Calderon Garcia, J. S.; Costalunga, G.; Vogels, T. P.; Vallentin, D.

While real-time vocal adjustments are crucial for interactive communication, not much is known about the spectral and temporal vocal flexibility of animals. Here, using a combination of field song recordings and controlled playback experiments, we show that wild nightingales imitate 'whistle song' syllable durations in real time. However, when exposed to playbacks with variations in whistle pitch and duration that are beyond their natural range of vocalizations, nightingales emulated temporal or spectral features, approximating the whistle playbacks within the constraints of their natural whistle song repertoire. Our findings reveal a previously unknown dimension of real-time vocal flexibility in songbirds and suggest complex auditory-motor integration during song interactions.