Vocal convergence and social proximity shape the calls of the most basal Passeriformes, New Zealand Wrens

Despite extensive research on avian vocal learning, we still lack a general understanding of how and when this ability evolved in birds. As the closest living relatives of the earliest Passeriformes, the New Zealand wrens (Acanthisitti) hold a key phylogenetic position for furthering our understanding of the evolution of vocal learning because they share a common ancestor with two vocal learners: oscines and parrots. However, the vocal learning abilities of New Zealand wrens remain unexplored. Here, we test for the presence of prerequisite behaviors for vocal learning in one of the two extant species of New Zealand wrens, the rifleman (Acanthisitta chloris). We detect the presence of unique individual vocal signatures and show how these signatures are shaped by social proximity, as demonstrated by group vocal signatures and strong acoustic similarities among distantly related individuals in close social proximity. Further, we reveal that rifleman calls share similar phenotypic variance ratios to those previously reported in the learned vocalizations of the zebra finch, Taeniopygia guttata. Together these findings provide strong evidence that riflemen vocally converge, and though the mechanism still remains to be determined, they may also suggest that this vocal convergence is the result of rudimentary vocal learning abilities.

. This model shows genetic (dark green) and residual (turquoise) variance components with the proportion of variance (in percentage) and the absolute values of the total estimated variance.The variance components of acoustic parameters best explained by this model are marked with a star (* based on Deviance information criterion values; Table S5; n=37 parameters; Table S1; n=38 birds, n=1,067 sound clips).Acoustic parameters were measured using specan from warbleR v.1.1.27 65package. .This model shows social (dark blue) and residual (turquoise) variance components with the proportion of variance (in percentage) and the absolute values of the total estimated variance (n=37 parameters; n=47 individuals; Table S1).The social proximity model did not explain any of the variance components of the acoustic parameters (based on Deviance information criterion (DIC) values comparing the three models; Table S5).Acoustic parameters were measured using specan from warbleR v.1.1.27 65package.S5; (n=37 parameters; Table S1; n=38 birds).Rifleman feeding calls were measured using specan from warbleR v.1.1.27 65ackage.Table S1: List of the 37 acoustic parameters used to measure rifleman feeding call features.Acoustic parameters were measured with WarbleR (specan) v1.1.27 65, Seewave v2.2.0 108 and Raven Pro 107

Supplementary Tables
. All the acoustic parameters are alphabetically ordered.Definitions were extracted and modified from WarbleR (specan) 65 and RavenPro 107 .

Vocal parameters Definition
ACIs Acoustic Complexity Index: Index that measures acoustic complexity of a signal.

RavenPro duration 90
RavenPro duration: The di erence between the 5% and 95% times.Units: s RavenPro freq Q5 Hz RavenPro Frequency 5% quartile: The frequency that divides the selection into two frequency intervals containing 5% and 95% of the energy in the selection.The computation of this measurement is similar to that of centre Frequency, except that the summed energy has to exceed 5% of the total energy instead of 50%.Units: Hz.

RavenPro freq Q95 Hz
RavenPro Frequency 95%: The frequency that divides the selection into two frequency intervals containing 95% and 5% of the energy in the selection.The computation of this measurement is similar to that of centre Frequency, except that the summed energy has to exceed 95% of the total energy instead of 50%.

RavenPro low Freq Hz
RavenPro Low Frequency: The lower frequency bound of the selection.Units: Hz.

Figure S1 :Figure S2 :
Figure S1: Relationship between genetic similarity, acoustic similarity and social proximity.a) Relationship between pairwise genetic similarity and social proximity determined based on relatedness estimates and mean social proximity (based on geodesic distances between nests visited by individuals (1,176 bird pairs across 49 birds).A large social proximity between two birds corresponds to a small geographic distance.Fitted quadratic curve is shown for reference.b) Relationship between pairwise acoustic similarity (mean acoustic cross-correlation) and social proximity either among distantly related pairs of riflemen (1,149 bird pairs across 49 birds, black points) or among closely related pairs of riflemen (27 bird pairs across 29 birds).Fitted linear curves are shown for reference.In both figures, each circle represents one bird pair, and birds without genetic data are not represented.

Figure S3 :
Figure S3: Selected example of Markov Chain Monte Carlo Trace of the intercept and posterior density for the average slope of the peak frequency contour (Raven_PFC_avgSlope_Hzms) and the variances (six bottom panels).Markov Chain Monte Carlo (MCMCglmm) Traces for social and genetic components showing successful convergence.Trace of Intercept are shown on the left panels.The term units refers to the Residual variance.

Figure S4 :
Figure S4: Variance component estimates of rifleman feeding calls for the genetic similarity model.Estimation of call variance components followed methods from Thomson et al. 41 .This model shows genetic (dark green) and residual (turquoise) variance components with the proportion of variance (in percentage) and the absolute values of the total estimated variance.The variance components of acoustic parameters best explained by this model are marked with a star (* based on Deviance information criterion values; TableS5; n=37 parameters; TableS1; n=38 birds, n=1,067 sound clips).Acoustic parameters were measured using specan from warbleR v.1.1.2765

Figure S5 :
Figure S5: Variance component estimates of rifleman feeding calls for the social proximity model.Estimation of call variance for the social proximity model followed methods from Thomson et al. 41.This model shows social (dark blue) and residual (turquoise) variance components with the proportion of variance (in percentage) and the absolute values of the total estimated variance (n=37 parameters; n=47 individuals; TableS1).The social proximity model did not explain any of the variance components of the acoustic parameters (based on Deviance information criterion (DIC) values comparing the three models; TableS5).Acoustic parameters were measured using specan from warbleR v.1.1.2765package.

Figure S6 :
Figure S6: Variance component estimates of rifleman feeding calls for the social and genetic similarity model.Estimation of call variance components for the Social and Genetic similarity model followed methods from Thomson et al. 41.This model shows social (dark blue), genetic (dark green) and residual (turquoise) variance components with the proportion of variance (in percentage) and the absolute values of the total estimated variance.The variance components of acoustic parameters best explained by this model are marked with a star (* based on Deviance information criterion (DIC) values comparing three models; TableS5; (n=37 parameters; TableS1; n=38 birds).Rifleman feeding calls were measured using specan from warbleR v.1.1.2765package.
Range of dominant frequency measured across the acoustic signal.
dfrange Dominant frequency range: inflections Inflections: The number of inflections in a frequency contour (or any time series).maxdom Maximum dominant frequency: Maximum of dominant frequency measured across the acoustic signal.meandom Mean dominant frequency: Mean dominant frequency measured across the acoustic signal.meanfreq Mean frequency : Mean of frequency spectrum (i.e., weighted average of frequency by amplitude within supplied band pass).Units: kHz.meanpeakf Mean peak frequency: Frequency with highest energy from the mean frequency spectrum (see meanspec).Typically more consistent than peakf.mindom Minimum dominant frequency: Minimum of dominant frequency measured across the acoustic signal.modindx Modulation index: Calculated as the cumulative absolute di erence between adjacent measurements of dominant frequencies divided by the dominant frequency range. 1 means the signal is not modulated.sd Standard deviation: Standard deviation of frequency.Units: kHz.sfm Spectral flatness: Similar to sp.ent (Pure tone ≥ 0; noisy ≥ 1).skew Skewness: Asymmetry of the spectrum (see note in specprop description).sp.ent Spectral entropy: Energy distribution of the frequency spectrum.Pure tone ≥ 0; noisy ≥ 1. startdom Start of dominant frequency: Dominant frequency measurement at the start of the signal time.entTime entropy: Energy distribution on the time envelope.Pure tone ≥ 0; noisy ≥ 1. time.IQR Interquartile time range: Time range between 'time.Q25' and 'time.Q75'.Units: s.RavenPro center Time Rel RavenPro centre Time Relative.

tive RavenPro Peak Time Relative: In
a waveform view, the first time in a selection at which a sample with amplitude equal to Peak Amplitude occurs, the time expressed as a proportion of the duration of the selection.In a spectrogram view, the first time in a selection at which a spectrogram bin with power density equal to Peak Power occurs, the time expressed as a proportion of the duration of the selection.RavenPro PFC avgSlope Hz ms RavenPro Maximum Entropy: The maximum entropy calculated for a spectrogram slice within the selection bounds.RavenPro peak Freq Hz RavenPro Peak Frequency: The frequency at which Max Power/ Peak Power occurs within the selection.If Max Power/ Peak Power occurs at more than one time and/or frequency, the lowest frequency at Max Time at which Max Power/ Peak Power occurs.Units: Hz.RavenPro peak Time Rela-

Peak Frequency Contour Average Slope:
Mean of the Peak Frequency Contour Slope.

Frequency Contour Max Frequency:
Maximum of the Peak Frequency Contour.Minimum of the Peak Frequency Contour Slope Series.

Peak Frequency Contour Number of Inflection Points:
Number of times the slope changes sign in Peak Frequency Contour Slope.

Table S2 : Spearman's correlation between the genetic distance and mean absolute di erence of each acoustic parameter.
Spearman's correlations (Mantel Í; two-sided)and significance values are presented for each acoustic parameter (n=1,110 call clips; n=49 birds; npairs=1,176).None of the acoustic parameters (n=37 acoustic parameters) were significantly correlated with genetic proximity.

Table S3 : Spearman's correlation between the social proximity and mean absolute di erence of 37 acoustic parameters in distantly related pairs of birds.
Spearman's  correlations (Mantel Í; two-sided)and significance values are presented for distantly pairs of related riflemen (1,149 pairs of birds across 49 birds).Significant correlations between acoustic parameters and social proximity are highlighted.

Table S5 : Deviance Information criterion (DIC) for all three of the multiple-matrix animal models and for each acoustic parameter (n=37).
The multiple-matrix animal models include the genetic similarity model (G model), the social proximity model (S model), and the genetic similarity and social proximity model (G & S model).For each acoustic parameter, models with the smallest DIC are highlighted in yellow.Models with smaller DIC best explain the phenotypic call variance components of the acoustic parameter.