Short first click intervals in echolocation trains of three species of deep diving odontocetes

All odontocetes produce echolocation clicks as part of their vocal repertoire. In this paper we analysed inter-click-intervals in recordings from suction cup tags with a focus on the first inter-click interval of each click train. We refer to shorter first inter-click intervals as short first intervals (SFIs). We found that the context of SFI occurrence varies across three deep-diving species. In Blainville’s beaked whales, 87% of click trains that were preceded by a terminal buzz started with SFIs. In Cuvier’s beaked whales, only sub-adult animals produced notable amounts of SFIs. In contrast, sperm whales were much more likely to produce SFIs on the first click train of a dive. While the physiological and/or behavioural reasons for SFI click production are unknown, species differences in their production could provide a window into the evolution of odontocete echolocation.