Communication sounds produced by captive narrow-ridged finless porpoises (Neophocaena asiaeorientalis)

Toothed whales are the ideal model to validate the hypothesis that the complexity of sound communication relates to sociality. Compared to the numerous studies on several toothed whale species with complex social systems, there are very few studies on sound communication in species with simple social systems, such as narrow-ridged finless porpoises (Neophocaena asiaeorientalis). The sounds and behaviors of six captive narrow-ridged finless porpoises (two males and four females) were recorded at the Toba Aquarium, Japan, to reveal the existence of sound communication in this species. We compared the frequency and probability of the production of various sound types in three recording groups and between behaviors. We identified two novel sound types that were separate from echolocation clicks. The packet sound was a pulse sequence with repeated pulse packets (sound series of a few pulses with irregular, short inter-pulse intervals) and was produced by the one-porpoise group. The burst pulses was a pulse train in which the inter-pulse intervals were significantly shorter than those in packet sounds and were produced during contact behaviors. We considered that these two sound types were the communication sounds in narrow-ridged finless porpoises.

Automated summary

Toothed whales are an ideal model for studying the relationship between sound communication complexity and sociality. However, there have been limited studies on species with simple social systems. This study discovered two new types of communication sounds in narrow-ridged finless porpoises and confirmed their existence in the species.