I have checked the air sacs, now on day 15, and some seem to be too small, some too big, and some just right. And they are off by a lot from each other - it's not minor differences. What could be the cause? The books make air sac size seem like a really big deal, and their relationship to humidity. However I am wondering how chickens in particuarly humid areas, like the tropics, don't all have air sac problems. If too much humidity causes small air sacs, why don't all tropical chickens die when they go to hatch? Also, they are weird shapes, not like the perfect crescent shaped air sac I see in drawings.