there, but it seemed within what we in our inexperience guessed was normal. We went away over the weekend and had the neighbors look after the chicks. My husband explained what he had been doing and asked the neighbors to check in twice a day. We have no reason to think they neglected this. But they had trouble moving the tractor, so we didn't ask them to do it each visit, but to sprinkle in some pine shavings if it looked like it was needed. They did move the tractor once during our absence. Today, although our chickens seem to be behaving normally, we've noticed that they are all almost completely bald on their rumps and forward under them toward their chest. On the more upright part of their chests, the feathering seems normal again. Is this the normal way chicks loose their down in these areas? Or is it irritation from being on ground that was too manure-y; or are they sick with something? Thanks for your wisdom.