I am so glad I found this thread even though I wish I had when I first discovered our broody hen. Here's what's happened so far and lessons I'm learning along the way:
1. Over a month ago, we had one Sussex cross hen start making funny noises and spending time in one of the laying boxes. Not knowing what this was about, we researched and discovered that she was brooding. After about a week or so of watching her sit in her box, the look on her face made us feel sorry for her and we thought we'd do a little experiment, so we put three eggs in, one of each colour that we have (this was over a two day period).
2. A couple of days later, we discovered that the eggs multiplied from 3 to 5. we realized that when the brooder was out in the run getting food or water, the other hens were going in her box and laying eggs. After more research, we decided to mark these eggs so that if it happened again, we would collect the unmarked ones.
3. After another week, when I went to collect eggs, we found that there were now 9 in her box. So, I took out the unmarked ones only to discover that I was removing 6. There were only 3 marked ones. Knowing that racoons and crows can't get in the run or coop because of how secure we made them, we could only conclude that maybe a mouse or snake took two of them. We did find the carcass of a mouse in the run with a chicken running around with it's tail in its mouth.
4. 21 days later, the first egg hatched. We didn't see the whole process though. I was out of town and my partner went out to collect eggs and there was a freshly hatched chick, no egg shell to be seen anywhere. Momma took care of baby and within a day she had it out and about in the run with the rest of the flock. I was worried about this but Momma kept the baby protected and went after the other hens who got to close. The only problem was, she wasn't sitting on the nest with the other eggs.
5. About 5 days later, egg two hatched. When I woke up and let the chickens out of their coop, I looked in the brooder's nest (who was outside already with the chick) and I saw two little beady eyes staring up at me. I put momma and first baby back in the nest so she could keep the baby warm. an hour later, I found momma and first baby outside again and the newly hatched one laying on its side in the brooding box with its eyes closed. worried it was dead, I picked it up and it woke up chirping. I brought it in the house and kept it wrapped up in towels in a box. I put the box in a window and let the sun warm it up. Baby slowly started eating and drinking. Once it got dark, I put the baby under momma while she was sleeping.
6. Momma took to the new baby just fine and two days later, when collecting eggs. I noticed the third egg had a beak peaking out of it. I didn't think this one would hatch since momma wasn't sitting on it regularly. Over the course of several hours, I saw the egg slowly breaking apart but a lot of blood was coming out of it. I was worried since momma was with the other two chicks wandering around. I quickly grabbed the egg and chick and did the same thing I did with #2. By the evening, the shell was half off and the chick was kicking with its legs. We put an electric heating pad underneath towels and left it for the night. My partner woke up during the night and realized it was cold in the house. By this time the chick was completely out of the shell but was lethargic, so my partner wrapped it in a towel, held it close and fell asleep with it wrapped in his arms. I woke up to them both asleep on the couch together.
7. We nursed number 3 all day and then at night put the baby under momma. The next day I found that momma would keep an eye on 1 and 2 but 3 had a hard time keeping up with them and then got confused as to who momma was. It would run and hide under the rooster (who was very good at protecting it). It didn't seem momma was interested so we decided to lock momma and the three chicks up in a small rabbit hutch that we had sitting empty. That was two days ago, right now all are doing well except momma is now giving me dirty looks because she can't go running around free.
Lesson learned: don't give the eggs to a brooding hen intermittently. give them all on the same day, make sure they are all marked, and let them all hatch around the same time, not days apart.