I was going to suggest a light, but you beat me to it. I have some young birds outside in a large cage, and I have just been leaving them there, and putting a quilt over the cage at night. I go out to check after dark and they are quiet, not peeping, and they look perky in the morning. I have some about three or four weeks old that I am putting out during the warmer part of the day, just for sunshine and fresh air. (and less cleaning of the brooder boxes, LOL) We are spoiled here in So Cal. Having chickens is just plain ol' easy compared to what the other people with "weather" write on here. I don't think I'd have the guts to try it in NY, MN, or some of those really frozen places.