Once the hen on the eggs begins to sense the chicks readying for hatch, she hardly leaves the nest. Early in her "confinement" she leaves every day or so for a time to poop, drink, eat, maybe take a dust bath, catch some rays, stretch her legs, etc. The last few days, when the chicks are positioning themselves to hatch, and the eggs move, and when they cheep, she tends to them much more closely, talking to them, moving them around, settling down over them, and may not leave the nest at all.
Humans, not being able to fit on nests without squashing the eggs, have developed alternate methods of hatching fertile eggs: the electric incubator! Replicating what goes on under a broody hen is very difficult. So, for the last three days, we try not to introduce too many variables by "locking down" the incubator. The eggs are no longer turned, the humidity is raised, and we keep our hands off the eggs.
