The diverse vocal repertoire of killer whales comprises clicks, whistles, and pulsed calls 33. Pods that have one or more discrete calls in common are classified as one acoustic clan 32. Ford 30 and Wiles 31 suggested that individuals from the same matriline and originating from a common ancestor most likely share similar acoustic vocal behaviors. Different pods produce distinct vocal repertoires, consisting of a mixture of unique and shared (between matrilines) discrete call types, which are referred to as dialects. Resident killer whales live in stable matrilineal units that join together to socialize on a regular basis, forming subpods and pods 28, 29. Figure 1 shows the population distribution and geographic ranges of killer whales in the Northeast Pacific. They differ greatly in prey preferences, vocal activity, behavior, morphology and genetics 23, 24, 25, 26, 27. Extensive research on killer whale acoustic behavior has taken place in the Northeast Pacific where resident fish-eating, transient mammal-eating and offshore killer whales can be found, the three ecotypes of killer whales in this region. They are believed to play an important role in their communicative abilities and complex information processing 22. Recent studies on killer whale and bottlenose dolphin brains reveal striking and presumably adaptive features to the aquatic environment 18, 19, 20, 21. Killer whales ( Orcinus orca) are the largest members of the dolphin family and are one of several species with relatively well-studied and complex vocal cultures 17. In this study, the killer whale was used as a prototype in order to confirm the importance and general feasibility of using machine-based deep learning methods to study animal communication. Many different animal species have a strong ability to communicate. Moreover, studies on captive and temporarily captured wild bottlenose dolphins (Tursiops truncatus) have shown that individually distinct, stereotyped signature whistles are used by individuals when they are isolated from the group 13, 14, 15, in order to maintain group cohesion 16. These are believed to attract prospective female mates and/or establish dominance within male groups 11, 12. In cetacean communication, whale songs are a sophisticated communication system 9, as in humpback whales (Megaptera novaeangliae) whose songs were found to be only sung by males and mostly during the winter breeding season 10. Recent research indicates that bird calls or songs display interesting phonological, syntactic, and semantic properties 4, 5, 6, 7, 8. Studies on mixed-species groups have advanced the knowledge of how non-human primates decipher the meaning of alarm calls of other species 2, 3. There has been a long-standing interest to understand the meaning and function of animal vocalizations as well as the structures which determine how animals communicate 1. ORCA-SPOT can be adapted to other animal species. The code will be publicly available in October 2019 to support the application of deep learning to bioaoucstic research. This approach enables an automated annotation procedure of large bioacoustics databases to extract killer whale sounds, which are essential for subsequent identification of significant communication patterns. It achieved a time-based precision or positive-predictive-value (PPV) of 93.2% and an area-under-the-curve (AUC) of 0.9523. An automated segmentation of the entire Orchive recordings (about 2.2 years) took approximately 8 days. The resulting toolkit ORCA-SPOT was tested on a large-scale bioacoustic repository – the Orchive – comprising roughly 19,000 hours of killer whale underwater recordings. In this study deep neural networks were trained on 11,509 killer whale ( Orcinus orca) signals and 34,848 noise segments. A main challenge remains that most large-scale bioacoustic archives contain only a small percentage of animal vocalizations and a large amount of environmental noise, which makes it extremely difficult to manually retrieve sufficient vocalizations for further analysis – particularly important for species with advanced social systems and complex vocalizations. Large bioacoustic archives of wild animals are an important source to identify reappearing communication patterns, which can then be related to recurring behavioral patterns to advance the current understanding of intra-specific communication of non-human animals.
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