Alarm call responsivity of mallard ducklings: I. The acoustical boundary between behavioral inhibition and excitation

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Abstract
Mallard (Anas platyrhynchos) maternal assembly calls have fast repetition rates (noteslsec,) which promote behavioral excitation in ducklings (i.e., vocalizing, approaching). On the other hand, maternal alarm calls have slow repetition rates, which promote behavioral inhibition (i.e., cessation of vocalizations, “freezing”). This study assesses the nature of the acoustical boundary separating these 2 behavioral states. Maternally naive ducklings were tested to 1 of 2 series of altered alarm calls that either increased or decreased in repetition rate every minute by 2/10 sec. Ducklings in control groups were exposed to a constant repetition rate for comparable periods of time. The inhibitory and disinhibitory responses of ducklings revealed that a relatively sharp acoustical boundary between inhibitory and excitatory repetition rates exists around 2.6 to 2.8 noteslsec. This transitional region happens to coincide with the range within which neither maternal assembly nor maternal alarm calls occur. Thus, there is a genuine match along this acoustical dimension between auditory perception of ducklings and the 2 major species-typical maternal vocalizations of mallards.