I live in Oklahoma. Right now we are in a Winter Storm Warning. There is two inches of sleet and ice on ground. I have an open air coop. Meaning there is no hen house. My five RIRs are exposed to the wind. I have a board over the north side and a tarp over the top. I have put out a box with straw in it. Do I need a heat lamp? They have survived this harsh winter so far, but I lost a chicken in the last storm( I think she was sickly anyway) but I'm afraid of losing another one.