I'm in Seattle, so trust me, I get plenty of rain! I have an elevated hen house, and they mostly stay under it during rainy days. The litter in their house does get wet right around the door, which I always worry about but can't seem to prevent. They haven't suffered any ill effects yet, so I think it is mainly an issue of how healthy they are, and if they are adult. I wouldn't have the babies out in the rain, though.