Alarm call responsivity of mallard ducklings: III. Acoustic features affecting behavioral inhibition.

Mallard ducklings (Anas platyrhynchos) inhibit their vocal and locomotor behavior upon hearing the maternal alarm call of their species. This study assesses the effects of varying acoustic features of alarm calls on the ducklings' freezing response (i.e., vocal and locomotor inhibition). Domestic mallard (Peking) ducklings were tested individually to alarm calls that varied either in note duration, frequency modulation, dominant frequency, repetition rate, or repetition rate in combination with these other features. The present study demonstrates that ducklings show a high degree of behavioral specificity to repetition rate (i.e., number of notes per second), relative to other acoustic features. This study also revealed that ducklings also exhibit some degree of behavioral specificity to note duration. Dominant frequency and frequency modulation play only a minor role in affecting behavioral inhibition. The behavioral specificity of mallard ducklings to slow repetition rates (that are typical of maternal alarm calls) provides a basis for the importance of their slow-rate perinatal vocalizations in the development of alarm call responsivity.