Whistle structure variation between two sympatric dolphin species in the Gulf of California

Dolphins produce narrowband and frequency modulated sounds called whistles during a variety of behavioral contexts. Dolphin species vary in their whistle contour composition, frequency range, modulation, and duration, and these differences can be useful in their identification. Here, we compare the whistle contours of two sympatric dolphin species at La Paz Bay, Gulf of California, the Eastern Tropical Pacific bottlenose dolphin, and the long-beaked common dolphin. Dolphins were recorded (7 h and 1 min recording effort) from the research vessel with the engine off using an over-the-side hydrophone and a broadband recording system. A total of 666 high quality whistles (bottlenose dolphin, n = 415; long-beaked common dolphin, n = 251) were analyzed. A Random Forest Analysis identified duration, ending frequency, and maximum frequency as the most important variables that distinguish the two dolphin species. The most common whistle contour types of bottlenose dolphins were sine and convex, while the long-beaked common dolphins produced mainly upsweep and concave whistles. The results showed that bottlenose dolphins and long-beaked common dolphins differ in their whistle variables and contours facilitating their identification in future passive acoustic studies.