I have 4 BRs, 3 silkies, and 1 who knows. I am in central NC with a 4x8 coop. Do I need to put a heat lamp in at night? If so, how cold is too cold? I have noticed the silkies huddle together in one corner and the others line up next to each other on one of the roosts inside. Is there any reason the silkies choose not to roost?