I went out to feed the chickens this morning and one of my 6-week-old Black Australorp pullets was dead and there’s not a mark on her?!? I even pulled feathers off looking for an injury and there wasn't one. There was no sign of a break in and the rest of the 6-week-old chicks are fine. I haven’t been letting them out of the chicken house because they are still small enough to be easily taken by a hawk so there is no chance that she could have come into contact with something toxic. I’ve seen no sigh of any illness in the group and all was well last night when I checked on them right before dark. Does anyone know what would cause a seemingly healthy chick to just drop dead?