ABSTRACT
While the impressive singing abilities of birds are made possible by the syrinx, the upper vocal system (i.e. trachea, larynx and beak) could also play a role in sound filtration. Yet, we still lack a clear understanding of the range of elongation this system can undertake, especially along the trachea. Here, we used biplanar cineradiography and X-ray reconstruction of moving morphology (XROMM) to record 15 species of cadaveric birds from 9 different orders while an operator moved the birds’ heads in different directions. In all studied species, we found elongation of the trachea to be correlated with neck extension, and significantly greater (ranging from 18 to 48% for the whole motion; and from 1.4 to 15.7% for the singing positions) than previously reported on a live singing bird (3%). This elongation or compression was not always homogeneous along its entire length. Some specimens showed increased lengthening in the rostral part and others in both the rostral and caudal parts of the vocal tract. The diversity of elongation patterns shows that trachea elongation is more complex than previously thought. Since tracheal lengthening affects sound frequencies, our results contribute to our understanding of the mechanisms involved in complex communication signals, one of the amazing traits we share with birds.
Footnotes
Author contributions
Conceptualization: P.P.; Methodology: M.F., R.O., S.V., P.P.; Software: M.F., P.P.; Investigation: P.P., M.F.; Resources: P.P.; Data curation: P.P.; Writing - original draft: M.F., R.O., S.V., P.P.; Writing - review & editing: M.F., R.O., S.V., P.P.; Visualization: M.F.; Supervision: P.P.; Project administration: P.P.; Funding acquisition: P.P.
Funding
This work was funded by a Fondation Bettencourt Schueller long term partnership, partly supported by the Learning Planet Institute (LPI) via a research fellowship to P.P. Funding was also received from Emergence Sorbonne Université and Agence Nationale de la Recherche ‘Young researchers’ instrument (JCJC) BiSEV ANR-23-CE02-0018.
Data availability
The data underlying this article (R scripts, output data from X-ray videos and 3D animations) are available in Dryad (Fournier et al., 2024): https://doi.org/10.5061/dryad.6t1g1jx7q.
