Individually distinctive acoustic features in sperm whale codas

Abstract

Social animals may develop behavioural strategies that are based on individualized relationships among members. In these cases, there might be selection pressures for the development of identity signals and mechanisms that allow discrimination and recognition of particular individuals. Female sperm whales, Physeter macrocephalus, live in long-term, stable social units. Differential interactions among unit members suggest the need for an individual discrimination system. Sperm whales produce stereotyped series of click sounds called codas, which are thought to be used for communication. Although codas were initially proposed as individual signatures, later studies did not support this hypothesis. Using linear discriminant functions and Mantel tests, we tested variation within coda types as a means for individual identification, using recordings where codas were assigned to individual whales. While most coda types showed no indication of individual-specific information, individual differences that were robust to variation among recording days were found in the 5 Regular coda type. Differences in individual-specific information between coda types suggest that different coda types may have distinct functions.