Individual vocal production in a sperm whale (Physeter macrocephalus) social unit

The vocal repertoires of group-living animals may communicate individual or group identity. Female and juvenile sperm whales live in long-term social units that can be assigned to vocal clans based on the pattern of clicks in coda vocalizations. An unusual set of circumstances allowed us to record the vocalizations of photo-identified individuals within a single social unit over a 41 d period. Using click interpulse intervals, we were able to assign codas to individuals and investigate coda production at the individual level within a social unit for the first time. Adult females in the unit vocalized at approximately equal rates. A calf and juvenile, both male, vocalized less often than the adult females. Repertoires were indistinguishable for all unit members apart from a mother and her calf, which possessed significantly different repertoires-even from one another. We suggest that similarity among the coda repertoires of most unit members indicates a function in advertising unit identity. In contrast, the distinctive repertoires of the calf and its mother may facilitate reunions between these whales. We hypothesize that sperm whales may be able to vary their vocal repertoires as their reproductive status alters the trade-off between the benefits of individual and group identification.