A Call to Expand Avian Vocal Development Research

Abstract

Birds are our best models to understand vocal learning – a vocal production ability guided by auditory feedback, which includes human language. Among all vocal learners, songbirds have the most diverse life histories, and some aspects of their vocal learning ability are well-known, such as the neural substrates and vocal control centers, through vocal development studies. Currently, species are classified as either vocal learners or non-learners, and a key difference between the two is the development period, extended in learners, but short in non-learners. But this clear dichotomy has been challenged by the vocal learning continuum hypothesis. One way to address this challenge is to examine both learners and canonical non-learners and determine whether their vocal development is dichotomous or falls along a continuum. However, when we examined the existing empirical data we found that surprisingly few species have their vocal development periods documented. Furthermore, we identified multiple biases within previous vocal development studies in birds, including an extremely narrow focus on (1) a few model species, (2) oscines, (3) males, and (4) songs. Consequently, these biases may have led to an incomplete and possibly erroneous conclusions regarding the nature of the relationships between vocal development patterns and vocal learning ability. Diversifying vocal development studies to include a broader range of taxa is urgently needed to advance the field of vocal learning and examine how vocal development patterns might inform our understanding of vocal learning.

Importance of sleep for avian vocal communication

“…Open-ended vocal learners go through a similar vocal development phase but maintain varying degrees of plasticity, allowing them to continue learning new vocalizations or modify existing ones throughout their lives [ 45 ]. There is tremendous variation in the timing and length of learning stages; some close-ended learners crystalize within three months, while others take up to a year [ 46 ]. The ‘end goal’ of vocal learning also varies depending on the species.…”

Toward a Computational Neuroethology of Vocal Communication: From Bioacoustics to Neurophysiology, Emerging Tools and Future Directions

“…While much of vocal neuroethology has recently focused on songbirds and mammals the techniques discussed here are equally applicable to the abundance of other species studied in bioacoustics and behavioral ecology including fish, amphibians, and insects. Even within songbirds, research on vocal learning in songbirds has ignored the majority of species, female birdsong, and most call types (Loo and Cain, 2021 ). Likewise, because these new computational methodologies can often deal with unstructured data, they enable us to expand beyond simplified, isolated behaviors in controlled environments to more natural or naturalistic behavioral contexts where dynamics involving multi-modal integration and multi-animal social interactions arise.…”

Beyond a biased binary: A perspective on the misconceptions, challenges, and implications of studying females in avian behavioral endocrinology

“…Despite the dearth of research on tropical species, the available evidence undermines traditional hypotheses, especially as related to the role of testosterone (hereafter, “T”) in aggression and song ( Peters et al, 2001 ; Moore et al, 2004 ; York et al, 2016 ). For example, in tropical and southern hemisphere species, females defend territories ( Levin, 1996 ; Hall, 2004 ; Tobias et al, 2011 ; Cain and Langmore, 2016 ), sing in the context of territorial defense ( Illes, 2015 ; Riebel et al, 2019 ; Loo and Cain, 2021 ), and are brightly colored ( Dale et al, 2015 ; Price, 2015 ), all traits which are more traditionally associated with T and male-male competition in the northern hemisphere ( Hau and Goymann, 2015 ).…”