Fertilization and early stages of embryonic development of birds

Birds are characterized by physiological polispermią , it means that many spermatozoa to penetrate the egg cytoplasm during normal fertilization , but only one of the male pronuclei formed participates in the formation of the zygote nucleus . However, all overtime degenerate male pronucleus during early cleavage . Has not yet been explained , what in fact happens to those overtime przedjądrzami and what mechanism is responsible for their degradation.