My 5 month old bantam mix cockerel, Buttercup, acts fine during the day, but when he's sleeping or resting, he starts slowly opening and closing his eyes and breathing with his mouth open as if he was having a hard time breathing. It started when the cold weather came and I think it may be from the cold air. I brought him inside and about after 5 minutes he was acting perfectly fine. It looks very concerning when he does it. Any ideas why he may be doing it and how to help him?