Acoustic Identity Transmission within Long-finned Pilot Whale Groups (Globicephala melas) in the Strait of Gibraltar

Abstract

Because of the environmental constraints placed on the evolution of communicative signals, marine mammals rely heavily on sound to receive and transmit information in their aquatic environment. According to the social complexity hypothesis for communication, social structure places various demands on the animals' recognition systems; therefore, complex social systems may require more complex communicative systems to navigate group interactions and meet the same intraspecific goals as terrestrial mammals. Although little is known about the communicative function of odontocete vocalizations, long-finned pilot whales provide a good, natural study system to explore how and what odontocete vocalizations may communicate. Long-finned pilot whales display matrilineal units, coupled with long-term individual associations of pairs or trios with heterogeneous affiliations. Under the framework of the social complexity hypothesis, the presence of this multi-layered social structure suggests that long-finned pilot whales need a communication system in which multiple levels of identity transmission are possible to maintain the integrity of the group as well as individual relationships. By considering individual vocal repertoire composition and response patterns from digital acoustic data collected from long- finned pilot whale populations in Strait of Gibraltar, this study suggests that (1) long-finned pilot whales use stereotyped, repeated call types, (2) these repeated call types are shared extensively, suggesting that they may transmit group identity information and maintain specific intra-unit associations, (3) long-finned pilot whales can discriminate between individuals within the matrilineal group and (4) the mother, the oldest female in the group, may be critical to information flow within the group. Inter and intragroup differences in vocal repertoires between subunits and call copying may allow for group identity transmission and discrimination in long-finned pilot whales but nuanced differences in these shared call repertoires or within these shared call types may allow for the individual identity transmission that leads to the individually specific response patterns observed. Future research is necessary to consider the possibility of more subtle individual differences within call types to tease apart the nuanced acoustic discrimination and recognition system of long-finned pilot whales.