Potential signature whistle production by Indo-Pacific humpback dolphins, Sousa chinensis, in the northern South China sea

Abstract

Dolphin communication involves acoustic signals, including whistles, and the well-studied bottlenose dolphins produce individually distinctive whistles called signature whistles (SWs). The production of a potential SW by an injured Indo-Pacific humpback dolphin has been reported, but no study has attempted to validate this finding in this species. Using data collected during encounters with free-ranging Indo-Pacific humpback dolphins at two locations in the northern South China Sea, we investigated the production of SWs by these dolphins. Of the 3846 analysed whistles, 37% were identified as potential SWs (PSWs) using the SIGnature whistle IDentification method and categorized into 82 PSW types. Overall, PSWs were identified during 54% of encounters. Given the high production rate of stereotyped whistles (62% of all whistles in 90% of encounters) compared with the identified PSWs, we suggest that the SIGnature whistle IDentification method criteria cannot be fully adapted for the detection of SWs in Indo-Pacific humpback dolphins, and more research should be conducted to adapt the criteria to the species. In addition, the characteristics of PSWs differed slightly between locations, potentially because of the geographical separation of populations and habitat differences (e.g. noise levels). The present results confirm the production of stereotyped whistles, including PSWs, by Indo-Pacific humpback dolphins. Further research should be conducted to confirm whether these whistles are similar to bottlenose dolphins’ SWs.