Javier Sierro

To me, science is a matter of replication and innovation. Testing new ideas is exciting and often results in leaps in our cumulative knowledge, but revisiting published worked with a fresh perspective is crucial to strengthen the foundations.

In my research, I aim to bring together two theoretically related fields that I think, are not sufficiently interconnected in practice: vocal production physiology and eco-acoustics. The physiological studies bring evidence of the underlying mechanics needed to produce song. The extremely sophisticated physiological processes discovered suggest directional selection pressures where singing performance becomes more and more mechanically and neurologically complex. In fact, several authors have described birdsong as “vocal athletics” because of the extreme precision, power and coordination needed to produce such a signal. The physiological studies are elegant and impressive, but sometimes do not transcend into the ecological studies which assess the evolutionary and ecological function of birdsong. My work aims to bring these two worlds together to determine which song features are relevant and what information can be conveyed during animal interactions. Using acoustic analysis methods which reflect muscle physiology processes, we can assess motor performance individually through birdsong. This can be in fact extended to other types of signalling processes that include movement (i.e., dancing rituals) and many taxa apart from songbirds. To date, I have published a series of works that show how this specifically selected song parameters are relevant in the ecology and evolution of signals, ultimately serving as fitness indicators of individuals.

During my Masters in Science (University of Leiden), I conducted my first studies of birdsong. We carried out a classic playback study but applying a novel approach to describe the dynamic change in singing behaviour during the interaction. The analysis revealed that certain song parameters follow opposite patterns of variation to signal aggression, remarking a sophisticated, scaled and dynamic signalling system as had not been shown before. In 2017, I worked at the National Museum of Natural sciences of Spain to study the impact of aircraft noise on the singing behaviour of birds. We found that European blackbirds show a flexible, seasonal-dependent response to noise in our population, with a detailed and quantitative characterization of noise properties around the airport. During my PhD at Lancaster University, I studied the blue tit (Cyanistes caeruleus) as a model species to further understand the evolution of birdsong. Here, I published the first comprehensive description of female song in blue tits, despite being a well-studied songbird for nearly 50 years. Furthermore, we published a series of works that partly resolve a long-standing paradox in birdsong research; “why do birds, with their famous song repertoires, always repeat?”. The study provides an explanation for the role of song diversity and song repetition during courtship in birds, two antagonistic song traits that find a balance due to conflicting selection pressures. Apart from these two scientific papers, my PhD thesis resulted in four more publications, one of which is now under review. These include a 600 bird species comparative analysis, a methodological work validating a bio-acoustics analysis method and a detailed description of begging calls during development in blue tits. 

PUBLICATIONS

Sierro, J., Gil, D., Sáez-Gómez, P., Hidalgo-Rodríguez, P., Rabadán-Gonzalez, J., Camacho, C. (2024). Call for your life: acoustic structure and age-sex differences in distress calls of red-necked nightjars. Ethology

https://onlinelibrary.wiley.com/doi/10.1111/eth.13513

de Kort, S. R., Porcedda, G., Slabbekoorn, H., Mossman, H. L., Sierro, J., & Hartley, I. R. (2024). Noise impairs the perception of song performance in blue tits and increases territorial response. Animal Behaviour 215, 131-141.
https://www.sciencedirect.com/science/article/abs/pii/S0003347224002094

Sierro, J., de Kort, S. R., & Hartley, I. R. (2024). Differential impact of anthropogenic noise during the acoustic development of begging calls in Blue Tits (Cyanistes caeruleus). Ibis.
https://onlinelibrary.wiley.com/doi/full/10.1111/ibi.13299

Sierro, J., de Kort, S.R. & Hartley, I.R. (2023). Sexual selection for both diversity and repetition in birdsong. Nature Communications 14, 3600
https://www.nature.com/articles/s41467-023-39308-5

Sierro, J., de Kort, S. R., & Hartley, I. R. (2023). A limit to sustained performance constrains trill length in birdsong. iScience, 26(11)
https://www.cell.com/iscience/fulltext/S2589-0042(23)02283-6

Sierro, J., de Kort, S.R. & Hartley, I.R. (2023). Sound properties affect measurement of vocal consistency in bird- song: validation of the Spectrogram Cross-Correlation method (SPCC). Journal of the Acoustic Society of America (JASA). 154 (2). 699–708.
https://pubs.aip.org/asa/jasa/article/154/2/699/2905841/Sound-properties-affect-measurement-of-vocal

Sierro, J., Sierro, J., & Slabbekoorn, H., (2023) Angry birds calling: an advanced system of signalling aggression to moderate conflict in the common chiffchaff, Animal Behaviour. 201, 211-221.
https://www.sciencedirect.com/science/article/pii/S0003347223001021

Sierro, J., de Kort, S. R., Riebel, K., & Hartley, I. R. (2022). Female blue tits sing frequently: a sex comparison of occurrence, context and structure of song. Behavioral Ecology. 33(5), 912–925.
https://academic.oup.com/beheco/article/33/5/912/6611755

Sierro, J., Sierro, J., & Slabbekoorn, H. (2020). Experimental test of the communicative value of syllable diversity and syllable switching in the common chiffchaff. Animal Behaviour, 165, 11-21.
https://www.sciencedirect.com/science/article/abs/pii/S0003347220301147

Sierro, J., Loretto, M. C., Szipl, G., Massen, J. J., & Bugnyar, T. (2020). Food calling in wild ravens (Corvus corax) revisited: Who is addressed? Ethology, 126(2), 257-266.
https://onlinelibrary.wiley.com/doi/abs/10.1111/eth.12991

Alquezar, R. D., Macedo, R. H., Sierro, J., & Gil, D. (2020). Lack of consistent responses to aircraft noise in dawn song timing of bird populations near tropical airports. Behavioral Ecology and Sociobiology, 74(7), 1-12.
https://link.springer.com/article/10.1007/s00265-020-02865-6

Sierro, J., Schloesing, E., Pavón, I., & Gil, D. (2017). European blackbirds exposed to aircraft noise advance their chorus, modify their song and spend more time singing. Frontiers in Ecology and Evolution, 5, 68.
https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2017.00068/full