Acoustic signals as indicators of animal behavior, presence and location in delphinids

Abstract

Animal acoustic behavior systems are complex and the lifestyle of marine mammals makes understanding these systems difficult as they spend much time submerged underwater and are often difficult to observe visually. Using passive acoustic monitoring to record and interpret cetacean vocalizations provides insights into how these animals use different vocalizations in various contexts. This thesis investigates the use of acoustic signals in foraging and communication in two wild delphinid species, the short-finned pilot whale and the bottlenose dolphin using animal attached digital recording devices (DTAG). In chapter 2, bottlenose dolphin clicks were recorded in Sarasota Bay, Florida to document click production rates among three behavioral contexts for application in density estimations. In chapter 3, bottlenose dolphin signature whistles were identified using the SIGID method to document temporal variations in signature whistle production. Combined application of passive acoustic monitoring with mark-recapture methods proved feasible with information on temporal variations in signature whistle production. In chapter 4, short-finned pilot whale buzzes were defined based on a maximum inter-click interval. Furthermore, the relationship of pilot whale buzzes and whistles with depth was investigated. A buzz duration, number of buzz clicks, whistle output, duration and energy flux density significantly decreased with increasing dive depths. In chapter 5, three buzz types produced by pilot whales were categorized. Analysis of the acoustic events occurring after each buzz showed that different buzz types are used for different biosonar tactics in foraging or communication. Gulps were investigated to identify potential cues for foraging success. The acoustic repertoire of delphinids is highly complex and the research in this thesis documents the variability in whistle and click production in bottlenose dolphins and pilot whales, which is fundamental to understand how passive acoustic monitoring can be used for interpreting delphinid behavior and documenting presence and location of animals.