A preliminary study of vocal communication in wild long-tailed macaques (Macaca fascicularis). I. Vocal repertoire and call emission

Vocal communication in wild long-tailed macaques (Macaca fascicularis) is described in terms of (1) a preliminary vocal repertoire and the situations in which calls occur in the natural habitat of this species and (2) quantitative measurement of the natural occurrence of calls in the field. Although a number of calls are relatively discrete (e.g., a male loud call), gradation is pronounced for both wide-spectrum (“harsh”) and narrow-spectrum (“clear”) vocal signals. Thirteen general types of harsh calls are identified provisionally as elements of the vocal repertoire. The exact number of discrete clear calls contributing to the vocal repertoire could not be ascertained precisely, but these calls were classified operationally into six broadly acoustically different classes in order to measure natural vocal behavior. Vocalizations tended to occur in temporal “clusters” during sample, periods. Narrow-band clear or “coo” calls were more frequently performed by macaques than wide-band harsh calls. The possible functional implications of the correlated occurrence of multiple vocal signals are discussed.     

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.     

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.     

Age- and sex-specific patterns of vocal behavior in De Brazza's monkeys (Cercopithecus neglectus)

Although vocal production is strongly genetically determined in nonhuman primates, vocal usage is more likely to be influenced by experience. Nonetheless, sex differences in both production and usage can be found in the vocal repertoire of adults, but little attention has been paid to their ontogeny. Here, we provide the first comprehensive analysis of the vocal repertoire of De Brazza's monkeys (Cercopithecus neglectus), with particular attention to age- and sex-specific patterns. This species has special interest because it is the only monogamous species of guenons, but it nevertheless shares the strong sexual morphological and behavioral dimorphism seen in other guenons. A structurally based classification of calls recorded in 23 captive individuals has been cross-validated by an analysis of the associated contexts of emission. We identified sound units that could be uttered alone or concatenated to form 10 call types, including only three types shared by all age-sex-classes. Both age- and sex-discrepancy in terms of phonation could be explained by maturational changes and morphological dimorphism. In general, call production and usage parallel those seen in other guenons, suggesting that phylogeny and sexual dimorphism play important roles in vocal communication in this species. However, the boundary between adult male and female vocal repertoires appeared to be less strict than previously reported, suggesting that both sexes have the capacity to produce calls of the other sex but that social roles may constrain this expression. Similarly, age-specific vocal patterns would reflect respective social roles, and experience to some extent. Finally, calling rates would reflect age-/sex-specific degree of involvement in intragroup social networks. These findings highlight the relative importance of phylogeny, morphology, and social system on the shaping of individual repertoires in nonhuman primates.     

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.     

Brays and bits: information theory applied to acoustic communication sequences of bottlenose dolphins

Acoustic call sequences are important components of vocal repertoires for many animal species. Bottlenose dolphins (Tursiops truncatus) produce a wide variety of vocalizations, in different behavioural contexts, including some conspicuous vocal sequences – the ‘bray series’. The occurrence of brays is still insufficiently documented, contextually and geographically, and the specific functions of these multi-unit emissions are yet to be understood. Here, acoustic emissions produced by bottlenose dolphins in the Sado estuary, Portugal, were used to provide a structural characterization of the discrete elements that compose the bray series. Information theory techniques were applied to analyse bray sequences and explore the complexity of these calls. Log-frequency analysis, based on bout criterion interval, confirmed the bout structure of the bray series. A first-order Markov model revealed a distinct pattern of emission for the bray series’ elements, with uneven transitions between elements. The order in these sequential emissions was not random and consecutive decreases in higher order entropy values support the notion of a well-defined structure in the bray series. The key features of animal signal sequences here portrayed suggest the presence of relevant information content and highlight the complexity of the bottlenose dolphin’s acoustic repertoire.     

Development of vocal behaviour in Peking ducklings

Vocal communication appears to play an important role in maintaining group cohesion in broods of Peking ducklings (Anas platyrhynchos). In order to describe the development of the vocal repertoire of the young, the present study examined the vocalizations of six ducklings from several hours before hatching through 48 h posthatching. Vocalizations were recorded in standardized situations in the laboratory, including the presence of conspecific peers, exposure to maternal calls, and social isolation. A major methodological aim of the present study was to determine whether the vocal repertoire of the ducklings would sort itself on objectively measured acoustic features without the necessity of experimenter preclassification (as has been relied upon in the past). This objective procedure produced two acoustically distinct (and conventional) types: (a) contentment calls, which have short note durations, fast repetition rates, and low pitch, and are elicited by the presence of peers and/or the maternal call; (b) distress calls, with longer note durations, slower repetition rates, and higher pitch, which are uttered in social isolation and emerge in mature form only after hatching. A simple physiological model based on respiratory activity is proposed to account for the acoustic variation between the two vocalization types.     

Vocal repertoire of cooperatively breeding Smooth‐billed Anis

Calls are functionally diverse signals that mediate behavior in a wide variety of contexts in both passerines and non‐passerines. However, the call‐based acoustic communication systems of non‐passerines have received less attention from investigators than those of passerines. We examined the vocal repertoire of Smooth‐billed Anis (Crotophaga ani), cooperatively breeding cuckoos that live in groups with multiple breeding pairs. We recorded calls from 22 groups over two breeding seasons at the Cabo Rojo National Wildlife Refuge in Puerto Rico. We identified 11 call types and one group vocalization, and used an automated sound measurement program to quantify their acoustic features. Discriminant function analysis (DFA) correctly classified 74.2% of calls based on these features. The vocal repertoire of Smooth‐billed Anis is larger than that reported for the three other species in the subfamily Crotophaginae. Smooth‐billed Anis have at least two alarm calls, two nest‐specific calls, and one nest defense call. We also identified one possible signal of aggressive intent, one possible appeasement signal, and two calls that may communicate identity. The relatively large vocal repertoire of Smooth‐billed Anis and association of distinct call types with different functions and contexts supports the main prediction of the social complexity hypothesis, i.e., species with more complex social systems will have more complex communication systems.     

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.     

Cultural transmission of vocalizations in ravens, Corvus corax

As ravens have pronounced learning capabilities, especially in the vocal domain, cultural transmission might be a relevant factor affecting the composition of their vocal repertoires. We investigated how important cultural transmission is in establishing a raven's vocal repertoire and whether there are different pathways of transmission. We studied individually known free-ranging breeding pairs whose vocalizations were recorded during interactions with a caged pair. The mean repertoire size of these vocalizations was 12 call types per individual (from 79 types recorded from 74 individuals), with no difference between the sexes. In 81% of individuals the repertoire was composed entirely of calls also used by other individuals. Analysis of the distribution of call types among individuals regarding sex, partnership and neighbourhood and aspects of the geographical distribution of calls showed that the main pathway of cultural transmission was within the sexes. In addition, transmission occurred between pair partners, as well as between neighbouring and more distant pairs. About 40% of the calls in a raven's repertoire were transmitted within a sex and 10% between pair partners. Any two given birds in the population shared on average 20% (0-77%) of their calls. Cultural transmission within the sexes led to a pronounced sexual dimorphism in vocal behaviour. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Stereotyped acoustic signals of the killer whale <Emphasis Type="Italic">Orcinus orca</Emphasis> (Cetacea: Delphinidae) from the Northwestern Pacific

In this paper the classification of the discrete calls of killer whales recorded in the Northwest Pacific is presented. It was shown that most of the calls can be divided into 20 discrete types easily distinguished by ear. The frequency parameters of the sounds made the maximum contribution into discrimination between call types, while their temporal parameters turned out to be less significant. The repertoires of stereotyped calls of killer whales from Chukot, Kamchatka, and the Commander and Kurile Islands were similar, due to the presence of shared types of calls. The greater the distance between the above-mentioned regions the fewer calls were shared by the resident killer whales. High vocal activity and the phenotypic features of the surveyed killer whales implied their attribution to the resident ecological type.     

Microgeographic Variation and Sharing of the Gargle Vocalization and Its Component Syllables in Black-Capped Chickadee (Aves, Paridae, Poecile atricapillus) Populations

Throughout the year during agonistic encounters, black‐capped chickadees (Poecile atricapillus) emit a vocal signal known as the gargle call. Each bird has a repertoire of structurally differing gargle calls; some are shared with others in the local area. As a basis for understanding the cultural evolution of this social signal, we initiated a study of gargle call repertoires of birds living in a narrow belt of continuous riparian habitat occupied throughout by a resident population of chickadees. During two consecutive winter seasons, we sampled repertoires at three locations over a distance of 8.4 km to quantify micro‐geographical variation. Analyses of vocal sharing and population differentiation were carried out on whole gargle calls and on the individual acoustic units (syllables) from which the whole calls are constructed. We analysed 28 380 calls of 46 subjects in the two seasons of study. Birds averaged 7.6 different calls in their gargle repertoires. Calls were composed of about 10 syllables on average. Fifty‐six different syllables were used to construct the calls of all birds. Each study site had some gargle calls unique to the local birds and some that were shared with one or both of the other two sites. There was significantly greater sharing of both calls and syllables among birds within sample sites than between sample sites. The frequencies of the different kinds of gargles and syllables were significantly correlated across the 2 yr of the study, but the correlation was stronger (r² = 0.93) for syllables than for whole gargle calls (r² = 0.61).     

Selection for acoustic individuality within the vocal repertoire of wild chimpanzees

Individual primates typically produce acoustically distinct calls. To investigate the factors that facilitate the evolution of individual vocal signatures, we examined two components of the call repertoire of chimpanzees: the pant hoot and pant grunt. Pant hoots are long-distance signals whose recipients can be several hundred meters away, while pant grunts are short-range calls given to conspecifics within close visual range. Given their markedly different contexts of emission, we predicted that natural selection would favor the elaboration of individually distinctive acoustic features in pant hoots compared with pant grunts. Analyses of nine acoustic features revealed that pant hoots are more stereotyped within-individuals and variable between-individuals than pant grunts. These data are consistent with the hypothesis that selection may act to encode varying degrees of individuality in different components of the vocal repertoire of a single species.     

VOCAL BEHAVIOUR AND CALL DEVELOPMENT IN THE BULLFINCH (PYRRHULA PYRRHULA)

ABSTRACT

A sonagraphic analysis of the vocalizations of bullfinches Pyrrhula pyrrhula is presented and their behavioural contexts and functions noted. The vocal repertoire of the bullfinch is compared to that of other finches with particular attention to repertoire size and sexual specificity; the repertoire of 14–17 vocal categories is comparatively greater than that of most carduelines and the majority of vocalizations were given by both sexes. The development of nestling, fledgling and some adult calls is described. Early vocal ontogeny in the bullfinch was similar to that previously described for the chaffinch. The earliest recorded calls of nestling bullfinches showed a single fundamental. The independent use of two sound sources became apparent on the second day after hatching and the major elements of the three best studied call types were all derived from the lower fundamental of the nestling begging call.     

Horizontal transmission of vocal traditions in killer whale (<Emphasis Type="Italic">Orcinus orca</Emphasis>) dialects

Unlike most other mammals, killer whales are capable of vocal learning and learn the dialect of their natal pod from their mothers. The classical model of killer whale dialect development suggests that the repertoire of calls is learned only “vertically” from mother to offspring, and calls evolve gradually with time by random drift caused by the accumulation of copying errors. However, some observations suggest that not only “vertical” (from mother to offspring) vocal learning can occur in killer whales, but also “horizontal” (between adult animals). In this study we analyzed the distribution of different call types and similarity of calls from the same type in different pods of killer whales from Kamchatka waters to estimate the probability of existence of interpod horizontal transmission of vocal traditions in killer whales. We found that the degree of similarity of K1 calls and K5 calls in different pods can differ. This situation contradicts the classical hypothesis and is possible in two cases: if different call types change with various speed in different pods, or if horizontal transmission of call features takes place. The distribution of K4 and K10 call types across pods also suggests the existence of horizontal transmission: K4 calls occur in the dialects of five of ten pods, and K10 calls, in six of ten pods, but only one pod has both K4 and K10 calls. Our results suggest that the real picture of the distribution of call features and call types in killer whale dialects contradicts the classical hypothesis of killer whale dialect evolution through the accumulation of copying errors.