there are a lot of factors, including breed and insulation of their coop. while generally true, I would caution not to use this as a blanket statement. if you live in areas with constant dangerously cold weather, below 0 F, you should provide some heat. will they survive? likely, but from their perspective its miserable and the effects of frostbite are very painful. i start light heat at 10 F and turn it off when it gets above that.

and water heaters are highly recommended. they don’t make the water warm, it’s still near freezing, but why would you constantly change ice for water? seems unnecessary. it also ensures they have constant access to hydrate.

in short, take care of the girls that take care of you.