The mallard was recorded by Jack Berteau in the Vendée, France (recording XC613266) and the blackbird by Pierre Foulquier in Le Mans, France (recording XC622587).Ī single audio file is included in the Supplementary Material which covers all the figures in this paper. The mallard quacks and the blackbird call in Figure 1 were obtained from the Xeno-Canto database. We argue here that the variegated morphing modes observed across mockingbirds’ phrase transitions are distinct from these cases of stereotyped within-phrase morphing, less easily explained by muscular constraints, and surprisingly similar to certain strategies in music. (B) A series of mallard quacks (XC613266, recorded by Jack Berteau in the Vendée, France) and (C) a blackbird’s alarm call (XC622587, recorded by Pierre Foulquier in Le Mans, France) that both contain a specific kind of acoustic morphing: one repeated note/syllable gradually slows down and descends in pitch (after an initial rise for the blackbird call). Both spectrogram and waveform illustrate the organization of Birdsong material in distinct phrases of repeated syllables (e.g., phrase 3) or syllable groups (e.g., phrase 1). Spectrogram (top) and waveform (bottom, green) of mockingbird song, illustrating its hierarchical structure, and mallard and blackbird calls for comparison. This is the first time such transition rules in any complex birdsong have been specifically articulated. In our paper, we categorize four common modes of morphing: timbre change, pitch change, squeeze (shortening in time), and stretch (lengthening in time). We find that more often than chance, syllables before and after the transition are spectrally related, i.e., transitions are gradual, which we describe as morphing. In this paper, we present our initial attempts to describe the specific compositional rules behind the mockingbird song, focusing on the way the bird transitions from one syllable type to the next. It resembles a common strategy in human composing, which can be described as variation of a theme. What is rarely noted is the systematic way the bird changes from one syllable to the next, often with a subtle transition where one sound is gradually transformed into a related sound, revealing an audible and specific compositional mode. When they do study it, the specific imitations are often noted, and the total number of varying phrases. Because of its complexity, it is not widely studied by birdsong scientists. The song of the northern mockingbird, Mimus polyglottos, is notable for its extensive length and inclusion of numerous imitations of several common North American bird species.
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