Group fission-fusion dynamics and communication in the bottlenose dolphin
By Ester Quintana-Rizzo, PhD

The bottlenose dolphin exhibits a fission-fusion social structure characterized by temporary associations lasting from minutes to hours. Such flexible grouping patterns in which dolphins are constantly changing associates is intriguing and raises the question as to what factors are influencing a dolphin's decision to leave and join a temporary group. As groups change in composition, dolphins must be able to find each other when they are separated over long distances, and those distances must be within communication range. The purpose of my dissertation project was to (1) examine fission-fusion grouping patterns, (2) examine the communication signals produced during temporary separations, and (3) estimate the distances over which dolphins could remain in acoustic contact while separated.

It was found that a dolphin's decision to join or leave a group was related to social considerations such as the class of individual encountered (e.g., mothers with calves, adult single females, adult males, and juveniles) as dolphins move in different environments. The decision was also influenced by ecological characteristics such as the habitat where a dolphin was found. Mothers with calves regularly using deep waters frequently encountered other females in the same reproductive condition and associated with them. In contrast, mothers with calves using shallow waters often encountered juvenile dolphins but they did not associate with them frequently. When dolphins were temporarily separated, they did not always produce the sounds typically used for long-distance communication. When both whistles and echolocation were produced, they were apparently involved in maintaining contact between mothers and their calves and other associates. Estimates of active spaces defined by whistle transmission indicated that communication range varied between habitats. Shallow seagrass areas had the smallest active space while channels had the greatest active space. Findings indicated that the distances over which dolphins remain in acoustic contact and can be considered members of groups are much greater than has been described from observations of dolphin spacing and activity alone.

This project was successfully defended and accepted by the Graduate School Office of the University of South Florida. My studies at USF were supported by several graduate student fellowships from the College of Marine Science and the USF Library Fellowship Program. Fieldwork was supported by a grant from the National Marine Fisheries Service.