We live in the Colorado mountains. My 12 hens, Araucanas and barred rocks, have an insulated 64 sq ft coop and a hoop run of about same size just covered in plastic except at the far end. I leave the poop door to the run open all the time and figure that plus the 3/4" opening above the main people door is their winter ventilation. ( in summer they are outside in 2000 sq ft yard almost all day and no plastic on run). I think it's a good setup BUT OUR RECENT WEATHER HAS BEEN CRAZY. Just last week daytime temps were in mid 70s and overnight lows in 50s. Now we have a 5 day winter storm and as I write daytime highs are in the 30s and overnight lows going as low as 10-15 tonight. Since storm hit I have not let chickens out except in their plastic covered run as I don't want them wet and I'm even thinking of covering their pop door tonight. My main concern is not the temps so much as it will get colder than that before winter is over here. But the cold came on so SUDDENLY. Don't they develop extra downy feathers under their normal coats as winter comes on? And if so, they wouldn't have developed them yet with recent weather so warm. Should I try to add a heater tonight? I have an oil filled radiator type I could plug in out there set on low and I don't think that would burn straw. Anyone know about the extra downy feathers for winter thing?