Search

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.

Bottlenose dolphin signature whistles are individually specific, modulated tonal sounds that have been the focus of interest for studying the social acoustic repertoire in this species. However, there is still limited understanding about the factors that might drive variation in these signals. The dolphin community in Sarasota Bay is ideal for investigating the influence of interspecific and intraspecific characteristics as well as the social structure on signature whistles as it has been a long-term study for over 30 years. In this thesis, I investigated whether sex, age and size affected the acoustic parameters and modulation patterns of signature whistles. I also determined the variation in signature whistle acoustic characteristics over a long period of time to test the stability of contour patterns. To look at the possible influence of genetic relationships on whistle structure, I studied the influence of maternal kinship (including mothers, grandmothers, siblings and aunts or uncles) and associations during the first year of life on signature whistle acoustic parameters and contour modulation patterns. Since short-term responses to environmental changes can also be encoded in whistles and can lead to changes in whistle parameters, I investigated the effect of carrying digital acoustic devices (D-TAGs) after brief capture-release session on the acoustic properties of signature whistles and dolphin behaviour. The overall results of this thesis highlighted that signature whistles are arbitrary signals that have long-term stability allowing them to be reliable signature calls. Mother-calf relations and social interactions during very early development were found to have the highest influence on the crystallisation of a signature whistle modulation pattern. Carrying suction cup D-TAGs, on the other hand, had no clear effect on the dolphins' signature whistles and surface behaviour, confirming that these research methods are appropriate for studying vocal behaviour in bottlenose dolphins.

Geographic variation in the whistle vocalisations of dolphins has previously been reported. However, most studies have focused on the whole whistle repertoire, with little attempt to classify sounds into biologically relevant categories. Common bottlenose dolphins (Tursiops truncatus) use individually distinctive signature whistles which are thought to help maintain contact between conspecifics at sea. These whistles may show a different kind of variation between populations than non-signature whistles. Here I investigate signature whistle use and variation in the two recognised species of bottlenose dolphins (T. truncatus and T. aduncus) from populations inhabiting the coastal waters of the North America, Scotland, South Africa, Tanzania, Japan, Australia and New Zealand, and one captive colony. I identified likely signature whistles (signature whistles types, SWTs) from acoustic recordings by combining two novel techniques: automated contour categorisation in ARTwarp (Deecke and Janik, 2006) and a specific bout analysis based on the timing of signature whistle production in T. truncatus termed SIGID (Janik et al. in press). Three ways of categorising the contours were tested and between 87 and 111 SWTs were identified in total. Repeated emissions of stereotyped contours were apparent in the repertoire of all T. aduncus populations using both automated and human observer categorisation, providing good evidence for signature whistle use in this species. There was significant inter-specific variation in the frequency parameters, looping patterns and duration of SWTs. Inflection points, duration and measures of SWT complexity showed high variation within populations, suggesting inter- and intra-individual modification of these parameters, perhaps to enhance identity encoding or convey motivational information. Using 328 bases of the mtDNA control region, I found high levels of population differentiation (FST and φST) within the genus Tursiops. These data do not support a link between mtDNA population differentiation and variability in call type. Instead, morphological variations at the species level, and learned differences at the population level, better explain the variation found.

The aim of this thesis was twofold. Firstly I investigate the fine scale abundance of the population of wild bottlenose dolphins off north-east Scotland and secondly I provide further insights into the vocalisation capabilities of bottlenose dolphins with the use of acoustic localisation and behavioural observations. Photo-identification undertaken during focal follows allowed sighting histories of individuals to be established. These histories were run through three abundance estimation techniques to establish the abundance of bottlenose dolphins in St Andrews bay. Results showed differences in estimation techniques, but all concluded that a large proportion of the bottlenose dolphin population found off north-east Scotland are present in the St Andrews bay area during the summer. The development of a mobile two dimensional hydrophone array allowed accurate localisation of calls to positions around the research boat that could then be correlated with surface observations of dolphin groups. By localisation of stereotyped sequences of whistles, to identify caller position, I was able to show a context related use for these sequences as a precursor to subgroups joining. These sequences were unlikely to occur by chance and the whistles in these sequences were shown to have stereotypy matching that seen in signature whistles. Stereotypy of these whistles was further investigated through a computer based categorisation program where the percentage similarity of contours was investigated when assigning whistles to like categories. Finally, whistle rates were shown to significantly vary with activity type and increased whistle rates were observed during direction changing and socialising compared to surface travel. These increased rates suggest a communicative function related to behavioural activity, as group size was shown to not be a significant predictor of increased whistle rates.