I have a flock of eight hens, eight months old. All laying very nicely even during the cold winter months so I think that they're healthy and enjoying life. They have a very secure coop with an automatic door that closes at dusk and opens at dawn. When out of the coop they are in a secure, covered chicken yard. They have access to food and water both in the coop and in the yard. Until this past week, all of the chickens would be in the coop and roosting long before the door closed. In the past week, when temperatures have been in the single digits, I've found anywhere from two to six hens outside the coop at night. I did put a heat lamp out in the coop with the drop in temperature and think that this may have spooked them. I'd like to hear any opinions as to the need for a heat lamp in the coop and what else might be causing the hens to stay out in the cold.