Acoustic behavior of endangered false killer whales (Pseudorca crassidens) using biologging devices in Hawaiʻi

The main Hawaiian Islands insular false killer whale (Pseudorca crassidens) population is endangered due to anthropogenic stressors; therefore, understanding the acoustic behavior of this social species is imperative to conservation. Previous studies have used satellite telemetry tags to track movement, distribution, and diving behavior but provide little information on behavioral context related to acoustic communication and foraging behavior. Suction cup multi-sensor Customized Animal Tracking Solutions (CATS) tags and a digital acoustic recording tag (DTAG) containing hydrophones (SR 96 and 240 kHz, respectively) and a camera (CATS) were deployed off the main Hawaiian Islands in 2011 and 2023–2024 (n = 4). Cumulatively, 21 h of acoustic data were recorded. Calls were manually detected/classified using Raven Pro and features extracted using PAMGuard ROCCA. Individuals predominantly produced rarely documented pulsed calls and repertoires consisted of 10 previously undescribed stereotyped calls. Call types were associated with dive phase and call rates varied across individuals. Nonlinear phenomena were common including biphonation, frequency jumps, and deterministic chaos. This study marks the first-time concurrent audio/video tags have been deployed on odontocetes in Hawaiʻi and provides high-resolution insight into call function and behavioral states to supplement passive acoustic monitoring efforts and inform species management and conservation.