Vocal Repertoire of Captive Capybara (Hydrochoerus hydrochaeris): Structure,Context and Function

In this work we describe the structure, behavioral context and functionality of the vocal repertoire of capybaras, a social Caviomorph rodent. Additionally, since territoriality is present in this species, we hypothesize the occurrence of vocal differences among social groups. We analyzed a total of 2069 calls emitted by 28 animals from three different social groups. The capybara’s repertoire is comprised by seven call types (whistle, cry, whine, squeal, bark, click and tooth‐chattering). The vocalizations were functionally categorized as contact, alarm, distress and agonistic calls considering their behavioral contexts. The click calls emitted by the adults of the three captive capybara groups were significantly different, confirming our hypothesis of social groups’ vocal differences. The richness of interactions mediated by vocalization in capybaras suggests that the species’ communication is an important mechanism to regulate social encounters and to alert members of the group about environmental cues.     

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.     

VOCAL REPERTOIRE OF WILD BREEDING ORANGE-WINGED PARROTS AMAZONA AMAZONICA IN AMAZONIA

ABSTRACT

The vocal repertoire of Amazona amazonica during its breeding season has been recorded from wild individuals in Santa Bárbara do Pará, Pará State, Brazil. At individual nests, we continuously recorded vocalizations and behaviour for four hours in the early morning and three hours in the late afternoon, three times a week throughout the breeding season. We identified nine vocalizations that we classified in three behavioural categories: (1) Flight call—emitted when parrots arrive in the nest area; (2) Perched contact calls—two different vocalizations, one of them related to feeding, were emitted when the pair was perched in the nest area and interacted socially between themselves or with other individuals; (3) Aggressive calls—emitted when birds were in a dangerous situation, i.e. alarm (three types of calls), agonistic contact and distress calls (two types of call). The Orange-winged Parrot is a highly social species and the complexity of its social interactions is reflected in the diversity of its vocal repertoire.     

Calling at the highway: The spatiotemporal constraint of road noise on Pacific chorus frog communication

Loss of acoustic habitat due to anthropogenic noise is a key environmental stressor for vocal amphibian species, a taxonomic group that is experiencing global population declines. The Pacific chorus frog (Pseudacris regilla) is the most common vocal species of the Pacific Northwest and can occupy human‐dominated habitat types, including agricultural and urban wetlands. This species is exposed to anthropogenic noise, which can interfere with vocalizations during the breeding season. We hypothesized that Pacific chorus frogs would alter the spatial and temporal structure of their breeding vocalizations in response to road noise, a widespread anthropogenic stressor. We compared Pacific chorus frog call structure and ambient road noise levels along a gradient of road noise exposures in the Willamette Valley, Oregon, USA. We used both passive acoustic monitoring and directional recordings to determine source level (i.e., amplitude or volume), dominant frequency (i.e., pitch), call duration, and call rate of individual frogs and to quantify ambient road noise levels. Pacific chorus frogs were unable to change their vocalizations to compensate for road noise. A model of the active space and time (“spatiotemporal communication”) over which a Pacific chorus frog vocalization could be heard revealed that in high‐noise habitats, spatiotemporal communication was drastically reduced for an individual. This may have implications for the reproductive success of this species, which relies on specific call repertoires to portray relative fitness and attract mates. Using the acoustic call parameters defined by this study (frequency, source level, call rate, and call duration), we developed a simplified model of acoustic communication space–time for this species. This model can be used in combination with models that determine the insertion loss for various acoustic barriers to define the impact of anthropogenic noise on the radius of communication in threatened species. Additionally, this model can be applied to other vocal taxonomic groups provided the necessary acoustic parameters are determined, including the frequency parameters and perception thresholds. Reduction in acoustic habitat by anthropogenic noise may emerge as a compounding environmental stressor for an already sensitive taxonomic group.     

Time course of vocal modulation during isolation in common marmosets (Callithrix jacchus)

Common marmosets vocalize phee calls as isolation calls, which seem to facilitate their reunion with family groups. To identify multiple acoustic properties with different time courses, we examined acoustic modulations of phees during different social contexts of isolation. Subject marmosets were totally isolated in one condition, were visually isolated and could exchange vocalizations in another condition, and were visually isolated and subsequently totally isolated in a third condition. We recorded 6,035 phees of 10 male–female marmoset pairs and conducted acoustic analysis. The marmosets frequently vocalized phees that were temporally elongated and louder during isolation, with varying time courses of these changes in acoustic parameters. The vocal rates and sound levels of the phees increased as soon as the marmosets saw their pair mates being taken away, and then gradually calmed down. The phee duration was longer in conditions during which there were no vocal responses from their pair mates. Louder vocalizations are conspicuous and seem to be effective for long‐distance transmission, whereas shorter call duration during vocal exchanges might avoid possible vocal overlap between mates. Am. J. Primatol. 72:681–688, 2010. © 2010 Wiley‐Liss, Inc.     

The Function of Click Call Emission in Capybaras (Hydrochoerus hydrochaeris)

Contact calls are used to promote cohesion among individuals that live in social groups. Capybaras are very gregarious and often vocalize. This species emits a vocalization known as a click, which has been observed during aggregating and foraging behaviors, suggesting contact or monitoring call function. We carried out a playback experiment to evaluate behavioral responses to the capybara's click call and to a bird call, used as control in ten capybaras. We compared animals' latency to respond to stimuli, the time spent in behavioral patterns, alertness, head orientation toward the sound source, and approach to the sound source. All capybaras responded to the emission of the click call playback. Most of them assumed an alert position, showed head orientation toward the sound source, and approached the sound source. They promptly reacted to the first click call emission, while few reacted to the first bird call emission, used as control. All subjects showed behavioral changes after the second emission of the click call, and some responded to the third emission. Just three individuals answered after the first control emission, while none of them responded to the second and third emission of the playback. Therefore, click call playback promotes prompt behavioral changes in capybaras, including approach to the sound source. These results indicate that this vocalization functions as a contact or monitoring call in the species.     

Spectrographic Description of Vocalizations in Captive Otolemur garnettii

To advance knowledge of the vocal communication associated with close proximity social interactions in Garnett's greater bush baby (Otolemur garnettii), we measured acoustic and temporal properties of vocalizations from videotaped recordings of captives in two main social contexts: mother-infant interactions and adult male-female pair introductions and reintroductions. We used a real-time sonagraph or software program to display, edit, and analyze vocal waveforms, and to provide wideband and narrowband spectrograms. Vocalization characteristics measured include fundamental frequency (via inspection of harmonics) and spectral features such as formant frequency, intensity, and duration. The vocal repertoire contained 4 major types of vocalizations: 1) barks and complex multiple bark sequences, 2) low frequency flutter/hums and growls, 3) high frequency clicks and spits, and 4) noisy shrieks. We describe several vocalizations for the first time and provide a clear classification of some of them on the basis of call durations (long/short growls). Complex bark sequences, previously described as distant communication calls, were invariant and were not often emitted by individuals when in close proximity. When classified spectrographically, the remaining 3 call types, which occurred when individuals were in close proximity, were less stereotypical, and gradations within call types were apparent. Our results show that although nocturnal and non-gregarious, complex communicatory signals of bush babies constitute a vocal repertoire formerly thought to be characteristic only of diurnal, gregarious primates.     

Resting-Associated Vocalization Emitted by Captive Asian House Shrews (Suncus murinus): Acoustic Structure and Variability in an Unusual Mammalian Vocalization

Shrews have rich vocal repertoires that include vocalizations within the human audible frequency range and ultrasonic vocalizations. Here, we recorded and analyzed in detail the acoustic structure of a vocalization with unclear functional significance that was spontaneously produced by 15 adult, captive Asian house shrews (Suncus murinus) while they were lying motionless and resting in their nests. This vocalization was usually emitted repeatedly in a long series with regular intervals. It showed some structural variability; however, the shrews most frequently emitted a tonal, low-frequency vocalization with minimal frequency modulation and a low, non-vocal click that was clearly noticeable at its beginning. There was no effect of sex, but the acoustic structure of the analyzed vocalizations differed significantly between individual shrews. The encoded individuality was low, but it cannot be excluded that this individuality would allow discrimination of family members, i.e., a male and female with their young, collectively resting in a common nest. The question remains whether the Asian house shrews indeed perceive the presence of their mates, parents or young resting in a common nest via the resting-associated vocalization and whether they use it to discriminate among their family members. Additional studies are needed to explain the possible functional significance of resting-associated vocalizations emitted by captive Asian house shrews. Our study highlights that the acoustic communication of shrews is a relatively understudied topic, particularly considering that they are highly vocal mammals.     

Individual vocal production in a sperm whale (Physeter macrocephalus) social unit

The vocal repertoires of group‐living animals may communicate individual or group identity. Female and juvenile sperm whales live in long‐term social units that can be assigned to vocal clans based on the pattern of clicks in coda vocalizations. An unusual set of circumstances allowed us to record the vocalizations of photo‐identified individuals within a single social unit over a 41 d period. Using click interpulse intervals, we were able to assign codas to individuals and investigate coda production at the individual level within a social unit for the first time. Adult females in the unit vocalized at approximately equal rates. A calf and juvenile, both male, vocalized less often than the adult females. Repertoires were indistinguishable for all unit members apart from a mother and her calf, which possessed significantly different repertoires—even from one another. We suggest that similarity among the coda repertoires of most unit members indicates a function in advertising unit identity. In contrast, the distinctive repertoires of the calf and its mother may facilitate reunions between these whales. We hypothesize that sperm whales may be able to vary their vocal repertoires as their reproductive status alters the trade‐off between the benefits of individual and group identification.     

Vocal divergence between two disjunct populations of Giant Antshrike (Batara cinerea) is related to environmental conditions

Variation in the avian vocal signals emitted may have a significant impact on species evolution. Vocal divergence in suboscine species like Giant Antshrike (Batara cinerea) may be associated with selective adaptation, since learning has little influence on vocal development and variation in acoustic structure cannot be attributed to learning deviation. Consequently, tracheophone suboscine species are ideal subjects to explore vocal variation, since cultural evolution does not seem to influence vocal variation in this group. Environmental conditions may determine the selection of vocal features because acoustic transmission could be attenuated under certain conditions of temperature, humidity and vegetation cover. Here, we examined vocalizations of Giant Antshrike and assessed possible acoustic variations between two disjunct groups (Andean and Atlantic), correlating the differences to the environmental structure. Univariate and multivariate analysis show temporal and spectral differences between both groups. Andean individuals produce vocalizations with longer duration, faster trill rates, shorter syllable duration and higher frequencies. Environmental features are different between the two populations, and they are correlated to the acoustic structure of vocalizations. Temporal variations arise directly from climatic influence, while spectral divergence could be a secondary effect of morphological adaptation to habitat structure.     

Spectral call features provide information about the aggression level of greater mouse-eared bats (Myotis myotis) during agonistic interactions

Bats rely heavily on acoustic signals in order to communicate with each other in a variety of social contexts. Among those, agonistic interactions and accompanying vocalizations have received comparatively little study. Here, we studied the communicational behaviour between male greater mouse-eared bats (Myotis myotis) during agonistic encounters. Two randomly paired adult males were placed in a box that allowed us to record video and sound synchronously. We describe their vocal repertoire and compare the acoustic structure of vocalizations between two aggression levels, which we quantified via the bats’ behaviour. By inspecting thirty, one-minute long encounters, we identified a rich variety of social calls that can be described as two basic call types: echolocation-like, low-frequency sweeps and long, broadband squawks. Squawks, the most common vocalization, were often noisy, i.e. exhibited a chaotic spectral structure. We further provide evidence for individual signatures and the presence of nonlinear phenomena in this species’ vocal repertoire. As the usage and acoustic structure of vocalizations is known to encode the internal state of the caller, we had predicted that the spectral structure of squawks would be affected by the caller’s aggression level. Confirming our hypothesis, we found that increased aggression positively correlated with an increase in call frequency and tonality. We hypothesize that the extreme spectral variability between and within squawks can be explained by small fluctuations in vocal control parameters (e.g. subglottal pressure) that are caused by the elevated arousal, which is in turn influenced by the aggression level.     

A comparison of individual distinctiveness in three vocalizations of the dwarf mongoose (Helogale parvula)

Individual specificity can be found in the vocalizations of many avian and mammalian species. However, it is often difficult to determine whether these vocal cues to identity rise from “unselected” individual differences in vocal morphology or whether they have been accentuated by selection for the purposes of advertising caller identity. By comparing the level of acoustic individuality of different vocalizations within the repertoire of a single species, it is possible to ascertain whether selection for individual recognition has modified the vocal cues to identity in particular contexts. We used discriminant function analyses to determine the level of accuracy with which calls could be classified to the correct individual caller, for three dwarf mongoose (Helogale parvula) vocalizations: contact, snake, and isolation calls. These calls were similar in acoustic structure but divergent in context and function. We found that all three call types showed individual specificity but levels varied with call type (increasing from snake to contact to isolation call). The individual distinctiveness of each call type appeared to be directly related to the degree of benefit that signalers were likely to accrue from advertising their identity within that call context. We conclude that dwarf mongoose signalers have undergone selection to facilitate vocal individual recognition, particularly in relation to the species’ isolation call.     

Geographic Variation in the Long Calls of Male Orangutans (Pongo spp.)

Relatively few data exist on population differences in the vocal behavior of mammals. Geographic variation in calls is of special interest because of the implications for resolving evolutionary and behavioral questions. For example, information on geographic variation in vocalizations complements morphological and molecular data used to infer phylogenetic relationships and provides evidence for the mechanisms underlying call development. A quantitative acoustic analysis of orangutan long calls was undertaken, comparing flanged adult males from four geographically distinct sites across Borneo and Sumatra, revealing consistent differences among the calls of individuals. Long calls produced by orangutans from the four sites in Borneo and Sumatra differ in quantitative acoustic measures. Discriminant function analysis reveals that acoustic variables can be used in combination to assign calls to the correct individual, site and island at rates higher than that expected by chance. Specifically, four acoustic parameters proved reliable for distinguishing among the individuals, between sites, and across the two islands that arguably represent populations from separate species or subspecies. Although Bornean and Sumatran long calls share a repetitive structure and show similar call rates (0.100–0.500 LCs/h) and maximum frequency bands (0.400–1.500 kHz), they differ significantly in the number of pulses per call, call speed, call duration, bandwidth, pulse duration, and dominant frequency. Strong consistency in these acoustic parameters is also seen among males within sites and the observed variation may allow for individual recognition. Individual identification by call structure presumably benefits dispersed orangutans, where individuals characteristically forage independently and both encounters and interactions with signaling males are highly variable and largely dependent on context. Acoustic recognition of callers facilitates the choice of which males to join or avoid, thus allowing receivers to manipulate potential costs and benefits of association.     

Bilateral lesions of the medial frontal cortex disrupt recognition of social hierarchy during antiphonal communication in naked mole-rats (<Emphasis Type="Italic">Heterocephalus glaber</Emphasis>)

Generation of the motor patterns of emotional sounds in mammals occurs in the periaqueductal gray matter of the midbrain and is not directly controlled by the cortex. The medial frontal cortex indirectly controls vocalizations, based on the recognition of social context. We examined whether the medial frontal cortex was responsible for antiphonal vocalization, or turn-taking, in naked mole-rats. In normal turn-taking, naked mole-rats vocalize more frequently to dominant individuals than to subordinate ones. Bilateral lesions of the medial frontal cortex disrupted differentiation of call rates to the stimulus animals, which had varied social relationships to the subject. However, medial frontal cortex lesions did not affect either the acoustic properties of the vocalizations or the timing of the vocal exchanges. This suggests that the medial frontal cortex may be involved in social cognition or decision making during turn-taking, while other regions of the brain regulate when animals vocalize and the vocalizations themselves.     

Structural Classification of Wild Boar (Sus scrofa) Vocalizations

Determining whether a species' vocal communication system is graded or discrete requires definition of its vocal repertoire. In this context, research on domestic pig (Sus scrofa domesticus) vocalizations, for example, has led to significant advances in our understanding of communicative functions. Despite their close relation to domestic pigs, little is known about wild boar (Sus scrofa) vocalizations. The few existing studies, conducted in the 1970s, relied on visual inspections of spectrograms to quantify acoustic parameters and lacked statistical analysis. Here, we use objective signal processing techniques and advanced statistical approaches to classify 616 calls recorded from semi‐free ranging animals. Based on four spectral and temporal acoustic parameters—quartile Q25, duration, spectral flux, and spectral flatness—extracted from a multivariate analysis, we refine and extend the conclusions drawn from previous work and present a statistically validated classification of the wild boar vocal repertoire into four call types: grunts, grunt‐squeals, squeals, and trumpets. While the majority of calls could be sorted into these categories using objective criteria, we also found evidence supporting a graded interpretation of some wild boar vocalizations as acoustically continuous, with the extremes representing discrete call types. The use of objective criteria based on modern techniques and statistics in respect to acoustic continuity advances our understanding of vocal variation. Integrating our findings with recent studies on domestic pig vocal behavior and emotions, we emphasize the importance of grunt‐squeals for acoustic approaches to animal welfare and underline the need of further research investigating the role of domestication on animal vocal communication.     

The acoustic expression of stress in a songbird: Does corticosterone drive isolation-induced modifications of zebra finch calls?

Animal vocalizations convey multiple pieces of information about the sender. Some of them are stable, such as identity or sex, but others are labile like the emotional or motivational state. Only a few studies have examined the acoustic expression of emotional state in non-human animals and related vocal cues to physiological parameters. In this paper, we examined the vocal expression of isolation-induced stress in a songbird, the zebra finch (Taeniopygia guttata). Although songbirds use acoustic communication extensively, nothing is known to date on how they might encode physiological states in their vocalizations. We tested the hypothesis that social isolation in zebra finches induces a rise of plasma corticosterone that modifies the vocal behavior. We monitored plasma corticosterone, as well as call rate and acoustic structure of calls of males in response to the playback of female calls of varied saliences (familiar versus stranger) in two situations: social isolation and social housing. Social isolation induced both a rise in plasma corticosterone, and a range of modifications in males' vocal behavior. Isolated birds showed a lower vocal activity, an abolition of the difference of response between the two stimuli, and evoked calls with longer duration and higher pitch. Because some of these effects were mimicked after oral administration of corticosterone in socially housed subjects, we conclude that corticosterone could be partly responsible for the isolation-related modifications of calls in male zebra finches. To our knowledge, this is the first demonstration of the direct implication of glucocorticoids in the modulation of the structure of vocal sounds.     

Social vocalizations of big brown bats vary with behavioral context

Bats are among the most gregarious and vocal mammals, with some species demonstrating a diverse repertoire of syllables under a variety of behavioral contexts. Despite extensive characterization of big brown bat (Eptesicus fuscus) biosonar signals, there have been no detailed studies of adult social vocalizations. We recorded and analyzed social vocalizations and associated behaviors of captive big brown bats under four behavioral contexts: low aggression, medium aggression, high aggression, and appeasement. Even limited to these contexts, big brown bats possess a rich repertoire of social vocalizations, with 18 distinct syllable types automatically classified using a spectrogram cross-correlation procedure. For each behavioral context, we describe vocalizations in terms of syllable acoustics, temporal emission patterns, and typical syllable sequences. Emotion-related acoustic cues are evident within the call structure by context-specific syllable types or variations in the temporal emission pattern. We designed a paradigm that could evoke aggressive vocalizations while monitoring heart rate as an objective measure of internal physiological state. Changes in the magnitude and duration of elevated heart rate scaled to the level of evoked aggression, confirming the behavioral state classifications assessed by vocalizations and behavioral displays. These results reveal a complex acoustic communication system among big brown bats in which acoustic cues and call structure signal the emotional state of a caller.     

Vocal repertoire ontogeny of the captive Asian house shrew Suncus murinus suggests that the male courtship call develops from the caravanning call of the young

Soricids produce a considerable variety of vocalizations. However, these calls have been studied insufficiently with the exception of echolocation calls. In this study, 1,645 calls from 18 juvenile, ten sub-adult and 36 adult Asian house shrews (Suncus murinus) were acoustically and statistically analyzed to describe this species’ vocal repertoire and its ontogeny. The vocal repertoire of S. murinus includes 17 call types, seven tonal (whistle, chirp, twitter, whimper, squeak, scream and short scream) and ten non-tonal (churr, shriek, babble, click, boom, snort, screech, short screech, sniff and low click), of which ten call types (whimper, squeak, scream, short scream, churr, babble, snort, short screech, sniff and low click) were newly described by this study. This relatively extensive vocal repertoire, including one call type emitted during collective resting, indicates that this species possibly possesses a higher degree of sociality and cohesiveness than previously expected. High structural similarities were observed between calls produced by juveniles and sub-adults during caravanning and those produced by adult males during courtship. Therefore, the results of this study support a previously suggested hypothesis that in shrews, adult courtship calls are derived from calls emitted by the young. The results of this study also showed that the largest changes in the ontogeny of the vocal repertoire occurred at approximately 10 days old and was in close connection to the eyes opening. The results are discussed with available information on the vocal repertoires of other soricids.     

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.