Do sperm whales share coda vocalizations? Insights into coda usage from acoustic size measurement

Abstract

Group-specific communication signals are found in many group-living species. One example is group variation in the production of codas, which are short stereotyped patterns of clicks produced in social contexts, by sperm whales, Physeter macrocephalus. However, little is known about how codas are used by groups and individuals. We used the multipulse structure of sperm whale clicks to estimate the size of animals producing codas. Recordings of a single social unit containing nine largely unrelated animals made over a 1-month period yielded 879 codas of 32 distinctive types. We used an automatic technique to measure the interpulse interval of the clicks in these codas because the interpulse interval is closely related to the size of the animal. Ninety-four codas had sufficiently accurate measurements to be included in further analysis. Modes in the distribution of these measurements showed that more than one animal was producing codas. Comparing the measurements within coda types revealed that several coda types were produced by more than one animal. Thus, the codas recorded from these animals represent a shared repertoire, whereby coda production is not limited to a single animal and coda types are shared between individuals within the unit.