personally I would think that the temp is from the hen and eggs, but more hens, but the humidity is actually the egg. When you think about it they can "sweat" and in a small area they would actually increase the humidity, and the inside of a egg is very wet and the egg's pores would allow some moisture out. Heat would also help humidty rise......................also magic probably helps! hehe
Also if the hen stops turning the eggs and doesn't move, all the moisture stays there. When she's turning the eggs on a regular basis, she's letting all the humidity out.