Vocal repertoires and insights into social structure of sperm whales (Physeter macrocephalus) in Mauritius,southwestern Indian Ocean

Sperm whales communicate using codas (stereotyped click sequences). Females and juveniles live in long-term social units, and units with similar coda repertoires share vocal clan membership. Vocal clans exhibit culturally defined differences in their multilevel social structure. Here, we aimed to identify different social units among sperm whales in Mauritius in the southwestern Indian Ocean, and to describe and compare their coda repertoires to investigate the presence of different vocal clans. We conducted six boat-based surveys between 2008 and 2013, during which 101 different individuals were photo-identified. Analysis of associations between 22 resighted individuals divided them into four candidate social units, but a lack of resightings impedes solid delineation of social units. Based on number and rhythm of clicks, at least 24 discrete coda types were detected among 4,767 analyzed codas using two different classification methods. Comparison of coda repertoires recorded from seven sperm whale groupings revealed the possible existence of two sympatric vocal clans, but the size differences of recorded repertoires warrant caution of interpretation. To further evaluate social structuring and the presence of different vocal clans in this region, future surveys should aim at obtaining long-term sighting and acoustic data, and cover a more extensive area.     

How does social behavior differ among sperm whale clans?

When individuals primarily associate with and learn from those who behave similarly, society and culture become closely tied. Sperm whales (Physeter macrocephalus) exhibit multilevel social structure, the levels of which are differentiated in part by characteristic cultural behaviors. Sperm whales are organized into sympatric clans, with distinctive vocal repertoires that are socially learned. Other behaviors, such as movement patterns and foraging, also differ among clans. Here we ask whether the clan partition also includes divergences in social behavior. Off the Galápagos Islands, members of two clans differed consistently in diving synchrony, heterogeneity, and temporal stability of social relationships. While number of associates (indicated by social unit, group, and cluster sizes) were similar between clans, Regular clan members dived more synchronously and had more homogeneous relationships than the Plus‐One clan members. Plus‐One social units had generally longer associations than those of the Regular clan. Differences in surface‐time coordination and quality of social relationships are likely byproducts of the clan segregation, which could affect alloparental care giving, therefore scaling up to differential calf survival rates between clans. This new dimension of behavioral divergence between sperm whale clans indicates that sympatric, socio‐cultural entities of nonhumans can also display characteristic social behavior.     

Vocal clans in sperm whales (Physeter macrocephalus)

Cultural transmission may be a significant source of variation in the behaviour of whales and dolphins, especially as regards their vocal signals. We studied variation in the vocal output of 'codas' by sperm whale social groups. Codas are patterns of clicks used by female sperm whales in social circumstances. The coda repertoires of all known social units (n = 18, each consisting of about 11 females and immatures with long-term relationships) and 61 out of 64 groups (about two social units moving together for periods of days) that were recorded in the South Pacific and Caribbean between 1985 and 2000 can be reliably allocated into six acoustic 'clans', five in the Pacific and one in the Caribbean. Clans have ranges that span thousands of kilometres, are sympatric, contain many thousands of whales and most probably result from cultural transmission of vocal patterns. Units seem to form groups preferentially with other units of their own clan. We suggest that this is a rare example of sympatric cultural variation on an oceanic scale. Culture may thus be a more important determinant of sperm whale population structure than genes or geography, a finding that has major implications for our understanding of the species' behavioural and population biology.     

Non-geographically based population structure of South Pacific sperm whales: dialects, fluke-markings and genetics

1. This study addresses the issue of structure in sperm whale ( Physeter macrocephalus Linnaeus) populations and whether it is geographically based.
2. During a survey around the South Pacific Ocean, we collected sloughed skin for genetic analyses, recorded coda vocalizations, and photographed fluke markings.
3. Groups of female and immature sperm whales had characteristic mitochondrial haplotypes, coda repertoires, and fluke-mark patterns, but there was no clear geographical structure in any of these attributes.
4. However, similarities of coda repertoire and mitochondrial haplotype distribution were significantly correlated among pairs of groups in a manner that was not geographically based. There was also a significant canonical correlation coefficient between coda repertoire and fluke-mark patterns.
5. These results suggest that attributes (such as vocal repertoire and techniques of predator defence) which are acquired matrilineally, and probably culturally, are conserved during the fission and dispersal of groups.     

Vocal Signature in Wild Infant Chimpanzees

A large array of communication signals supports the fission/fusion social organization in chimpanzees, and among them the acoustic channel plays a large part because of their forest habitat. Adult vocalizations convey social and ecological information to their recipients allowing them to obtain cues about an ongoing event from calls only. In contrast to adult vocalizations, information encoded in infant calls had been hardly investigated. Studies mainly focused on vocal development. The present article aims at assessing the acoustic cues that support individual identity coding in infant chimpanzees. By analyzing recordings performed in the wild from seven 3‐year‐old infant chimpanzees, we showed that their calls support a well‐defined individual vocal signature relying on spectral cues. To assess the reliability of the signature across the calls of an individual, we defined two subsets of recordings on the basis of the characteristics of the frequency modulation (whimpers and screams) and showed that both call types present a reliable vocal signature. Early vocal signature may allow the mother and other individuals in the group to identify the infant caller when visual contact is broken. Chimpanzee mothers may have developed abilities to cope with changing vocal signatures while their infant, still vulnerable, gains in independence in close habitat. Am. J. Primatol. 75:324‐332, 2013. © 2012 Wiley Periodicals, Inc.     

Social Affiliations within Sperm Whale (Physeter macrocephalus) Groups

We examined patterns of affiliation within groups of sperm whales ( Physeter macrocephalus ), particularly concentrating on how short-term spatio–temporal associations reflect long-term relationships. Female and immature sperm whales live in stable, and partially matrilineal, social units. Two or more social units may move together for periods of several days, forming a cohesive group of about 20 animals. We observed that sperm whales in the eastern tropical Pacific quite consistently associated with members of their own social unit more than they did with other animals in their group with whom they did not share a long-term relationship. There was little evidence for preferred, or avoided, affiliations within social units, except in two large and relatively unstable units. In two well-studied groups, individuals did not show consistently favoured positions in the foraging rank relative to other members of their social unit. These results indicate the importance of long-term relationships to female and immature sperm whales, but suggest that relationships are quite homogeneous within social units.     

Convergence and divergence in Diana monkey vocalizations

Individually distinct vocalizations are widespread among social animals, presumably caused by variation in vocal tract anatomy. A less-explored source of individual variation is due to learned movement patterns of the vocal tract, which can lead to vocal convergence or divergence in social groups. We studied patterns of acoustic similarity in a social call produced by 14 female Diana monkeys (Cercopithecus diana) in two free-ranging groups. Calls showed variability in fundamental frequency contours owing to individual identity and external context. Vocal divergence increased significantly between females during poor visibility and tended to increase in the presence of neighbours. In contrast, vocal convergence increased significantly between females during vocal interactions, because females matched the frequency contour of their own call with another female's preceding call. Our findings demonstrate that these primates have some control over the acoustic fine structure of their most important social vocalization. Vocal convergence and divergence are two opposing processes that enable callers to ensure spatial proximity and social cohesion with other group members.     

Seasonal Changes of Vocal Rates and Their Relation to Territorial Status in Male Galápagos Sea Lions (Zalophus wollebaeki)

Male vocal displays play an important role in sexual selection through both male–male competition and female choice. While this is supported by numerous studies in birds, much less attention has been paid to the role of such displays in mammals. We investigated the function of vocal displays in a polygynous mammal, the Galápagos sea lion (Zalophus wollebaeki). In our study population a large proportion of mature males are unable to establish a territory, providing the opportunity to compare the vocal behaviour between territorial and non‐territorial males. We examined how seasonal patterns of vocalizations differed between territorial and non‐territorial males and how the number of females present in a territory influenced behaviour of territorial males. We found that territorial males vocalized at higher rates than non‐territorial males, and territorial males vocalized more at the onset than towards the end of territory tenure. During the onset of territory‐tenure vocalizations of territorial males were directed more often towards other males than females. Furthermore, we found that vocalizations of territorial males were not only given in male–male interactions, but were also actively directed towards females. Territorial males vocalized at higher rates when more females were present in their territory. Our results suggest that vocalizations are important in male–male interactions, are relevant in territorial disputes and are used as a proxy for females to assess a male’s quality.     

Derived vocalizations of geladas (Theropithecus gelada) and the evolution of vocal complexity in primates

Primates are intensely social and exhibit extreme variation in social structure, making them particularly well suited for uncovering evolutionary connections between sociality and vocal complexity. Although comparative studies find a correlation between social and vocal complexity, the function of large vocal repertoires in more complex societies remains unclear. We compared the vocal complexity found in primates to both mammals in general and human language in particular and found that non-human primates are not unusual in the complexity of their vocal repertoires. To better understand the function of vocal complexity within primates, we compared two closely related primates (chacma baboons and geladas) that differ in their ecology and social structures. A key difference is that gelada males form long-term bonds with the 2-12 females in their harem-like reproductive unit, while chacma males primarily form temporary consortships with females. We identified homologous and non-homologous calls and related the use of the derived non-homologous calls to specific social situations. We found that the socially complex (but ecologically simple) geladas have larger vocal repertoires. Derived vocalizations of geladas were primarily used by leader males in affiliative interactions with 'their' females. The derived calls were frequently used following fights within the unit suggesting that maintaining cross-sex bonds within a reproductive unit contributed to this instance of evolved vocal complexity. Thus, our comparison highlights the utility of using closely related species to better understand the function of vocal complexity.     

Vocal Repertoire of Cebus capucinus: Acoustic Structure, Context, and Usage

Researchers studying nonhuman primate vocal repertoires suggest that convergent environmental, social, and motivational factors account for intra- and interspecific vocal variation. We provide a detailed overview of the vocal repertoire of white-faced capuchins, including acoustic analyses and contextual information of vocal production and vocal usage by different age-sex classes in social interactions. The repertoire is a mixture of graded and discrete vocalizations. In addition, there is general support for structural variation in vocalizations with changes in arousal level. We also identified several combined vocalizations, which might represent variable underlying motivations. Lastly, by including data on the social contexts and production of vocalizations by different age-sex classes, we provide preliminary information about the function of vocalizations in social interactions for individuals of different rank, age, and sex. Future studies are necessary to explore the function of combined vocalizations and how the social function of vocalizations relate to their acoustic structure, because social use of vocalizations may play an important role in shaping vocal evolution.     

Do sperm whales share coda vocalizations? Insights into coda usage from acoustic size measurement

Group-specific communication signals are found in many group-living species. One example is group variation in the production of codas, which are short stereotyped patterns of clicks produced in social contexts, by sperm whales, Physeter macrocephalus. However, little is known about how codas are used by groups and individuals. We used the multipulse structure of sperm whale clicks to estimate the size of animals producing codas. Recordings of a single social unit containing nine largely unrelated animals made over a 1-month period yielded 879 codas of 32 distinctive types. We used an automatic technique to measure the interpulse interval of the clicks in these codas because the interpulse interval is closely related to the size of the animal. Ninety-four codas had sufficiently accurate measurements to be included in further analysis. Modes in the distribution of these measurements showed that more than one animal was producing codas. Comparing the measurements within coda types revealed that several coda types were produced by more than one animal. Thus, the codas recorded from these animals represent a shared repertoire, whereby coda production is not limited to a single animal and coda types are shared between individuals within the unit.     

Pilot Whales Attracted to Killer Whale Sounds: Acoustically-Mediated Interspecific Interactions in Cetaceans

In cetaceans’ communities, interactions between individuals of different species are often observed in the wild. Yet, due to methodological and technical challenges very little is known about the mediation of these interactions and their effect on cetaceans’ behavior. Killer whales (Orcinus orca) are a highly vocal species and can be both food competitors and potential predators of many other cetaceans. Thus, the interception of their vocalizations by unintended cetacean receivers may be particularly important in mediating interspecific interactions. To address this hypothesis, we conducted playbacks of killer whale vocalizations recorded during herring-feeding activity to free-ranging long-finned pilot whales (Globicephala melas). Using a multi-sensor tag, we were able to track the whales and to monitor changes of their movements and social behavior in response to the playbacks. We demonstrated that the playback of killer whale sounds to pilot whales induced a clear increase in group size and a strong attraction of the animals towards the sound source. These findings provide the first experimental evidence that the interception of heterospecific vocalizations can mediate interactions between different cetacean species in previously unrecognized ways.     

Resightings of humpback whales in Hawaiian waters over spans of 10–32 years: Site fidelity,sex ratios,calving rates,female demographics,and the dynamics of social and behavioral roles of individuals

From a database of approximately 5,000 Hawaiian humpback whales identified photographically between 1976 and 2010, we extracted 71 males and 39 females having resighting spans of 10 or more years, from first to most recent sighting. Findings included: (1) the male‐biased sex ratio was like that found in breeding grounds worldwide; (2) the mean span for males of 20.7 yr (maximum = 32 yr) did not differ significantly from the mean of 19.8 yr (maximum = 29 yr) for females, but males were seen in significantly more years during their spans than were females; (3) the mean number of females seen with and without calf across 11 three‐year intervals from 1977 to 2009 did not differ significantly; (4) the calving rate for the 39 females was 0.48 and seven females produced two to eight calves over spans of 22–26 yr; (5) females attracted significantly more escorts in years without calf than in years with calf; (6) individuals showed great diversity in the social units they occupied over their sighting spans, but with the most frequently observed unit for both sexes being the trio of mother, calf, and escort. Males were also observed frequently in competitive groups centered about a female without calf.     

Signature information and individual recognition in the isolation calls of Amazonian manatees,Trichechus inunguis (Mammalia: Sirenia)

Acoustic signals are assumed to form the basis of manatee communication. Empirical evidence of individual vocal recognition has been reported. If manatees can recognize one another by acoustical means, it should be possible to identify individual vocal patterns. We recorded vocalizations of 14 individually housed Amazonian manatees and then digitized selected vocalizations, allowing seven variables to be measured and subjected to multivariate statistical treatment. Discriminant function analysis indicated that individuals can be separated on the basis of variables related to the fundamental frequency and signal duration. We observed significant differences in the vocal patterns between sexes and age classes. Females tended to have greater fundamental frequency and shorter note duration than males. Calves had shorter note durations and greater values for the fundamental frequency range than subadults and adults. An inverse relationship between total body length and fundamental frequency range suggests that the fundamental frequency becomes more defined as the animal ages. The similar individual patterns in the vocalizations of a mother and calf pair are discussed. Individual recognition by Amazonian manatees according to their vocal patterns is suggested through a preliminary playback experiment.     

Repeated call sequences and behavioural context in long-finned pilot whales off Cape Breton,Nova Scotia,Canada

Repeated calls are part of the vocal repertoire of a diverse array of species, often presented in sequences that take time and effort on the part of the signal producer. Rhythmic repeated call sequences make up a significant portion of long-finned pilot whale (Globicephala melas) vocal production, yet the function of these sequences has not been investigated until now. In this study, we explored the relationship between behavioural context and the presence of these vocal sequences using recordings of a population of pilot whales found off Cape Breton, Nova Scotia, Canada. We used a binomial logit-link generalized linear model to look for possible predictors of the presence of repeated call sequences. They were more common in recordings of socializing whales than in those of whales in other behavioural states, and least common in resting whales. These vocal repetitions were also more common with larger group size. These results suggest that sequences function in maintaining contact and cohesion within this social species, possibly also serving in individual or group identification. The context of repeated call sequences indicate that they are not primarily mother–calf interactions, as they are heard just as commonly from groups without young. Future studies of pilot whale repeated call sequences should include individual-level behaviour and detailed acoustic calling context.     

Seasonal changes in pod characteristics of eastern Australian humpback whales (Megaptera novaeangliae), Hervey Bay 1992–2005

We investigated the characteristics and composition of 4,506 humpback whale pods observed in Hervey Bay between 1992 and 2005. We use these data to analyze and model the variability of pod size and composition, and to assess the importance of Hervey Bay for particular classes of humpback whales. Pods ranged in size from one to nine individuals. Pairs were the most frequent pod type (1,344, 29.8%), followed by mother‐calf alone (1,249, 27.7%), trios (759, 16.8%), singletons (717, 15.9%), and 4+ whales (437, 9.7%). Of the 4,506 pods, calves were present in 40%, and 10.8% of all pods had one or more escorts present. Of the 1,804 pods observed with calves present, 1,251 (69.4%) were mothers alone with their calves. The size and composition of pods in the study area varied significantly as the season progressed. Pods with calves present were rarely recorded early in the season but dominated later in the season. A significant increase over years in larger groups may be related to social and behavioral changes as the population expands. The data indicate that Hervey Bay is important to immature males and females early in the season, to mature males and females in mid‐season, and to mother‐calf pairs (either alone or with escorts) in mid‐to‐late season.     

Social,contextual, and individual factors affecting the occurrence and acoustic structure of drumming bouts in wild chimpanzees (Pan troglodytes)

The production of structured and repetitive sounds by striking objects is a behavior found not only in humans, but also in a variety of animal species, including chimpanzees (Pan troglodytes). In this study we examined individual and social factors that may influence the frequency with which individuals engage in drumming behavior when producing long distance pant hoot vocalizations, and analyzed the temporal structure of those drumming bouts. Male chimpanzees from Budongo Forest, Uganda, drummed significantly more frequently during travel than feeding or resting and older individuals were significantly more likely to produce drumming bouts than younger ones. In contrast, we found no evidence that the presence of estrus females, high ranking males and preferred social partners in the caller's vicinty had an effect on the frequency with which an individual accompanied their pant hoot vocalization with drumming. Through acoustic analyses, we demonstrated that drumming sequences produced with pant hoots may have contained information on individual identity and that qualitatively, there was individual variation in the complexity of the temporal patterns produced. We conclude that drumming patterns may act as individually distinctive long‐distance signals that, together with pant hoot vocalizations, function to coordinate the movement and spacing of dispersed individuals within a community, rather than as signals to group members in the immediate audience. Am J Phys Anthropol 156:125–134, 2015 © 2014 Wiley Periodicals, Inc.     

High site fidelity,strong associations,and long‐term bonds: Short‐finned pilot whales off the island of Hawai‘i

Studies of short‐finned pilot whales suggest they travel in stable mixed‐sex groups composed of strongly associated individuals; however, temporal analyses of social structure are lacking. To examine site fidelity, association patterns, and temporal relationships, we analyzed data from 267 encounters of this species off the island of Hawai‘i from 2003 through 2007, identifying 448 distinctive individuals (68.1% seen more than once). About 72% of the whales were linked by association into a single social network, suggesting the possibility of multiple populations using the area. Sighting histories suggested that only some individuals exhibit high site fidelity. Individuals demonstrated preferential associations and community division was strongly supported by average‐linkage hierarchical cluster analysis of the association data. Nine longitudinally stable social units composed of key individuals and their constant companions were identified. Qualitative assignment of age and sex classes of unit members indicated that some segregation between adult males and female/calf pairs may occur. Temporal analyses of individuals encountered on the same day indicate stable long‐term associations. Differential patterns of residency and site fidelity were unexpected and may be indicative of multiple populations around the main Hawaiian Islands. The presence of a resident population demonstrating strong, long‐term site fidelity and associations off Hawai‘i Island may warrant special management considerations.     

Deep-diving beaked whales dive together but forage apart

Echolocating animals that forage in social groups can potentially benefit from eavesdropping on other group members, cooperative foraging or social defence, but may also face problems of acoustic interference and intra-group competition for prey. Here, we investigate these potential trade-offs of sociality for extreme deep-diving Blainville′s and Cuvier''s beaked whales. These species perform highly synchronous group dives as a presumed predator-avoidance behaviour, but the benefits and costs of this on foraging have not been investigated. We show that group members could hear their companions for a median of at least 91% of the vocal foraging phase of their dives. This enables whales to coordinate their mean travel direction despite differing individual headings as they pursue prey on a minute-by-minute basis. While beaked whales coordinate their echolocation-based foraging periods tightly, individual click and buzz rates are both independent of the number of whales in the group. Thus, their foraging performance is not affected by intra-group competition or interference from group members, and they do not seem to capitalize directly on eavesdropping on the echoes produced by the echolocation clicks of their companions. We conclude that the close diving and vocal synchronization of beaked whale groups that quantitatively reduces predation risk has little impact on foraging performance.