Pelagic delphinids of the Mediterranean Sea have different whistles

Whistles from three delphinid species (Stenella coeruleoalba, Grampus griseus, Delphinus delphis) commonly observed in pelagic waters of the western Mediterranean Sea were taken from GREC sound archives. FFT contours (window size 512, hanning, sampling frequency 44.1 kHz) were extracted with a custom developed Matlab software: 277 samples of striped dolphins (northwestern basin), 158 of Risso's dolphin and 120 of common dolphins were selected. Fifteen variables were extracted from the contours, including: duration, frequency range, number of frequency extrema, beginning, ending, maximal and minimal frequencies, initial, final, maximal and minimal frequency slopes, presence of harmonics. All three species were significantly different (Mann-Whitney test) for average durations (respectively 0.72, 0.65 and 0.47 sec.), frequency ranges (respectively 7296, 6365 and 4622 Hz) and max frequencies. Initial and final slopes were significant to discriminate common dolphins from the two other species. Beginning and minimal frequencies were significantly different for striped dolphins and other species. A discriminant analysis was carried out and showed that two species could be discriminated with a good confidence level (chi
²
test, alpha = 0.05).