Hello, I have a hen that has hatched four healthy chicks, and two were dead new borns. One was lying out side of it's shell dead and the other three days later dead in it's broken shell. I checked out the last five eggs and they are warm and mom wants to keep them warm. I can see she wants to hatch them but can't understand why I keep finding them dead. Any ideas why? I'd apprciate any advice to what to do or even why this is happening.