Whistles emitted by Atlantic spotted dolphins (Stenella frontalis) in southeastern Brazil

Abstract

The whistles of Atlantic spotted dolphins have been studied in a few localities of the North Atlantic Ocean and those studies revealed that the species emits whistles within a broad frequency range, with a high number of inflection points and presence of harmonics. In the South Atlantic Ocean, there is no information about the sounds produced by Atlantic spotted dolphins. A total of 1092 whistles emitted by free-ranging Atlantic spotted dolphins in Southeastern Brazilian coastal waters were analyzed. Whistles recorded in this study had a broad frequency range from 1.15 to 23.44 kHz. Whistles without harmonics were frequently emitted (N=701; 64.2%) and those signals with zero up to two inflection points corresponded to 94% of all whistles. Some differences in whistle characteristics (inflection points and duration) were found in relation to areas in North Atlantic Ocean and whistles were shorter and with a smaller number of inflection points in Brazil. Whistles produced by Atlantic spotted dolphins varied between the two behavioral states in which dolphins were engaged. Whistles were more frequently emitted when dolphins presented behaviors that included fast movement at surface, prey pursuit, aerial behavior, and physical contact. In these situations, whistles were on average longer and had higher frequency parameters than those emitted when animals were engaged in slowly and moderate traveling. The findings presented herewith reveal that dolphins modified whistle structures within behavioral states.