that happened to one of my most recent hatch toostray chicks falling out of the nest

that's what the old book says too. He also points out that a broody often comes back from daily ablutions with a wet belly (he's British, it rains a lot, plus morning dew) and snuggles straight down on the eggs, damping them as well as warming them.if the nest box soil is in contact with the ground and outside environment then the moistness in the surrounding soil is enough to stop the soil in the box from drying out