Many strains of birds were bred to be fast/slow feathering so they could be feather sexed at birth. The females were bred to be fast feathering and males bred to be slow feathering. When they are crossed, you get feather sexable chicks. I think that this female trait does get passed on to some extent and thus why so many female chicks feather faster. However, I don't know if it does or will hold true for all brids/generations.