The meaning of the ‘variations’ in the babbler ‘shout’: A musical-ethological approach

Abstract

This study is focused on the shout of the babbler Turdoides squamiceps, as a model for interpreting the meaning of the variations in animal vocal expressions, using a ‘musical-ethological approach’. Vocalizations were recorded in nature, where all babblers were individually marked. The field events were classified into different communicative categories, and the recordings of 170 shouts of the eight most intensively studied babblers, were analyzed with respect to the ‘basic rules’ observed in music. Visually defined ‘variation types’ and mathematically defined musical variables of the variations were related to the birds' field behaviour in order to determine the correlations between the variations and the different categories. The results indicate the existence of variations in the babbler shout that may be important for communication. Border situations were accompanied by longer ‘syllable variations’ and by an increase in the musical variables, which were defined according to the ‘basic rules’ observed in music. Other, more subtle variations of the intensity curves could be related to motivations such as joining the group members or searching for affiliation. An increase in the distance between communicating babblers was accompanied by an increase in the number of syllables per shout. It is suggested that this is because the variations in the tempo and staccato are better identified in long shouts with many syllables. It is suggested that variations in vocal expressions play a role in animal communication. The resemblance of the ‘basic musical factors’ of the variations in the babbler shout to the basic rules observed in human speech intonation and in music suggests that the same set of rules may be found in many other animals. Thus, it is appropriate to apply certain musical terms to animal communication.