The Relationship Between Whistle Structure and Behavioral Context In Bottlenose Dolphins

Bottlenose dolphins (Tursiops truncatus) create sound such as whistles, clicking, squeaking, creaking, and buzzing clicks by producing air movements in the nasal passage. We expect there to be a correlation between the structure of whistles and affective or emotional states because of previous theories such as Morton’s motivational-structural rules which hypothesized that mammals produce low-frequency (wide bandwidth) sounds when in aggressive or hostile circumstances and high-frequency (narrow bandwidth) sounds in a fearful context. For example, a mother dolphin produces a vocalization called a “thunk” (broad-band burstpulse vocalization that sounds like a machine gun) in contexts where her infant has wandered too far and she is urgently signaling it to return to her. The purpose of this project was to explore the relationship between captive bottlenose dolphin whistles and behavior in specific social contexts and emotional states. We recorded two male dolphins, Avalon and Brisby, and their mothers, Chelsea and Jasmine, several times a week from infant’s birth through their first year of life using an underwater hydrophone. Recording sessions lasted 30 minutes each; the behavior of all individuals was recorded continuously along with their vocalizations. The dolphins were housed at what was then Marine World Africa, USA in Vallejo, CA (now Six Flags Discovery Kingdom). We converted the recordings from analog to digital format and analyzed them using Audacity sound analysis software. Then, we compared our measurements of the dolphin whistle structure across different behavioral contexts to determine if there was a relationship. Analysis is ongoing, but we expect to find what whistles produced in different social contexts, such as aggressive interactions or sexual play, will be different in their acoustic structure. The results of this work will help us better understand the kinds of information contained in dolphin vocal signals