Behavioral displays and interactions during babbling and maternal influence on the amount of vocal practice.

(A) to (C) shows the typical social behaviors and interactions of mother-pup pairs during a babbling bout. Note: all these behaviors could occur singly or in an interactive way (i.e. a behavioral display was followed by another in less than one second). (A) In on average 80% of cases, the interaction was initiated by the pup, normally by crawling towards the mother while babbling. A mother initiated interactions by hovering in front of or landing next to her pup. (B) After the start of an interaction, mother and pup engaged in a number of different behaviors, which were performed equally by both mother and pup (Table S1), with the exception of “wing poking”, which was mostly observed in pups (Table S1). The different behaviors could variably succeed after one another (large arrows); however, “crawl towards” and “crawl away”, as well as “short flights” respectively “hover flights” and a temporarily “change in the roosting spot” were often observed in repetitive sequences (bold black arrows). Hover flights in front of the interactive partner were the most conspicuous behavior, followed by the short flights either next to the interaction partner or within the day roost. With increasing pup age, short flights became progressively longer, e.g. pups even briefly left the day roost and landed on an adjacent tree. (C) Interactions between mother and pup could be terminated in two ways: Either the pup continued to babble alone or the mother allowed nursing. Maternal behavior did not differ with regard to pup sex (SI). Drawing credit: C. A. S. Mumm. (D) shows the positive influence of the maternal behaviors displayed during babbling bouts on babbling bout duration [s] (N=19 pups, N=186 babbling bouts, GLMM, family Gamma with log link). (E) shows that higher maternal activity scores led to a longer babbling phase duration [days] (N=19 pups, LMER). The figure legends represent the raw data whereas the fitted lines (with lower (2.5th percentile) and upper (97.5th percentile) confidence intervals) are based on the calculated model. Neither bout duration nor babbling phase duration differed between pup sex (SI).

The influence of the social environment on the amount of vocal practice.

Response variables (first column): A: Babbling bout duration [s]: the babbling bout duration measured in seconds (N=19 pups, N=186 babbling bouts, GLMM, family Gamma with log link, random factor pup ID: repeated measurements over time of the same focal pups). B: Babbling phase duration: The number of days pups spent babbling (N=19 pups, LMER, random factor colony ID: measurements of pups from the same colony). The predictor variables for both models were z-transformed, a standardisation procedure that facilitates convergence of the model. The second column depicts the fixed and random effects for both models. The third column depicts the estimate and the standard error as well as the standard deviation for the random effect, and the last column the p-value (bold if influence is significant). Abbreviations: “Mat. behav.” = maternal behaviors.

Maternal influence on learned syllables in babbling bouts.

(A) shows a typical multisyllabic territorial song produced by an adult male. The most characteristic syllable type is called “B2” (i.e. the last six syllables of this song), composed of a buzzed part connected to a tonal part. This is also the most common song syllable type in pup babbling (Table S2). The spectrogram was created in Avisoft SasLab Pro (Hamming window, 1024 FFT, 50% overlap resulting in 317 Hz frequency and 2.048ms time resolution). (B) shows the positive significant influence of maternal behavioral displays on the total number of learned syllables within babbling bouts (N=10 pups, N=90 babbling bouts, GLMM, family negative binomial with log link). Territorial songs can be flexibly composed of different buzz syllable types (Fig. S1). (C) shows that maternal behavior positively influences the versatility (i.e. number of different learned syllable types) of babbling bouts (N=10 pups, N=90 babbling bouts, LMER). (D) The most commons song syllable type B2 (Table S2) was categorized into precursor and mature syllables. Maternal behavioral displays positively influenced the percentage of mature song syllables (N=10 pup, N=90 babbling bouts, GLMM family binomial with logit link). The figure legends represent the raw data whereas the fitted lines (with lower (2.5th percentile) and upper (97.5th percentile) confidence intervals) are based on the calculated model. (E) shows the acoustic movement of pups during their vocal ontogeny based on acoustic parameters of the syllable type B2, the most common song syllable type (N=8 pups, N=220 syllable trains). The larger the value on the y-axis, the larger the acoustic movement during the pup’s vocal ontogeny. The acoustic movement was positively correlated with the maternal activity score.

The influence of the social environment on learned syllables.

Response variables: A: Total number of song syllables: the learned territorial song syllables which were present in a babbling bout, (N=10 pups, N=90 babbling bouts, GLMM, family negative binomial with log link, random factor ID: repeated measurements over time of the same focal pups). B: Song syllable versatility: how many of the five different song syllable types (Fig. S1) were present in a babbling bout, (N=10 pups, N=90 babbling bouts, LMER, random factor ID: repeated measurements over time of the same focal pups). Neither the total number of song syllables nor song syllable versatility differed between pup sex (SI). C: Percentage of mature song syllables: We investigated the influence of different predictor variables on the percentage of mature song syllables of the most common syllable type, B2 (Table S2, N=10 pup, N=90 babbling bouts, GLMM family binomial with logit link, random factor ID: repeated measurements over time of the same focal pups, random factor observation-level: to avoid overdispersion). The predictor variables for both models were z-transformed, a standardisation procedure that facilitates convergence of the model. Fixed and random effects are depicted in the second column. The third column depicts the estimate with standard error, and the last column the p-value (significant influence indicated in bold). Abbreviations: “Mat. behav.” = maternal behaviors.