This is my first time to own chickens. I have a hen that hatched 6 out of 11 eggs. We built a run that is about 3ft wide and 7ft long and placed a small pet taxi with hay in there for her and the chicks. They all seem content. My question is how cold outside before I need to get concerned. Will the hen keep them warm without having to use some kind of heat source? Also is there anyway to tell the sex when they are small? Really need advice !!