Why hatching on different days when all put in the incubator at once?

[Taniam]

Hi there. Can anyone tell me why our chicks are hatching on different days.
We had one hatch on day 21, then two on day 22 and one on day 23.
We put 18 eggs in at once and only 4 have hatched.
Thanks in advance.

 

[JHorn91180]

At some point at least for a while or even now your incubator temp was too low. Double check with another thermometer and on your next clutch turn the bator up about 1 full degree and see if that helps. Lower temps retard development and cause late and poor hatches with a high percentage of late quitters(mortality) in the other developed eggs. Usually the chicks that do hatch are a bit weaker then normal also in the beginning and take longer to actually zip and hatch out of the egg but not in all cases.