QI set 12 goose eggs in an incubator, 10 were fertile but in the end only three hatched. Four out of the seven that didn’t hatch had started to crack but the goslings didn’t manage to get all the way out. Why is this? Should I have helped them?
AJack Smellie: It is really hard to lose birds at such a late stage in the incubation process. I am sorry!
The most likely reason that this happened is down to humidity. Once the gosling pips internally (i.e. breaks through into the air sac inside the egg), the humidity in your incubator needs to be increased from 55% to 75% in order that external pipping can then occur. As the bird starts to crack open the actual egg itself, it is crucial that the humidity is right to stop the egg membranes drying out and trapping the gosling inside the shell. A crucial point to note is that if you open your incubator at this point, even if for just a few seconds, the humidity level will quickly fall and that can be enough to dry the membranes out.
As to whether you should have helped: it’s tricky. When a bird breaks out of its shell, it naturally strengthens its neck muscles in doing so and if you therefore ‘help’ it you run the risk of having a bird with a weak neck that may then remain weak. On the other hand, if you have not kept the humidity levels high and the bird is trapped, it seems almost cruel to condemn it to die due to human error! If you do decide to help next time, make sure you have given the bird enough time to try on its own (24 hours at least from when you first see external pipping) and that you do it slowly and carefully. Any sign of blood, stop and return the egg to the incubator. Good luck!