Signature-whistle production in undisturbed free-ranging bottlenose dolphins (Tursiops truncatus)

Data from behavioural observations and acoustic recordings of free-ranging bottlenose dolphins (Tursiops truncatus) were analysed to determine whether signature whistles are produced by wild undisturbed dolphins, and how whistle production varies with activity and group size. The study animals were part of a resident community of bottlenose dolphins near Sarasota, Florida, USA. This community of dolphins provides a unique opportunity for the study of signature-whistle production, since most animals have been recorded during capture-release events since 1975. Three mother-calf pairs and their associates were recorded for a total of 141.25 h between May and August of 1994 and 1995. Whistles of undisturbed dolphins were compared with those recorded from the same individuals during capture-release events. Whistles were conservatively classified into one of four categories: signature, probable signature, upsweep or other. For statistical analyses, signature and probable signature whistles were combined into a 'signature' category; upsweep and other whistles were combined into a 'non-signature' category. Both 'signature' and 'non-signature' whistle frequencies significantly increased as group size increased. There were significant differences in whistle frequencies across activity types: both 'signature' and 'non-signature' whistles were most likely to occur during socializing and least likely to occur during travelling. There were no significant interactions between group size and activity type. Signature and probable signature whistles made up ca. 52% of all whistles produced by these free-ranging bottlenose dolphins.     

INCREASED AVOIDANCE OF SWIMMERS BY WILD BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) DUE TO LONG-TERM EXPOSURE TO SWIM-WITH-DOLPHIN TOURISM

The responses of wild, non-provisioned bottlenose dolphins ( Tursiops truncatus ) to swim attempts from commercial swim-with-dolphin tour boats were systematically observed during two research periods: 1994–1995 and 1997–1998. A total of 255 groups of dolphins was encountered during boat-based surveys and 36% ( n = 93) were exposed to at least one swim attempt. The operators' success with swim attempts, defined as at least one dolphin milling within 5 m of at least one swimmer, decreased from 48% in 1994–1995 to 34% in 1997–1998, and avoidance responses to swimmers increased from 22% to 31%. Dolphin response was found to vary according to swimmer placement. The greatest increase in avoidance occurred when swimmers were placed in the dolphins' path of travel. Based on sighting records of 266 individually identified dolphins, it was estimated that an average dolphin was exposed to 31 swim attempts per year. This level of exposure suggests that individual dolphins have, with cumulative experience, become sensitized to swim attempts. When a swim attempt was successful, on average it involved 19% of the group. Age-class differences in interaction rates showed that juveniles were significantly more likely to interact with swimmers than adults. This study highlights the importance of longitudinal studies in evaluating human impact and suggests the urgent need for similar studies of potential human impact on other toothed cetaceans.     

DUSKY DOLPHIN (LAGENORHYNCHUS OBSCURUS) FORAGING IN TWO DIFFERENT HABITATS: ACTIVE ACOUSTIC DETECTION OF DOLPHINS AND THEIR PREY

Active-acoustic surveys were used to determine the distribution of dusky dolphins and potential prey in two different New Zealand locations. During seven survey days off Kaikoura Canyon, dusky dolphins were found within the DeepScattering Layer (DSL) at 2000 when it rose to within 125 m of the surface. As the DSL rose to 30 m at 0100, the observed depth of dolphins decreased, presumably as the dolphins followed the vertical migration of their prey. Acoustically identified subgroups of coordinated animals ranged from one to five dolphins. Time, depth of layer, and layer variance contributed significantly to predicting foraging dusky dolphin subgroup size. In the much shallower and more enclosed Admiralty Bay, dolphins noted at the surface as foraging were always detected with the sonar, but were never observed in coordinated subgroups during the brief (two-day) study there. In Admiralty Bay dolphin abundance was correlated with mean volume scattering from potential prey in the water column; and when volume scattering, an index of prey density, was low, dolphins were rarely present. Ecological differences between the deep waters of Kaikoura Canyon and the shallow nearshore waters of Admiralty Bay may result in differences in how, when, and in what social groupings dusky dolphins forage.     

Cultural transmission of tool use by Indo-Pacific bottlenose dolphins (Tursiops sp.) provides access to a novel foraging niche

Culturally transmitted tool use has important ecological and evolutionary consequences and has been proposed as a significant driver of human evolution. Such evidence is still scarce in other animals. In cetaceans, tool use has been inferred using indirect evidence in one population of Indo-Pacific bottlenose dolphins (Tursiops sp.), where particular dolphins (‘spongers’) use marine sponges during foraging. To date, evidence of whether this foraging tactic actually provides access to novel food items is lacking. We used fatty acid (FA) signature analysis to identify dietary differences between spongers and non-spongers, analysing data from 11 spongers and 27 non-spongers from two different study sites. Both univariate and multivariate analyses revealed significant differences in FA profiles between spongers and non-spongers between and within study sites. Moreover, FA profiles differed significantly between spongers and non-spongers foraging within the same deep channel habitat, whereas the profiles of non-spongers from deep channel and shallow habitats at this site could not be distinguished. Our results indicate that sponge use by bottlenose dolphins is linked to significant differences in diet. It appears that cultural transmission of tool use in dolphins, as in humans, allows the exploitation of an otherwise unused niche.     

Changes in Whistle Structure of Two Dolphin Species During Interspecific Associations

Dolphin communicative signals show great plasticity. Dolphins modify signal structure to cope with their environment, in response to stress, and in some species to mimic group members. Hence, whistle structure variations may offer insights to interspecific associations among dolphin species, which although temporal and opportunistic are common. In this study, I test the hypothesis that interspecific interactions influence dolphin whistle structure, particularly during social events. The study took place in the Southern Caribbean coast of Costa Rica, where interspecific associations of the distantly related Guyana and Bottlenose dolphins occur on daily basis. The results indicate that interspecific groups emit whistles that show intermediate whistle structure compared to whistles emitted in intraspecific groups. This pattern is seen during social interactions between species, but not when interspecific groups are traveling. Social events in interspecific groups were of antagonistic nature, where Bottlenose dolphins isolated and harassed one or two Guyana dolphins. Contour data suggest that the most vocal species during these encounters was the Guyana dolphin. Therefore, the observed modifications in whistles structure likely reflect a stress response by the Guyana dolphins. Another alternative explanation includes signal convergence between interacting species. However, to understand the nature of these potential modifications, future studies should combine acoustic tags and directional recording systems to follow the vocalizing animals. Despite the shortcomings of this study, it provides some of the first insights into dolphin interspecific communication, providing evidence of overall signal change during interspecific interactions.     

Synchrony during aggression in adult male Atlantic spotted dolphins <Emphasis Type="Italic">(Stenella frontalis)</Emphasis>

Synchrony among Atlantic spotted dolphins (Stenella frontalis) is crucial for successfully overcoming bottlenose dolphins (Tursiops truncatus) during interspecies aggression (Cusick and Herzing 2014). The present study examined synchrony in adult Atlantic spotted dolphins during aggressive encounters with bottlenose dolphins. Across group size, aggressive behaviors increased preceding synchrony, peaked during synchrony, and decreased dramatically after synchrony. Although smaller groups (< 10 dolphins) became synchronous more frequently than larger groups (> 10 dolphins), larger groups remained synchronous longer; however, smaller groups exhibited greater aggressive behaviors during synchrony, suggesting that additional aggressive behaviors may be necessary to compensate for the smaller group size, whereas larger groups may be able to rely on synchrony with less aggression. Disorganized squawk bouts synchronized as physical synchrony began, but only if coupled with escalating aggression.     

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, Anthony's 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.     

Synchrony,leadership, and association in male Indo-pacific bottlenose dolphins (Tursiops aduncus)

Male Indo-pacific bottlenose dolphins in Shark Bay, Western Australia, have converged with humans in the formation of nested male alliances and the use of synchrony in alliance behavior. Further, the strength of association among allied male dolphins varies and the stability of alliances correlates with the rate that males consort with estrus females (and is thus a possible indicator of dominance). To examine the possibility that synchrony reflects alliance association strength and dominance relationships, we analyzed videotapes from focal follows of two groups of males that reflect the range of alliance size and the strength of association between individuals in the population. We examined two variables: leadership during synchronous behaviors, based on which animal in a synchronously surfacing pair surfaced first, and the degree of synchrony, based on temporal differences in synchronous surfacing. We predicted that closer associates would exhibit a greater degree of synchrony and that one dolphin in a dyad would consistently lead. Contrary to our predictions, the degree of synchrony was inversely related to strength of association within alliances. This surprising result suggests that individuals with less secure bonds may strive more to achieve synchrony. We found no evidence of leadership during synchronous surfacing or between synchrony and other behavioral variables. Proximate mechanisms for synchronous behavior, such as entrainment and mutual motor imitation (“the mirror game” paradigm), may inhibit leadership in this context. Our results show that synchrony during surfacing is not a useful behavior to examine for dominance relationships in wild dolphins but it may be a useful tool to examine variation in alliance relationships.     

Captive environment influences the composition and diversity of fecal microbiota in Indo-Pacific bottlenose dolphins,Tursiops aduncus

Captive environments impact the microbiota of captive animals; however, the comparison of microbiota between wild and captive dolphins has been poorly investigated. To explore the impact of a captive environment, we characterized the fecal microbiota of nine wild and four captive Indo-Pacific bottlenose dolphins, Tursiops aduncus, using a next-generation sequencing and revealed differences in the fecal microbiota between the analyzed groups. Statistical differences in abundances of the phyla Firmicutes and Proteobacteria were found between the wild and captive dolphins. Thirty-six genera (22.9% of the total genera detected in all dolphins) were shared between the groups, whereas 79 (50.3%) and 42 (26.8%) genera were found only in the wild or captive dolphins, respectively. Several pathogenic bacterial genera, including Morganella and Mycoplasma, were detected only in the captive dolphins, and the genus Lactobacillus was found only in the wild dolphins. LefSe and SIMPER analyses revealed that the genus Clostridium sensu stricto 1 was significantly more abundant in the captive dolphins than in the wild ones and contributed the most to the dissimilarity of fecal microbiota between the groups. Our results indicate that the captive environment impacts the fecal microbiota of dolphins and reinforces the importance of monitoring potentially pathogenic bacteria in captivity.     

Differences in acoustic signals from Delphinids in the western North Atlantic and northern Gulf of Mexico

Whistle characteristics were quantitatively compared between both geographically separated and neighboring populations of Atlantic spotted dolphins (Stenella frontalis), bottlenose dolphins (Tursiops truncatus), and pilot whales (Globicephala spp.) in U.S. waters to evaluate if intraspecific acoustic differences exist between groups. We compared nine whistle characteristics between continental shelf and offshore Atlantic spotted dolphins in the western North Atlantic and between northern Gulf of Mexico and western North Atlantic bottlenose dolphins and pilot whales using discriminant analysis. Offshore Atlantic spotted dolphin whistles were significantly different (Hotelling's T², P= 0.0003) from continental shelf whistles in high frequency, bandwidth, duration, number of steps, and number of inflection points. Atlantic bottlenose dolphin whistles were significantly different (Hotelling's T², P < 0.0001) from those in the Gulf of Mexico in duration, number of steps, and number of inflection points. There was no significant difference between pilot whale whistles in the two basins. The whistle differences indicate acoustic divergence between groups in different areas that may arise from geographic isolation or habitat separation between neighboring but genetically distinct populations of dolphins. This study supports the premise that acoustic differences can be a tool to evaluate the ecological separation between marine mammal groups in field studies.     

BEHAVIOR AND ECOLOGY OF THE ATLANTIC WHITE-SIDED DOLPHIN (LAGENORHYNCHUS ACUTUS) IN COASTAL NEW ENGLAND WATERS

Atlantic white-sided dolphins ( Lagenorhynchus acutus ) are among the most abundant, and least studied, cetaceans in coastal New England. Between April and October 1984 through 1997 we sighted 1,231 groups of Atlantic white-sided dolphins, primarily on Stellwagen Bank and Jeffreys Ledge (two shallow glacial deposits along the coasts of Massachusetts, New Hampshire, and Maine). Mean group size was 52 (≥90.9), and was significantly larger from August through October (71.9 ± 111.4) than April through June (35.0 ± 45.4). Calf sightings were uncommon until June and July, after which they were present in over 50% of groups. Combined with observations of apparent newborn calves, this confirms that early summer is an important calving period. The presence of calves did not, however, solely account for the increase in group size. Boat interaction (bow- and stern-wake riding) was the most commonly recorded behavior (47.4% of sightings), followed by traveling (31.4%), interactions with other cetacean species (27.6%), social interaction (15.5%), and feeding (9.5%). While feeding was uncommon, one observation of apparently coordinated "ball" feeding was seen with sand lance ( Ammodytes spp.) as the visible prey. Aerial behavior showed a positive correlation with group size, although it was often impossible to tell whether the same dolphins were leaping repeatedly. Eighty-eight dolphins were photo-identified using either unusual body pigment or a distinctive dorsal fin. While several individuals were reidentified between years and between areas, no reidentifications were made within a year in the same area. Unusually pigmented individuals were much more likely to be reidentified than those with distinctive dorsal fins, most likely due to higher visibility. We suggest that Atlantic white-sided dolphins are generally using the study area as transients in what appears to be a large home range.     

Bottlenose dolphins exchange signature whistles when meeting at sea

The bottlenose dolphin, Tursiops truncatus, is one of very few animals that, through vocal learning, can invent novel acoustic signals and copy whistles of conspecifics. Furthermore, receivers can extract identity information from the invented part of whistles. In captivity, dolphins use such signature whistles while separated from the rest of their group. However, little is known about how they use them at sea. If signature whistles are the main vehicle to transmit identity information, then dolphins should exchange these whistles in contexts where groups or individuals join. We used passive acoustic localization during focal boat follows to observe signature whistle use in the wild. We found that stereotypic whistle exchanges occurred primarily when groups of dolphins met and joined at sea. A sequence analysis verified that most of the whistles used during joins were signature whistles. Whistle matching or copying was not observed in any of the joins. The data show that signature whistle exchanges are a significant part of a greeting sequence that allows dolphins to identify conspecifics when encountering them in the wild.     

Abundance and site fidelity of Indo‐Pacific Humpback dolphins in the Great Sandy Strait,Queensland, Australia

This study examined the population of Indo‐Pacific humpback dolphins, Sousa chinensis, inhabiting the Great Sandy Strait Marine Park, Queensland, Australia. A total of 106 dolphins were identified during 228 boat‐based surveys, completed between April 2004 and April 2007. Based on the distribution of resighted individuals and the pattern of associations, it was established that this population consists of two largely geographically distinct communities, referred to as the Northern Community (NC) and the Southern Community (SC). The only recorded interaction between the two groups was a single pod composed of one member of the NC and 11 dolphins from the SC. Abundance was estimated for the entire population and by geographical area using open population models. Estimates for the Great Sandy Strait indicate that about 150 dolphins (N_GSS= 148.4, SE = 8.3, 95% CI: 132.5–165.2) used this area during the study. The NC and SC total population sizes was estimated to be 76 (N_NGSS= 75.80, SE = 3.88, 95% CI = 71–86) and 75 (N_SGSS= 74.98, SE = 4.43, 95% CI: 66–83), respectively. Analysis of residence patterns indicates that a majority of the identified dolphins are long‐term residents.     

Mating Group Size in Dusky Dolphins (Lagenorhynchus obscurus): Costs and Benefits of Scramble Competition

In fission–fusion social systems with scramble competition between males, multiple males join mating groups while surrounding an oestrous female. If male decisions to join a mating group have been shaped by natural selection, then there should be an optimal group size resulting from the trade‐offs between the benefits of monopolizing a female in small groups and the energy lost in defending her from rivals in large groups. Male dusky dolphins (Lagenorhynchus obscurus) off Kaikoura, New Zealand, provide a unique opportunity to assess the optimum mating group size because they join transient mating groups not confounded by foraging or predator evasion. Within aggregations of up to 1000 individuals, males search for oestrous females, encountering choices of staying with a large mating group or leaving to find a smaller group. Mating groups typically involve multiple males mating with a single female. We conducted focal follows of mating groups (N = 44) by vessel from November 2011 through January 2012. We used video and a GPS to record group size, behaviour and movement. For each group, we measured potential costs (Swim Speed, Loss of Monopolization Potential) and benefits (Copulation Rate and Duration, Energy Savings). Only Loss of Monopolization Potential was positively correlated with group size, while Energy Savings was negatively correlated. Using these two factors as utility functions, we constructed an optimality model and predicted the optimal mating group size to be seven individuals with a range of 4–11 individuals due to variance. The observed modal mating group size was five dolphins, with a range of 2–15. We compare variation in mating group currencies and sizes to past studies. We discuss potential limitations of applying optimality models to predict mating group size for socially complex and behaviourally plastic species such as dolphins.     

ABUNDANCE OF SOUTHERN CALIFORNIA COASTAL BOTTLENOSE DOLPHINS ESTIMATED FROM TANDEM AERIAL SURVEYS

We describe a tandem aerial survey method for bottlenose dolphins ( Tursiops truncatus ) that uses two aircraft and independent observer teams to conduct consecutive surveys of the same coastal strip one hour apart. Alternatively, one aircraft with one observer team surveys the same coastal strip twice over several hours. Using mark-recapture analysis, we corrected survey counts for visibility bias resulting from missing dolphin groups at the surface and submerged groups. Dolphin groups were considered "recaptured" when we determined that both observer teams had detected the same group. This tandem method is highly useful for estimating abundance (and visibility bias) for species where population closure may be assumed between flights. We assumed population closure between flights and matched groups using geographic location, group size, and expected travel rates. We derive a new variance estimator of population size which incorporates group-size variability commonly encounteted in cetacean surveys. From six tandem surveys conducted from 1991 to 1994, we estimated the abundance of southern California coastal bottlenose dolphins to be between 78 (95% CI 60-102) and 271 (240-306) animals, with an average of 140 (128-154). Variability in abundance estimates is likely due to seasonal and interannual movement of animals along the California and Baja California coast. Abundance estimates from tandem surveys averaged 53% higher than dolphin counts obtained from individual survey flights, demonstrating the importance of correcting for visibility bias.     

Fine-scale analysis of synchronous breathing in wild Indo-Pacific bottlenose dolphins (Tursiops aduncus)

We quantitatively analysed synchronous breathing for dyads in Indo-Pacific bottlenose dolphins at Mikura Island, Tokyo, Japan. For most cases, we observed dyads swimming in the same direction (97%), in close proximity (i.e., less than 1.5 m) and with their body axes parallel as they breathed synchronously. Moreover, the pairs engaged in identical behaviour before and after the synchronous breathing episodes. These results suggest that the dolphins synchronize their movements, and that synchronous breathing is a component of “pair-swimming”, an affiliative social behaviour. Same sex pairs of the same age class frequently engaged in synchronous breathing for adults and subadults, as well as mother-calf and escort-calf pairs. The distance between individuals during synchronous breathing for mother-calf pairs was less than for other pairs. The distance observed between individuals for female pairs was less than for male pairs. The time differences between each exhale for each of the two dolphins involved in synchronous breathing episodes for female pairs were smaller than for male pairs, and time differences for adult pairs were smaller than subadult pairs. These results suggest that age and sex class influenced the characteristics of this behaviour.     

Bottlenose dolphins that forage with artisanal fishermen whistle differently

Acoustic communication is a taxonomically widespread phenomenon, crucial for social animals. We evaluate social sounds from bottlenose dolphins (Tursiops truncatus) of Laguna, southern Brazil, whose social structure is organized around a cooperative foraging tactic with artisanal fishermen. This tactic involves stereotyped and coordinated behaviour by dolphins and fishermen and is performed by a subset of the dolphin population, splitting it into two distinct social communities. We compared the acoustic parameters and type of whistles emitted by dolphins of the “non‐cooperative” and “cooperative” communities, both during their interactions with fishermen and in times where dolphins were engaged in other types of foraging. Our findings show how dolphins’ social sounds differ between foraging tactics and social communities. The frequencies of six whistle types (ascending, descending, concave, convex, multiple, flat) were significantly dependent on tactics and communities. Ascending whistles were more common than expected during foraging without fishermen, and among dolphins of the non‐cooperative community. Whistle acoustic parameters (duration, number of inclination changes and inflection points, and initial, final, maximum, minimum frequencies) also varied between social communities. In general, whistles emitted by cooperative dolphins, mainly when not interacting with fishermen, tended to be shorter, had higher frequency and more inflections than those emitted by non‐cooperative dolphins. These results suggest that different whistles may convey specific information among dolphins related to foraging, which we hypothesize promote social cohesion among members of the same social community. These differences in acoustic repertoires add a new dimension of complexity to this unique human–animal interaction.     

SEASONAL PATTERNS IN THE ABUNDANCE AND DISTRIBUTION OF CALIFORNIA CETACEANS, 1991–1992

This study presents a detailed seasonal comparison of the abundance and distribution of cetaceans within 100-150 nmi (185-278 km) of the California coast during 1991 and 1992. The results of a shipboard line-transect survey conducted in July-November 1991 ("summer") were compared to those from aerial line-transect surveys conducted in March-April 1991 and February-April 1992 ("winter"). Using a confidence-interval-based bootstrap procedure, abundance estimates for six of the eleven species included in the comparison exhibited significant (α= 0.05) differences between the winter and summer surveys. Pacific white-sided dolphins ( Lagenorhynchus obliquidens ), Risso's dolphins ( Grampus griseus ), common dolphins ( Delphinus spp.), and northern right whale dolphins ( Lissodelphis borealis ) were significantly more abundant in winter. The abundance of blue whales ( Balaenoptera musculuss ) and gray whales ( Eschrichtius robustus ) reflected well-documented migratory patterns. Fin whales ( B. physalus ) were significantly more abundant during summer. No significant differences in seasonal abundance were identified for Dall's porpoises ( Phocoenoides dalli ), bottlenose dolphins ( Tursiops truncatus ), killer whales ( Orcinus orca ), sperm whales ( Physeter macrocephalus ), or humpback whales ( Megaptera novaeangliae ). Significant north/south shifts in distribution were found for Dall's porpoises, common dolphins, and Pacific white-sided dolphins, and significant inshore/offshore differences were identified for northern right whale dolphins and humpback whales.