I have a nice clutch of chickens, with a rooster. We allow them to free range all year but the winter. A large group of them end up in the trees around the coop- with or without the rooster. The last week my daughter left the coop door open and a few got out. Needless to say, we found them in the morning. They had frozen to death and fell out of the trees they were roosting in. They have a clean coop, with lots of straw, and roosting room, and a light on a timer. What am I missing to keep them out of the trees?