Have 9 chickens since last April and starting the winter season in Massachusetts. Currently 18 degrees. Our Orpington has decided to roost outside by herself at night instead of going into the coop with the other chickens. Should I be concerned or is this normal behavior? It has been in the 20's for the last week and she doesn't seem to be affected by the cold. Two nights ago she stayed out during the snow and was covered with icy feathers in the morning. She roosted inside until it started to get cold. Any thoughts?