Beekissed did a natural incubating experiment last year, a huge part of the inspiration for setting up Mama Heating Pad. Here's the link to her thread.
https://www.backyardchickens.com/t/...ral-nest-incubation-experiment-1-so-it-begins
As for concerns about power going out, we had that happen. Had winds of 60 mph and sideways blowing snow that night too. We went to bed about 11, and at 4 Ken woke me up with two little words - "The chicks!" They were less than a week old, living outside in the run, and we'd had a power outage! It must have lasted at
least 2-3 hours. The power coming back on is what woke him. We threw on our clothes and ran out there. The cave still retained residual warmth from the towel, and from all the straw packed on top of, around, and inside it. The chicks were just fine. We turned on the heating pad, remembering to hit that "auto-off" function, and went back inside to bed. Later that morning when I went out to check on the chicks, there were 8 little hineys stuck in the air and 8 little heads stuck in the feeder. No problem! When a heat lamp goes out, the surrounding air cools off really quickly. With the straw insulated cave, that heat is retained. As Bee noted, though, when the power comes back on the heat lamp goes right back on too, unlike the pad where I have to physically turn in it back on. But the cave buys me much more time than the lamp going out would give me.
Having had it put to the test in such cold, nasty weather, I'm no longer worried about it. They'll find the furthest corner inside the cave and cuddle, and they'll be just fine until I turn it back on. Chicks often wander too far away from Mama Broody Hen too, and they are usually back to their snoopy little selves after a short warm-up once they find her again.
Seymore, the temperature inside the cave the second or third night I had it going was 82.9 degrees. The room temperature was 69 degrees. They were perfectly content. That "95 for the first week, lowering by 5 degrees weekly" is such an arbitrary instruction. Folks panic if the brooder drops to 93. Why? They're fine. If they weren't they'd be huddled up underneath all of the time. They don't do that - they are out in the main part of the brooder almost all of the time and just duck into the cave for short periods to warm up or hide if they're spooked. I only put the thermometer in there because a question by azygous got me wondering. After my curiosity was satisfied and I'd posted the result in this thread, the thermometer came out and the chicks told me what they needed.
Right now it's 30 degrees outside. My latest chicks are 3 weeks old today. The heating pad is set on 4. And when I went out this morning they are running all over the brooder - some eating, some drinking, some playing "King of the Mountain" on top of the heating pad. All's well at Oleo Acres.