At -22 F last winter my girls were out in the run, eating and drinking and pecking and scratching like it was a normal day. For them, it was. Wind chill factor only counts if the birds are out in the wind. If they are in a protected run or in the coop there is no wind chill to factor in.
When it's cold the sparrows and wrens are out flying around from place to place. They are not huddled up in a ball trying to stay warm. Like the chickens they also wear a down coat year round.
Strange that no one worries about air conditioning for the birds on 80 degree days in the summer. It must be more uncomfortable for the birds to be wearing those down coats in the summer than it is to be wearing those down coats in the winter.