Haven't been on here in a while, but I wanted to share what happened to one of our silkies not in the most recent record cold temps but afterwards. Last Friday it was down to at least -2 in our unheated coop, and while we usually keep the pop door open at night we had it shut. We had also gotten lax on the poop scooping (we have a poop board with PDZ in it). Our chickens were all fine the next day (Saturday), walking around and eating and drinking.
Sunday late-morning (back to normal temps in the teens overnight) we found one silkie dead in a nest box, frozen stiff (husband had replaced the water early in the morning but she was likely already dead then and he thought she was just laying or brooding). She'd shown no signs of distress. We'd had the pop door closed again overnight. It was pretty stinky in the coop, as the back vent was closed too.
I'm thinking it was not just the cold but the excessive moisture/ammonia from the waste buildup. We had 6 silkies and 2 large fowl in a 5x6 coop. I'd been reminding my husband of this and I know it's a risk factor but now we've had the rotten experience of possibly being responsible for the loss of a chicken. The others are doing great, even the weak little silkie who makes thin-shelled eggs and recently had a prolapse followed by a molt. They have a run to go out in during the day and we offer them supervised free roaming, but this winter they've mostly elected to stay inside. Just rotten weather.
Anyways, just wanted to put it out there. Could have been a random loss, but they're all 1.5 years old and had been doing just fine. Birds sadly don't always give much warning.