A good primer for newbies, with useful reminders for veterans. I would add that older hens, like older people, are less resilient to temperature extremes. I sometimes use oil-filled radiators to heat near the roost on extremely cold nights (low teens, single digits). They are safe, throw a nice radiant heat and do not emit light. Even having done so, and used petroleum jelly, my 10-year-old buff orpington got some frostbite on that big single comb last winter, when temps dipped well below zero. I learned not long after that she had cancer, which was likely also eating into her resilience. I will heat on very cold nights this winter as well, as I have another 10-year-old, and three 5-year-olds. No one is young anymore (including me)!