Insights into Blainville's (Mesoplodon densirostris) beaked whale communication

Abstract

Lack of knowledge regarding beaked whale biology restricts our ability to evaluate their vulnerability to anthropogenic threats. This work addresses critical data gaps in Blainville’s beaked whale social structure and communication systems. Social analysis shows that Blainville’s beaked whales in the Bahamas exhibit group living through a harem structure characterised by a single male accompanying a group of females for up to a year. This study also reveals that females preferentially associate with conspecifics in the same reproductive state, remaining together for up to three years. I show what may be the first example of social philopatry in beaked whales, with adult males possibly providing protection for kin. Analysis of data from acoustic tags reveals previously undescribed sexually distinctive vocalisations. These sounds might serve a communicative function helping to form and maintain groups. Acoustic data also reveals a distinctive double click pattern in Blainville’s beaked whales that is likely physiological in nature. The same pattern is also shown in two other deep diving species, Cuvier’s beaked whales and sperm whales. Species differences in the frequency of production of these double clicks may be providing a window into the evolution of odontocete echolocation. Data from a bottom-mounted hydrophone array reveals a lack of sex and / or age specific information in this species’ echolocation clicks. Analysis of mother-calf pairs indicate calves from at least three months of age echolocate using clicks similar to those of adults. This work provides the first comprehensive study of possible communicative sounds in an elusive deep-diving cetacean species exhibiting a complex social structure that lies somewhere between stable groups and fission-fusion societies. Understanding the interaction between communication and social organisation enhances our ability to predict the effects of anthropogenic disturbance on this species.