Identifying Foraging Behaviour of Wild Bottlenose Dolphins (Tursiops truncatus) and Harbour Porpoises (Phocoena phocoena) with Static Acoustic Dataloggers

Sound is the main means of communication for cetaceans, and studying their vocal behaviour can reveal important information about their activity patterns. As static acoustic monitoring (SAM) of whales, dolphins, and porpoises becomes more widespread, it is important to understand how data collected with automated click loggers relate to their behaviour. To assess whether behaviour can be inferred from automated click train data, echolocation click trains (series of clicks) of bottlenose dolphins and harbour porpoises recorded by C-PODs were examined with simultaneous visual observations. Recorded click trains from both species had different characteristics for the two observed behavioural categories: (1) travelling and (2) foraging. Foraging click trains for both species were of shorter duration and had shorter inter-click intervals. The distinction in the click trains between the two behaviours was stronger for harbour porpoises. More than one quarter of the harbour porpoise click trains represented a distinct group of very fast click trains or buzzes, which were thought to be associated with foraging, whereas only a small fraction of such trains was found in the bottlenose dolphin click data. For both species, the C-PODs showed potential in detecting foraging behaviour and in identifying potential feeding sites and trends in foraging activity.