I know that duck eggs require more humidity than chickens. Makes sense, after all they are water fowl. However, I was surprised when my humidity jumped from 63% to 71% after I set my eggs. I mean, we are expecting rain and the overall humidity is up too... but this is in a closed incubator! How much can overall weather humidity affect humidity inside the incu? 8% seemed like a significant bump in humidity to me!
I've learned that in my styrofoam incubator (LG), and my wooden homemade incubator both are affected by the outside humidity in the room.I believe it is because the they are made with "breathable" materials. In summer when it is drier here I have to use more water than when it is in the more humid months. Sometimes it is fine without water at all. My plastic incubator that does not let as much air in stays pretty steady on humidity as long as I keep it filled with water (the fan dries it up fast). I have hatched tons of ducks over the years and have found that although they are waterfowl they can still drown in the egg from too much humidity. I have had good hatches keeping it around 40-45% humidity and 65-70% at lockdown. I have drowned a few in the past accidentally when keeping humidity too high. I do recommend you keep it 5% more if you are using a fan though. It tends to dry up the membrane when they are hatching and they have a hard time making it out (in my experience).
