Dudzinski, K. (1996) Communication and Behavior in the Atlantic Spotted Dolphins (Stenella frontalis): Relationships Between Vocal and Behavioral Activities.
The University of Connecticut

This work presents a description of behaviors and vocalizations of freeranging Atlantic spotted dolphins (Stenella frontalis) in Bahamian waters.The objective is to elucidate mechanisms of intraspecific communication in these dolphins by interpretation of associations between vocal structures, social context, and observed behaviors. The ultimate goal is to evaluate communication and behavior of spotted dolphins in order to eventually understand how an aquatic mammal’s sensory abilities permit it to adapt to an environment foreign to terrestrial mammals. While this work does not yield the Rosetta stone to dolphin communication, it does provide a beginning description of associations among their intraspecific interactions, behaviors,and vocalizations. To facilitate this work, I developed a system that allowed concurrent recording of underwater vocal activity and behavior among dolphins. With this system, the vocalizing dolphin could be identified for approximately 38% of all recorded vocalizations, thereby facilitating examination of relationships between an individual’s vocalizations, behaviors, age, and gender. Behavior units varied with behavioral activity, group type, and age, but not gender. Some behaviors and vocalizations were produced only by particular ages. For example, melon-to-genital contact was observed between mother/calf dyads, while screams were recorded only from calves and juveniles. Vocal type varied significantly with behavioral activity, group type, and spot class: whistles and chirps were observed mostly during social and play activity, and click trains more during inquisitive and forage modes. No evidence for signature whistles was indicated from the data, although their presence and potential use as contact calls is suggested from anecdotal observations. Spotted dolphins use vocal, visual, and tactile pathways for signal exhange. Behaviors and vocal signals were used concurrently, apparently to maximize or enhance a message. Behaviors and vocalizations were also used separately, but with similar functions. For example, a click train with a chirp produced while one individual approached another appeared to indicate the same message as a pectoral fin to pectoral fin rub between individuals that joined after a separation.

Gregg, J. D. (2008). Joint Attention and Echoic Eavesdropping in Wild Bottlenose Dolphins (Tursiops aduncus). Unpublished doctoral dissertation, University of Dublin, Trinity College, Dublin, Ireland.

Experimental work has provided initial evidence that dolphins are able to use the information present in click echoes generated from the echolocation of conspecifics to succeed in object detection and discrimination tasks. The ‘echoic eavesdropping hypothesis’ suggests that dolphins in the wild may behave in ways that exploit this ability, and has been offered as a possible explanation as to why dolphins perform well on experiential tasks involving joint attention and point comprehension. In this thesis, I tested the echoic eavesdropping hypothesis using data collected from wild Indo-Pacific bottlenose dolphins (T. aduncus) inhabiting the waters around Mikura island, Japan. A method was developed to accurately measure distance and head angles between dolphin dyads during analysis of underwater video in conjunction with echolocation information collected on a 3-hydrophone system: the 3D MASC method. During investigative events (N=170) in which one dolphin initiated echolocation on a specific target (i.e., the camera system), the behavior of a potential eavesdropping dolphin was analyzed in order to determine if it: 1) remained silent, and 2) remained within an hypothesized ‘ideal eavesdropping position’ (i.e., measurements between rostrums of ≤1 m, and ≤10°). It was found that the dolphins in the potential eavesdropping scenario were significantly more likely to remain silent than those than those in the baseline condition (p<0.001). However, the dolphins did not enter into or remain in an ideal eavesdropping position during eavesdropping events. A decrease in head angle during eavesdropping events was observed, although smaller head angles were correlated with more echolocation from the eavesdropper rather than more silence. It was found that dolphins move farther apart when positioned less than 1 m at the start of an echolocation/eavesdropping event, and closer together when positioned greater than 1 m at the start of the event. As a general observation, dolphins do not appear to enter into or remain in an ‘ideal eavesdropping position’ as has been defined for this study. These results suggest that dolphins may limit their own echolocation emissions when given the opportunity to eavesdrop, but that close swimming proximity and head alignment do not seem to be required for echoic eavesdropping to occur. Overall, these results find some support for the hypothesis that dolphins engage in eavesdropping behaviors in the wild, and bolster the idea that dolphins may have a special sensitivity to joint attention like scenarios, although modifications to the current hypothesis are required in order to address some of the observed behaviors.

Melillo, K. (2008). Interspecific interactions between Atlantic spotted (Stenella frontalis) and bottlenose dolphins (Tursiops truncatus) off Bimini, Bahamas 2003 – 2007. Unpublished Master’s thesis, Alaska Pacific University, Anchorage, USA. 68 pp.

Interspecific interactions have been observed in a variety of social animals. Functional explanations include foraging, antipredatory and social advantages. These behaviors are little understood in marine mammals, but are increasingly studied phenomena in sympatric populations. Resident Atlantic spotted dolphins Stenella frontalis) off Bimini, The Bahamas have been the subject of ongoing photo-identification and behavioral studies since 2001. A lesser known population of bottlenose dolphins (Tursiops truncatus) has been observed interacting with the S. frontalis since 2003. The interactions were documented with underwater video using focal animal sampling. Mating or sexual play are the primary activities observed in nearly 50% of these interactions, with male T. truncatus as the initiators. The most likely functional explanation for these interactions is social. The T. truncatus males may be failing to gain access to T. truncatus females because of immaturity or lack of social status. Alternatively, these interactions may be attempts to diffuse aggressive tensions that might exist
between the populations.

Beard, K. (2008) Use of Bubble Emissions by Bottlenose (Tursiops truncatus) and Atlantic Spotted Dolphins (Stenella frontalis) Relative to Age and Sex (Please contact DCP for a PDF of this thesis)

In marine mammals, communication is a combination of acoustic, visual, and tactile signals, which may be used singly or concurrently to modify the intended message(s). While most cetacean species have been reported using visual signals as communicative displays, and visual communication is believed to be important to cetaceans, current literature reveals less research on visual communication in dolphins than on acoustic communication. For years, cetaceans have been documented to produce bubbles in a variety of forms from the blowhole. In dolphins, streams of bubbles have been documented synchronously with and without whistles, but bubble streams are a rare event. The function of bubble streams is not known, and there is debate as to whether their presence with whistles is representative of the entire whistle repertoire, or if bubbles are instead used as visual cues that accompany certain whistles in certain contexts. Bubble production in dolphins may be affected by factors such as sex, age, group type, and whether the dolphins are wild or in human care. In this study, it was hypothesized that calves and juveniles would produce bubble streams more often than sub-adults and adults, and that females would produce more bubble streams than males. Underwater data were collected from bottlenose dolphins (Tursiops truncatus) at Dolphin Encounters in Nassau, The Bahamas, and from Atlantic spotted dolphins (Stenella frontalis) around Bimini, The Bahamas. The Poisson regression model of general loglinear analysis was used to determine if there were significant interactions between sex and age class at both research sites. If there was no significant interaction, the Poisson regression was used to determine the main effects of sex and age class on the number of bubble streams produced. In Bimini, 12 of the 32 dolphins of known identity were recorded on video producing bubble streams. Of these 12 animals, females produced significantly more bubble streams (n = 84; 83%) than males produced (n = 17; 17%), (p < .001). There was a significant difference in the number of bubble streams produced by dolphins in each age class (p < .001). Adults produced 2% of these bubble streams, sub-adults 54%, juveniles 44%, calves and neonates 0%. At Dolphin Encounters, seven of the 20 dolphins were recorded on video producing bubble streams. Females produced significantly more bubble streams (n = 46; 82%) than males produced (n = 10; 18%), (p < .001). There was a significant difference in the number of bubble streams produced by dolphins in each age class (p < .001). Adults produced 59% of the bubble streams, sub-adults 21%, juveniles 13%, calves and neonates 7%. In both locations, females produced the majority of bubble streams; calves and neonates produced the least amount of bubble streams. The significant difference in bubble production between sexes and age classes indicates that bubble streams may not function the same for all dolphins or in all situations.

Makepeace, S. (2008) Structural changes in dolphin tonal vocalizations in a changing soundscape: A field study. Unpublished Master’s Thesis (Please contact DCP for a PDF of this thesis)

The ocean is a naturally noisy environment. Until recently, understanding of the effects of ambient noise on cetacean vocalizations has been limited. Cetaceans have to cope with not only naturally occurring noise such as wind, waves, precipitation, ice, biological and seismic activity, but also with man-made noise as well. Varying noise levels can have deleterious effects on a dolphin’s ability to communicate. This study focused on a population of wild Indo-Pacific bottlenose dolphins (Tursiops aduncus) residing around Mikura Island, Japan. This population is exposed to a wide variety of soundscapes including anthropogenic noise from watercraft. A manually operated mobile video/acoustical array was used to collect the vocalizations from the population. Based on spectral and kepstral analysis were used.

Paulos, R. (2004). Non-vocal communication in the Atlantic spotted dolphin (Stenella frontalis) and the bottlenose dolphin (Tursiops truncatus): sequential analyses of inter- and intra-specific patterns of behavior. Unpublished Master’s Thesis, College of Education and Psychology of The University of Southern Mississippi Download as PDF – PDF Document

The goal of this project was to increase our understanding of non-vocal communication in the social lives of two species of dolphins, the Atlantic spotted dolphin (Stenella frontalis) and the Indo-Pacific bottlenose dolphin (Tursiops aduncus). The non-vocal behaviors produced by dolphins in various social contexts and the reactions of other dolphins to these behaviors were described and analyzed. Although no specific patterns of behavior (defined as sequences comprised of greater than two behaviors) were found in either species based on lag sequential analysis, significant associations between target events and non-vocal behaviors were identified. Several behaviors were significantly associated with three “target events” (depart, join, and contact) in both study groups including contact behaviors. Spotted dolphins were more likely to touch another individual after joining than before departing (76.47% vs. 28.57%). The Indo-Pacific bottlenose dolphins were equally likely to touch another after joining or before departing (44.44% vs. 57.14%). However, there was no significant difference between species in the use of these behavioral combinations. Both species engaged in reciprocated contact in only two behavioral contexts (mingle and play). The spotted dolphins, however, use a wider variety of contact behaviors than do the Indo-Pacific bottlenose dolphins. Serendipitously, a behavior previously undocumented in the literature was observed in both species of dolphin during data analyses for this study. This behavior was labeled an “oscillating swim”. This swim behavior is defined as a dolphin moving forward while its entire body is involved in a rolling-type movement. The oscillating swim was documented in five social contexts (general social, travel, forage, play, and inquisitive) for both species, but the use of this behavior varied with age (χ2 = 24.241; df = 3; p<.001) as well as by sex (χ2 = 3.98; df = 1; p<.05).

Van Hoey, N. (2013). Photo-identification and distribution of bottlenose dolphins (Tursiops truncatus) off Bimini, The Bahamas, 2006-2009. Unpublished master’s thesis, Alaska Pacific University.

The recognition of an individual within a population can be a valuable tool in science. The ability to recognize an individual allows for the study of distribution, population dynamics, social structure and behavior of an individual or group over time. Photo-identification has been used by scientists since the 1970s to identify individuals within a population for a variety of animal species including cetaceans. Dorsal fin identification, when combined with natural markings, is a useful technique to identify and study the ecology, behavior and distribution of bottlenose dolphins (Tursiops truncatus). In this study I confirmed an established photo-identification catalog (2006-2008) of individual bottlenose dolphins off the Bimini Islands in The Bahamas, as well as identified undocumented dolphins (2009) by using the computer-assisted program DARWIN. I also used Geographic Information Systems (GIS) to assess the distribution and re-sightings of the dolphins from 2006-2009.