Chorussing in delphinids

Abstract

The evolution of communication is strongly influenced by the social structure of animals. Here, we report how a group of offshore bottlenose dolphins in the Gulf of Mexico used chorusing of the same whistle type, while no such behavior was observed in inshore populations of the same species. We recorded 166 whistles from a group of 6 bottlenose dolphins in the Gulf of Mexico, 19 nm from the Florida coast. In an examination of the timing of whistle production, we found nine sequences in which there was considerable overlap (i.e., >50%) between whistles and another eight sequences with almost perfect overlap of the same whistle type produced by two to six animals simultaneously. Such synchrony was not expected by chance. To investigate how unique this behavior was, we also analyzed 300 h of recordings of inshore bottlenose dolphins in Florida and Scotland. In these data we found three non-significant cases of two animals showing >50% overlap. Thus, chorusing appears to be absent in inshore animals. Our data suggest that offshore bottlenose dolphins live in closed social units, which could be the result of enhanced difficulties in maintaining contact if home ranges are large.