Sunday night, our low was 4 degrees F. I have 36 chickens, and 13 guineas, the guineas have taken to staying inside with the chickens at night. I have 3 little chicken doors that open to the runs. I closed 2 of them, and left the 3rd one just open enough for chickens to go out to the smaller run in the daytime. That door is on a hinge so I could leave it where it blocks most of the wind. The other 2 are boards that slide into place. I left a heat lamp on a timer to come on at 4AM. I started to leave it in when I went to close them up for the night, but they all got agitated and were knocking each other off the roosts, etc.
I was worried that I'd find bird-cicles this morning, but they're fine. Today, I went down about 2 hours before dark, and turned on the heat lamp. Then, at dusk, they all went in and settled, no fuss. I think the key was having the light already on, so there was no sudden light added to agitate them.
They were sounding a little odd, sort of wheezy, so I added the heat, and put some strong immune-boosting and respiratory health herbs in the water, too. Tomorrow I'll add cayenne to the feed, too.
The rest of the week's supposed to be a lot warmer, so I'll be able to take out the heat lamp, and put the compact florescent bulb back in, to come on at 4AM.