Mine are five weeks old and the last nights have been in the low forties with no light. They are in a coop with pine shavings and have no problems. Tonight it is supposed to get down to 38F, but there is no electricity in their new coop. I have no doubts they will make it through the night just like they did in the old days when there was no electricity. Don't get me wrong - I am getting tired of these chilly nights all the way into the middle of June.