I have 6 adult chickens in Denver. They have a large barnyard and a large daytime shelter. Their nighttime coop is quite small (about 7 square feet). They rest in thick straw bedding, and the coop is pretty draft-free. Most winter nights in Denver are in the low teens, but we do get nights in the single digits and even occasionally a couple of degrees below zero. Most of my friends with chickens use supplemental heat in winter, although I do know one person who doesn't. I'm debating whether it's really necessary to put in the supplemental heat this year, and I'd like to hear from other people who are raising small flocks in similar-ish climates. Do you think the chickens can burrow in their straw and keep each other warm, or is it just too cold for that in Denver? Many thanks.