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1. Vitelline Warbler (Setophaga vitellina) songs, calls, and habitat preferences: novel acoustic descriptions of a range-restricted Caribbean songbird

   https://doi.org/10.1371/journal.pone.0312636  

   Cummings, Wyatt J; Goodman, David_D L; Layne, Craig D; Singer, Katherine I; Thomas, M Whitney (April 2025, PLOS One)

   Harris, Bert (Ed.)

   The Vitelline Warbler (Setophaga vitellina) is an understudied species endemic to a few small islands in the western Caribbean. Little is known beyond its phylogenetic relationship to other New World warblers. We used island-wide surveys and bioacoustic recordings to investigate the distribution, vocalizations, and ecology of S. vitellina across a significant portion of the species’ range on Little Cayman Island. We recorded 417 songs from 91 individuals and analyzed the length, frequency, and shape of various song components. We observed and characterized high variation in the composition and character of songs within the Little Cayman population. We also describe the call of the species and use sound files from across the species’ range to compare vocalizations between islands. Vitelline Warbler abundance is highest in dry forest and dry scrub habitats, suggesting that these habitats are most important for the species. Elaboration of the vocalizations of understudied species like the Vitelline Warbler has the potential to further our understanding of avian evolution and behavior. As much still remains to be learned from this species, action must be taken to protect its critical habitats, especially dry forests, among other conservation measures. 

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2. Punctuated evolution in the learned songs of African sunbirds

   https://doi.org/10.1098/rspb.2021.2062  

   McEntee, Jay P.; Zhelezov, Gleb; Werema, Chacha; Najar, Nadje; Peñalba, Joshua V.; Mulungu, Elia; Mbilinyi, Maneno; Karimi, Sylvester; Chumakova, Lyubov; Gordon Burleigh, J.; et al (November 2021, Proceedings of the Royal Society B: Biological Sciences)

   Learned traits are thought to be subject to different evolutionary dynamics than other phenotypes, but their evolutionary tempo and mode has received little attention. Learned bird song has been thought to be subject to rapid and constant evolution. However, we know little about the evolutionary modes of learned song divergence over long timescales. Here, we provide evidence that aspects of the territorial songs of Eastern Afromontane sky island sunbirds Cinnyris evolve in a punctuated fashion, with periods of stasis of the order of hundreds of thousands of years or more, broken up by evolutionary pulses. Stasis in learned songs is inconsistent with learned traits being subject to constant or frequent change, as would be expected if selection does not constrain song phenotypes over evolutionary timescales. Learned song may instead follow a process resembling peak shifts on adaptive landscapes. While much research has focused on the potential for rapid evolution in bird song, our results suggest that selection can tightly constrain the evolution of learned songs over long timescales. More broadly, these results demonstrate that some aspects of highly variable, plastic traits can exhibit punctuated evolution, with stasis over long time periods. 

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3. The calling songs of some katydids (Orthoptera, Tettigonioidea) from the tropical forests of Southeast Asia

   https://doi.org/10.3897/jor.32.84563  

   Tan, Ming Kai; Duncan, Jacob; Wahab, Rodzay bin; Lee, Chow-Yang; Japir, Razy; Chung, Arthur Y.; Baroga-Barbecho, Jessica B.; Yap, Sheryl A.; Montealegre-Z, Fernando (January 2023, Journal of Orthoptera Research)

   Katydids produce sound for signaling and communication by stridulation of the tegmina. Unlike crickets, most katydids are known to sing at ultrasonic frequencies. This has drawn interest in the investigation of the biophysics of ultrasonic sound production, detection, evolution, and ecology (including predator–prey interactions) of these katydids. However, most of these studies are based on species from the Neotropics, while little is known about katydid species from the hyperdiverse region of Southeast Asia. To address this, a concerted effort to document, record, and describe the calling songs of Southeast Asian katydids, especially species that call at ultrasonic frequencies, was made. A study spanning two years (2018–2020) in the Malay Peninsula (Singapore and Malaysia), Borneo (Brunei Darussalam and Sabah), and the Philippines revealed previously unknown calls of 24 katydid species from four subfamilies. The calling songs of Southeast Asian katydid species are highly diversified in terms of time and frequency. Call structure can range from isolated syllables (e.g.,Holochlora), continuous trills (e.g.,Axylus philippinus), to short pulse-trains (e.g.,Euanisous teuthroides) and complex echemes (e.g.,Conocephalusspp.), with 87.5% of species having ultrasonic peak frequencies and 12.5% being considered extreme ultrasonic callers (peak frequency >40 kHz). The call spectrum ranges from tonal (e.g., spectral entropy is 6.8 inCasignetasp. 2) to resonant (entropy is 8.8 inConocephalus cognatus). Of the 24 species whose calls are described here, we imaged and described the sound-producing structures of 18. This study provides a preliminary overview of the acoustic diversity of katydids in Southeast Asia, and the authors hope to inspire further investigation into the bioacoustics of little-known katydids from these areas. Amassing a database of calling songs and sound-producing organ illustrations from different species is important to address taxonomic impediments while advancing our knowledge about the bioacoustics of Southeast Asian katydids. 

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4. The role of learned song in the evolution and speciation of Eastern and Spotted towhees

   https://doi.org/10.1101/2023.05.15.540821  

   Du’Mottuchi, Ximena León; Creanza, Nicole (May 2023, bioRxiv)

   Oscine songbirds learn vocalizations that function in mate attraction and territory defense. Sexual selection pressures on these learned songs could accelerate speciation. The Eastern and Spotted towhees are sister species that diverged recently (0.28 Ma) but now have partially overlapping ranges with evidence of some hybridization; widespread community-science recordings of these species, including songs within their zone of overlap and from potential hybrids, enable us to investigate whether song differentiation might facilitate their reproductive isolation. Here, we quantify 16 song features to analyze geographic variation in Spotted and Eastern towhee songs and test for species-level differences. We then use random-forest models to measure how accurately their songs can be classified by species, both within and outside the zone of overlap. While no single song feature reliably distinguishes the two species, a random-forest model trained on 16 features accurately classified 89.5% of songs; interestingly, species classification was less accurate in the zone of overlap. Finally, our analysis of the limited publicly available genetic data from each species supports the hypothesis that they are reproductively isolated. Together, our results suggest that, in combination, small variations in song features may contribute to these sister species’ ability to recognize their species-specific songs. 

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5. The role of learned song in the evolution and speciation of Eastern and Spotted towhees

   https://doi.org/10.1371/journal.pcbi.1013135  

   León_Du’Mottuchi, Ximena; Creanza, Nicole (June 2025, PLOS Computational Biology)

   Oscine songbirds learn vocalizations that function in mate attraction and territory defense; sexual selection pressures on these learned songs could thus accelerate speciation. The Eastern and Spotted towhees are recently diverged sister species that now have partially overlapping ranges with evidence of some hybridization. Widespread community-science recordings of these species, including songs within their zone of overlap and from potential hybrids, enable us to investigate whether song differentiation might facilitate their reproductive isolation. Here, we quantify 16 song features to analyze geographic variation in Spotted and Eastern towhee songs and assess species-level differences. We then use several machine learning models to measure how accurately their songs can be classified by species. While no single song feature reliably distinguishes the two species, machine learning models classified songs with relatively high accuracy (random forest: 89.5%, deep learning: 90%, gradient boosting machine: 88%, convolutional neural network: 88%); interestingly, species classification was less accurate in their zone of overlap. Finally, our analysis of the limited publicly available genetic data from each species supports the hypothesis that the species are reproductively isolated. Together, our results suggest that small variations in multiple features may contribute to these sister species’ ability to recognize their species-specific songs. 

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