Peale's dolphins (Lagenorhynchus australis) are acoustic mergers between dolphins and porpoises

Abstract

Most dolphin species produce broadband clicks for echolocation (i.e., biosonar pulses), and whistles and burst-pulsed calls for communication purposes. A few dolphin species in the southern hemisphere are reported to only produce clicks of a more narrowband high-frequency (NBHF) type, very similar to the clicks produced by porpoises. Here, we use underwater acoustic recordings of Peale's dolphins (Lagenorhynchus australis) in the Falkland Islands to show that they also can produce broadband clicks and tonal whistle sounds similar to other whistling odontocete species in addition to NBHF clicks. Whistles and broadband clicks co-occurred in seven out of twelve acoustic encounters with Peale's dolphins. The co-occurrence of whistles and broadband signals, which were predominately burst-pulses, produced by Peale's dolphins in this study points to a probable function as communication signals. Furthermore, the measured frequency and time parameters of Peale's dolphin whistles were comparable with whistles recorded from four additional species in the Lagenorhynchus genus in various parts of their ranges. This is the only species of Lagenorhynchus recorded to date that can relax acoustic crypsis in a similar manner as Heaviside's (Cephalorhynchus heavisidii), Commerson's (C. commersonii), and Hector's (C. hectori) dolphins. Our findings make it likely that additional NBHF species have the ability to generate both pulsed signal types and whistles, and further challenges the acoustic classification of NBHF species.