My main reason for death after hatch was overcrowding and the one at the bottom of the pile suffocated. I now have 2 light bulbs in the brooder so they spread out but I still had two that died . So on your question-2-5% mortality after hatch for me. And I found the opposite- smaller hatch less death. Larger hatch - more dying.What percentage of mortality rate after hatch for quail is typical