I have a group of 18 chicks, I'm really wanting to move them outdoors. Our daytime temps have been 75-85 and our lows between 45-55. My chicks are 4-7 weeks old. I'm thinking if I add a heat source to their coop will they be fine outside? They've been spending their days outside in the coop for about 2 weeks now, with their heat lamp only in for the fist few days to acclimate them. Here's a picture of their coop.