By Chrissy in CA
Hatching eggs isn’t always as easy as setting eggs in an incubator, waiting 21 days, and waking up to chicks on the twenty-first morning. There are a few things that can go wrong – especially in less-expensive incubators. Humidity and temperature issues can cause chicks to become “shrink wrapped” or to be overly-sticky at hatch.
The highest risk of shrink wrapping is after the eggs have externally pipped, have already been in lock down with high humidity... and then the incubator is opened for some reason. If the ambient humidity in the room is lower and the temp is cooler than the humidity and temp are inside of the incubator, (which is often the case) then opening an incubator lets a rush of cool, dry air into the incubator that exchanges with/replaces the warm moist air in the incubator, and does this inside the eggs as well. That is what dries out and shrinks the membranes. The membranes were moist, and then quickly lost moisture and shrank when the cold dry air rushed in. This is why incubator instructions always clearly state not to open the incubator until the hatch is completely over.
Shrink wrapping can also happen to eggs that have only internally pipped, but is a little less likely and less damaging since the air and humidity can't exchange as quickly thru an un-pipped shell. This is why we can get away with waiting to lock down eggs until they have internal pipped and we can also candle prior to lock down without doing damage. Personally, I wait until I see internal pips before locking down... I have never had any shrink wrapping issues doing this.
High temps can also cause shrink wrapping, especially in forced air incubators with fans when there is not enough humidity in the incubator. Moisture is continually being lost at a time when the chick needs a little extra moisture to keep the membrane from becoming leathery/tough, when the chick needs to stay slick enough to spin in the eggs and also when the extra moisture is needed to keep the shell a little softer.
Sticky chicks are usually caused by overly high humidity during incubation that did not allow the chick to grow as large as it should have or let the egg lose enough moisture as the chick developed, so at hatch time those chicks are coated with more liquid (albumen) than they should be. A sticky chick's movement is restricted, but the stronger chicks usually manage to hatch ok (just extra sticky). The weak chicks will expire trying to hatch because they just don't have the strength. if they can't spin, and can't zip, they expire. Sometimes that extra sticky liquid can clog the chick's nostrils (aka drowning the chick), and the sticky liquid can also cause the opening of the internally pipped membrane to glue down onto the chick's nostril shortly after they have pipped internally, suffocating it.
(This chick was "sticky" at hatch, but is now a healthy, happy pullet.)
This is why it is important to know your incubator – practice managing the temperature and humidity prior to trying to hatch chicks. If you are experiencing losses at hatch, chances are it has to do with one of the above factors. Invest in a good hygrometer (or 2) and good thermometer(s) to keep inside your incubator – checking them regularly throughout incubation and hatch should alert you to any issues.
To hatch chicks, an incubator should remain at about 99.5 °Ffor all 21 days. Many people use a “dry incubation” method where humidity levels are kept lower (16% - 40%) up until the eggs internally pip, while other people keep their humidity a bit higher (40%-50%) throughout incubation.
At lockdown or after the chicks have internally pipped, humidity should be raised to about 65% and the incubator should not be opened until the last chick has hatched... or they'll chop your fingers off with a light saber...
(Just kidding! But I did think this picture was cute - the reflection of my flashlight used for candling gave the appearance my chicks were Jedi knights.)
Hope this helps, and happy hatching!
Chrissy in CA -
(Photos and lame humor by Leigh)