I have no idea, it's just what I was told. Pheasant chicks are extremely reactive, and can fly, or run long distances when frightened, which happen often. They aren't as domesticated as chickens. It would be near impossible to keep track of them in a free range situation. I'm sure the mom...
I was told by an experienced pheasant keeper that you can have hens hatch the eggs, but you better pull the chicks. Pheasant chicks will take off and disappear, and won't stick with the chicken hen.