Our chicks are 4.5 weeks old and have been spending nights in the coop with no heat lamp all week. Temps only fell to the high 60's at night tho and they have literally never shown signs of being cold. I was concerned tho because tomorrow night it is supposed to slowly drop all day to 48 at night...based upon what I have read here I am going to leave them out with no heat and extra pine shavings...they appear almost completely feathered with just a little bit of fuzzy down still peaking out around the feathers in their necks. Ill check on them frequently and make changes before bed if needed but I will post back here and let you know how it goes!!
Update: woke up this morning to 60 degrees the coldest the chicks have seen yet.. When I openned the coop they happily flew out into the run and began flying and chipping around as usual. Its supposed to drop to 48 by tonight so I will monitor them closely but am hoping to avoid returning to the brooder as it is fall and they will need to adjust!