Characteristics of Guiana dolphins ( Sotalia guianensis) burst-pulse sounds emitted during different surface activity rates in Rio de Janeiro’s coast

Burst-pulses are still the least studied signals in delphinid acoustic repertoire. In this study, acoustic data were gathered in two Rio de Janeiro coastal bays where groups of Guiana dolphins can be found regularly. The acoustic equipment consisted of a C54XRS hydrophone (-155.8 dBV, 0.006 Hz a 203 kHz) and a Fostex digital recorder (192 kHz sampling rate). During each recording, the surface activity rate of the group was classified as being high or low. Burst-pulses were analyzed using SoundRuler software. Fifty signals were randomly selected and the values for duration (low = 143.9 ± 145.4; high = 82.2 ± 74.8), interpulse interval (low = 2.81 ± 1.92; high = 1.34 ± 1.35), number of pulses (low = 52.6 ± 55.7; high = 71.6 ± 64.5), peak frequency (low = 37.4 ± 2.5; high = 38.5 ± 3.2), and minimum frequency (low = 15.4 ± 6.5; high = 6.7 ± 5.3) were measured. Additionally, a Mann-Whitney U test compared all acoustic parameters of burst-pulses emitted during both surface activity rates. Significant differences between activity rates were found for interpulse interval (p<0.01) and minimum frequency (p<0.01). This scenario could indicate that some burst-pulse parameters are related to group arousal and behavior.