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Song parameters, repertoire size and song sharing within and across age classes in the saffron finch

Citation

Benitez Saldivar, Maria Juliana; Miño, Carolina Isabel; Massoni, Viviana (2020), Song parameters, repertoire size and song sharing within and across age classes in the saffron finch, Dryad, Dataset, https://doi.org/10.5061/dryad.pc866t1mr

Abstract

Birds sing mostly to attract partners or to defend territories or resources. In relation to the first function, song can vary with age if older experienced males signal their quality through their vocal output. Regarding the second function, song can also vary with age if singing behavior helps mediate social interactions through repertoire sharing with neighbors. Here, we investigate whether song parameters change with age, and in which direction, in saffron finches Sicalis flaveola pelzelni, obligate secondary cavity nesters which produce elaborate melodious songs and show delayed plumage maturation. Cross-sectional comparisons revealed that second year (SY) males sing shorter syllables, and shorter and less versatile songs than older after second year males (ASY), as expected if the latter are more experienced singers. Longitudinal comparisons, which better depict age-related changes, showed that as birds age one year, song length and repertoire size do not change significantly, syllable duration shortens and, as expected for experienced singers, song versatility increases. Correlations between repertoire distance and nesting distance suggest that both SY and ASY males might be adjusting their repertoires to those of ASY neighbors; the former pattern conforms to the expectations if young birds try to emulate the songs of more experienced birds, while the latter is expected if song sharing helps de-escalating antagonistic social interactions amongst males. This research, which provides the first description of song parameters in young second year saffron finches, expands our knowledge of song variation across age classes in songbirds.

Methods

For the spectrograms of each bird in each season, we measured, by hand with on-screen cursor, the following acoustic parameters: maximum frequency (the frequency of the highest syllable in the song, kHz), minimum frequency (the frequency of the lowest syllable in the song, kHz), frequency bandwidth (difference between the maximum and the minimum syllable frequencies in the song, kHz), peak frequency (frequency of maximum power of the song, kHz), song length (duration of a song from the beginning of the first syllable to the end of the last syllable, s) and syllable duration (the mean syllable duration per song and male, s). We computed the syllable rate (the number of syllables produced per second, song and male, as in Potvin et al. 2011), the song versatility index (SVI)(the ratio between different syllables and the total number of syllables per song and male, Slater and Gil 2000) and the syllable repertoire size (the number of different syllables produced by a given male, once the cumulative number of syllables reached an asymptote with increasing number of songs analyzed). 

Using cross-sectional analyses, we compared the above mentioned spectrotemporal variables and indexes between SY (n = 22) and ASY males (n = 17). The group of ASY males includes individuals that were banded as SY and are, therefore, of known age, as well as males that were banded as ASY, and are of unknown age. To avoid pseudo-replication, we used, for each male, data from a single breeding season. We computed the repertoire similarity index, i.e. a pairwise comparison of the syllable repertoire of two males, using the formula: 2 Ns/(R1 + R2), where Ns is the number of syllables shared; R1 is the repertoire size of male 1 and R2 is the repertoire size of male 2 (McGregor and Krebs 1982). 

We conducted longitudinal analyses to compare the above mentioned spectrotemporal variables and indexes between SY males (n = 8) and the same males becoming ASY in the next year, and between ASY males (n = 8) of unknown age and the same males becoming ASY + 1 males in the second year recorded. For these two age classes, we also adjusted the formula of the repertoire similarity index described above to focus on the proportion of syllables sung by the same males in two seasons, such that R1 is the repertoire size of a male in the first season, and R2 that of the same male in the second season recorded (Mamede and Mota 2012). We computed repertoire similarity separately for both age groups because one includes males of known age (SY becoming ASY), and the other includes males of unknown age (ASY-ASY+1). All of the cross-sectional and longitudinal comparisons described above were made using two-sample Student’s t-tests or Wilcoxon Rank Sum tests when data did not distribute normally. 

To evaluate the degree of syllable sharing amongst reproductive males at the study site, we tested the association between the geographic proximity of males, and their syllable repertoire distance (Demko et al. 2016). We used the linear distance between nest-boxes (m), as a measure of distance between males, and built a matrix of distances using geographic distance matrix generator (Ersts 2011), based on the geographical position of each nest-box recorded with a Garmin Etrex GPS (precision ± 3 m). As a measure of repertoire distance, we used the syllable repertoire dissimilarity, 1-RS (Vargas-Castro 2015, Demko et al. 2016), and built a matrix of this index between pairs of males. To account for the possible influence of plumage coloration (proxy of age) on the association between geographic distance and repertoire similarity, we carried out Partial Mantel test separately for each breeding season. The ‘color’ matrix was built by coding 0 for pairs of same-colored SY males, 1 for same-colored ASY males and 2 for pairs of dissimilar color (following   Forstmeier et al. 2006). All of these tests were carried using the ‘partial.mantel’ function implemented in the ‘vegan’ package, setting 10 000 iterations (Oksanen et al. 2017) in R.

Usage Notes

cross-sectional_and_longitudinal_analyses.xlsx: contains measurements  of song parameters to perform analyses of cross-sectional comparisons between SY and ASY males; and longitudinal analyses of: SY males that became ASY males and, ASY males turning into ASY + 1 males

repertoire_dissimilarity_and_nest-box_distance.xlsx: contains data for the analyses of sharing, nest-box distance, and age between males.

Funding

Consejo Nacional de Investigaciones Científicas y Técnicas, Award: 11220130100342CO (PIP 2014–2017 )

Universidad de Buenos Aires, Award: 20020130100772BA (UBACyT2014-2017 )

Consejo Nacional de Investigaciones Científicas y Técnicas, Award: 4370/2012 Doctoral Scholarship

Animal Behavior Society, Award: Developing Nations Award