Laryngeal biomechanics and vocal communication in the squirrel monkey (Saimiri boliviensis)

Nonlinear features in whistles produced by the short-beaked common dolphin (Delphinus delphis) off southeastern Brazil

Animal vocalizations have nonlinear characteristics responsible for features such as subharmonics, frequency jumps, biphonation, and deterministic chaos. This study describes the whistle repertoire of a short-beaked common dolphin (Delphinus delphis) group at Brazilian coast and quantifies the nonlinear features of these whistles. Dolphins were recorded for a total of 67 min around Cabo Frio, Brazil. We identify 10 basic categories of whistle, with 75 different types, classified according to their contour shape. Most (45) of these 75 types had not been reported previously for the species. The duration of the whistles ranged from 0.04 to 3.67 s, with frequencies of 3.05-29.75 kHz. Overall, the whistle repertoire presented here has one of the widest frequency ranges and greatest level of frequency modulation recorded in any study of D. delphis. All the nonlinear features sought during the study were confirmed, with at least one feature occurring in 38.4% of the whistles. The frequency jump was the most common feature (29.75% of the whistles) and the nonlinear time series analyses confirmed the deterministic chaos in the chaotic-like segments. These results indicate that nonlinearities are a relevant characteristic of these whistles, and that are important in acoustic communication.

Physical modeling of the vocal membranes and their influence on animal voice production

The vocal membrane, i.e., an extended part of the vocal fold, is observed in a wide range of species including bats and primates. A theoretical study [Mergell, Fitch, and Herzel (1999). J. Acoust. Soc. Am. 105(3), 2020-2028] predicted that the vocal membranes can make the animal vocalizations more efficient by lowering the phonation threshold pressure. To examine this prediction, a synthetic model of the vocal membrane was developed, and its oscillation properties were examined. The experiments revealed that the phonation threshold pressure was lower in the vocal membrane model compared to that in a model with no vocal membrane. Chaotic oscillations were observed as well.

Acoustic structure and information content of trumpets in female Asian elephants (Elephas maximus)

Most studies on elephant vocal communication have focused on the low-frequency rumble, with less effort on other vocalization types such as the most characteristic elephant call, the trumpet. Yet, a better and more complete understanding of the elephant vocal system requires investigating other vocalization types and their functioning in more detail as well. We recorded adult female Asian elephants (Elephas maximus) at a private facility in Nepal and analyzed 206 trumpets from six individuals regarding their frequency, temporal and contour shape, and related acoustic parameters of the fundamental frequency. We also tested for information content regarding individuality and context. Finally, we recorded the occurrence of non-linear phenomena such as bifurcation, biphonation, subharmonics and deterministic chaos. We documented a mean fundamental frequency ± SD of 474 ± 70 Hz and a mean duration ± SD of 1.38 ± 1.46 s (Nindiv. = 6, Ncalls = 206). Our study reveals that the contour of the fundamental frequency of trumpets encodes information about individuality, but we found no evidence for trumpet subtypes in greeting versus disturbance contexts. Non-linear phenomena prevailed and varied in abundance among individuals, suggesting that irregularities in trumpets might enhance the potential for individual recognition. We propose that trumpets in adult female Asian elephants serve to convey an individual's identity as well as to signal arousal and excitement to conspecifics.

Treefrogs adjust their acoustic signals in response to harmonics structure of intruder calls

Spectral properties of animal acoustic signals may help individuals to assess the characteristics of rivals and to adjust their competitive strategies in territorial disputes. Thus, we hypothesized that the distribution of energy across frequency bands in anuran calls determines behavioral responses in male–male competition. Using playback experiments, we investigated the relevance of the harmonic calls in the acoustic communication of the treefrog Dendropsophus minutus. We exposed territorial males to three synthetic acoustic stimuli composed of aggressive notes: 1) standard call (all harmonics and peak frequency corresponding to the second band); 2) inverted-energy call (all harmonics and peak frequency corresponding to the first band); and 3) concentrated-energy call (all energy contained in the second harmonic). Males responded aggressively to all stimuli, mainly by increasing the rate and duration of their aggressive notes. However, when exposed to stimuli with different harmonic configurations, males changed the harmonic structure of their own calls, emitting more A- and B-notes with peak power in the fundamental frequency, particularly when exposed to the concentrated-energy call. Our results suggest that male frogs may use the harmonic structure of calls to assess opponents and modulate territorial and aggressive behavior, triggering complex acoustic adjustments. This study contributes to our knowledge about the functions of acoustic traits in amphibian social interactions, and particularly of the presence of harmonics that has received less attention compared to other acoustic properties in the study of animal acoustic communication.

Effect of Ventricular Folds on Vocalization Fundamental Frequency in Domestic Pigs (Sus scrofa domesticus)

This study investigates the effect of the ventricular folds on fundamental frequency (f_o) in the voice production of domestic pigs (Sus scrofa domesticus). The excised larynges of six subadult pigs were phonated in two preparation stages, with the ventricular folds present (PS1) and removed (PS2). Vocal fold resonances were tested with a laser vibrometer, and a four-mass computational model was created. Highly significant f_o differences were found between PS1 and PS2 (means at 93.7 and 409.3 Hz, respectively). Two tissue resonances were found at 115 Hz and 250-290 Hz. The computational model had unique solutions for abducted and adducted ventricular folds at about 150 and 400 Hz, roughly matching the f_o measured ex vivo for PS1 and PS2. The differing f_o encountered across preparation stages PS1 and PS2 is explained by distinct activation of either a high or a low eigenfrequency mode, depending on the engagement of the ventricular folds. The inability of the investigated larynges to vibrate at frequencies below 250 Hz in PS2 suggests that in vivo low-frequency calls of domestic pigs (pre-eminently grunts) are likely produced with engaged ventricular folds. Allometric comparison suggests that the special, mechanically coupled "double oscillator" has evolved to prevent signaling disadvantages. Given these traits, the porcine larynx might - apart from special applications relating to the involvement of ventricular folds - not be an ideal candidate for emulating human voice production in excised larynx experimentation.

Independent acoustic variation of the higher- and lower-frequency components of biphonic calls can facilitate call recognition and social affiliation in killer whales

Each resident-type (R-type) killer whale pod has a set of stereotyped calls that are culturally transmitted from mother to offspring. The functions of particular call types are not yet clearly understood, but it is believed that calls with two independently modulated frequency components (biphonic calls) play an important role in pod communication and cohesion at long ranges. In this study we examined the possible functions of biphonic calls in R-type killer whales. First, we tested the hypothesis that the additional component enhances the potential of a call to identify the family affiliation. We found that the similarity patterns of the lower- and higher frequency components across the families were largely unrelated. Calls were classified more accurately to their respective family when both lower- and higher-frequency components were considered. Second, we tested the long-range detectability of the lower- and higher-frequency components. After adjusting the received levels by the killer whale hearing sensitivity to different frequency ranges, the sensation level of the higher-frequency component was higher than the amplitude of the lower-frequency component. Our results suggest that the higher-frequency component of killer whale biphonic calls varies independently of the lower-frequency component, which enhances the efficiency of these calls as family markers. The acoustic variation of the higher-frequency component allows the recognition of family identity of a caller even if the shape of the lower-frequency component accidentally becomes similar in unrelated families. The higher-frequency component can also facilitate family recognition when the lower-frequency component is masked by low-frequency noise.

Cold call: the acoustic repertoire of Ross Sea killer whales (Orcinus orca, Type C) in McMurdo Sound, Antarctica

Killer whales (Orcinus orca) are top marine predators occurring globally. In Antarctic waters, five ecotypes have been described, with Type C being the smallest form of killer whale known. Acoustic recordings of nine encounters of Type C killer whales were collected in 2012 and 2013 in McMurdo Sound, Ross Sea. In a combined 3.5 h of recordings, 6386 killer whale vocalizations were detected and graded based on their signal-to-noise ratio. Spectrograms of the highest-quality calls were examined for characteristic patterns yielding a catalogue of 28 call types (comprising 1250 calls). Acoustic parameters of each call were measured and summarized by call type. Type C killer whales produced complex calls, consisting of multiple frequency-modulated, amplitude-modulated and pulsed components. Often, two components occurred simultaneously, forming a biphonation; although the biphonic components did not necessarily start and end together, with one component lasting over several others. The addition and deletion of components yielded call subtypes. Call complexity appears stable over time and may be related to feeding ecology. Characterization of the Type C acoustic repertoire is an important step for the development of passive acoustic monitoring of the diverse assemblage of killer whale ecotypes in Antarctica's rapidly changing marine ecosystems.

The evolution of the syrinx: An acoustic theory

The unique avian vocal organ, the syrinx, is located at the caudal end of the trachea. Although a larynx is also present at the opposite end, birds phonate only with the syrinx. Why only birds evolved a novel sound source at this location remains unknown, and hypotheses about its origin are largely untested. Here, we test the hypothesis that the syrinx constitutes a biomechanical advantage for sound production over the larynx with combined theoretical and experimental approaches. We investigated whether the position of a sound source within the respiratory tract affects acoustic features of the vocal output, including fundamental frequency and efficiency of conversion from aerodynamic energy to sound. Theoretical data and measurements in three bird species suggest that sound frequency is influenced by the interaction between sound source and vocal tract. A physical model and a computational simulation also indicate that a sound source in a syringeal position produces sound with greater efficiency. Interestingly, the interactions between sound source and vocal tract differed between species, suggesting that the syringeal sound source is optimized for its position in the respiratory tract. These results provide compelling evidence that strong selective pressures for high vocal efficiency may have been a major driving force in the evolution of the syrinx. The longer trachea of birds compared to other tetrapods made them likely predisposed for the evolution of a syrinx. A long vocal tract downstream from the sound source improves efficiency by facilitating the tuning between fundamental frequency and the first vocal tract resonance.

Nocturnal "humming" vocalizations: adding a piece to the puzzle of giraffe vocal communication

BACKGROUND

Recent research reveals that giraffes (Giraffa camelopardalis sp.) exhibit a socially structured, fission-fusion system. In other species possessing this kind of society, information exchange is important and vocal communication is usually well developed. But is this true for giraffes? Giraffes are known to produce sounds, but there is no evidence that they use vocalizations for communication. Reports on giraffe vocalizations are mainly anecdotal and the missing acoustic descriptions make it difficult to establish a call nomenclature. Despite inconclusive evidence to date, it is widely assumed that giraffes produce infrasonic vocalizations similar to elephants. In order to initiate a more detailed investigation of the vocal communication in giraffes, we collected data of captive individuals during day and night. We particularly focussed on detecting tonal, infrasonic or sustained vocalizations.

FINDINGS

We collected over 947 h of audio material in three European zoos and quantified the spectral and temporal components of acoustic signals to obtain an accurate set of acoustic parameters. Besides the known burst, snorts and grunts, we detected harmonic, sustained and frequency-modulated "humming" vocalizations during night recordings. None of the recorded vocalizations were within the infrasonic range.

CONCLUSIONS

These results show that giraffes do produce vocalizations, which, based on their acoustic structure, might have the potential to function as communicative signals to convey information about the physical and motivational attributes of the caller. The data further reveal that the assumption of infrasonic communication in giraffes needs to be considered with caution and requires further investigations in future studies.

Silky sifaka (Propithecus candidus) "zzuss" vocalizations: sexual dimorphism, individuality, and function in the alarm call of a monomorphic lemur

Vocalizations of Madagascar's lemurs have generally been less investigated than those of other primate groups, with virtually no information available about calling in the silky sifaka (Propithecus candidus), a large rainforest species. Current work examined the "zzuss" vocalization, one of the most common and loudest sounds produced by this monomorphic species, and included 160 calls from nine adults (five males, four females) in three groups. Analyses focused on overall acoustic features, individual and sex differences, call usage, and likely function. Acoustically, the calls included separable turbulent noise and tonal components, with the later often marked by frequency jumps and dramatic frequency modulation. Male and female zzuss calls differed most in F0- and amplitude-related features, characteristics that are relatively unconstrained by overall body size. All measures differed among individual callers, with F0-related variables again playing the largest role. Based on usage, these calls most likely function both as generalized alarm and group-coordination signals. The sounds were thus of interest in several regards, including showing sexual differentiation in the absence of other dimorphisms, exhibiting primarily F0-based differentiation in both sex- and individual-based comparisons, and combining apparent alarm and coordination functions across a variety of contexts.

Vocal cues indicate level of arousal in infant African elephant roars

Arousal-based physiological changes influence acoustic features of vocalizations in mammals. In particular, nonlinear phenomena are thought to convey information about the caller's arousal state. This hypothesis was tested in the infant African elephant (Loxodonta africana) roar, a call type produced in situations of arousal and distress. Ninety-two percent of roars exhibited nonlinear phenomena, with chaos being the most common type. Acoustic irregularities were strongly associated with elevated fundamental frequency values. Roars produced in situations of highest urgency, based on the occurrence of behavioral indicators of arousal, were characterized by the lowest harmonics-to-noise ratio; this indicates low tonality. In addition, roars produced in these situations lasted longer than those produced in contexts of lower presumed urgency. Testing the infant roars for individual distinctiveness revealed only a moderate classification result. Combined, these findings indicate that infant African elephant roars primarily function to signal the caller's arousal state. The effective communication of this type of information may allow mothers to respond differentially based on their infant's degree of need and may be crucial for the survival of infant African elephants in their natural environment.

Subglottal pressure, tracheal airflow, and intrinsic laryngeal muscle activity during rat ultrasound vocalization

Vocal production requires complex planning and coordination of respiratory, laryngeal, and vocal tract movements, which are incompletely understood in most mammals. Rats produce a variety of whistles in the ultrasonic range that are of communicative relevance and of importance as a model system, but the sources of acoustic variability were mostly unknown. The goal was to identify sources of fundamental frequency variability. Subglottal pressure, tracheal airflow, and electromyographic (EMG) data from two intrinsic laryngeal muscles were measured during 22-kHz and 50-kHz call production in awake, spontaneously behaving adult male rats. During ultrasound vocalization, subglottal pressure ranged between 0.8 and 1.9 kPa. Pressure differences between call types were not significant. The relation between fundamental frequency and subglottal pressure within call types was inconsistent. Experimental manipulations of subglottal pressure had only small effects on fundamental frequency. Tracheal airflow patterns were also inconsistently associated with frequency. Pressure and flow seem to play a small role in regulation of fundamental frequency. Muscle activity, however, is precisely regulated and very sensitive to alterations, presumably because of effects on resonance properties in the vocal tract. EMG activity of cricothyroid and thyroarytenoid muscle was tonic in calls with slow or no fundamental frequency modulations, like 22-kHz and flat 50-kHz calls. Both muscles showed brief high-amplitude, alternating bursts at rates up to 150 Hz during production of frequency-modulated 50-kHz calls. A differentiated and fine regulation of intrinsic laryngeal muscles is critical for normal ultrasound vocalization. Many features of the laryngeal muscle activation pattern during ultrasound vocalization in rats are shared with other mammals.

Elasticity and stress relaxation of a very small vocal fold

Across mammals many vocal sounds are produced by airflow induced vocal fold oscillation. We tested the hypothesis that stress-strain and stress-relaxation behavior of rat vocal folds can be used to predict the fundamental frequency range of the species' vocal repertoire. In a first approximation vocal fold oscillation has been modeled by the string model but it is not known whether this concept equally applies to large and small species. The shorter the vocal fold, the more the ideal string law may underestimate normal mode frequencies. To accommodate the very small size of the tissue specimen, a custom-built miniaturized tensile test apparatus was developed. Tissue properties of 6 male rat vocal folds were measured. Rat vocal folds demonstrated the typical linear stress-strain behavior in the low strain region and an exponential stress response at strains larger than about 40%. Approximating the rat's vocal fold oscillation with the string model suggests that fundamental frequencies up to about 6 kHz can be produced, which agrees with frequencies reported for audible rat vocalization. Individual differences and time-dependent changes in the tissue properties parallel findings in other species, and are interpreted as universal features of the laryngeal sound source.

Elasticity and stress relaxation of rhesus monkey (Macaca mulatta) vocal folds

Fundamental frequency is an important perceptual parameter for acoustic communication in mammals. It is determined by vocal fold oscillation, which depends on the morphology and viscoelastic properties of the oscillating tissue. In this study, I tested if stress-strain and stress-relaxation behavior of rhesus monkey (Macaca mulatta) vocal folds allows the prediction of a species' natural fundamental frequency range across its entire vocal repertoire as well as of frequency contours within a single call type. In tensile tests, the load-strain and stress-relaxation behavior of rhesus monkey vocal folds and ventricular folds has been examined. Using the string model, predictions about the species' fundamental frequency range, individual variability, as well as the frequency contour of 'coo' calls were made. The low- and mid-frequency range (up to 2 kHz) of rhesus monkeys can be predicted relatively well with the string model. The discrepancy between predicted maximum fundamental frequency and what has been recorded in rhesus monkeys is currently ascribed to the difficulty in predicting the behavior of the lamina propria at very high strain. Histological sections of the vocal fold and different staining techniques identified collagen, elastin, hyaluronan and, surprisingly, fat cells as components of the lamina propria. The distribution of all four components is not uniform, suggesting that different aspects of the lamina propria are drawn into oscillation depending on vocal fold tension. A differentiated recruitment of tissue into oscillation could extend the frequency range specifically at the upper end of the frequency scale.

A cervid vocal fold model suggests greater glottal efficiency in calling at high frequencies

Male Rocky Mountain elk (Cervus elaphus nelsoni) produce loud and high fundamental frequency bugles during the mating season, in contrast to the male European Red Deer (Cervus elaphus scoticus) who produces loud and low fundamental frequency roaring calls. A critical step in understanding vocal communication is to relate sound complexity to anatomy and physiology in a causal manner. Experimentation at the sound source, often difficult in vivo in mammals, is simulated here by a finite element model of the larynx and a wave propagation model of the vocal tract, both based on the morphology and biomechanics of the elk. The model can produce a wide range of fundamental frequencies. Low fundamental frequencies require low vocal fold strain, but large lung pressure and large glottal flow if sound intensity level is to exceed 70 dB at 10 m distance. A high-frequency bugle requires both large muscular effort (to strain the vocal ligament) and high lung pressure (to overcome phonation threshold pressure), but at least 10 dB more intensity level can be achieved. Glottal efficiency, the ration of radiated sound power to aerodynamic power at the glottis, is higher in elk, suggesting an advantage of high-pitched signaling. This advantage is based on two aspects; first, the lower airflow required for aerodynamic power and, second, an acoustic radiation advantage at higher frequencies. Both signal types are used by the respective males during the mating season and probably serve as honest signals. The two signal types relate differently to physical qualities of the sender. The low-frequency sound (Red Deer call) relates to overall body size via a strong relationship between acoustic parameters and the size of vocal organs and body size. The high-frequency bugle may signal muscular strength and endurance, via a 'vocalizing at the edge' mechanism, for which efficiency is critical.

The function of nonlinear phenomena in meerkat alarm calls

Nonlinear vocal phenomena are a ubiquitous feature of human and non-human animal vocalizations. Although we understand how these complex acoustic intrusions are generated, it is not clear whether they function adaptively for the animals producing them. One explanation is that nonlinearities make calls more unpredictable, increasing behavioural responses and ultimately reducing the chances of habituation to these call types. Meerkats (Suricata suricatta) exhibit nonlinear subharmonics in their predator alarm calls. We specifically tested the 'unpredictability hypothesis' by playing back naturally occurring nonlinear and linear medium-urgency alarm call bouts. Results indicate that subjects responded more strongly and foraged less after hearing nonlinear alarm calls. We argue that these findings support the unpredictability hypothesis and suggest this is the first study in animals or humans to show that nonlinear vocal phenomena function adaptively.

Cervids with different vocal behavior demonstrate different viscoelastic properties of their vocal folds

The authors test the hypothesis that vocal fold morphology and biomechanical properties covary with species-specific vocal function. They investigate mule deer (Odocoileus hemionus) vocal folds, building on, and extending data on a related cervid, the Rocky Mountain elk (Cervus elaphus nelsoni). The mule deer, in contrast to the elk, is a species with relatively little vocal activity in adult animals. Mule deer and elk vocal folds show the typical three components of the mammalian vocal fold (epithelium, lamina propria and thyroarytenoid muscle). The vocal fold epithelium and the lamina propria were investigated in two sets of tensile tests. First, creep rupture tests demonstrated that ultimate stress in mule deer lamina propria is of the same magnitude as in elk. Second, cyclic loading tests revealed similar elastic moduli for the vocal fold epithelium in mule deer and elk. The elastic modulus of the lamina propria is also similar between the two species in the low-strain region, but differs at strains larger than 0.3. Sex differences in the stress-strain response, which have been reported for elk and human vocal folds, were not found for mule deer vocal folds. The laminae propriae in mule deer and elk vocal folds are comparatively large. In general, a thick and uniformly stiff lamina propria does not self-oscillate well, even when high subglottic pressure is applied. If the less stiff vocal fold seen in elk is associated with a differentiated lamina propria it would allow the vocal fold to vibrate at high tension and high subglottic pressure. The results of this study support the hypothesis that viscoelastic properties of vocal folds varies with function and vocal behavior.

Two-voice complexity from a single side of the syrinx in northern mockingbird Mimus polyglottos vocalizations

The diverse vocal signals of songbirds are produced by highly coordinated motor patterns of syringeal and respiratory muscles. These muscles control separate sound generators on the right and left side of the duplex vocal organ, the syrinx. Whereas most song is under active neural control, there has been a growing interest in a different class of nonlinear vocalizations consisting of frequency jumps, subharmonics, biphonation and deterministic chaos that are also present in the vocal repertoires of many vertebrates, including many birds. These nonlinear phenomena may not require active neural control, depending instead on the intrinsic nonlinear dynamics of the oscillators housed within each side of the syrinx. This study investigates the occurrence of these phenomena in the vocalizations of intact northern mockingbirds Mimus polyglottos. By monitoring respiratory pressure and airflow on each side of the syrinx, we provide the first analysis of the contribution made by each side of the syrinx to the production of nonlinear phenomena and are able to reliably discriminate two-voice vocalizations from potentially similar appearing, unilaterally produced, nonlinear events. We present the first evidence of syringeal lateralization of nonlinear dynamics during bilaterally produced chaotic calls. The occurrence of unilateral nonlinear events was not consistently correlated with fluctuations in air sac pressure or the rate of syringeal airflow. Our data support previous hypotheses for mechanical and acoustic coupling between the two sides of the syrinx. These results help lay a foundation upon which to understand the communicative functions of nonlinear phenomena.

Vocal fold elasticity of the Rocky Mountain elk (Cervus elaphus nelsoni) - producing high fundamental frequency vocalization with a very long vocal fold

The vocal folds of male Rocky Mountain elk (Cervus elaphus nelsoni) are about 3 cm long. If fundamental frequency were to be predicted by a simple vibrating string formula, as is often done for the human larynx, such long vocal folds would bear enormous stress to produce the species-specific mating call with an average fundamental frequency of 1 kHz. Predictions would be closer to 50 Hz. Vocal fold histology revealed the presence of a large vocal ligament between the vocal fold epithelium and the thyroarytenoid muscle. In tensile tests, the stress-strain response of vocal fold epithelium and the vocal ligament were determined. Elasticity of both tissue structures reached quantitative values similar to human tissue. It seems unlikely that the longitudinal stress in elk vocal folds can exceed that in human vocal folds by an order of magnitude to overcome the drop in fundamental frequency due to a 3:1 increase in vocal fold length. Alternative hypotheses of how the elk produces high fundamental frequency utterances, despite its very long vocal fold, include a reduced effective vocal fold length in vibration, either due to bending properties along the vocal fold, or by actively moving the boundary point with muscle stiffening. The relationships between an individual's average fundamental frequency, vocal fold length and body size are discussed.

Nonlinear acoustics in the pant hoots of common chimpanzees (Pan troglodytes): vocalizing at the edge

Common chimpanzee (Pan troglodytes) "pant hoots" are multi-call events that build from quiet, consistently harmonic introductory sounds to loud, screamlike "climax" calls with acoustic irregularities known as "nonlinear phenomena" (NLP). Two possible functions of NLP in climax calls are to increase direct auditory impact on listeners and to signal physical condition. These possibilities were addressed by comparing climax calls from 12 wild chimpanzee males with "screams" and pant hoot "introduction" calls from the same individuals. Climax calls that included NLP were found to have higher fundamental frequencies (F0s) than introduction or climax calls that were purely harmonic. NLP onsets within climax calls were also specifically associated with local F0 maxima, suggesting vocalizers are vibrating their vocal folds at the upper limits of stability. Furthermore, climax calls showed far fewer NLP than did screams recorded from the same individuals, while showing equivalent or higher F0 values. Overall, the results are consistent with the hypothesis that the relative prevalence of NLP is a signal of physical condition, with callers "vocalizing at the edge" of regular, stable production while producing few NLP. The results are discussed in light of the initial hypotheses.

Acoustics and behavioral contexts of "gecker" vocalizations in young rhesus macaques (Macaca mulatta)

Loud, pulsed "gecker" vocalizations are commonly produced by young rhesus macaques in distressful circumstances. The acoustics, usage, and responses associated with these calls were examined using audio recordings and observational data from captive, socially living rhesus up to 24 months old. One-hundred-eleven gecker bouts were recorded from ten individuals (six males, four females), with most geckers produced during the first 6 months of age. A gecker call consisted of a bout of up to 28 pulses of spectrally structured noise with a single prominent frequency peak. Nine contexts of calling were identified, but little evidence of context-specific acoustic variation was found. While geckering often triggered responses by the vocalizer's mother, the most common outcome was the absence of any reaction. Females geckered longer and at higher rates than did males, while also showing acoustic evidence of greater vocal effort. Mothers nonetheless responded more often and more positively to males. Overall, results show that gecker acoustics vary somewhat with vocalizer sex, age, and likely arousal level, but do not reflect detailed aspects of behavioral context. Circumstances of production suggest that geckers function primarily to draw the attention of mothers, who in turn are selective in responding.

Anterior-posterior biphonation in a finite element model of vocal fold vibration

In this paper, a finite-element model is used to simulate anterior-posterior biphonation [Neubauer et al., J. Acoust. Soc. Am. 110(6), 3179-3192 (2001)]. The anterior-posterior stiffness asymmetric factor and the anterior-posterior shape asymmetric factor describe the asymmetry properties of vocal folds. Spatiotemporal plot, spectral analysis, anterior-posterior fundamental frequency ratio, cross covariation function, and correlation length quantitatively estimate the spatial asymmetry of vocal fold oscillations. Calculation results show that the anterior-posterior stiffness asymmetry decreases the spatial coherence of vocal fold vibration. When the stiffness asymmetry reaches a certain level, the drop in spatial coherence desynchronizes the vibration modes. The anterior and posterior sides of the vocal fold oscillate with two independent fundamental frequencies (f(a) and f(p)). The complex spectral characteristics of vocal fold vibration under biphonation conditions can be explained by the linear combination of f(a) and f(p). Empirical orthogonal eigenfunctions prove the existence of higher-order anterior-posterior modes when anterior-posterior biphonation occurs. Then, it is found that the anterior-posterior shape asymmetry also decreases the spatial coherence of vocal fold vibration, and shape asymmetry is a possible reason for anterior-posterior biphonation.

Characterizing noise in nonhuman vocalizations: Acoustic analysis and human perception of barks by coyotes and dogs

Measuring noise as a component of mammalian vocalizations is of interest because of its potential relevance to the communicative function. However, methods for characterizing and quantifying noise are less well established than methods applicable to harmonically structured aspects of signals. Using barks of coyotes and domestic dogs, we compared six acoustic measures and studied how they are related to human perception of noisiness. Measures of harmonic-to-noise-ratio (HNR), percent voicing, and shimmer were found to be the best predictors of perceptual rating by human listeners. Both acoustics and perception indicated that noisiness was similar across coyote and dog barks, but within each species there was significant variation among the individual vocalizers. The advantages and disadvantages of the various measures are discussed.

Nonlinear acoustics in pant hoots of common chimpanzees (Pan troglodytes): frequency jumps, subharmonics, biphonation, and deterministic chaos

The pant hoot calls produced by common chimpanzees (Pan troglodytes) are multi-call vocalizations that have figured prominently in investigations of acoustic communication in this species. Although pant hoots are predominantly harmonically structured, they can exhibit an acoustic complexity that has recently been linked to nonlinearity in the vocal-fold dynamics underlying typical mammalian sound production. We examined the occurrence of these sorts of nonlinear phenomena in pant hoot vocalizations, contrasting quieter and lower-pitched "introduction" components with loud and high-pitched "climax" calls in the same bouts. Spectrographic evidence revealed four kinds of nonlinear phenomena, including discrete frequency jumps, subharmonics, biphonation, and deterministic chaos. While these events were virtually never observed during the introduction, they occurred in more than half of the climax calls. Biphonation was by far the most common phenomenon, followed by subharmonics, chaos, and frequency jumps. Individual callers varied in the degree to which their climax calls exhibited nonlinear phenomena, but were consistent in showing more biphonation than other forms. These outcomes show that nonlinear phenomena are routinely present in chimpanzee pant hoots, and help lay the foundation for investigating the function of such events.

Dynamics of frequency and amplitude modulations in vocalizations produced by eastern towhees, Pipilo erythrophthalmus

Eastern towhees, Pipilo erythrophthalmus (Emberizidae, Passeriformes), appear to estimate source-SPL using spectral or temporal variables. Nevertheless, vocalizations are dynamic by nature and it remains unclear whether subjects pay attention to correlations between discrete variables or pay attention to the dynamics that these variables summarize. Sine functions are used to describe coarse (slow, < 10 Hz) frequency and amplitude modulations in towhee calls and correlations between variables are identified. Towhee calls are also finely (rapidly, > 400 Hz) modulated in both amplitude and frequency. Fine amplitude and frequency modulations correlate well (occur in phase) over relatively low fundamental frequencies (< approximately 3.5 kHz) and tend to have greater amplitudes and frequencies over these same frequencies. Modulations and correlations between modulations might exist due to stable dynamic interactions that occur within and between the physical forces that function to produce modulations in vocalizations. Results support the hypothesis that towhees communicate within separate sound frequency channels defined to each side of approximately 3.5 kHz.