Geographic variations in the whistles of spinner dolphins (Stenella longirostris)

Abstract

In order to better understand the reasons for geographic variations in the whistles of spinner dolphins (Stenella longirostris), recordings made in the Eastern Tropical Pacific will be compared to those recorded off Midway Atoll, Northwestern Hawai’ian Islands, the island of O’ahu, main Hawai’ian Islands, and Mo’orea, French Polynesia using discriminant function analysis. The values of 10 variables were extracted from the fundamental frequency (contour) of each whistle selected for analysis (begin, end, maximum, minimum and peak frequencies, center and peak times, duration, and number of turns and steps). Geographic variations in the whistles of spinner dolphins were found when comparing animals recorded in waters of Midway Atoll, off the main Hawai’ian Islands, and off Mo’orea. Greater differences were found between the Midway and Hawai’i and Mo’orea groups. The distinctiveness of Midway whistles could be due to geographic isolation and/or differences in population structure (habitat adaptation). The results indicate that geographic differences may not occur solely due to geographic isolation. Other factors, such as population structure and group size may be important when looking at differences in the whistles of spinner groups.