First description of whistles of Black Sea short-beaked common dolphins, Delphinus delphis ponticus

The study presents the first quantitative description of whistles (N = 1,017) recorded from free-range short-beaked common dolphins D. delphis ponticus, an endemic subspecies from the Black Sea. The dolphins produced high-pitched frequency-modulated whistles with the fundamental frequency of 1.6–33.2 kHz, the median values of minimum and maximum frequencies being 8.6 kHz and 16.0 kHz, respectively. Whistle duration varied from 0.16 to 2.94 s, with a median value of 1.04 s. Whistle contours with inflection points were the most common (74% of the whistles), followed by simpler whistles: downsweep (13%), upsweep (12%), and flat (1%). Stereotyped repeated frequency-modulated whistles registered in this and previous studies may serve as individual distinctive ‘signature whistles’ in common dolphins. Whistle parameters of the Black Sea subspecies correspond to those reported for D. delphis recorded in neighbouring regions: the Mediterranean Sea and Central–Eastern North Atlantic Ocean. Maximum whistle frequency in common dolphins exhibits a relationship with the body size, similarly to some other dolphin species. Together with minimum frequency, these are parameters with the least coefficients of variation; thus, they may be species-specific acoustic characteristics. This information can be used to distinguish between sympatric dolphin species during their passive acoustic monitoring.