This is my first winter with the girls, and I'm worried about them. I have four (2 BO, 2 EE) in a coop that is very well ventilated, but not well insulated. It's pretty much 4 boards and a roof. I threw a lot of shavings in there tonight, but I'm wondering if I should put in a heat lamp. Yes, I know all the negatives of providing artificial heat, and I agree with them. But how cold is too cold? It will be about 10 degrees F tonight. Should I be concerned? Thanks for indulging the newbie fraidy mama.