Kathleen M. Dudzinski

Communication in Marine Mammals

Publisher Summary Animals live in an ever-changing world. Reactions and responses to environmental and social variables must be flexible and adaptive for survival and reproduction. Examination of signaling behavior and subsequent receiver responses provides a window into nonhuman minds, as well as to the social complexity of other species. It can be assumed that evolutionary processes are at work on signals to keep them informative and useful to individuals. Ecological factors, coupled with social relationships and interactions, provide the principal force in the evolution of communication systems. Foraging, mating, and parental strategies are examples of components that influence signaling behavior. In marine mammals, coastal or oceanic species living in relatively clear water may be more likely to use visual signals (e.g., postures, coloration patterns) than species inhabiting riverine or turbid environments. Similarly, amphibious species require a suite of signals useful both in air and under water. Differential communication is also evidenced in the foraging methods of several delphinid species. Communal foragers have more complex signals compared with hunters that are more solitary. Frequent interactions with conspecifics necessitate a higher rate of information exchange than for solitary species. Observing and examining the social and ecological differences among individuals and groups will help elucidate the mechanisms underlying the use and evolution of different signals to exchange information among individuals, i.e., to communicate.

The role of touch in select social interactions of Atlantic spotted dolphin (Stenella frontalis) and Indo-Pacific bottlenose dolphin (Tursiops aduncus)

In this descriptive study, the potentially communicative functions of non-vocal behaviors produced by two species of dolphin, Atlantic spotted (Stenella frontalis) and Indo-Pacific bottlenose (Tursiops aduncus), were examined in the context of three focal events: depart (one or more dolphins depart company of others), join (two or more dolphins come together), and contact (dolphin makes contact with another using a part of its body). These particular events were chosen because they involve interactions between dolphins and so provide an opportunity to examine possible precursors or antecedents to specific social behaviors. Non-vocal behaviors occurring before and/or after these focal events were documented and analyzed in an attempt to determine if certain behaviors were consistently associated with the departure (depart) or arrival (join) of another dolphin, or with physical contact (contact) between dolphins in each species. Touch behaviors were found to be significantly related to each of the three focal events so were examined in further detail. Overall, in comparing species, the Indo-Pacific bottlenose and Atlantic spotted dolphins in this descriptive study exhibited more similarities than differences in their use of touch behaviors in potentially communicative situations across five broad behavioral contexts. However, a difference in the use of touch behaviors produced before departing or after joining a conspecific was noted. Specifically, the spotted dolphins were more likely to use contact after joining than before departing, whereas the bottlenose dolphins were equally likely to use contact in both situations.

A comparison of pectoral fin contact behaviour for three distinct dolphin populations

Tactile exchanges involving the pectoral fin have been documented in a variety of dolphin species. Several functions (e.g., social, hygienic) have been offered as possible explanations for when and why dolphins exchange pectoral fin contacts. In this study, we compared pectoral fin contact between dolphin dyads from three distinct dolphin populations: two groups of wild dolphins; Atlantic spotted dolphins (Stenella frontalis) from The Bahamas and Indo-Pacific bottlenose dolphins (Tursiops aduncus) from around Mikura Island, Japan; and one group of captive bottlenose dolphins (Tursiops truncatus) residing at the Roatan Institute for Marine Sciences, Anthonys Key Resort. A number of similarities were observed between the captive and wild groups, including; rates of pectoral fin contact, which dolphin initiated contact, posture preference, and same-sex rubbing partner preference. Unlike their wild counterparts, however, dolphins in the captive study group engaged in petting and rubbing at equal rates, females were more likely to contact males, males assumed the various rubbing roles more frequently than females, and calves and juveniles were more likely to be involved in pectoral fin contact exchanges. These results suggest that some aspects of pectoral fin contact behaviour might be common to many dolphin species, whereas other aspects could be species specific, or could be the result of differing environmental and social conditions.

Interactions Between Atlantic Spotted (Stenella frontalis) and Bottlenose (Tursiops truncatus) Dolphins off Bimini, The Bahamas, 2003-2007

Interspecific interactions have been observed in a variety of social animals. Functional explanations include foraging, anti-predatory, and social advantages. These behaviors are poorly 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 these S. frontalis since 2003. To examine the functional significance of these interactions, interspecific behaviors were documented with underwater video using focal animal sampling. Mating or sexual play were the primary activities observed in nearly 50% of interactions, with male T. truncatus as the initiators. Therefore, the most likely functional explanation for these interactions is social. We hypothesize that male T. truncatus which lack access to T. truncatus females because of sexual immaturity or low social status seek copulations with S. frontalis females as an alternative.

3D MASC: a method for estimating relative head angle and spatial distance of dolphins from underwater video footage

The method described here, the 3D model analogous scale calculator (3D MASC), was developed to address a need for obtaining accurate measurements of dolphin head and body positional information from segments of underwater video recordings. Various methods exist for obtaining precise positional or distance measurements to/between individuals or groups from observational research on cetaceans, for example, theodolite tracking (Bailey & Lusseau 2004), hydrophone array triangulation (Lammers et al. 2006), photogrammetry (Jaquet 2006) and videogrammetry (Spitz et al. 2000). However, these methods are not applicable to all field study situations and, consequently, observational data for cetaceans are often coded or scored based on subjective observer estimates. Several studies have used methods for obtaining cetacean swimming proximity by estimating distance apart and stagger (i.e. length ahead/behind) (Connor et al. 2006) and body length (Barrett-Lennard et al. 1996) based on observer ‘eyeball’ estimation techniques. The 3D MASC method was developed for application to determining more precise positional and distance estimates between individual wild dolphins from underwater video data. Methods that rely on simple and cost-effective techniques for measuring distance and relative size of animals from video data using handheld sonar devices in conjunction with video have been previously developed (e.g. underwater videogrammetry described by Spitz et al. 2000); however, the 3D MASC technique has the advantage of

Dolphin underwater bait-balling behaviors in relation to group and prey ball sizes

We characterized dusky dolphin (Lagenorhynchus obscurus) feeding behaviors recorded on underwater video, and related behaviors to variation in prey ball sizes, dolphin group sizes, and study site (Argentina versus New Zealand, NZ). Herding behaviors most often involved dolphins swimming around the side or under prey balls, but dolphins in Argentina more often swam under prey balls (48% of passes) than did dolphins in NZ (34% of passes). This result may have been due to differences in group sizes between sites, since groups are larger in Argentina. Additionally, in NZ, group size was positively correlated with proportion of passes that occurred under prey balls (p<0.001). Prey-capture attempts most often involved capturing fish from the side of prey balls, but dolphins in Argentina more often swam through prey balls (8% of attempts) than did dolphins in NZ (4% of attempts). This result may have been due to differences in prey ball sizes between sites, since dolphins fed on larger prey balls in Argentina (>74m(2)) than in NZ (maximum 33m(2)). Additionally, in NZ, dolphins were more likely to swim through prey balls to capture fish when they fed on larger prey balls (p=0.025).

Is blood thicker than water? The role of kin and non-kin in non-mother-calf associations of captive bottlenose dolphins (Tursiops truncatus)

Relationships are important for social animals and kinship can play a vital role. Still, occurrence and function of kin bonds (aside from mother) in delphinid calf associations, alloparenting, or calf rearing are poorly represented in the literature. This study examined the role of kin and non-kin in non-mother-calf associations for a managed population of bottlenose dolphins. Calf associations were event sampled to determine if kin and non-kin differences existed in frequency or duration. Calves with kin present exhibited a higher average number of associates than calves without kin. Yet calves showed no conclusive association preference in frequency; though some individuals showed early signs of developing kin preferences. Duration and context of associations did not differ between kin and non-kin, suggesting they serve the same developmental purpose. However, personality, calf age, and associate age played a greater role in the formation of calf associations, supporting the notion that calves choose associates with similar traits, aiding in their development in difficult and changing environments. Though kinship is important in the formation of relationships in older dolphins, it appears that outside the mother-calf bond, there are other more influential factors, such as age, personality, and sociality in the formation of early developmental bonds.

Short Note: Air Release from the Left Orbit of an Indo-Pacific Bottlenose Dolphin (Tursiops aduncus): Symptomatic and Anatomical Aspects

An unusual release of gas bubbles is described in an adult female Indo-Pacific bottlenose dolphin (Tursiops aduncus). We will refer to this gaseous mixture from the respiratory tract as air, although we recognize that it is not the exact composition of atmospheric air after respiration has occurred. This air bubble release was observed under water (~10 m depth, 10 to 15 m clarity) in June 2006 outside Chichi-Jima harbor, Ogasawara, Japan, during an eco-tour program involving swimming with a mixed group of spinner (Stenella longirostris) and bottlenose (T. truncatus) dolphins (Figure 1). Underwater observations of this air release were documented by John Anderson (video) and James Brinck (still frames), both associates of the primary author. The dolphin, which had distinctive scarring that would facilitate re-identification, swam up from the sea floor to the surface. During the ascent, she released a stream of bubbles from the region of her left orbit. Her ascent, air release, and following respiration at the surface were captured on video and transparency (Figure 2). Field-by-field video motion analysis confirmed that the point of bubble emergence was the medial angle of her left eye. The pathway for this unusual air release likely involves a communication with the respiratory tract.

Associations and the role of affiliative, agonistic, and socio-sexual behaviors among common bottlenose dolphins (Tursiops truncatus)

Little is known about the specific behavioral exchanges that occur on a day-to-day basis between dyads of common bottlenose dolphins (Tursiops truncatus). This study assesses the proportion of time dyads spend in proximity (within ∼2m) and the proportion of time spent in affiliative, agonistic, or socio-sexual contexts within and between age/sex dolphin pairings to better understand their social relationships. Observations of bottlenose dolphins housed at the Roatan Institute of Marine Sciences provided 10.5h of underwater footage from which to examine association coefficients and inter-individual interactions. These data suggest similar patterns to previous studies on bottlenose dolphins: mother-calf dyads shared the highest coefficients of association, followed by male-male, female-female, and male-female dyads. Four classes of association coefficients were defined for the population including low, medium, medium-high and high. This study is the first to quantitatively assess association patterns concurrently with affiliative, agonistic, and socio-sexual behaviors for bottlenose dolphins. The predominant relationships were affiliative.

Documenting and Assessing Dolphin Calls and Ambient and Anthropogenic Noise Levels via PAM and a SPL Meter.

Song Meter SM2M marine recorders were deployed to document dolphin calls and ambient and anthropogenic noise. Recordings from Bimini were split into 2-h segments; no segment was without dolphin calls. At Dolphin Encounters, average noise levels ranged from 110 to 125 dB; the highest source level was 147.98 dB re 1 μPa at 1 m. Average ambient-noise levels documented at 4 sites in Guam were below 118 dB re 1 μPa at 1 m. These data were compared with values from a custom-built sound pressure level (SPL) meter and confirm that the SM2M recorder is a useful tool for assessing animal calls and ambient and anthropogenic noise levels.