Abstract
The sequences in which songbirds deliver their songs may help serve song’s primary functions related to territorial defense and mate attraction but determining that requires a clear understanding of the syntax of the species in question. Hermit Thrush (Catharus guttatus) males sing with a degree of predictability, cycling up and down the frequency spectrum with immediate variety. The present work used two complementary approaches to better understand Hermit Thrush song syntax by investigating the degree to which song type choice relies upon the identity of preceding songs within large (> 1000) song sets from 12 males. In one analysis, Fisher’s tests were used to assess whether the song immediately before the next song—or two, three, or four spots before it—influenced the next song. Results indicated that the next song is influenced by both the previous song and the one before it, and less so by those three or four songs back. In addition, simulated sequences were generated that reflect Markov models from zero-order (the next song depends on no preceding songs) through fourth-order (it depends on the previous four songs), and then compared back to the bird’s observed song sequence. This analysis revealed that naturally occurring sequences are best described by second-order Markov models, indicating a reliance upon the previous two songs. Together, the results indicate that Hermit Thrush song sequences are determined mainly by preceding two songs. Future work will further explore the presence of higher level dependencies, along with the role of syntax in territorial defense and aggression.
Zusammenfassung
Markov-Abhängigkeiten in der Gesangssyntax der Einsiedler-Musendrossel (Catharus guttatus)
Die Abfolge, in der Singvögel ihre Gesänge darbieten, kann dazu beitragen, die primären Funktionen des Gesangs hinsichtlich Revierverteidigung und Partneranlockung zu erfüllen, doch um dies zu bestätigen, benötigt man ein klares Verständnis der Gesangssyntax der betreffenden Art. Männliche Einsiedler-Musendrosseln (Catharus guttatus) singen mit einer gewissen Berechenbarkeit das Frequenzspektrum rauf und runter mit sofortiger Abwechslung. Die vorliegende Arbeit nutzte zwei sich ergänzende Ansätze, um die Gesangssyntax der Einsiedler-Musendrossel besser zu verstehen, indem sie anhand großer (> 1000) Gesangs-Datensätze von 12 Männchen untersuchte, inwieweit die Wahl des Gesangstyps von den zuvor dargebotenen Gesängen abhing. In einer Analyse wurden Fisher-Tests benutzt, um einzuschätzen, ob ein Gesang von dem ihm unmittelbar vorausgehenden Gesang (oder von den Gesängen zwei, drei oder vier Positionen vorher) beeinflusst wird. Die Ergebnisse deuteten darauf hin, dass ein Gesang sowohl durch den ihm unmittelbar vorausgehenden Gesang als auch durch den Gesang davor beeinflusst wird, jedoch weniger durch drei oder vier Positionen zurückliegenden Gesang. Außerdem wurden Gesangsabfolgen simuliert, die Markov-Modelle von nullter (der Gesang hängt von keinem vorherigen Gesang ab) bis vierter Ordnung (der Gesang hängt von den vier vorherigen Gesängen ab) repräsentierten. Diese simulierten Abfolgen wurden dann mit der bei einem Vogel tatsächlich beobachteten Gesangsabfolge verglichen. Diese Analyse zeigte, dass die natürlich vorkommenden Gesangsabfolgen am besten durch Markov-Modelle zweiter Ordnung beschrieben werden, was wiederum darauf hindeutet, dass der Gesang auf die zwei zuvor dargebotenen Gesänge baut. Zusammengenommen zeigen die Ergebnisse, dass die Gesangsabfolgen von Einsiedler-Musendrosseln hauptsächlich durch die zwei zuvor dargebotenen Gesänge bestimmt werden. Zukünftige Arbeiten werden das Vorhandensein von Abhängigkeiten höherer Ordnung weiter erforschen, sowie auch die Rolle der Syntax in der Revierverteidigung und Aggression.
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Acknowledgements
We thank Kendra DeMerchant and Morgan Nesbitt for assistance with recording and Dr. David Speed for advice regarding data analysis.
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Start-up funding to corresponding author was used to purchase recording equipment.
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Conceptualization: SPR; Methodology: LCM and SPR; Formal analysis and investigation: LCM; Writing (honours thesis): LCM; Writing (manuscript): SPR and LCM; Supervision: SPR.
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McLean, L.C., Roach, S.P. Markov dependencies in the song syntax of Hermit Thrush (Catharus guttatus). J Ornithol 162, 469–476 (2021). https://doi.org/10.1007/s10336-020-01840-2
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DOI: https://doi.org/10.1007/s10336-020-01840-2