Yep! Mine have begrudgingly handled -25f real temp for two days and no one got frostbite. I have a mixed flock ranging from lavender orps to banties. They were ok! No supplemental heat. They’ll be fine. Just annoyed.Lol, they don't need it to be 40 degrees. My chickens don't even get annoyed until it goes down to single digits. The teens don't even bother them much. Below zero worries me although it will be short lived and they have a heating pad so they'll be fine. If I had no heat I'd be worried about below zero. Like another person in this thread had mentioned - it isn't just about whether they survive but also about frost bite. But they don't need the temp to be 40 degrees to avoid frostbite. As long as you keep the coop very dry I would be surprised if they ever got frostbite in 20 degrees or over.