BIOACOUSTIC PUBLICATIONS, 1988

ABSTRACT

We examined vocalisations of a solitary subterranean rodent, the Silvery Mole-rat Heliophobius argenteocinereus (Bathyergidae). Seven true vocalisations and one mechanical vocalisation were identified. The main frequencies of the analysed sounds (0.34–13.17 kHz) match to a great extent the frequency range suitable for transmission in underground burrows. Due to the narrow frequency range of vocalisations, motivation is predominantly expressed by the rate of tonality rather than by frequency changes. The vocal repertoire of the Silvery Mole-rat perfectly matches to Morton's MS rules, i.e. that low-frequency and harsh vocalisations indicate hostility whereas high tonal calls signalise appeasement or fear. In comparison with social species, this solitary bathyergid produces fewer calls. It lacks contact and alarm calls, but has a rich repertoire of mating calls (mating ends with duet vocalization of male and female). Acoustic signals seem to play a major role in lowering natural aggressiveness during the mating period.     

EQUIPMENT REVIEW

ABSTRACT

The Northern White Rhinoceros Ceratotherium simum cottoni is a subspecies of the White Rhino that is almost extinct in the wild. We studied the last reproducing herd kept in Zoo Dvur Kralove to describe its vocal repertoire. The calls produced by eight individuals were recorded and analysed as concerned both sound properties and behavioural contexts in which they were emitted. We distinguished 11 calls belonging to four categories: (1) tonal harmonic sounds, (2) puffing sounds, (3) growling sounds, and (4) repetitive sounds. We found an apparent similarity between acoustic parameters of homologous calls recorded in both white rhino subspecies. We further confirmed that the repertoire of white rhino calls is much larger than that reported in other rhino species. We tentatively interpret this finding as an adaptation to increased sociality. Four calls reach the infrasound range; nevertheless, they are probably not used for communication over distance. This is obvious in the case of the grouch call, which contains the highest infrasound component. There are, however, other candidates for such a communication function: the repetitive pant sound, which is not known in other rhino species. We hypothesise that the repetitions may enhance their audibility in the typical open habitats of white rhinos.     

SOCIETY FOR EXPERIMENTAL BIOLOGY CONFERENCE,UNIVERSITY OF ST. ANDREWS,APRIL 1995

We describe the interactive nature of vocalizations emitted by African elephant (Loxodonta africana) family groups while visiting waterholes. Despite being in close visual contact with each other, individuals called interactively within a series of overlapping or antiphonal vocal bouts that increased significantly while departing from the waterhole. After initiating departure from the waterhole, elephants in this study increased their calling rate and their production of overlapping vocal bouts. The majority of calls either overlapped or occurred within 1.5 seconds of another call as part of an antiphonal bout, rather than as isolated calls. The departure of larger herds was accompanied by a greater number of calling bouts. The increase in interactive antiphonal bouts during departure might serve to facilitate group coordination and cohesion, as well as possibly reinforce social bonds. The longer repeated bouts could also facilitate eavesdropping by distant elephants by boosting signal detection since the repetition of these longer calls may yield an increase in the signal-to-noise ratio (SNR) that reduces the noise floor for better longer distance communication.     

Subharmonics increase the auditory impact of female koala rejection calls

Although non‐linear phenomena are common in human and non‐human animal vocalisations, their functional relevance remains poorly understood. One theory posits that non‐linear phenomena generate unpredictability in vocalisations, which increases the auditory impact of vocal signals, and makes animals less likely to habituate to call repetition. Female koalas (Phascolarctos cinereus) produce vocal signals when they reject male copulation attempts that contain relatively high levels of non‐linear phenomena, and thus may function as attention grabbing vocal signals during the breeding season. To test this hypothesis, we used playback experiments: firstly, to determine whether female rejection calls induce heightened behavioural responses in free‐ranging male koalas during the breeding season, and secondly, to examine how the relative amount of non‐linear phenomena in rejection calls influences male behavioural response. The results show that male koalas look for longer towards speakers broadcasting playback sequences of male bellows followed by a series of female rejection calls than those broadcasting only male bellows. In addition, female rejection call sequences with more subharmonics, higher harmonics‐to‐noise ratios, and less biphonation produced the greatest male looking responses. Our findings support the hypothesis that female koala rejection calls function to grab male attention during the breeding season, and indicate that subharmonics are the main acoustic feature that increases the auditory impact of these vocal signals.     

Maternal presence influences vocal development in the Japanese quail (Coturnix c. japonica)

Social influences on vocal development of young birds have been widely studied in oscine songbirds who learn to sing by vocal imitation of conspecifics, mainly male adults. In contrast, vocal development of non-vocal learners such as Galliformes is considered as being under strong genetic influence and independent of the social environment. In this study, we investigated the role of the mother on the vocal development of young Japanese quail (Coturnix coturnix japonica). We compared the vocal development of mothered and non-mothered chicks during the first 21 days of life. We analysed the structural changes of two vocalisations: a) the rally call, emitted during long-distance communication and in stressful situations, b) the contact call, emitted during short-distance communication when chicks are in visual and/or auditory contact with congeners. We showed that temporal and spectral structures of the two types of calls changed during development and differed between mothered and non-mothered chicks. These results demonstrate that maternal presence influences the vocal development of the young in the Japanese quail. Even if the adaptive value of such changes was not assessed, these results highlight that plasticity of vocalisations in species considered as non-vocal learners has been underestimated.     

EQUIPMENT REVIEWS

ABSTRACT

Research on African elephant (Loxodonta africana) vocal communication has increased in recent years, yet there has been very little data collected on the vocal production of infant African elephants. Vocalizations were recorded from a group of five adult female African elephants and 3 dependent offspring (1 male and 2 female) at Disney's Animal Kingdom, Florida, U.S.A., using custom-designed audio-recording collars worn by the adult females. We measured both source and filter features of infant ‘rumble’ vocalizations made during affiliative social interactions and after cessation of nursing from adult females. Rumble vocalizations produced in the ‘nurse cessation’ context exhibited an upward shift in formant frequency locations, compared to rumbles produced during the ‘affiliation’ context. Additionally, call duration increased and fundamental frequencies decreased after nurse cessations for the male, but both females showed the opposite acoustic response. When infant rumbles accompanied nurse cessations, nursing was more likely to resume within 30 seconds compared to nurse cessations without vocalizations. These results suggest that infant rumbles associated with cessation of nursing reflect the motivational state of infants and may influence maternal responsiveness.     

The Acoustic Structure and Information Content of Female Koala Vocal Signals

Determining the information content of animal vocalisations can give valuable insights into the potential functions of vocal signals. The source-filter theory of vocal production allows researchers to examine the information content of mammal vocalisations by linking variation in acoustic features with variation in relevant physical characteristics of the caller. Here I used a source-filter theory approach to classify female koala vocalisations into different call-types, and determine which acoustic features have the potential to convey important information about the caller to other conspecifics. A two-step cluster analysis classified female calls into bellows, snarls and tonal rejection calls. Additional results revealed that female koala vocalisations differed in their potential to provide information about a given caller’s phenotype that may be of importance to receivers. Female snarls did not contain reliable acoustic cues to the caller’s identity and age. In contrast, female bellows and tonal rejection calls were individually distinctive, and the tonal rejection calls of older female koalas had consistently lower mean, minimum and maximum fundamental frequency. In addition, female bellows were significantly shorter in duration and had higher fundamental frequency, formant frequencies, and formant frequency spacing than male bellows. These results indicate that female koala vocalisations have the potential to signal the caller’s identity, age and sex. I go on to discuss the anatomical basis for these findings, and consider the possible functional relevance of signalling this type of information in the koala’s natural habitat.     

BIOACOUSTIC PUBLICATIONS, 1989

ABSTRACT

Coruros Spalacopus cyanus, social fossorial rodents from Chile, use a complex acoustic repertoire with eleven different true vocalisations and one mechanical sound in various behavioural contexts. The complex of contact calls is particularly well differentiated. Juvenile coruros produced six true vocalisations of which four were structurally identical to adult calls. One vocalisation had components of two adult sounds and one occurred only in juvenile animals. Certain calls from the adult repertoire were lacking. The frequencies of sounds of juveniles were considerably higher than those of adults, with many sounds reaching the ultrasonic range. Nevertheless, pure ultrasonic sounds were not recorded.

The frequencies of the analysed sounds of coruros extended from 0.17 to 20.33 kHz with dominant frequency components between 0.17 and 10 kHz. The acoustic properties of calls are suitable for transmission above and below ground, thus providing further indirect evidence that coruros are not strictly confined to an underground way of life. Indeed, the great variability of frequency ranges, with lower frequencies always being included, reflects a specialisation for communication in variable acoustic environments.

The most distinctive and unique vocalisation of coruros is the long duration musical trilling (lasting up to two minutes), which is a long-distance call emitted in alarm and arousal contexts. Recordings of this call from natural burrows in the field in Chile showed similar structural features to vocalisations from captive colonies in the laboratory.

Our findings provide a further example of matching physical properties of vocalisations to the acoustic conditions of the habitat. However, vocalisations in subterranean rodents consist almost exclusively of short-distance calls, the trilling of coruros being the notable exception. Since the selective pressure of the acoustic environment upon the evolution of short-distance vocalisations is probably minimal, we suggest that during their evolution, subterranean mammals have matched their vocalisations primarily to their hearing range and not directly to the acoustics underground. Hearing probably has been the primary target of natural selection, serving not only for communication but also for detection of predators (and, in carnivores, of prey).     

Social vocal communication in captive Pacific walruses Odobenus rosmarus divergens

Walrus are highly gregarious pinnipeds that can form herds of several hundreds or thousands of individuals when hauling out on ice or on land. They produce vocalisations in almost all social interactions, from aggressive vocalisations, contact calls involved in mother–calf bond to adult–adult communication to stereotyped courtship display during the mating season. The knowledge on walrus’ vocal behaviour and its perceptual abilities is limited due to the extreme difficulty of studying these animals in their natural environment. In the present study, we reported the results of a pilot experimental work on group/social vocal communication in captive Pacific Walruses (Odobenus rosmarus divergens). By analysing the main vocalisations produced by females and males during social interactions, we found some differences in their call characteristics compared to the Atlantic subspecies. In a second step, we experimentally demonstrated the abilities of females and mature males to discriminate between vocalizations of individuals from their own group and those of unknown individuals. In spite of the low sample size of animals, these findings on captive walruses improved knowledge of the cognitive abilities of this endemic Arctic species.     

RECENT BIOACOUSTIC PUBLICATIONS—from 1991 and a few from 1990 and 1989

ABSTRACT

The focus of this study was to determine whether individual vocal identification of Scops Owls Otus scops was possible and if there was a stability of the hoot-calls over a short time period in the same individuals. Spontaneous vocalizations of 13 owls were recorded in 2004 in Southern Tuscany, Italy. Visual analysis of spectrograms and quantitative multivariate analysis of six vocal features showed marked individual differences. In some owls a repertoire of two different hoot types was found. In 2005, 10 Scops owls were recorded three times in the same breeding season (2 hours and 10 days after the first session). Statistical analysis of data showed that 60% of owls did not change call features over time. However a slight but significant variability between successive vocal performances of the same owl was found in 40% of cases. This variability may decrease the recognition power by acoustic analysis. To overcome this obstacle I suggest a multi step qualitative/quantitative approach. A Difference Index (DI) was calculated to set a threshold between the slight intra-individual and the very high inter-individual variability. This method allowed the recognition of calls of each owl recorded over time in 2005.     

Invited review: The evolution of cattle bioacoustics and application for advanced dairy systems

Vocalisations are commonly expressed by gregarious animals, including cattle, as a form of short- and long-distance communication. They can provide conspecifics with meaningful information about the physiology, affective state and physical attributes of the caller. In cattle, calls are individually distinct meaning they assist animals to identify specific individuals in the herd. Consequently, there is potential for these vocalisations to be acoustically analysed to make inferences about how individual animals or herds are coping with their external surroundings, and then act on these signals to improve feed conversion efficiency, reproductive efficiency and welfare. In the case of dairy farming, where herd sizes are expanding and farmers are becoming more reliant on technologies to assist in the monitoring of cattle, the study of vocal behaviour could provide an objective, cost effective and non-invasive alternative to traditional measures of welfare. The vocalisations of cattle in response to calf separation, social isolation and painful husbandry procedures, alongside changes to feeding and oestrous activity are here reviewed. For future application of sound technology, research is first necessary to analyse the acoustic structure of cattle vocalisations and determine the specific information they encode. This review draws together the latest research in field of cattle bioacoustics highlighting how the source–filter theory and affective state dimensional approach can be adopted to decode this information and improve on-farm management.     

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.     

Individual variation in pup vocalizations and absence of behavioral signs of maternal vocal recognition in Weddell seals (Leptonychotes weddellii)

Individually stereotyped vocalizations often play an important role in relocation of offspring in gregarious breeders. In phocids, mothers often alternate between foraging at sea and attending their pup. Pup calls are individually distinctive in various phocid species. However, experimental evidence for maternal recognition is rare. In this study, we recorded Weddell seal (Leptonychotes weddellii) pup vocalizations at two whelping patches in Atka Bay, Antarctica, and explored individual vocal variation based on eight vocal parameters. Overall, 58% of calls were correctly classified according to individual. For males (n= 12) and females (n= 9), respectively, nine and seven individuals were correctly identified based on vocal parameters. To investigate whether mothers respond differently to calls of familiar vs. unfamiliar pups, we conducted playback experiments with 21 mothers. Maternal responses did not differ between playbacks of own, familiar, and unfamiliar pup calls. We suggest that Weddell seal pup calls may need to contain only a critical amount of individually distinct information because mothers and pups use a combination of sensory modalities for identification. However, it cannot be excluded that pup developmental factors and differing environmental factors between colonies affect pup acoustic behavior and the role of acoustic cues in the relocation process.     

DEVELOPMENT OF VOCALISATIONS IN NESTLING AND FLEDGLING HOUSE WRENS IN NATURAL POPULATIONS

ABSTRACT

We conducted a field study of the ontogeny of vocal signals in the house wren Troglodytes aedon during the nestling and fledgling phases of life. We did spectrographic analyses and quantification of the developmental changes that occurred in the acoustic features of the vocalisations. Evidence of progress to adult-like vocal patterns was of two types. First, nestling calls changed into a harsh-sounding call that resembles the adult chatter call, functionally a warning call. Second, fledglings also uttered subsong, and these vocalisations were similar to notes typical of adult male song. When the vocalisations produced by developing young were broken down into their constituent vocal features, we found that the time course of development was not strictly linear. Instead of a unidirectional change through the course of nestling and fledgling life, the trajectories of the vocal features fluctuated through time and sometimes exhibited abrupt changes. These sudden shifts occurred during nestling life as well as at the time of fledging. We speculate on the possible causes of these abrupt transitions. Changes in acoustic features upon fledging appear to be linked to new social functions.     

Quality prevails over identity in the sexually selected vocalisations of an ageing mammal

Background

Male sexually selected vocalisations generally contain both individuality and quality cues that are crucial in intra- as well as inter-sexual communication. As individuality is a fixed feature whereas male phenotypic quality changes with age, individuality and quality cues may be subjected to different selection pressures over time. Individuality (for example, morphology of the vocal apparatus) and quality (for example, body size and dominance status) can both affect the vocal production mechanism, inducing the same components of vocalisations to convey both kinds of information. In this case, do quality-related changes to the acoustic structure of calls induce a modification of vocal cues to identity from year to year? We investigated this question in fallow deer (Dama dama), in which some acoustic parameters of vocalisations (groans) code for both individuality and quality.

Results

We carried out a longitudinal analysis of groan individuality, examining the effects of age and dominance rank on the acoustic structure of groans of the same males recorded during consecutive years. We found both age- and rank-related changes to groans; the minimum values of the highest formant frequencies and the fundamental frequency increased with the age of males and they decreased when males became more dominant. Both age- and rank-related acoustic parameters contributed to individuality. Male quality changed with age, inducing a change in quality-related parameters and thus, a modification of vocal cues to male individuality between years.

Conclusions

The encoding of individuality and quality information in the same components of vocalisations induces a tradeoff between these two kinds of signals over time. Fallow deer vocalisations are honest signals of quality that are not fixed over time but are modified dynamically according to male quality. As they are more reliable cues to quality than to individuality, they may not be used by conspecifics to recognize a given male from one year to another, but potentially used by both sexes to assess male quality during each breeding season.

     

Social associations and vocal communication in wild and captive male savannah elephants Loxodonta africana

相似文献   

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.     

STRUCTURE AND FUNCTION OF RED FOX VULPES VULPES VOCALISATIONS

ABSTRACT

A sonagraphic analysis of the structure of fox vocalisations, based on 512 adult and 73 cub vocalisations obtained from archive recordings, was combined with field data on the vocal behaviour of an urban fox population. Calls were described quantitatively by six variables: duration, lowest and second lowest frequency bands (from sonagrams), highest and second highest peak frequencies (from power spectra) and the number of components. They were separated into 20 call types, eight of which were cub vocalisations. Call types were used singly or in combination, and some gradation between particular call types was apparent. Hypotheses regarding call function were generated based on the matching of acoustic properties with their seasonal occurrence and the socioecological pressures acting on foxes at different times of the year. Calls that were structurally suited to agonistic and contact functions were found to be significantly more common during the winter, the time of mating and dispersal, when foxes move over greater areas.