Syringeal vocal folds do not have a voice in zebra finch vocal development

Abstract

Vocal behaviour can be dramatically changed by both neural circuit development and postnatal maturation of the body. During song learning in songbirds, both the song system and syringeal muscles are functionally changing, but it is unknown if maturation of sound generators within the syrinx contributes to vocal development. Here we densely sample the respiratory pressure control space of the zebra finch syrinx in vitro. We show that the syrinx produces sound very efficiently and that key acoustic parameters, minimal fundamental frequency, entropy and source level, do not change over development in both sexes. Thus, our data suggests that the observed acoustic changes in vocal development must be attributed to changes in the motor control pathway, from song system circuitry to muscle force, and not by material property changes in the avian analog of the vocal folds. We propose that in songbirds, muscle use and training driven by the sexually dimorphic song system are the crucial drivers that lead to sexual dimorphism of the syringeal skeleton and musculature. The size and properties of the instrument are thus not changing, while its player is.

How Loud Can you go? Physical and Physiological Constraints to Producing High Sound Pressures in Animal Vocalizations

“…When measured in vivo, ME captures both (i) the transformation of aerodynamical power into acoustic flow within the vocal tract, (ii) transmission efficiency through the airways, and (iii) the transformation of sound from the surface (mouth/beak/air sacs) to the environment (Titze and Palaparthi, 2018). ME varies greatly with bronchial pressure (Herbst, 2014), frequency (Zhang et al, 2019), vocal fold position, geometry and pathologies and also in between species (e.g., Brackenbury, 1979;Titze et al, 2010;Herbst, 2014;Maxwell et al, 2021) and values are reported between 10 −4 to 2% (e.g., a factor of −60 to −20 dB).…”