Acoustic behaviour of endangered Hawaiian false killer whales

Abstract Understanding the acoustic communication of the endangered main Hawaiian Islands insular population of false killer whales (Pseudorca crassidens) is essential for effective management. In this study, biologging tags were deployed on four individuals, recording 26.2 h of acoustic data. A total of 5940 high-quality possible focal pulsed calls were analysed and 52 stereotyped call types were characterized. The fundamental frequency contour ranged from a mean minimum frequency of 7.22 ± 0.78 to 9.28 ± 0.80 kHz (mean maximum frequency) with a mean duration of 0.32 ± 0.08 s. Predominant call types and call rates across dive states varied by individual. Probability of calling was higher during the descent and bottom phase compared with the surface. Four types of nonlinear phenomena (NLP) were documented including biphonation (call + clicks, 78% of all NLP), secondary sidebands, chaos and frequency jumps. Frequency jumps were commonly produced by two animals from the same group (13–19%). Most calls contained NLP (80%). The average call rate recorded by the tags on two individuals was 17.5 calls m−1 (hourly average) and call rates decreased as swim speed increased. Our findings suggest high repertoire diversity and high signal complexity informing future passive acoustic monitoring efforts.