Possible individual differences in burst-pulses in captive Commerson's dolphins ( Cephalorhynchus commersonii )

Burst-pulses, generally defined as pulse trains with inter-pulse intervals of 10 ms or less, are fundamental sounds produced by odontocetes and are thought to function as communication signals. In Commerson's dolphins (Cephalorhynchus commersonii), both NBHF burst-pulses above 100 kHz and broadband burst-pulses at lower frequencies have been reported. However, whether frequency differences reflect individual variation remains unclear. Here, we report possible individual differences in the peak frequency of burst-pulses produced by three captive Commerson's dolphins (one adult male and two adult females) at Toba Aquarium, Japan. Approximately 25 h of recordings were made in June and July 2024, and April and July 2025, under three conditions: all three dolphins together and two male–female pairs. Burst-pulses were visually extracted using Avisoft SASLab Pro. The peak frequencies of high signal-to-noise burst-pulses ranged from 67 to 175 kHz. A Gaussian Mixture Model assessed whether peak frequency distributions consisted of multiple groups, and the Wilcoxon rank-sum test evaluated significant distribution differences. A specific peak frequency was detected only in conditions involving a particular individual, suggesting the existence of individual differences. Commerson's dolphins may use burst-pulses to convey individual identity in acoustic communication.