Our winters here can be pretty brutal in the mountains of Idaho, our chickens do what they want though.as they free range. we built them a nice insulated coop and they weren't having anything to do with that unless they want to brood, they prefer the empty open horse stall. When they need to go in they do so. We stacked in hay bales on the 2 open sides and in winter put wood up over the door no supplemental heating or light and they do fine even in -40 temps. They did fine without us interfering for a very long time., as long as they aren''t used to having heat source they do well on their own their bodies adapt to the season changes like getting more down if it's going to be super cold. Your roosters may need vaseline on their combs to prevent frost bite, ours lost their combs the first winter because they are always up as high as they can get watching for anything that might wanna bug the hens, it didn't affect them really just took a while to get used to seeing them without their pretty combs.