Songs of humpback whales Megaptera novaeangliae in the Ryukyu and Bonin regions

Changes in the songs of humpback whales Megaptera novaeangliae in the Ryukyu and Bonin regions of Japan were examined, and songs from the two regions were compared. Eighty-four song sessions in the Ryukyu region, from 1991 to 1997, and eleven song sessions in the Bonin region, from 1992 to 1995, were analyzed. The mean number of theme types was 6.9 for the Ryukyu samples and 7.6 for the Bonin samples. Song similarities were higher within winter than between winters and similarity declined as the number of intervening years increased, indicating that in these regions songs change with time. Song similarities for consecutive years varied, suggesting that the rate of change varies annually. Songs in the same year were very similar in both the Ryukyu and Bonin samples, furthermore site-specific theme types were not found. These results suggest there may be acoustic contact between animals using the two regions, supporting a previous photographic study which indicated that humpback whales migrate between these two regions.