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1. Prenatal exposure to incubation calls affects song learning in the zebra finch

   https://doi.org/10.1038/s41598-018-33301-5  

   Katsis, Andrew C. ; Davies, Mzuri H. ; Buchanan, Katherine L. ; Kleindorfer, Sonia ; Hauber, Mark E. ; Mariette, Mylene M. ( October 2018 , Scientific Reports)

   Songbirds are important models for understanding the mechanisms and fitness consequences of imitative vocal learning. Although the effects of early-life environmental and social conditions on song learning are well-established, the impact of early sound exposure has received surprisingly little attention. Yet recent evidence hints at auditory sensitivity in songbird embryos, including in the zebra finch (Taeniopygia guttata), a classic model species for song learning. Here, we tested whether prenatal exposure to incubation calls—highly rhythmic parental vocalisations produced on the nest—affected song learning in zebra finches. Embryos were exposed in the egg to either incubation (treatment) or contact (control) calls, and after hatching were reared in a large colony. The playback treatment did not affect song complexity nor the accuracy of song copying from the social father, but instead increased learning of non-paternal song syllables. This, in turn, improved males’ mounting success in mating trials. These effects may be attributable to changes in juvenile social behaviours, as playback also influenced male behaviour during mating trials. Our study provides the first experimental evidence that prenatal acoustic environment affects song learning and courtship behaviour in songbirds, thereby raising interesting questions on the role of innate versus acquired biases for vocal learning.

    

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2. Territory Quality Predicts Avian Vocal Performance Across an Urban-Rural Gradient

   https://doi.org/10.3389/fevo.2020.587120  

   Phillips, Jennifer N. ; Cooper, W. Justin ; Luther, David A. ; Derryberry, Elizabeth P. ( December 2020 , Frontiers in Ecology and Evolution)

   Human activity around the globe is a growing source of selection pressure on animal behavior and communication systems. Some animals can modify their vocalizations to avoid masking from anthropogenic noise. However, such modifications can also affect the salience of these vocalizations in functional contexts such as competition and mate choice. Such is the case in the well-studied Nuttall's white-crowned sparrow ( Zonotrichia leucophrys nuttalli ), which lives year-round in both urban San Francisco and nearby rural Point Reyes. A performance feature of this species' song is salient in territorial defense, such that higher performance songs elicit stronger responses in simulated territorial intrusions; but songs with lower performance values transmit better in anthropogenic noise. A key question then is whether vocal performance signals male quality and ability to obtain high quality territories in urban populations. We predicted white-crowned sparrows with higher vocal performance will be in better condition and will tend to hold territories with lower noise levels and more species-preferred landscape features. Because white-crowned sparrows are adapted to coastal scrub habitats, we expect high quality territories to contain lower and less dense canopies, less drought, more greenness, and more flat open ground for foraging. To test our predictions, we recorded songs and measured vocal performance and body condition (scaled mass index and fat score) for a set of urban and rural birds ( N = 93), as well as ambient noise levels on their territories. Remote sensing metrics measured landscape features of territories, such as drought stress (NDWI), greenness (NDVI), mean canopy height, maximum height, leaf area density (understory and canopy), slope, and percent bare ground for a 50 m radius on each male territory. We did not find a correlation between body condition and performance but did find a relationship between noise levels and performance. Further, high performers held territories with lower canopies and less dense vegetation, which are species-preferred landscape features. These findings link together fundamental aspects of sexual selection in that habitat quality and the quality of sexually selected signals appear to be associated: males that have the highest performing songs are defending territories of the highest quality. 

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3. Neurotensin and neurotensin receptor 1 mRNA expression in song‐control regions changes during development in male zebra finches

   https://doi.org/10.1002/dneu.22589  

   Merullo, Devin P. ; Asogwa, Chinweike N. ; Sanchez‐Valpuesta, Miguel ; Hayase, Shin ; Pattnaik, Bikash R. ; Wada, Kazuhiro ; Riters, Lauren V. ( March 2018 , Developmental Neurobiology)

   Learned vocalizations are important for communication in some vertebrate taxa. The neural circuitry for the learning and production of vocalizations is well known in songbirds, many of which learn songs initially during a critical period early in life. Dopamine is essential for motor learning, including song learning, and dopamine‐related measures change throughout development in song‐control regions such as HVC, the lateral magnocellular nucleus of the anterior nidopallium (LMAN), Area X, and the robust nucleus of the arcopallium (RA). In mammals, the neuropeptide neurotensin strongly interacts with dopamine signaling. This study investigated a potential role for the neurotensin system in song learning by examining how neurotensin (Nts) and neurotensin receptor 1 (Ntsr1) expression change throughout development.NtsandNtsr1mRNA expression was analyzed in song‐control regions of male zebra finches in four stages of the song learning process: pre‐subsong (25 days posthatch; dph), subsong (45 dph), plastic song (60 dph), and crystallized song (130 dph).Ntsexpression in LMAN during the subsong stage was lower compared to other time points.Ntsr1expression was highest in HVC, Area X, and RA during the pre‐subsong stage. Opposite and complementary expression patterns for the two genes in song nuclei and across the whole brain suggest distinct roles for regions that produce and receiveNts. The expression changes at crucial time points for song development are similar to changes observed in dopamine studies and suggestNtsmay be involved in the process of vocal learning. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 78: 671–686, 2018

    

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4. Female zebra finches do not sing yet share neural pathways necessary for singing in males

   https://doi.org/10.1002/cne.24569  

   Shaughnessy, Derrick W. ; Hyson, Richard L. ; Bertram, Richard ; Wu, Wei ; Johnson, Frank ( December 2018 , Journal of Comparative Neurology)

   Adult female zebra finches (Taeniopygia guttata), which do not produce learned songs, have long been thought to possess only vestiges of the forebrain network that supports learned song in males. This view ostensibly explains why females do not sing—many of the neural populations and pathways that make up the male song control network appear rudimentary or even missing in females. For example, classic studies of vocal‐premotor cortex (HVC, acronym is name) in male zebra finches identified prominent efferent pathways from HVC to vocal‐motor cortex (RA, robust nucleus of the arcopallium) and from HVC to the avian basal ganglia (Area X). In females, by comparison, the efferent targets of HVC were thought to be only partially innervated by HVC axons (RA) or absent (Area X). Here, using a novel visually guided surgical approach to target tracer injections with precision, we mapped the extrinsic connectivity of the adult female HVC. We find that female HVC shows a mostly male‐typical pattern of afferent and efferent connectivity, including robust HVC innervation of RA and Area X. As noted by earlier investigators, we find large sex differences in the volume of many regions that control male singing (male > female). However, sex differences in volume were diminished in regions that convey ascending afferent input to HVC. Our findings do not support a vestigial interpretation of the song control network in females. Instead, our findings support the emerging view that the song control network may have an altogether different function in nonsinging females.

    

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5. Evidence for differing trajectories of songs in urban and rural populations

   https://doi.org/10.1093/beheco/arz142  

   Moseley, Dana L ; Phillips, Jennifer N ; Derryberry, Elizabeth P ; Luther, David A ( August 2019 , Behavioral Ecology)

   Candolin, Ulrika (Ed.)

   Abstract Learned traits, such as foraging strategies and communication signals, can change over time via cultural evolution. Using historical recordings, we investigate the cultural evolution of birdsong over nearly a 50-year period. Specifically, we examine the parts of white-crowned sparrow (Zonotrichia leucophrys nuttalli) songs used for mate attraction and territorial defense. We compared historical (early 1970s) recordings with contemporary (mid-2010s) recordings from populations within and near San Francisco, CA and assessed the vocal performance of these songs. Because birds exposed to anthropogenic noise tend to sing at higher minimum frequencies with narrower frequency bandwidths, potentially reducing one measure of song performance, we hypothesized that other song features, such as syllable complexity, might be exaggerated, as an alternative means to display performance capabilities. We found that vocal performance increased between historical and contemporary songs, with a larger effect size for urban songs, and that syllable complexity, measured as the number of frequency modulations per syllable, was historically low for urban males but increased significantly in urban songs. We interpret these results as evidence for males increasing song complexity and trilled performance over time in urban habitats, despite performance constraints from urban noise, and suggest a new line of inquiry into how environments alter vocal performance over time. 

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