Vocal exchanges are commonly observed in the sound communication of many animals. In birds and primates, vocal exchange—responding after other’s call—is the predominant pattern, whereas odontocetes often exhibit vocal overlap. These overlaps may not reflect immediate responses to others’ calls but instead may arise from anticipatory, chorus-like vocalizations. In this study, we investigated the mechanisms underlying vocal overlap in five female bottlenose dolphins at Adventure World, Japan. First, we examined whether signature whistles exhibited isochronous timing, by comparing to a null model. The result showed no significant difference between the actual and randomized data (Kolmogorov–Smirnov test, p = 0.68), suggesting that the timing was not predictable. Next, we tested whether the dolphins produced anticipatory vocalizations in response to the rhythm of conspecific sounds, using a playback experiment with two conditions: predictable isochronous and unpredictable random. We compared the rate of vocal overlap between the two conditions. No significant difference was found between them (generalized linear model with a Conway–Maxwell–Poisson error distribution, p = 0.25), indicating a lack of predictive vocal timing. These findings suggest that the dolphins responded rapidly after hearing conspecific sounds, engaging in vocal exchange similar to that seen in other taxa.
Terada et al. (Wed,) studied this question.