Perception of the Frequency Characteristics of Distress Calls by Mallard Ducklings (Anas Platyrhynchos)

Three playback experiments demonstrated that mallard ducklings are perceptually tuned to the dominant frequency and rate of frequency sweep found in conspecific distress calls. We separated ducklings from their brood to induce them to distress call, and then measured the effectiveness of various synthesized distress calls in inhibiting the ducklings’ own calls. The dominant frequency and the rate of the terminal downward frequency sweep were estimated in 280 domesticated mallard duckling distress notes. In Experiment 1, ducklings were tested with synthesized distress calls having notes with dominant frequencies which differed from the population mean by 0-6 standard deviations. The ducklings’ responses to the synthesized calls were tightly linked to the natural distribution of this parameter. That is, calls which differed by 2-4 standard deviations from the population mean elicited significantly weaker responses than did the call with the mean dominant frequency. Domesticated mallard ducklings may be less sensitive to their own call frequency than to the slightly higher frequency of wild mallard distress calls. In Experiments 2a and 2b, ducklings were tested with synthesized calls having rates of terminal frequency sweep which differed from the species-typical value by 0-4 standard deviations, or with constant frequency control calls which matched the amplitude envelopes of the frequency modulated calls. Calls having rates of frequency sweep which significantly deviated from the norm elicited a weaker response. The results also suggested that mallard ducklings are sensitive to the amplitude envelopes of distress notes. These experiments extend our previous research indicating that mallard ducklings’ responses are linked to the natural distributions of the acoustic parameters of their vocal signals.