Denise L. Herzing

The broadband social acoustic signaling behavior of spinner and spotted dolphins

Efforts to study the social acoustic signaling behavior of delphinids have traditionally been restricted to audio-range (<20 kHz) analyses. To explore the occurrence of communication signals at ultrasonic frequencies, broadband recordings of whistles and burst pulses were obtained from two commonly studied species of delphinids, the Hawaiian spinner dolphin (Stenella longirostris) and the Atlantic spotted dolphin (Stenella frontalis). Signals were quantitatively analyzed to establish their full bandwidth, to identify distinguishing characteristics between each species, and to determine how often they occur beyond the range of human hearing. Fundamental whistle contours were found to extend beyond 20 kHz only rarely among spotted dolphins, but with some regularity in spinner dolphins. Harmonics were present in the majority of whistles and varied considerably in their number, occurrence, and amplitude. Many whistles had harmonics that extended past 50 kHz and some reached as high as 100 kHz. The relative amplitude of harmonics and the high hearing sensitivity of dolphins to equivalent frequencies suggest that harmonics are biologically relevant spectral features. The burst pulses of both species were found to be predominantly ultrasonic, often with little or no energy below 20 kHz. The findings presented reveal that the social signals produced by spinner and spotted dolphins span the full range of their hearing sensitivity, are spectrally quite varied, and in the case of burst pulses are probably produced more frequently than reported by audio-range analyses.

Echolocation signals of wild Atlantic spotted dolphin (Stenella frontalis)

An array of four hydrophones arranged in a symmetrical star configuration was used to measure the echolocation signals of the Atlantic spotted dolphin (Stenella frontalis) in the Bahamas. The spacing between the center hydrophone and the other hydrophones was 45.7 cm. A video camera was attached to the array and a video tape recorder was time synchronized with the computer used to digitize the acoustic signals. The echolocation signals had bi-modal frequency spectra with a low-frequency peak between 40 and 50 kHz and a high-frequency peak between 110 and 130 kHz. The low-frequency peak was dominant when the signal the source level was low and the high-frequency peak dominated when the source level was high. Peak-to-peak source levels as high as 210 dB re 1 microPa were measured. The source level varied in amplitude approximately as a function of the one-way transmission loss for signals traveling from the animals to the array. The characteristics of the signals were similar to those of captive Tursiops truncatus, Delphinapterus leucas and Pseudorca crassidens measured in open waters under controlled conditions.

Acoustics and Social Behavior of Wild Dolphins: Implications for a Sound Society

Understanding and documenting the characteristics and features of the social sounds and associated behavior of free-ranging delphinids has historically been limited by lack of access to animals and poor underwater viewing conditions. Communication studies of delphinids have been undertaken in both captivity (see Herman and Tavolga 1980 for review) and in the wild (Connor et al. 1992; Norris et al. 1994). Even with a wealth of information about dolphin sound production and hearing capabilities from captivity, there are significant gaps in understanding how dolphins detect, decode, and decipher both their environmental and social signals in the wild. Although the abilities of dolphins to actively produce both echolocation signals and social sounds have been documented, little is understood about the sensory exposure and information available to, and utilized by, free-ranging delphinids. One way to address this issue is to review the use of conspecific social signals and behavior. Dolphins, like other animals, have been under evolutionary pressures for increased efficiency in their communication system. By observing critical environmental and social aspects of delphinid society we might gain insight into how these animals learn and selectively filter information in their environment.

Evidence of teaching in atlantic spotted dolphins (Stenella frontalis) by mother dolphins foraging in the presence of their calves

Teaching is a powerful form of social learning, but there is little systematic evidence that it occurs in species other than humans. Using long-term video archives the foraging behaviors by mother Atlantic spotted dolphins (Stenella frontalis) were observed when their calves were present and when their calves were not present, including in the presence of non-calf conspecifics. The nine mothers we observed chased prey significantly longer and made significantly more referential body-orienting movements in the direction of the prey during foraging events when their calves were present than when their calves were not present, regardless of whether they were foraging alone or with another non-calf dolphin. Although further research into the potential consequences for the naïve calves is still warranted, these data based on the maternal foraging behavior are suggestive of teaching as a social-learning mechanism in nonhuman animals.

Mixed-species associations between Pantropical spotted dolphins (Stenella attenuata) and Hawaiian spinner dolphins (Stenella longirostris )o ff Oahu, Hawaii

Mixed-species interactions were observed between Pantropical spotted dolphins, Stenella attenuata, and spinner dolphins, Stenella longirostris ,i n Hawaiian waters between 1996 and 1998. Yearround observations were made of spinner dolphins entering a shallow bay off the Waianae (western) coast of Oahu. Mixed-species observations occurred on 19 days between 1996–1998. Spinner dolphins were typically present in greater numbers than spotted dolphins with ratios as high as 75:1. Interspecific behaviours observed include aggression, copulation, and travelling. Five aggressive interactions are described in detail. These behavioural observations are similar to those observed between other delphinid species around the world and suggest that sympatric delphinid species may be more common than previously reported and may have common communication and social signals.

The Currency of Cognition: Assessing Tools, Techniques, and Media for Complex Behavioral Analysis

Since 1985, long-term underwater observations of 220 Atlantic spotted dolphins (Stenella frontalis) and 200 bottlenose dolphins (Tursiops truncatus), have provided a unique opportunity to observe the flow of information within and between these societies in the clear waters of the Bahamas. Spotted dolphins are of known gender, relationships (mother/calf, siblings), and association patterns, thus providing a rich social relationship framework. In addition, human researchers enter into interactions with dolphins, providing flow of information between humans and these two delphinid species. Underwater video with hydrophone input has been used to capture contextually sensitive information, including associated vocalizations and behaviors (e.g., foraging, aggression, courtship, and discipline) with known individuals. These specific actions (e.g., gestures, vocalizations, gaze, body/head orientation, etc.) represent the potential media of information, or currency of cognition, available to dolphins. Such media are real-world, observable, and measurable signals through detailed behavioral analysis (i.e., Microethology). By measuring this flow of information in context, in real-time interactions, and through changes over time, we may be able to assess the potential for distributed cognition in this social species. Issues such as gender, age, social relations, and developmental aspects will be brought into context for applying distributed cognition analysis techniques to dolphins in ecologically valid ways.

Molecular assessment of mating strategies in a population of Atlantic spotted dolphins.

Similar to other small cetacean species, Atlantic spotted dolphins (Stenella frontalis) have been the object of concentrated behavioral study. Although mating and courtship behaviors occur often and the social structure of the population is well-studied, the genetic mating system of the species is unknown. To assess the genetic mating system, we genotyped females and their progeny at ten microsatellite loci. Genotype analysis provided estimates of the minimum number of male sires necessary to account for the allelic diversity observed among the progeny. Using the estimates of male sires, we determined whether females mated with the same or different males during independent estrus events. Using Gerud2.0, a minimum of two males was necessary to account for the genetic variation seen among progeny arrays of all tested females. ML-Relate assigned the most likely relationship between offspring pairs; half or full sibling. Relationship analysis supported the conservative male estimates of Gerud2.0 but in some cases, half or full sibling relationships between offspring could not be fully resolved. Integrating the results from Gerud2.0, ML-Relate with previous observational and paternity data, we constructed two-, three-, and four-male pedigree models for each genotyped female. Because increased genetic diversity of offspring may explain multi-male mating, we assessed the internal genetic relatedness of each offspring’s genotype to determine whether parent pairs of offspring were closely related. We found varying levels of internal relatedness ranging from unrelated to closely related (range -0.136–0.321). Because there are several hypothesized explanations for multi-male mating, we assessed our data to determine the most plausible explanation for multi-male mating in our study system. Our study indicated females may benefit from mating with multiple males by passing genes for long-term viability to their young.

Measurement of the echo location signals of the Atlantic Spotted Dolphin Stenella frontalis in the waters off the Grand Bahamas

A line array of three hydrophones with a video camera attached to the array was used to measure the echo location signals of wild Atlantic Spotted Dolphins. The separation distance between hydrophones in the array was 30 cm. The array was attached to a float that supported an amplifier–line driver assembly with the signals sent via a 76‐m multi‐conductor cable back to the support boat. The float and array assembly was oriented by a swimmer. The echo location signals from the hydrophone were digitized simultaneously at a sample rate of 500 kHz. Twenty files of echo location click trains were collected with the quality of the data varying from poor (files with lots of whistles and off‐axis signals) to very good. The on‐axis signals typically had a bimodal spectrum with a low‐frequency peak at 45–60 Hz and a high‐frequency peak at 120–140 kHz. Peak‐to‐peak source levels up to 210 dB re: 1 μPa were measured. The rms bandwidth varied between 32 and 46 kHz, with a cluster around 40 kHz.

Primate, Cetacean, and Pinniped Cognition Compared: An Introduction

When we were students attending our first Society for Marine Mammalogy conferences, a small but devoted group of us would eagerly search the conference schedule for talks on cognition and social behavior. Although there were never many in the offering, we could almost always find a couple of great presentations. The latest works from the cognitive science laboratories of Herman (e., for example , were among the high points for us of each five-day, biennial event. And, if there were indeed any reports on social behavior from the field (see reviews, this issue), they would make the conference an especially exciting one for us. There were, of course, good logistical reasons why talks on such topics were so few and far between. Identifying individuals, tracking their relationships, and collecting data on their social interactions underwater pose a daunting challenge to even the most intrepid, and well-funded, field biologists. Maintaining marine mammals in the laboratory was likewise difficult and expensive, and funding for research on the cognition of these alien creatures, so different from ourselves, was, and continues to be, particularly hard to come by. But, inspired by the research that had, against these odds, provided such fascinating glimpses into the cognitive and communicative skills of these animals, we were determined to do more of the same. Many of the people who have worked to carry on that tradition are, happily, represented in this issue. We, the Guest Editors of this special issue, also went off to try and do our part. One of us (Herzing) established a field site in the Bahamas at which audio-video recordings of social interactions among wild, but human-acclimated, dolphins have now been the focus of study for over twenty years In recent years, however, Johnson has shifted to primarily studying primate behavior instead (Johnson et al., 1999; Johnson, 2001). It was this shift to comparative studies that provided the kernel that was to grow into the workshop upon which this issue is based. Given the close genetic relationship between humans and other primates, there long has been a strong impetus to study our simian kin, to learn more about both our origins and our uniqueness as a species. In both the laboratory and the field, research on primate sociality and problem solving has been pursued with great vigor and ingenuity, producing, over 100 years, a literature vast compared to that available, even now, on marine …

Synchrony during aggression in adult male Atlantic spotted dolphins (Stenella frontalis)

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.