Bottlenose dolphin whistle repertoires: Size and stability over time

Bottlenose dolphins possess vocal learning abilities that influence the development of individually distinctive signature whistles. While signature whistles have been studied in detail, little is known about other whistle types in bottlenose dolphin communication or the size of their whistle repertoires. We made 24-hour acoustic recordings from a group of 13 bottlenose dolphins at Oceanogràfic (Valencia, Spain) for two months to determine the whistle repertoire size of this group and investigate whether learning leads to changes in existing whistle types over time. We extracted fundamental frequency contours from 50 randomly chosen whistles per day (n = 3,119 whistles) and categorised them using ARTwarp (96% vigilance level), resulting in 701 whistle types. The whistle type discovery curve did not plateau after two months, indicating that we did not capture the entire repertoire. Three analytical methods were used to estimate repertoire size (curve-fitting, a capture-recapture model, and the coupon collectors method). These produced repertoire size estimates between 888 and 1358 whistle types. Whistle types appeared and disappeared over time; however, exact randomization tests showed no significant differences between the observed patterns of appearance and disappearance and time-randomized permutations. Our results suggest that these dolphins possess a large whistle repertoire that is stable over time.