This right here. I try to keep reminding myself that the chickens have built in down jackets that they can't take off. I know what it feels like when I am out working in the yard and then come into the warm house. I can't wait to take that jacket off. The chickens don't have that option and are very comfortable in the cold as far as I can tell. I too keep watching their behavior to see how they are acting.
This.
To those in the south worried about your birds, you will never see temps cold enough to stress your birds. You do have to worry about heat stress--heat is far more harmful to birds than cold.
I am in Ohio, and we have snow on the ground. My birds are moulting like crazy, and some of them just look like pincushions with no feathers at all. They were all outside yesterday scratching around in the snow. If they were cold, they could go inside--the coop is always many degrees warmer than the outside, just because of the sun coming in though the windows. But most of the birds stayed out. If you watch behavior, you'll see how much they relish the colder temps.