Interplay between syllable duration and pitch during whistle matching in wild nightingales

During complex vocal interactions, different features of acoustic stimuli are integrated to produce appropriate vocal responses,¹ such as copying sounds during vocal matching behavior in some animals.^{2,3,4,5,6,7,8,9,10,11,12} However, little is known about the interplay and possible trade-offs between the different temporal and spectral acoustic features during these vocal exchanges.^2,13,14 Nightingales can flexibly match the pitch of their tonal "whistle songs" in real time during counter-singing duels.^15,16 Here, we show that the syllable duration of whistle playbacks could alter the song responses of wild nightingales, causing their whistle duration distribution to shift toward the presented stimulus duration. When exposed to whistle playbacks featuring unnatural combinations of pitch and duration, nightingales demonstrate a flexible trade-off between pitch matching and temporal imitation, yet they are constrained by their vocal repertoire. They selectively adapted their vocal responses to approximate these novel stimuli, aligning them with their natural whistle repertoire. We developed a computational model of nightingale whistle-matching behavior that revealed a hierarchical organization of acoustic feature production. During whistle matching, the feature integration process is constrained by the duration of syllables, and pitch matching follows within this temporal framework, forcing a trade-off between the two features. Our findings reveal a complex interplay between the spectral and temporal domains that shapes song-matching behavior.