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.     

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.     

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.     

Rhesus monkey (Macaca mulatta) screams: Representational signalling in the recruitment of agonistic aid

Free-ranging rhesus monkeys on Cayo Santiago (Puerto Rico) give five acoustically distinct scream vocalizations during agonistic encounters. These calls are thought to be an important mechanism in the recruitment of support from allies against opponents. Alliance formation during agonistic encounters is known to vary with the dominance rank and matrilineal relatedness of opponents, as well as with the severity of aggression. In contrast to previous interpretations of screams as graded signals reflecting the level of arousal of the caller, we found these calls to be much more discrete, with each of the five acoustic types significantly associated with a particular class of opponent and level of physical aggression. We performed a series of field experiments in which tape-recorded screams of immature rhesus monkeys were played to their mothers in the absence of any other information. The results suggest that the information necessary for differential responses is conveyed by the scream vocalizations themselves. We conclude that screams are representational signals that refer to external objects and events and function in the system of agonistic alliance formation.     

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.     

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.     

The use of Vocalizations of the Sambirano Mouse Lemur (<Emphasis Type="Italic">Microcebus sambiranensis</Emphasis>) in an Acoustic Survey of Habitat Preference

Primate vocalizations convey a variety of information to conspecifics. The acoustic traits of these vocalizations are an effective vocal fingerprint to discriminate between sibling species for taxonomic diagnosis. However, the vocal behavior of nocturnal primates has been poorly studied and there are few studies of their vocal repertoires. We compiled a vocal repertoire for the Endangered Sambirano mouse lemur, Microcebus sambiranensis, an unstudied nocturnal primate of northwestern Madagascar, and compared the acoustic properties of one of their call types to those of M. murinus and M. rufus. We recorded vocalizations from radio-collared individuals using handheld recorders over 3 months. We also conducted an acoustic survey to measure the vocal activity of M. sambiranensis in four forest habitat types at the study site. We identified and classified five vocalization types in M. sambiranensis. The vocal repertoires of the three Microcebus species contain very similar call types but have different acoustic properties, with one loud call type, the whistle, having significantly different acoustic properties between species. Our acoustic survey detected more calls of M. sambiranensis in secondary forest, riparian forest, and forest edge habitats, suggesting that individuals may prefer these habitat types over primary forest. Our results suggest interspecific differences in the vocal repertoire of mouse lemurs, and that these differences can be used to investigate habitat preference via acoustic surveys.     

Sound production in <Emphasis Type="Italic">Etheostoma oophylax</Emphasis> (Percidae) and call characteristics correlated to body size

Sound production in fishes is common in marine and freshwater species, however there are still many vocal species for which sound production has not been documented. This paper is the first account of sound production in the Guardian Darter (Etheostoma oophylax). Laboratory recordings revealed that males produced several vocalizations, including single pulse knocks, multi-pulsed purrs, and tonal drums. All vocalizations were documented during agonistic and courtship encounters, including spawning. We also investigated possible correlations between call characteristics and male size. Male standard length was found to be correlated to inter-pulse interval of purrs, as well as the slope of the drum vocalizations. Determining a link between male size and acoustic characteristics could be the first step in documenting mate or male-male assessment by acoustic communication in darters.     

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.     

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.     

Call-based species recognition in black-capped chickadees

Species recognition is essential for efficient communication between conspecifics. For this to occur, species information must be unambiguously encoded in the repertoire of each species’ vocalizations. Until now, the study of species recognition in songbirds has been focused mainly on male songs and male territorial behaviour. Species recognition of other learned vocalizations, such as calls, have not been explored, and could prove useful as calls are used in a wider range of contexts. Here, we present an experimental field study investigating the coding of species information in a learned vocalization, the ‘chick-a-dee’ call of the black-capped chickadee (Poecile atricapillus). By modifying natural calls in both temporal and spectral domains and by observing the vocal responses of black-capped chickadees following the playback of these modified calls, we demonstrate that species recognition in chickadees relies on several acoustic features including syntax, frequency modulation, amplitude modulation, and to a lesser extent, call rhythmicity and frequency range.     

A field study on the vocalizations of Goeldi's monkeys (Callimico goeldii)

The vocalizations ofCallimico goeldii inhabiting North Bolivia were recorded and analyzed. A total vocal repertoire of 40, including two ultrasonic vocalizations, was recognized. The situation in which each vocalization was emitted is described. The phonetic structure of the longdistance location calls varied precisely dependent on the interindividual distances, while distinct individual variations were seen in the short-distance location calls. Every agonistic call could grade into another, from that reflecting the most aggressive tendency to that of fear emotion. The repertoire and characteristics of the infantile calls are also described, and their ontogeny is discussed.     

Vocal learning by greater spear-nosed bats.

Vocal learning is well known among passerine and psittacine birds, but most data on mammals are equivocal. Specific benefits of vocal learning are poorly understood for most species. One case where vocal learning should be favoured by selection is where calls indicate group membership and group mates are unrelated. Female greater spear-nosed bats, Phyllostomus hastatus, live in stable groups of unrelated bats and use loud, broadband calls to coordinate foraging movements of social group mates. Bats benefit from group foraging. Calls differ between female social groups and cave colonies, and playback experiments demonstrate that bats perceive these acoustic differences. Here I show that the group distinctive structure of calls arises through vocal learning. Females change call structure when group composition changes, resulting in increased similarity among new social group mates. Comparisons of transfers with age-matched half-sibs indicate that call changes are not simply due to maturation, the physical environment or heredity. These results suggest that studies testing vocal learning in mammals could profit by focusing on vocalizations that signify group membership.     

Vocal signature in capybara,Hydrochoerus hydrochaeris

Social groups of capybaras are stable and cohesive. The species’ vocal communication is complex and mediates social interaction. The click call is emitted in a variety of contexts by animals from all age groups, but differs among groups; its attributed function is to keep contact among animals. To evaluate the presence of individual characteristics in the click call of capybaras, we recorded the vocalizations emitted spontaneously by six adults kept either solitary or in groups. We selected and measured the acoustic parameters of 300 click call phrases, 50 per individual. The parameters were submitted to a discriminant function analysis that revealed a classification accuracy of 76.8 %. A General Linear Model analysis revealed significant differences among the six individuals, and post hoc results showed that differences between a given pair were different from those of any other pair. The acoustic parameters that most contributed to discriminate the individual calls were click interval duration and click duration, suggesting that temporal parameters are more important than frequency parameters for individuals’ discrimination. The findings of individual characteristics in the click calls indicate that these vocalizations can be used as vocal signatures during social interactions.     

Territorial vocalization in sympatric damselfish: acoustic characteristics and intruder discrimination

Damselfishes are well known for their aggressive, territorial behaviour during which the use of vocalization behaviour has been well documented. However, agonistic acoustic signalling has been understudied in particular when the vocalizations are interspecific. In this study, we characterize and compare the previously undescribed vocalization behaviour of longfin damselfish (Stegastes diencaeus), in an agonistic context, with the closely related and sympatric dusky damselfish (Stegastes adustus). Next, we examined if these congeneric species modulate their vocalizations in a similar pattern to previously described aggressive behaviour patterns. Audio field recordings of territorial males were obtained in response to three separate stimuli: (1) conspecific male damselfish, (2) heterospecific male damselfish and (3) a common intruder, the slippery dick wrasse (Halichoeres bivittatus). The vocal repertoires of both longfin and dusky damselfish comprised the same three distinct call types: chirps, pops and pulse trains. However, temporal measures of the calls showed significant differences between species. Additionally, dusky damselfish were more vocal overall, producing more calls and spending more time calling than longfin damselfish. These responses were stimulus and species dependent, as the two species modulated acoustic response by modulating pulse number based on intruder species. These results suggest that these closely related species of damselfish use vocalization behaviours that are both unique and context dependent.     

The Vocal Repertoire of Barbary Macaques: A Quantitative Analysis of a Graded Signal System

The vocal behavior of Barbary macaques (Macaca sylvanus) was studied in an outdoor enclosure at Rocamadour, France. Ad libitum recordings were made across a broad array of socioecological contexts from 92 individually identified subjects from all age—sex classes. From the recordings, 8479 calls were sampled and submitted to a Fourier transform. A custom software program was used to determine 35 acoustic parameters describing the call in terms of its frequency and time dynamics. On these parameters a cluster analysis was used to examine the acoustic morphology of the Barbary macaque vocal repertoire. The analysis revealed a highly graded structure with intergraded variations between different clusters (‘call types’). There were clear age-related preferences in usage of different clusters, but animals of all ages were potentially able to produce the whole array of call types. The major sex difference was a differential use of certain call types in specific situations. Despite a clear sex dimorphism in body size no significant sex differences in the acoustic structure of calls in adults was found. There were no unidirectional relationships between the acoustic structure of a call and the context in which it was uttered, although call usage was more specific in some contexts than in others. The results suggest that the major factor underlying the variation in acoustic structure reflect the internal state of the caller.