Imprinting of the Peking duck (Anas platyrhynchos) and dependence on exposure to light during ontogenesis.

Embryos of Peking ducks were either incubated in complete darkness up t o hatching or were put into light one week before hatching. Control embryos were incubated under dim light conditions which corresponded broadly to the natural conditions. Under standardized imprinting conditions the controls and both groups of the light deprived ducklings showed the 'following response'. Most of the dark-incubated embryos, however, did not distinguish between imprinting and test objects of different shapes. Since most of the embryos kept in darkness only for 21 days also failed to develop the capacity for shape discrimination, there is apparently a critical period for light influences on the development of this capacity at some time during the early prenatal period.