A characterization of Guyana dolphin (Sotalia guianensis) whistles from Costa Rica: The importance of broadband recording systems

Abstract

Knowledge of the whistle structure in Guyana dolphins comes mostly from Brazilian populations where recordings have been made using limited bandwidth systems (18 and 24 kHz). In Brazil, Guyana dolphin whistle frequency span is 1.34-23.89 kHz, but authors have suggested that limits of their recording system may underestimate frequency span. Whistles of Guyana dolphins from Costa Rica were studied using a broadband recording system. How bandwidth limitations affect the understanding of whistle structure and species classification between sympatric dolphin species was evaluated. In addition, whistles were compared to Brazilian populations. Guyana dolphin whistle frequency span was 1.38 up to 48.40 kHz, greater than previously reported. Bandwidth limitations explained 89% of the whistle variation between studies, and increase in bandwidth improved the whistle classification of Guyana dolphins. Whistle duration and minimum frequency were the most important variables in dolphin species classification. Finally, after accounting for differences in recording systems, Costa Rican Guyana dolphins whistled with significantly higher frequency than Brazilian populations, providing evidence for a postulated increase in frequency from south to north. The study concludes that equipment with an upper frequency limit of at least 50 kHz (150 kHz for harmonics) is required to capture the entire whistle repertoire of the Guyana dolphin.

High-frequency whistles of Guiana dolphins (Sotalia guianensis) in Guanabara Bay, southeastern Brazil

“…Frequency parameters were measured in kilohertz (kHz) and the duration in milliseconds (ms). Acoustic parameters chosen were consistent with previous studies (e.g., Azevedo and Van Sluys, 2005;May-Collado and Wartzok, 2009). Whistles were classified into contour form categories following Azevedo and Van Sluys (2005).…”

“…In addition, these results further illustrate the significance of a broadband recording system to analyze the entire whistle repertoire of this species, point initially reported by May-Collado and Wartzok (2009). Finally, our results are important to characterize the full repertoire of Guiana dolphin whistles, and highlight the need for future research to elucidate the factors that might be related to the emission of high-frequency whistles in this species.…”

“…The maximum reported fundamental frequency in Guiana dolphin whistles to date is 48.40 kHz in Costa Rica (May-Collado and Wartzok, 2009). Since that study, there is no additional information about Guiana dolphin whistles with maximum frequency values above 48 kHz.…”

“…Guiana dolphin whistles span a broad frequency range, with the maximum frequency values well above the humanaudible range. The increased tonal sound modulation might be related to group size and social structure (May-Collado et al, 2007b). Guanabara Bay recordings were made with different group size, during two behavioral states.…”

“…Most studies of Guiana dolphin whistles have been conducted along the coasts of Brazil and Costa Rica (e.g., Azevedo and Van Sluys, 2005;May-Collado and Wartzok, 2009;May-Collado, 2013;. Previous studies have focused on the characteristics of acoustic parameters and comparisons between populations (e.g., Azevedo and Van Sluys, 2005;Rossi-Santos and Podos, 2006;May-Collado and Wartzok, 2009;.…”