Humans have long been captivated by the diverse sounds produced by birds, from melodious songs to distinctive calls. However, understanding the avian vocal organ, the syrinx, and its evolutionary origins has remained limited. Recent groundbreaking studies led by researchers from The University of Texas at Austin have shed new light on this enigmatic aspect of avian biology.

The studies, which include high-resolution anatomical scans of syrinxes from hummingbirds and ostriches, have revealed fascinating insights into the development and genetic connections of the syrinx. The researchers discovered that the syrinx, unique to birds, shares a common developmental programming with the larynx, the vocal organ found in reptiles and mammals, including humans. This genetic connection, termed “deep homology,” highlights the shared evolutionary origins of different tissues or organs.

Julia Clarke, a professor at UT’s Jackson School of Geosciences, emphasized the significance of this discovery, likening it to the transition from flippers to limbs. The studies have provided a deeper understanding of the syrinx’s structure and underscored its ancient and common function across bird species.

The research has lasted over a decade and has been a collaborative effort involving physiologists, developmental biologists, and paleontologists. It was initiated when Clarke discovered a syrinx in a fossil of a duck-like bird from the Late Cretaceous period in Antarctica, marking the oldest known syrinx. This discovery prompted the need to modernize and expand the understanding of syrinx structure across various bird groups.

Through innovative methods such as CT scanning and detailed dissection, the researchers have uncovered new insights into the syrinx of ostriches and hummingbirds. Notably, the study of ostrich syrinx anatomy revealed that both male and female birds possess similar vocal equipment. Yet, male ostriches exhibit a wider variety of sounds, often associated with aggressive behaviors.

The researchers compared hummingbirds’ syrinx to that of swifts and nightjars, revealing similar vocal fold structures despite differences in vocal learning abilities. This finding suggests a common ancestor with a similar vocal fold structure, providing clues to the evolution of vocal learning in hummingbirds.

Furthermore, the collaboration with developmental biologists led to the discovery of shared genetic pathways controlling the development of vocal organs in birds and mammals. This research also unveiled the ancestral syrinx’s likely possession of two sound sources, a feature observed in modern songbirds.

While these findings have significantly advanced our understanding of the syrinx, questions about its origins in non-avian dinosaurs and the timing of its development remain unanswered. Julia Clarke emphasized the importance of studying vocalization in living species to gain insights into the vocal capabilities of ancient dinosaurs.

In conclusion, the pioneering research led by the University of Texas at Austin has not only unraveled the mysteries of avian vocalization but has also provided crucial insights into the evolutionary origins of the syrinx, marking a significant milestone in avian biology research.

Further details about the research are available in the Journal of Anatomy, Zoological Journal of the Linnean Society, and Current Biology.

References

• Chiappone, M., Rodriguez‐Saltos, C., Legendre, L. J., Li, Z., & Clarke, J. (2024). Ostrich (Struthio camelus) syrinx morphology and vocal repertoire across postnatal ontogeny and sex: Implications for understanding vocal evolution in birds. Journal of Anatomy, 244(4), 541–556. https://doi.org/10.1111/joa.13992
• Legendre, L. J., Rodríguez-Saltos, C. A., Eliason, C. M., & Clarke, J. A. (2024). Evolution of the syrinx of Apodiformes, including the vocal-learning Trochilidae (Aves: Strisores). Zoological Journal of the Linnean Society, zlae001. https://doi.org/10.1093/zoolinnean/zlae001
• Longtine, C., Eliason, C. M., Mishkind, D., Lee, C., Chiappone, M., Goller, F., Love, J., Kingsley, E. P., Clarke, J. A., & Tabin, C. J. (2024). Homology and the evolution of vocal folds in the novel avian voice box. Current Biology, S0960982223016688. https://doi.org/10.1016/j.cub.2023.12.013
• University of Texas at Austin. (2024, May 23). Birdsong and human voice built from same genetic blueprint. Phys.Org; University of Texas at Austin. https://phys.org/news/2024-05-birdsong-human-voice-built-genetic.html