Figure 2. Syllable repetition rates develop faster in birds with prior singing experience.

(A) Syllable rate histogram from a female canary during two subsequent testosterone treatments. Color scales indicate the number of daily syllables produced for each discrete syllable rate. Curves were fitted through the most occurring syllable rates and are shown in red. (B) The correlation coefficient (CC) between the stabilized distribution of syllable rates at the end of the 1^st testosterone treatment and each other day during the development and re-development of song in the same bird as shown in A. (C) The mean syllable rate correlation plot for all animals. Grey bars indicate the SEM. (D) Group statistics of all studied birds demonstrating that stable syllable rates were achieved more quickly during a 2^nd testosterone treatment (red bars) than during the 1^st treatment (blue bars). (E) The peak day-to-day increase in the syllable rate CC (d_max) was higher during a 2^nd testosterone treatment than during the 1^st treatment. (F) Example spectral derivative spectrograms from one bird and corresponding bar graphs illustrating syllable rates at 15, 70, and 200 days after a 1^st testosterone treatment and 30 days after a 2^nd treatment. Columns in D-E represent the mean ± SEM and open circles indicate individual data points (*p<0.05, ***p≤0.001, paired t-test, n = 6 animals). Columns in F represent the mean ± SEM (a,b,c: p≤0.001, ANOVA; n = 100 syllables). Source data for temporal song features are available in the Figure 2—source data 1.

Figure 2—figure supplement 1. Differential re-development of temporal song features.

(A) Mean syllable duration correlation plot for all animals showing a gradual development during a 1^st testosterone treatment (T₁+), followed by an immediate recovery of syllable duration during a 2^nd treatment (T₂+). (B) Group statistics demonstrating that stable syllable durations were achieved more quickly during a 2^nd testosterone treatment (red bars) than during the 1^st treatment (blue bars). (C) The peak day-to-day increase in the syllable duration CC (d_max) for T₁+. D_max could not be calculated for T₂+, as we observed no developmental increase of this song feature during the 2^nd testosterone treatment. (D) Mean correlation plot for the pause duration between subsequent song syllables. Pause durations stabilized relatively fast during a 1^st testosterone treatment (T₁+), and required a phase of re-development during a 2^nd treatment (T₂+). (E) Group statistics demonstrating that stable pause durations were achieved more quickly during a 2^nd testosterone treatment (red bars) than during the 1^st treatment (blue bars). (F) The peak day-to-day increase in the pause duration CC (d_max) was significantly higher for T₂+ than for T₁+. Grey bars in A and D indicate the SEM. Columns in B,C,E,F represent the mean ± SEM and open circles indicate individual data points (*p<0.05, **p<0.01, ***p≤0.001, paired t-test, n = 6 animals).

Figure 2—figure supplement 2. Development and re-development of temporal song features.

Example song feature histograms from one individual illustrating the gradual acquisition during a 1^st testosterone treatment (T₁+) and the rapid recurrence during a 2^nd treatment (T₂+) for (A) syllable duration, and (B) pause duration. (C,D) Example spectral derivative spectrograms from two different birds illustrating a slower syllable rate with longer pause durations at the onset of song production during the 2^nd (T₂+ 3) testosterone treatment compared to stable songs during the 1^st (T₁+ 200) and 2^nd (T₂+ 30) treatment.