Characterization of a bimodal call rate from tracked minke whales

The minke whale call rate was characterized using 16 years of multi-channel passive acoustic data collected from bottom-mounted hydrophones off the coast of Kauai, HI at the U.S. Navy Pacific Missile Range Facility’s instrumented range. Recorded data were post-processed for minke whale (Balaenoptera acutorostrata) boing vocalizations that were seasonally present using automated detection, classification, and localization algorithms. Semi-automated processes were used to perform spatio-temporal association of localizations to create individual whale tracks. The inter-call intervals (ICIs) from the resulting minke whale tracks exhibited a bimodal distribution. Preliminary results show that the longer ICI mean was 349.7 s, and the shorter or “rapid” ICI mean was 28.6 s. It is believed that only sexually mature males produce the boing call for breeding purposes, and the rapid ICI is hypothesized to be a challenge behavior exhibited when animals are within close proximity to each other. Data from February 2017 were examined in detail and contained four minke whale tracks with rapid ICIs, which appeared to occur when the nearest conspecific was within 10 km. Additional datasets were analyzed to further investigate distance between conspecifics relative to call rate.