Well, I’ve got a few years of chickens behind me now, so I will venture an explanation. This is my take on the subject, not textbook information.
The hen sets until the first eggs hatch and since the chicks do not need food or water for a couple of days, she will continue to set for awhile longer. Unless the eggs are at various stages of development (i.e. the other hens have added eggs days later) the remaining viable eggs will be close to hatching. Chicks in the shell communicate with mom and with each other by peeping. So the hen has a pretty good idea of what’s going on and she clucks to the eggs to encourage them.
When there are no eggs still peeping, mom considers the hatch complete and goes into caregiver role… takes the chicks for their first walk, shows them how to eat and drink etc. Occasionally there will be an egg that hatches after she leaves the nest, but after a certain point the mother hen has to put the needs of the hatched chicks ahead of the needs of a latecomer. If this happens and I find the late chick still alive, I take it into the house and put it under a lamp to dry off, give it a bit of sugar water and return it to mom using the “2 for 1” trick.
“2 for 1” is simple and has always worked for me. I chicknap one of the babies and it hollers to its momma to save it. Momma gets indignant, then upset, then furious. When she is all worked up and the chick is screaming, I return the chick to her… and also the newcomer. Momma is pacified by the return of her baby and never realizes she got extra as well. Isn’t it handy that hens can’t count?
Hope you have a nice Day!
I’m here for you!!
Plant Your Dreams and Miracles Will Grow!!!