Vocal Signals Research Articles

Individual Signature in a Lekking Species: Visual and Acoustic Courtship Parameters May Help Discriminating Conspecifics in the Houbara Bustard

AbstractSelection pressures acting on both intrasexual competition and intersexual relationships may lead to the emphasis of individual variation and might thus lead to the expression of individual signature. This is particularly true in lek mating systems, where providing information on identity and/or quality to potential mates or congeners of the same sex can be essential for individuals to optimize their reproductive success. Visual and acoustic signals produced during the courtship of the lekking North African Houbara bustard (Chlamydotis undulata undulata), based on field data from wild birds, are investigated here for the first time. Results show that the vocal signals, called booms, are characterized by a very low frequency, a rare phenomenon in birds which should allow booms to propagate over long distances. Results also show that both visual and acoustic signals are individualized and stereotyped between males. Using three methods of analysis, we highlight the acoustic parameters likely to support vocal individual signature and show that such information mainly relies on frequency parameters.

Rapid encoding of an internal model for imitative learning

As in human infant speech development, vocal imitation in songbirds involves sensory acquisition and memorization of adult-produced vocal signals, followed by a protracted phase of vocal motor practice. The internal model of adult tutor song in the juvenile male brain, termed ‘the template’, is central to the vocal imitation process. However, even the most fundamental aspects of the template, such as when, where and how it is encoded in the brain, remain poorly understood. A major impediment to progress is that current studies of songbird vocal learning use protracted tutoring over days, weeks or months, complicating dissection of the template encoding process. Here, we take the key step of tightly constraining the timing of template acquisition. We show that, in the zebra finch, template encoding can be time locked to, on average, a 2 h period of juvenile life and based on just 75 s of cumulative tutor song exposure. Crucially, we find that vocal changes occurring on the day of training correlate with eventual imitative success. This paradigm will lead to insights on how the template is instantiated in the songbird brain, with general implications for deciphering how internal models are formed to guide learning of complex social behaviours.

Mechanisms of noise robust representation of speech in primary auditory cortex.

Humans and animals can reliably perceive behaviorally relevant sounds in noisy and reverberant environments, yet the neural mechanisms behind this phenomenon are largely unknown. To understand how neural circuits represent degraded auditory stimuli with additive and reverberant distortions, we compared single-neuron responses in ferret primary auditory cortex to speech and vocalizations in four conditions: clean, additive white and pink (1/f) noise, and reverberation. Despite substantial distortion, responses of neurons to the vocalization signal remained stable, maintaining the same statistical distribution in all conditions. Stimulus spectrograms reconstructed from population responses to the distorted stimuli resembled more the original clean than the distorted signals. To explore mechanisms contributing to this robustness, we simulated neural responses using several spectrotemporal receptive field models that incorporated either a static nonlinearity or subtractive synaptic depression and multiplicative gain normalization. The static model failed to suppress the distortions. A dynamic model incorporating feed-forward synaptic depression could account for the reduction of additive noise, but only the combined model with feedback gain normalization was able to predict the effects across both additive and reverberant conditions. Thus, both mechanisms can contribute to the abilities of humans and animals to extract relevant sounds in diverse noisy environments.

Treating Distressed Animals as Participants: I Know Responses in Veterinarians’ Pet-Directed Talk

This article reports on video analyses of 110 veterinary appointments in which pet-directed I know receipts were uttered by 15 veterinarians as responses to companion animals’ vocal and visible signals of distress. Patients’ distress was typically occasioned by medical activities constituting the appointment. The dual functions of I know as a claim of (a) prior knowledge of animals’ experiences and (b) shared feelings and affiliation with animals’ experiences made it an interactional resource for addressing client anxiety arising from the disalignment of animal patients with the goals of the appointment. Analysis of prosody, prefacing, the presence or absence of repeats, and postpositioned components demonstrated the flexibility of the I know receipt in modulating veterinarians’ stances toward their patients’ expressions of distress. Findings are discussed in relation to studies on the management of patient distress and pain in pediatric procedures and to previous research on clinician–patient empathy in veterinary medicine. Data are in Canadian English.

A virtual environment for modeling the acquisition of vowel normalization

Vowel normalization is a computation that is meant to account for the differences in the absolute direct (physical or psychophysical) representations of qualitatively equivalent vowel productions that arise due to differences in speaker properties such as body size types, age, gender, and other socially interpreted categories that are based on natural variation in vocal tract size and shape. We present a virtual environment for vocal learning which provides the means to model the acquisition of vowel normalization, along with other aspects of vocal learning. The environment consists of models of caretaker agents representing five different language communities—American English, Cantonese, Greek, Japanese, and Korean—derived from vowel category perception experiments (Munson et al., 2010, Plummer et al., 2013) and models of infant agents (Plummer, 2012, 2013) that “vocally interact” with their caretakers. Moreover, we develop a model of caretaker social and vocal signaling in response to infant vowel productions, and of an infant's internalization of these signals and the internal computations over them. More broadly, we model the acquisition of vowel normalization within a developmental framework encompassing a suite of vocal learning phenomena, including language-specific caretaker vocal exchanges, perceptual warping, and multisensory matching and narrowing.

Dynamics of an Aggressive Vocalization in the Common Loon (Gavia immer): A Review

Unlike most waterbirds, Common Loons (Gavia immer) have a dynamic vocal repertoire that includes the high-amplitude wail, tremolo, and yodel. This paper is a review of the acoustic structure of the yodel, an aggressive warning signal only given by male Common Loons. The context in which males yodel is described along with the possible adaptive functions of this signal. The yodel is the most acoustically complex vocalization of the Common Loon and contains a wealth of information about the signaler. Suites of frequency and time elements of the yodel appear to communicate information about the identity of the signaler, which may be important for neighbor-stranger, mate, and kin recognition. The peak frequencies of the final note of the introductory phrase and repeat phrases also appear to communicate the condition-dependent fighting ability. Finally, the number of repeat phrases a male adds to its yodel appears to communicate the aggressive motivation, or the willingness a male Common Loon has to escalate a contest. Under various contexts not necessarily unique to Common Loons, these functions may be mutually beneficial to signalers and conspecific and heterospecific receivers, and evoke a number of interesting questions regarding the function of this dynamic signal. Such dynamic vocal signals are rare among waterbirds, and among ornithologists and behaviorists alike elicit questions regarding the conditions that maintain signal honesty among birds communicating fighting ability and aggressive state within the same vocal signal.

Robust Unsupervised Arousal Rating: A Rule-Based Framework with Knowledge-Inspired Vocal Features.

Studies in classifying affect from vocal cues have produced exceptional within-corpus results, especially for arousal (activation or stress); yet cross-corpora affect recognition has only recently garnered attention. An essential requirement of many behavioral studies is affect scoring that generalizes across different social contexts and data conditions. We present a robust, unsupervised (rule-based) method for providing a scale-continuous, bounded arousal rating operating on the vocal signal. The method incorporates just three knowledge-inspired features chosen based on empirical and theoretical evidence. It constructs a speaker's baseline model for each feature separately, and then computes single-feature arousal scores. Lastly, it advantageously fuses the single-feature arousal scores into a final rating without knowledge of the true affect. The baseline data is preferably labeled as neutral, but some initial evidence is provided to suggest that no labeled data is required in certain cases. The proposed method is compared to a state-of-the-art supervised technique which employs a high-dimensional feature set. The proposed framework achieves highly-competitive performance with additional benefits. The measure is interpretable, scale-continuous as opposed to discrete, and can operate without any affective labeling. An accompanying Matlab tool is made available with the paper.

The animal nature of spontaneous human laughter

Laughter is a universally produced vocal signal that plays an important role in human social interaction. Researchers have distinguished between spontaneous and volitional laughter, but no empirical work has explored possible acoustic and perceptual differences. If spontaneous laughter is an honest signal of cooperative intent (e.g., derived from play breathing patterns), then the ability to mimic these sounds volitionally could have shaped perceptual systems to be attuned to aspects of spontaneous laughs that are harder to fake—features associated with phylogenetically older vocal control mechanisms. We extracted spontaneous laughs from conversations between friends and volitional laughs elicited by instruction without other provocation. In three perception experiments we found that, 1) participants could distinguish between spontaneous and volitional laughter, 2) when laugh speed was increased (duration decreased 33% and pitch held constant), all laughs were judged as more “real,” with judgment accuracy increasing for spontaneous laughter and decreasing for volitional laughter, and 3) when the laughs were slowed down (duration increased 260% and pitch altered proportionally), participants could not distinguish spontaneous laughs from nonhuman vocalizations but could identify volitional laughs as human-made. These findings and acoustic data suggest that spontaneous and volitional laughs are produced by different vocal systems, and that spontaneous laughter might share features with nonhuman animal vocalizations that volitional laughter does not.

Age-group estimation in free-ranging African elephants based on acoustic cues of low-frequency rumbles

Animal vocal signals are increasingly used to monitor wildlife populations and to obtain estimates of species occurrence and abundance. In future, acoustic monitoring should function not only to detect animals, but also to extract detailed information about populations by discriminating sexes, age groups, social or kin groups, and potentially individuals. Here we show that it is possible to estimate age groups of African elephants (Loxodonta africana) based on acoustic parameters extracted from rumbles recorded under field conditions in a National Park in South Africa. Statistical models reached up to 70% correct classification to four age groups (infants, calves, juveniles and adults) and 95% correct classification when categorizing into two groups (infants/calves lumped into one group vs. adults). The models revealed that parameters representing absolute frequency values have the most discriminative power. Comparable classification results were obtained by fully automated classification of rumbles by high-dimensional features that represent the entire spectral envelope, such as Mel-frequency cepstral coefficient (75% correct classification) and Greenwood function cepstral coefficient (74% correct classification). The reported results and methods provide the scientific foundation for a future system that could potentially automatically estimate the demography of an acoustically monitored elephant group or population.

Vocal repertoire, individual acoustic distinctiveness, and social networks in a group of captive Asian small-clawed otters (Aonyx cinerea)

Communication in solitary and social mustelids has been mainly studied in terms of olfactory abilities. However, most otters appear highly social and vocal, but little is known about the role of vocal signals in communication in those species. An analysis of the airborne vocal repertoire and social networks of Asian small-clawed otters (Aonyx cinerea) is reported herein. The vocal repertoire of a captive group of 10 individuals was composed of 4 context-dependent vocalization units, which were emitted alone, repeated, or combined in a nonrandom way, resulting in 7 vocalization types. Individuals varied in their preference to use certain vocalization types and to maintain bonds with some particular group members. Older, larger, and heavier otters produced lower-frequency sounds. Thus, Asian small-clawed otters are clearly social and possess a high potential for vocal communication, such as acoustic coding of messages about ongoing social activities and biologically important characteristics about the sender. Future comparative studies of mustelids will tell whether solitary species may use essentially olfactory communication, whereas social species use multimodal communication, including vocal cues.

Team of rivals: alliance formation in territorial songbirds is predicted by vocal signal structure

Cooperation and conflict are regarded as diametric extremes of animal social behaviour, yet the two may intersect under rare circumstances. We here report that territorial competitors in a common North American songbird species, the chipping sparrow (Spizella passerina), sometimes form temporary coalitions in the presence of simulated territorial intruders. Moreover, analysis of birds' vocal mating signals (songs) reveals that coalitions occur nearly exclusively under specific triadic relationships, in which vocal performances of allies and simulated intruders exceed those of residents. Our results provide the first evidence that animals like chipping sparrows rely on precise assessments of mating signal features, as well as relative comparisons of signal properties among multiple animals in communication networks, when deciding when and with whom to form temporary alliances against a backdrop of competition and rivalry.

Vocal tract biometry and acoustic features of dairy cows

Vocalization in dairy animals is thought to be one of the best mean of conversation between each other as well as with environment. The present investigation was carried out on 12 lactating crossbred Karan Fries cows. The vocal signals from these animals were recorded for sufficient time in order to receive 50 complete sound clips. The various acoustic features were extracted in order to establish the relationship between these and various vocal tract or other body related measurements. Call duration of KF crossbred cows in present investigation was found to have a significant (p significant (p

Infant Cry Detection and Pain Scale Assessment

A biological alarm system that connects mother and new born is referred as infant cry. Infant cry is a first means of communication through which mother understands the level of distress/ needs. Infant cry can be considered a multimodal behavior which involves limb movements, facial expressions which changes over time to identify the needs of an infant. The cry of the baby cannot be predicted accurately and it is hard to identify for what it cries for. The infant's cry is mainly a vocal signal which is a way of communication that aims to get attention of the listener to a physical state like hunger, pain, discomfort, fear, illness, wet diaper etc., .Pain is one of the most common symptoms experienced world over. Pain is an unpleasant feeling that is conveyed to the brain by sensory neurons. The discomfort signals actual or potential injury to the body. This pilot study gives an insight on the current state of works in infant cry analysis and pain scale assessment and also concludes with thoughts about the future directions for better representation and interpretation of infant cry signals.

Chilled frogs are hot: hibernation and reproduction of the endangered mountain yellow-legged frog Rana muscosa

In the face of the sixth great extinction crisis, it is imperative to establish effective breeding protocols for amphibian conservation breeding programs. Captive efforts should not proceed by trial and error, nor should they jump prematurely to assisted reproduction techniques, which can be invasive, difficult, costly, and, at times, counterproductive. Instead, conservation practitioners should first look to nature for guidance, and replicate key conditions found in nature in the captive environment, according to the ecological and behavioral requirements of the spe- cies. We tested the effect of a natural hibernation regime on reproductive behaviors and body con- dition in the Endangered mountain yellow-legged frog Rana muscosa. Hibernation had a clear positive effect on reproductive behavior, manifesting in vocal advertisement signaling, female receptivity, amplexus, and oviposition. These behaviors are critical components of courtship that lead to successful reproduction. Our main finding was that captive R. muscosa require a hiberna- tion period for successful reproduction, as only hibernated females produced eggs and only hiber- nated males successfully fertilized eggs. Although hibernation also resulted in a reduced body condition, the reduction appeared to be minimal with no associated mortality. The importance of hibernation for reproduction is not surprising, since it is a major component of the conditions that R. muscosa experiences in the wild. Other amphibian conservation breeding programs can also benefit from a scientific approach that tests the effect of natural ecological conditions on reproduc- tion. This will ensure that captive colonies maximize their role in providing genetic reservoirs for assurance and reintroduction efforts.

Song stability and neighbour recognition in a migratory songbird, the black redstart

Territorial male songbirds have the ability to discriminate between the songs of their neighbours and those of strangers and for a few species it has been shown that they maintain this ability from one breeding season to the next. To better understand the acoustic basis of this long-term discrimination ability we studied song stability across two breeding seasons in a migratory songbird with high inter-annual return rates and territory stability, the black redstart, Phoenicurus ochruros. Strophe repertoires of 14 males (≥2 years old) were stable from one breeding season to the next and high strophe sharing occurred for males within the same group of houses or hamlets (81%) in contrast to only limited sharing between different hamlets (15%). However, subtle differences exist between the renditions of the same strophe sung by neighbouring males and these differences equally show an inter-annual stability, providing an acoustic basis for long-term discrimination abilities. Playback tests showed the existence of a strong dear-enemy effect: males reacted less aggressively to the familiar, often shared song of a neighbour than to a stranger unshared song and this pattern was maintained when birds returned from migration one year later. We discuss on one side the possible mechanisms leading to the observed patterns of song sharing and on the other side the significance of stable vocal signatures for neighbour recognition.

Learning to cope with degraded sounds: female zebra finches can improve their expertise in discriminating between male voices at long distances.

Reliable transmission of acoustic information about individual identity is of critical importance for pair bond maintenance in numerous monogamous songbirds. However, information transfer can be impaired by environmental constraints such as external noise or propagation-induced degradation. Birds have been shown to use several adaptive strategies to deal with difficult signal transmission contexts. Specifically, a number of studies have suggested that vocal plasticity at the emitter's level allows birds to counteract the deleterious effects of sound degradation. Although the communication process involves both the emitter and the receiver, perceptual plasticity at the receiver's level has received little attention. Here, we explored the reliability of individual recognition by female zebra finches (Taeniopygia guttata), testing whether perceptual training can improve discrimination of degraded individual vocal signatures. We found that female zebra finches are proficient in discriminating between calls of individual males at long distances, and even more so when they can train themselves with increasingly degraded signals over time. In this latter context, females succeed in discriminating between males as far as 250 m. This result emphasizes that adaptation to adverse communication conditions may involve not only the emitter's vocal plasticity but also the receptor's decoding process through on-going learning.

Male hyraxes increase song complexity and duration in the presence of alert individuals

The goal of vocal communication is the efficient delivery of signals to a target audience. Long and complex vocalizations are especially challenging because they are subject to environmental interference and may incur significant costs for the signaler. One of the various ways of increasing the efficiency of signal delivery is enhancement of communicational efforts only when potential audience is perceived nearby in an attempt to maximize the benefit over the cost of signaling (audience effect). Another way is signaling subsequently to events that intensify individual alertness in order to ensure audience attentiveness and sensitivity to the transmitted information. Rock hyraxes (Procavia capensis) are social mammals that use complex acoustic signals to communicate. Adult male hyraxes produce elaborate vocalizations (known as songs) that serve as honest advertisements of their quality. By combining analysis of male hyrax songs recorded in the field over a period of 11 years and playback experiments, we found that songs performed during and following attention-grabbing events (agonistic interactions, alarm calls, predator presence, and songs performed as a reply to conspecific singing) have an increased structural and syntactic complexity in comparison to spontaneous singing. Male hyraxes demonstrate a cognitive ability to optimize their advertising efforts in response to multiple types of events. This signaling strategy exploits the effective communication window created by attention-grabbing events and by the presence of an alert audience to delivers structurally and syntactically enhanced signal. To our knowledge, this is the first report of syntactic complexity of vocal signaling being altered following various triggers that change conspecifics mental state in terrestrial mammals.

Assessing vocal performance in complex birdsong: a novel approach

BackgroundVocal performance refers to the ability to produce vocal signals close to physical limits. Such motor skills can be used by conspecifics to assess a signaler’s competitive potential. For example it is difficult for birds to produce repeated syllables both rapidly and with a broad frequency bandwidth. Deviation from an upper-bound regression of frequency bandwidth on trill rate has been widely used to assess vocal performance. This approach is, however, only applicable to simple trilled songs, and even then may be affected by differences in syllable complexity.ResultsUsing skylarks (Alauda arvensis) as a birdsong model with a very complex song structure, we detected another performance trade-off: minimum gap duration between syllables was longer when the frequency ratio between the end of one syllable and the start of the next syllable (inter-syllable frequency shift) was large. This allowed us to apply a novel measure of vocal performance - vocal gap deviation: the deviation from a lower-bound regression of gap duration on inter-syllable frequency shift. We show that skylarks increase vocal performance in an aggressive context suggesting that this trait might serve as a signal for competitive potential.ConclusionsWe suggest using vocal gap deviation in future studies to assess vocal performance in songbird species with complex structure.

Mothers' tone of voice depends on the nature of infants' transgressions.

Emotional vocal signals are important ways of communicating norms to young infants. The second year is a period of increase in various forms of child transgressions, but also a period when infants have limited linguistic abilities. Two studies investigated the hypothesis that mothers respond with different vocal emotional tones to 3 types of child transgressions: moral (harming others), prudential (harming oneself), and pragmatic (creating inconvenience, e.g., by spilling) transgressions. We used a combination of naturalistic observation (Study 1) and experimental manipulation (Study 2) to record, code, and analyze maternal vocal responses to child transgressions. Both studies showed that mothers were more likely to use intense, angry vocalizations in response to moral transgressions, fearful vocalizations in response to prudential transgressions, comforting vocalizations in response to pragmatic and prudential transgressions, and (in Study 2) playful vocalizations in response to pragmatic transgressions. Study 1 showed that this differential use of vocal tone is used systematically in everyday life. Study 2 allowed us to standardize the context of the maternal intervention and perform additional acoustical analyses. A combination of principal component analysis and linear discriminant analysis applied to pitch and intensity data provided quantitative measures of the differences in vocal responses. These differentiated vocal responses are likely contributors to children's acquisition of norms from early in life.

Love is in the air: sociality and pair bondedness influence sifaka reproductive signalling

Social complexity, often estimated by group size, is seen as driving the complexity of vocal signals, but its relation to olfactory signals, which arguably arose to function in nonsocial realms, remains underappreciated. That olfactory signals also may mediate within-group interaction, vary with social complexity and promote social cohesion underscores a potentially crucial link with sociality. To examine that link, we integrated chemical and behavioural analyses to ask whether olfactory signals facilitate reproductive coordination in a strepsirrhine primate, the Coquerel's sifaka, Propithecus coquereli . Belonging to a clade comprising primarily solitary, nocturnal species, the diurnal, group-living sifaka represents an interesting test case. Convergent with diurnal, group-living lemurids, sifakas expressed chemically rich scent signals, consistent with the social complexity hypothesis for communication. These signals minimally encoded the sex of the signaller and varied with female reproductive state. Likewise, sex and female fertility were reflected in within-group scent investigation, scent marking and overmarking. We further asked whether, within breeding pairs, the stability or quality of the pair's bond influences the composition of glandular signals and patterns of investigatory or scent-marking behaviour. Indeed, reproductively successful pairs tended to show greater similarity in their scent signals than did reproductively unsuccessful pairs, potentially through chemical convergence. Moreover, scent marking was temporally coordinated within breeding pairs and was influenced by past reproductive success. That olfactory signalling reflects social bondedness or reproductive history lends support to recent suggestions that the quality of relationships may be a more valuable proxy than group size for estimating social complexity. We suggest that olfactory signalling in sifakas is more complex than previously recognized and, as in other socially integrated species, can be a crucial mechanism for promoting group cohesion and maintaining social bonds. Thus, the evolution of sociality may well be reflected in the complexity of olfactory signalling. • Sifakas have a complex scent-signalling repertoire that coordinates reproduction. • Two families of diurnal, group-living lemurs converge on complex glandular signalling. • The quality of sifaka social bonds influences scent composition and deposition. • Olfactory signalling mediates social cohesion in group-living animals. • Sociality drives the complexity of both vocal and olfactory signals.