Bottlenose Dolphins (Tursiops truncatus) Increase Number of Whistles When Feeding

We examined the hypothesis that dolphins increase their rate of sound production during feeding events to recruit new individuals. We recorded 135.5 min of underwater sounds from bottlenose dolphins (Tursiops truncatus) near Isla del Coco, Costa Rica. Data were collected from eight feeding groups and three nonfeeding groups. We classified sounds as whistles, click trains, or pulse bursts. The number of whistles per min per dolphin was higher in feeding groups than in nonfeeding groups. More whistles than click trains or pulse bursts were produced when dolphins were feeding. On the other hand, there was no difference in the proportion of each sound type produced when dolphins were not feeding. New dolphins joined the feeding events for which we recorded dolphin sounds. Results supported the hypothesis that dolphin group size increases in response to an increase in the number of whistles by conspecifics; however, confounding factors, such as the use of specific feeding calls, need to be accounted for to support the increased sound-rate hypothesis.