Development of species identification in ducklings: XI. Embryonic critical period for species-typical perception in the hatchling

Abstract

In the embryonic stages prior to hatching, the contact-contentment call of the Peking duck (domesticated Anas platyrhynchos) is more highly variable (2–6 notes/s) than it is after hatching (4–6 notes/s). The embryos must be exposed to the normally wide range of repetition rates of their contact-contentment call (2, 4, 6 notes/s) if their preference for the species maternal call is to be normal at 24 h after hatching. Exposure of muted embryos to the higher (4, 6 notes/s) or lower (2, 4 notes/s) portions of the normal range was ineffective. Thus the normally highly variable nature of the embryo's vocalizations fits the requirements of its developing auditory system. An embryonic critical period was also demonstrated: when muted hatchlings were exposed to the rates typical of the postnatal period (4, 6 notes/s), or even the more widely variable rates of the embryonic period (2, 4, 6 notes/s), they failed to show a preference for the normal maternal call at 24 or 48 h after hatching. Thus the precise developmental linkage involves maturational stage as well as the representativeness of the stimulation.