Humidity during chicken incubation

Humidity is one of the most important factors determining your hatch rate, but, contrary to popular belief, high humidity is more troublesome than low humidity during most of the incubation period.  During hatch, of course, you want high humidity in the range of 65% or more so that the chicks won't get stuck in the shell, but the goal is 40 to 50% for the first 19 days.

In order to hatch correctly, a chicken egg should lose 13% of its weight during incubation, and that weight is lost in the form of water evaporating out of the egg.  Over time, the air pocket in the egg will get larger as water evaporates out, creating a safe spot for your chick to breath in between around day 19 and the time the chick hatches.  If the humidity in your incubator is too high, then your chick won't have the appropriate air pocket and will die soon before pipping.

There are a few different ways to get the right humidity in your incubator.  The simplest is to follow the instructions and fill a certain number of wells with water, but this is a very hit or miss approach --- humidity in your incubator is determined by the humidity outside the incubator as well as by the amount of water in the wells.  We live in a very damp climate, and I suspect that following the instructions last time around is part of what resulted in such a low hatch rate.

The second method is to pencil the size of the air pocket on the outside of each egg at intervals while candling.  A chart like the one shown here can be used to see if the egg's air pocket is growing at the right speed.  However, this technique requires a lot of judgement calls, and would be time consuming if you're hatching more than a few eggs.

Another easy method to get the proper level of humidity is to buy a fancy incubator with a humidity readout.  Our new Brinsea Octagon 20 incubator will definitely help us in that regard, but there's a big difference between 40 and 50% humidity and I'd like to know whether my eggs are losing weight at the proper rate.

Which brings us to the final method of determining egg weight loss --- weighing your eggs.  This is the method I've chosen, so I'll go over the specifics of the calculations in a later post.

No matter which method you choose, you should be aware that it's the average humidity over time that's important to your eggs, not the humidity at any given moment.  So it's okay to let the incubator wells completely dry out for a day if you need to in order to get the average humidity down lower.  In fact, some incubation experts practice dry incubation where they seldom or never fill the wells at the bottom of the incubator.  I plan to use a hybrid approach, adding water as needed to keep our eggs' weight loss on track.