Fig. 1

USV emission during the introduction phase compared to the interaction phase. Boxplots show median (center line), interquartile range (box), 95% variation (whiskers) and outliers (circles) of (a) the vocal performance (total number of USVs emitted during 10 min), (b) the vocal repertoire (number of syllable types emitted during 10 min) and (c) the mean length of USVs (ms). d Relationship between the total number of USVs (vocal performance) and number of syllable types (vocal repertoire) emitted by unrelated (blue circles) and related (red triangles) pairs during the introduction (left) and interaction phase (right). * p < 0.05