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1. Evolution and plasticity: Divergence of song discrimination is faster in birds with innate song than in song learners in Neotropical passerine birds: EVOLUTION OF SONG DISCRIMINATION IN NEOTROPICAL BIRDS

   https://doi.org/10.1111/evo.13311  

   Freeman, Benjamin G.; Montgomery, Graham A.; Schluter, Dolph (September 2017, Evolution)
2. Cooperative breeding in songbirds promotes female song but slows the evolution of song elaboration

   https://doi.org/10.1101/2024.06.26.600822  

   Snyder, Kate T; Loughran-Pierce, Aleyna; Creanza, Nicole (June 2024, bioRxiv)

   Bird song has historically been characterized as a primarily male behavior that evolves through sexual selection pressures involved in mate attraction. More recently, researchers showed that female song is far more prevalent in songbirds than previously thought, raising new questions about how other social functions of birdsong and sexual selection pressures on females might affect song evolution. Certain breeding systems, particularly cooperative breeding, are hypothesized to change social dynamics and sexual selection pressures on males and females and may thus influence song evolution in both. Here, we construct a large-scale database synthesizing species-level information on the presence of female song, the characteristics of presumably male song, social variables, and breeding systems, and we perform comparative phylogenetic analyses. Our results suggest that cooperative breeding and female song co-occur significantly more than expected and exhibit co-evolutionary dynamics; in particular, cooperative breeding appears to decrease the likelihood that female song is lost. Notably, we find evidence that these trends might be linked to certain social features associated with cooperative breeding, including social bond stability, but not others, such as increased group size. In addition, we observe that song repertoire size appears to evolve more slowly in cooperative breeding lineages. Overall, our findings demonstrate that cooperative breeding may have complex and sex-specific effects on song evolution, maintaining female song while slowing the rate of male song elaboration, suggesting that song in cooperatively breeding species could function in ways that differ from the traditional mate-attraction paradigm and that lesser-studied functions of songs may be evolutionarily consequential. 

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3. Effects of Song Experience and Song Quality on Immediate Early Gene Expression in Female Canaries ( Serinus canaria )

   https://doi.org/10.1002/dneu.22685  

   Haakenson, Chelsea M.; Madison, Farrah N.; Ball, Gregory F. (May 2019, Developmental Neurobiology)
4. Cultural shifts after punctuated environmental stress: a study of song distributions in Dark-eyed Junco and Song Sparrow populations

   https://doi.org/10.5751/JFO-00442-950203  

   Snyder, Kate; Sellers, Maria; Creanza, Nicole (January 2024, Journal of Field Ornithology)

   Environmental stress, especially during development, can cause important phenotypic changes in individuals. In songbirds, these stress-induced changes have been shown to include impaired learning of song and reduced song complexity in several species. Typically, developmental stress has been studied in terms of individual variation within a population; however, birdsong, a culturally transmitted trait, may undergo relatively rapid changes if widespread learning impairment results from population-level environmental stress, and these changes could potentially be amplified if affected individuals become the song tutors for future generations. We thus hypothesize that ecosystem-wide stressors may cause population-level changes to birdsong. Here, we use publicly available birdsong recordings to determine whether song differences were evident after an abnormal and severe 2016 drought in western New York State. We analyzed birdsong recordings of two species, the Dark-eyed Junco (Junco hyemalis) and the Song Sparrow (Melospiza melodia), recorded between 2006–2020 in the drought-affected region and, for comparison, in two nearby regions less affected by the drought. The population-level song features of the species with more complex songs (Song Sparrow) changed in the drought area after 2016, but not in the control area. In the species with a more simple song (Dark-eyed Junco), we detected song changes in both regions, suggesting that the drought did not have an outsized effect on song in this species. These findings support a more nuanced hypothesis that stress-induced deficits may disproportionately affect species with songs that are more difficult to learn. These conclusions are tempered by the relatively sparse recording availability from years prior to 2016, but we predict that future longitudinal studies of song evolution in natural populations will be more tractable given the nearly exponential increase in the number of song recordings deposited in public repositories in recent years, making this experimental design a useful framework for future studies. 

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5. Song Preference in Female and Juvenile Songbirds: Proximate and Ultimate Questions

   https://doi.org/10.3389/fphys.2022.876205  

   Fujii, Tomoko G.; Coulter, Austin; Lawley, Koedi S.; Prather, Jonathan F.; Okanoya, Kazuo (April 2022, Frontiers in Physiology)

   Birdsong has long been a subject of extensive research in the fields of ethology as well as neuroscience. Neural and behavioral mechanisms underlying song acquisition and production in male songbirds are particularly well studied, mainly because birdsong shares some important features with human speech such as critical dependence on vocal learning. However, birdsong, like human speech, primarily functions as communication signals. The mechanisms of song perception and recognition should also be investigated to attain a deeper understanding of the nature of complex vocal signals. Although relatively less attention has been paid to song receivers compared to signalers, recent studies on female songbirds have begun to reveal the neural basis of song preference. Moreover, there are other studies of song preference in juvenile birds which suggest possible functions of preference in social context including the sensory phase of song learning. Understanding the behavioral and neural mechanisms underlying the formation, maintenance, expression, and alteration of such song preference in birds will potentially give insight into the mechanisms of speech communication in humans. To pursue this line of research, however, it is necessary to understand current methodological challenges in defining and measuring song preference. In addition, consideration of ultimate questions can also be important for laboratory researchers in designing experiments and interpreting results. Here we summarize the current understanding of song preference in female and juvenile songbirds in the context of Tinbergen’s four questions, incorporating results ranging from ethological field research to the latest neuroscience findings. We also discuss problems and remaining questions in this field and suggest some possible solutions and future directions. 

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