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.