Hi GrandmaCluck, UGAChick, & Bugdoodle06.
Luna sat on eggs that were not hers. And right now, I have another BO, Loko, that is sitting on eggs that are not hers. They don't know the difference and the rooster doesn't know that they are his. The hens just want to sit & hatch, and take care of the chicks.
This is my 3rd experience. Loko tried in November, 6 eggs, but none of them developed at all. Then Luna, now Loko again.
I don't know what the hen does when the eggs starting to zip but she did whatever she needed to do her job. I think the chicks go under her wings. The chicks were fine. Instincts.
Let me know if I can help you with any other questions. I'll be happy to share what I've experienced with this beautiful process.
Val