Whistle comparison of four delphinid species in Southeastern Brazil

Vocal universals and geographic variations in the acoustic repertoire of the common bottlenose dolphin

Acoustical geographic variation is common in widely distributed species and it is already described for several taxa, at various scales. In cetaceans, intraspecific variation in acoustic repertoires has been linked to ecological factors, geographical barriers, and social processes. For the common bottlenose dolphin (Tursiops truncatus), studies on acoustic variability are scarce, focus on a single signal type-whistles and on the influence of environmental variables. Here, we analyze the acoustic emissions of nine bottlenose dolphin populations across the Atlantic Ocean and the Mediterranean Sea, and identify common signal types and acoustic variants to assess repertoires' (dis)similarity. Overall, these dolphins present a rich acoustic repertoire, with 24 distinct signal sub-types including: whistles, burst-pulsed sounds, brays and bangs. Acoustic divergence was observed only in social signals, suggesting the relevance of cultural transmission in geographic variation. The repertoire dissimilarity values were remarkably low (from 0.08 to 0.4) and do not reflect the geographic distances among populations. Our findings suggest that acoustic ecology may play an important role in the occurrence of intraspecific variability, as proposed by the 'environmental adaptation hypothesis'. Further work may clarify the boundaries between neighboring populations, and shed light into vocal learning and cultural transmission in bottlenose dolphin societies.

Whistles of Atlantic spotted dolphin from a coastal area in the southwestern Atlantic Ocean

Atlantic spotted dolphins were recorded on the coastal area of Rio de Janeiro with equipment of 192 kHz sampling rate. The animals produced an average of 33 whistles/min. The repertoire was balanced among four contour categories, with the occurrence of a stereotyped whistle. Frequency parameters were measured between 1.3 and 29 kHz, which represents an increase in the frequency range previously reported for this species in the southwestern Atlantic Ocean. With the use of a higher sampling rate, the acoustic parameters of S. frontalis whistles have changed significantly and became more similar to those reported for North Atlantic populations.