Do you know anyone that has used one of these?
https://www.incubators.org/gqf-mfg-radiant-heater-0470.html
https://www.incubators.org/gqf-mfg-radiant-heater-0470.html

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It's Not unusual for temperature to fluctuate to extreme highs and lows within short periods of time. This is just an unusually cold fluctuation. If you give your birds heat now, they may have to have heat for the rest of the winter. Once they become dependent on it they lose their ability at least temporarily to keep themselves warm. If your coop is properly secure from the wind, and they have plenty of fresh food and water, with good fluffy bedding, they will survive this cold without any harm.
If you do use heaters, make sure that they are at least double and, even safer, triple secured, without using plastic zip ties or materials that can melt. Wire or chain is much safer, and should be attached to several different places on the lights. You cannot underestimate the danger of such devices in a coop.
Got a question for you, Mary. They say that frostbite on a rooster affects fertility. Does it affect it until he's healed or forever? I mean, if it's forever, there would be a lot of infertile roosters out your way!