how do hens naturally change the humidity of their eggs?

[HelenaJean]

eggs need different humidity ranges at different parts of development, how do hens change and maintain this?
also, if a hen had been clucky for a week or so before eggs were put under her, would she still know when to change the humidity or would the eggs just have to deal with what they get?
i've been wonering for ages!!

 

[Baralak]

No worries.. Those hens transfer heat and humidity directly by skin contact. You will notice your broody plucked her own feathers on her bottom side.. She did this so that she would have direct contact. Broodys have been hatching eggs LONG before the invention of the incubator.

 

[Dipsy Doodle Doo]

Hi! Eggs don't really need different humidity at different parts of development.
Under the broody hens (at least the ones I've measured), a hygrometer read between 50% and 55% the whole incubation period. The only time the humidity was higher was after the first chick hatched.

Good luck!

Lisa