It's been cold outside. I have 6 chickens of different breeds. They're in a 6x8 coop with a roost going across the whole 8 foot back. Ive gone out to check on my chickens and for several nights in a row, 5 of the chickens are on one side all tucked together and my barred rock is on the other end of the roost. Is there any reason for this? Should I be concerned?