Development of species identification in ducklings: VII. Highly specific early experience fosters species-specific perception in wood ducklings.

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Abstract
Wood ducklings find the maternal assembly call of their species attractive in advance of exposure to it. A critical acoustic feature of the maternal call is the descending frequency modulation (FM) of its notes. The ducklings'' vocalizations themselves have a very pronounced descending FM, albeit in a much higher frequency range than the maternal call. To test the possibility that the maternally naive duckling''s sensitivity to the descending FM of the maternal call notes might derive from prior exposure to their own vocalizations, wood duck embryos were placed in individual auditory isolation several days before hatching and tested for their preference for the descending FM in choice tests with ascending and descending synthetic maternal calls after hatching. The isolates did not show the usual preference for the descending all at either 24 or 48 h after hatching. Isolates exposed to a wood duckling alarm-distress call for 5 min/h prior to the test did show a preference for the descending call. Isolates exposed to the same duckling distress call played backward (ascending FM) for 5 min/h prior to the test did not show a preference for the descending call. The wood ducklings'' usual preference for the descending frequency modulation in the maternal call of its species as a function of prior exposure to specific properties of their own vocalizations in the normal course of events. Since the fit between the relevant acoustic feature of the ducklings'' vocalizations and the critical perceptual feature of the maternal call is an abstract one, the present finding is an example of a nonobvious experiential precursor to behavior that otherwise would seem to be innate or instinctive.