The whistles of Hawaiian spinner dolphins

The characteristics of the whistles of Hawaiian spinner dolphins (Stenella longirostris) are considered by examining concurrently the whistle repertoire (whistle types) and the frequency of occurrence of each whistle type (whistle usage). Whistles were recorded off six islands in the Hawaiian Archipelago. In this study Hawaiian spinner dolphins emitted frequency modulated whistles that often sweep up in frequency (47% of the whistles were upsweeps). The frequency span of the fundamental component was mainly between 2 and 22 kHz (about 94% of the whistles) with an average mid-frequency of 12.9 kHz. The duration of spinner whistles was relatively short, mainly within a span of 0.05 to 1.28 s (about 94% of the whistles) with an average value of 0.49 s. The average maximum frequency of 15.9 kHz obtained by this study is consistent with the body length versus maximum frequency relationship obtained by Wang et al. (1995a) when using spinner dolphin adult body length measurements. When comparing the average values of whistle parameters obtained by this and other studies in the Island of Hawaii, statistically significant differences were found between studies. The reasons for these differences are not obvious. Some possibilities include differences in the upper frequency limit of the recording systems, different spinner groups being recorded, and observer differences in viewing spectrograms. Standardization in recording and analysis procedure is clearly needed.