Learned vocalizations in budgerigars (Melopsittacus undulatus): the relationship between contact calls and warble song

The budgerigar (Melopsittacus undulatus) has an extraordinarily complex, learned, vocal repertoire consisting of both the long rambling warble song of males and a number of short calls produced by both sexes. In warble, the most common elements (>30%) bear a strong resemblance to the highly frequency-modulated, learned contact calls that the birds produce as single utterances. However, aside from this apparent similarity, little else is known about the relationship between contact calls and warble call elements. Here, both types of calls were recorded from four male budgerigars. Signal analysis and psychophysical testing procedures showed that the acoustic features of these two vocalizations were acoustically different and perceived as distinctive vocalizations by birds. This suggests that warble call elements are not simple insertions of contact calls but are most likely different acoustic elements, created de novo, and used solely in warble. Results show that, like contact calls, warble call elements contain information about signaler identity. The fact that contact calls and warble call elements are acoustically and perceptually distinct suggests that they probably represent two phonological systems in the budgerigar vocal repertoire, both of which arise by production learning.     

Effects of deafening on the calls and warble song of adult budgerigars (Melopsittacus undulatus)

Budgerigars are small Australian parrots that learn new vocalizations throughout adulthood. Earlier work has shown that an external acoustic model and auditory feedback are necessary for the development of normal contact calls in this species. Here, the role of auditory feedback in the maintenance of species-typical contact calls and warble song in adult budgerigars is documented. Deafened adult birds (five male, one female) vocalized less frequently and showed both suprasegmental and segmental changes in their contact calls and warble song. Contact calls of all adult-deafened budgerigars showed abnormalities in acoustic structure within days to a few weeks following surgery. Within 6 months of surgery, nearly all contact calls produced by deafened birds were strikingly abnormal, showing highly variable patterns of frequency modulation and duration. The warble song of deafened male budgerigars also differed significantly from that of normal budgerigars on several acoustic measures. These results show that auditory feedback is necessary for the maintenance of a normal, species-typical vocal repertoire in budgerigars.     

Amplification and spectral shifts of vocalizations inside burrows of the frog Eupsophus calcaratus (Leptodactylidae)

A variety of animals that communicate by sound emit signals from sites favoring their propagation, thereby increasing the range over which these sounds convey information. A different significance of calling sites has been reported for burrowing frogs Eupsophus emiliopugini from southern Chile: the cavities from which these frogs vocalize amplify conspecific vocalizations generated externally, thus providing a means to enhance the reception of neighbor's vocalizations in chorusing aggregations. In the current study the amplification of vocalizations of a related species, E. calcaratus, is investigated, to explore the extent of sound enhancement reported previously. Advertisement calls broadcast through a loudspeaker placed in the vicinity of a burrow, monitored with small microphones, are amplified by up to 18 dB inside cavities relative to outside. The fundamental resonant frequency of burrows, measured with broadcast noise and pure tones, ranges from 842 to 1836 Hz and is significantly correlated with the burrow's length. Burrows change the spectral envelope of incoming calls by increasing the amplitude of lower relative to higher harmonics. The call amplification effect inside burrows of E. calcaratus parallels the effect reported previously for E. emiliopugini, and indicates that the acoustic properties of calling sites may affect signal reception by burrowing animals.     

Vocalization-correlated respiratory movements in the squirrel monkey

Respiratory abdominal movements associated with vocalization were recorded in awake squirrel monkeys. Several call types, such as peeping, trilling, cackling, and err-chucks, were accompanied by large vocalization-correlated respiratory movements (VCRM) that started before vocalization. During purring, in contrast, only small VCRM were recorded that started later after vocal onset. VCRM during trill calls, a vocalization type with repetitive frequency modulation, showed a modulation in the rhythm of the frequency changes. A correlation with amplitude modulation was also present, but more variable. As high frequencies need a higher lung pressure for production than low frequencies, the modulation of VCRM seems to serve to optimize the lung pressure in relation to the vocalization frequency. The modulation, furthermore, may act as a mechanism to produce different trill variants. During err-chucks and staccato peeps, which show a large amplitude modulation, a nonmodulated VCRM occurred. This indicates the existence of a laryngeal amplitude-controlling mechanism that is independent from respiration.     

The relationship between acoustic structure and semantic information in Diana monkey alarm vocalization

Mammalian vocal production mechanisms are still poorly understood despite their significance for theories of human speech evolution. Particularly, it is still unclear to what degree mammals are capable of actively controlling vocal-tract filtering, a defining feature of human speech production. To address this issue, a detailed acoustic analysis on the alarm vocalization of free-ranging Diana monkeys was conducted. These vocalizations are especially interesting because they convey semantic information about two of the monkeys' natural predators, the leopard and the crowned eagle. Here, vocal tract and sound source parameter in Diana monkey alarm vocalizations are described. It is found that a vocalization-initial formant downward transition distinguishes most reliably between eagle and leopard alarm vocalization. This finding is discussed as an indication of articulation and alternatively as the result of a strong nasalization effect. It is suggested that the formant modulation is the result of active vocal filtering used by the monkeys to encode semantic information, an ability previously thought to be restricted to human speech.     

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.     

A wavelet packet adaptive filtering algorithm for enhancing manatee vocalizations

Approximately a quarter of all West Indian manatee (Trichechus manatus latirostris) mortalities are attributed to collisions with watercraft. A boater warning system based on the passive acoustic detection of manatee vocalizations is one possible solution to reduce manatee-watercraft collisions. The success of such a warning system depends on effective enhancement of the vocalization signals in the presence of high levels of background noise, in particular, noise emitted from watercraft. Recent research has indicated that wavelet domain pre-processing of the noisy vocalizations is capable of significantly improving the detection ranges of passive acoustic vocalization detectors. In this paper, an adaptive denoising procedure, implemented on the wavelet packet transform coefficients obtained from the noisy vocalization signals, is investigated. The proposed denoising algorithm is shown to improve the manatee detection ranges by a factor ranging from two (minimum) to sixteen (maximum) compared to high-pass filtering alone, when evaluated using real manatee vocalization and background noise signals of varying signal-to-noise ratios (SNR). Furthermore, the proposed method is also shown to outperform a previously suggested feedback adaptive line enhancer (FALE) filter on average 3.4 dB in terms of noise suppression and 0.6 dB in terms of waveform preservation.     

Developmental changes in ultrasonic vocalizations by infant Japanese echolocating bats, Pipistrellus abramus

Developmental changes in vocalizations by Pipistrellus abramus were investigated during the first post-natal month. Vocalizations by pups on the day of birth were frequency-modulated ultrasounds from 30.0 ± 4.0 kHz to 19.3 ± 1.9 kHz with multiple harmonics. The terminal frequency of the second harmonic (TF(2)) of pup vocalizations corresponded to that of the fundamental (TF(1)) in adult bats (41.4 ± 2.6 kHz), suggesting that pup vocalizations can be easily detected by the mother. In addition, there are two types of infant vocalization: short duration echolocation precursor and long duration isolation calls, which showed separate developmental patterns over time.     

Vocal learning in Budgerigars (Melopsittacus undulatus): effects of an acoustic reference on vocal matching

Budgerigars were trained to produce specific vocalizations (calls) using operant conditioning and food reinforcement. The bird's call was compared to a digital representation of the call stored in a computer to determine a match. Once birds were responding at a high level of precision, we measured the effect of several manipulations upon the accuracy and the intensity of call production. Also, by differentially reinforcing other aspects of vocal behavior, budgerigars were trained to produce a call that matched another bird's contact call and to alter the latency of their vocal response. Both the accuracy of vocal matching and the intensity level of vocal production increased significantly when the bird could hear the template immediately before each trial. Moreover, manipulating the delay between the presentation of an acoustic reference and the onset of vocal production did not significantly affect either vocal intensity or matching accuracy. Interestingly, the vocalizations learned and reinforced in these operant experiments were only occasionally used in more natural communicative situations, such as when birds called back and forth to one another in their home cages.     

一维非线性声波传播特性

针对一维非线性声波的传播问题进行了有限元仿真和实验研究. 首先推导了一维非线性声波方程的有限元形式, 含有高阶矩阵的非线性项导致声波具有波形畸变、谐波滋生、基频信号能量向高次谐波传递等非线性特性. 编制有限元程序对一维非线性声波进行了计算并对仿真得到的畸变非线性声波信号进行处理, 分析其传播性质和物理意义. 为验证有限元计算结果, 开展了水中的非线性声波传播的实验研究, 得到了不同输入信号幅度激励下和不同传播距离的畸变非线性声波信号. 然后对基波和二次谐波的传播性质进行详细讨论, 分析了二次谐波幅度与传播距离和输入信号幅度的变化关系及其意义, 拟合出二次谐波幅度随传播距离变化的方程并阐述了拟合方程的物理意义. 结果表明, 数值仿真信号及其频谱均与实验结果有较好的一致性, 证实计算方法和结果的正确性, 并提出了具有一定物理意义的二次谐波随传播距离变化的简单数学关系. 最后还对固体中的非线性声波传播性质进行了初步探讨. 本研究工作可为流体介质中的非线性声传播问题提供理论和实验依据.     

Identification of fish vocalizations from ocean acoustic data

A new method for identification of fish vocalizations based on auditory analysis and support vector machine (SVM) classification is presented. In this method, high resolution features have been extracted from fish vocalization data using the amplitude modulation spectrogram (AMS) of the input signals to facilitate the identification of grunts and growls made by a highly vocal wild fish, Porichthys notatus. The comparison results made from ocean audio recordings verify the effectiveness of the proposed method in identifying various types of fish vocalizations. The relationships between signal-to-noise ratio (SNR) and ocean temperature with the accuracy of the proposed method have also been quantified. Moreover, a context-aware prediction algorithm is introduced for estimating the continuous data.     

Age-related differences in the acoustic characteristics of male leopard seals, Hydrurga leptonyx

During the breeding season, the underwater vocalizations and calling rates of adult male leopard seals are highly stereotyped. In contrast, sub-adult males have more variable acoustic behavior. Although adult males produce only five stereotyped broadcast calls as part of their long-range underwater breeding displays the sub-adults have a greater repertoire including the adult-like broadcast calls, as well as variants of these. Whether this extended repertoire has a social function is unknown due to the paucity of behavioral data for this species. The broadcast calls of the sub-adults are less stereotyped in their acoustic characteristics and they have a more variable calling rate. These age-related differences have major implications for geographic variation studies, where the acoustic behavior of different populations are compared, as well as for acoustic surveying studies, where numbers of calls are used to indicate numbers of individuals present. Sampling regimes which unknowingly include recordings from sub-adult animals will artificially exaggerate differences between populations and numbers of calling animals. The acoustic behavior of sub-adult and adult male leopard seals were significantly different and although this study does not show evidence that these differences reflect vocal learning in the male leopard seal it does suggest that contextual learning may be present.     

Amplitude modulation of turbulence noise by voicing in fricatives

The two principal sources of sound in speech, voicing and frication, occur simultaneously in voiced fricatives as well as at the vowel-fricative boundary in phonologically voiceless fricatives. Instead of simply overlapping, the two sources interact. This paper is an acoustic study of one such interaction effect: the amplitude modulation of the frication component when voicing is present. Corpora of sustained and fluent-speech English fricatives were recorded and analyzed using a signal-processing technique designed to extract estimates of modulation depth. Results reveal a pattern, consistent across speaking style, speaker, and place of articulation, for modulation at fo to rise at low voicing strengths and subsequently saturate. Voicing strength needed to produce saturation varied 60-66 dB across subjects and experimental conditions. Modulation depths at saturation varied little across speakers but significantly for place of articulation (with [z] showing particularly strong modulation) clustering at approximately 0.4-0.5 (a 40%-50% fluctuation above and below unmodulated amplitude); spectral analysis of modulating signals revealed weak but detectable modulation at the second and third harmonics (i.e., 2fo and 3fo).     

Obtaining acoustic similarity measures from animals: a method for species comparisons

An efficient procedure has been developed for obtaining similarity measures for complex acoustic signals in small birds. Birds were trained using operant conditioning procedures to detect changes in the repeating background of an ongoing sound. Response latencies for detection were used to construct similarity matrices. Multidimensional scaling procedures were then used to produce spatial maps of these complex sounds reflecting perceptual organization. An example using contact calls from two avian species is described.     

Analysis and localization of blue whale vocalizations in the Solomon Sea using waveform amplitude data

During the Woodlark Basin seismic experiment in eastern Papua New Guinea (1999-2000), an ocean-bottom seismic array recorded marine mammal vocalizations along with target earthquake signals. The array consisted of 14 instruments, 7 of which were three-component seismometers with a fourth component hydrophone. They were deployed at 2.0-3.2 km water depth and operated from September 1999 through February 2000. While whale vocalizations were recorded throughout the deployment, this study focuses on 3 h from December 21, 1999 during which the signals are particularly clear. The recordings show a blue whale song composed of a three-unit phrase. That song does not match vocalization characteristics of other known Pacific subpopulations and may represent a previously undocumented blue whale song. Animal tracking and source level estimates are obtained with a Bayesian inversion method that generates probabilistic source locations. The Bayesian method is augmented to include travel time estimates from seismometers and hydrophones and acoustic signal amplitude. Tracking results show the whale traveled northeasterly over the course of 3 h, covering approximately 27 km. The path followed the edge of the Woodlark Basin along a shelf that separates the shallow waters of the Trobriand platform from the deep waters of the basin.     

Accurate analysis of multitone signals using a DFT

Optimum data windows make it possible to determine accurately the amplitude, phase, and frequency of one or more tones (sinusoidal components) in a signal. Procedures presented in this paper can be applied to noisy signals, signals having moderate nonstationarity, and tones close in frequency. They are relevant to many areas of acoustics where sounds are quasistationary. Among these are acoustic probes transmitted through media and natural sounds, such as animal vocalization, speech, and music. The paper includes criteria for multitone FFT block design and an example of application to sound transmission in the atmosphere.     

Temporal integration of acoustic signals by the budgerigar (Melopsittacus undulatus)

Avoidance conditioning and a modified method of limits psychophysical procedure were used to study temporal integration of tone and noise signals in the budgerigar (Melopsittacus undulatus). Integration of both tone and noise signals can be described by a negative exponential function with a time constant of about 200 ms. At very short durations there were differences in the integration of tone and noise signals. These data are similar to those reported for a number of other vertebrates, including man. Thresholds for two complex natural vocalizations of the budgerigar are similar to those of pure tones of equivalent duration.     

Laryngeal and respiratory activity during vocalization in macaque monkeys

The present study describes the laryngeal and respiratory muscle activity associated with vocalizations in macaque monkeys. During the bark vocalization, a short, aperiodic call, the cricothyroid, thyroarytenoid, rectus abdominis, and intercostals were active while the posterior cricoarytenoid and diaphragm were quiet. During the coo vocalization, a longer, clear call, the cricothyroid, thyroarytenoid, intercostals, rectus abdominis, and diaphragm were active. In one monkey, the posterior cricoarytenoid was also active during the call, while in another monkey it was not. Laryngeal muscle activity was correlated with the amplitude and duration of the coo call. Results suggest that the amplitude and duration differences between calls are determined primarily by laryngeal modification of the airflow, and that the differences in posterior cricoarytenoid activity may be due to differences in voice intensity.     

Pulse register phonation in Diana monkey alarm calls

The adult male Diana monkeys (Cercopithecus diana) produce predator-specific alarm calls in response to two of their predators, the crowned eagles and the leopards. The acoustic structure of these alarm calls is remarkable for a number of theoretical and empirical reasons. First, although pulsed phonation has been described in a variety of mammalian vocalizations, very little is known about the underlying production mechanism. Second, Diana monkey alarm calls are based almost exclusively on this vocal production mechanism to an extent that has never been documented in mammalian vocal behavior. Finally, the Diana monkeys' pulsed phonation strongly resembles the pulse register in human speech, where fundamental frequency is mainly controlled by subglottal pressure. Here, we report the results of a detailed acoustic analysis to investigate the production mechanism of Diana monkey alarm calls. Within calls, we found a positive correlation between the fundamental frequency and the pulse amplitude, suggesting that both humans and monkeys control fundamental frequency by subglottal pressure. While in humans pulsed phonation is usually considered pathological or artificial, male Diana monkeys rely exclusively on pulsed phonation, suggesting a functional adaptation. Moreover, we were unable to document any nonlinear phenomena, despite the fact that they occur frequently in the vocal repertoire of humans and nonhumans, further suggesting that the very robust Diana monkey pulse production mechanism has evolved for a particular functional purpose. We discuss the implications of these findings for the structural evolution of Diana monkey alarm calls and suggest that the restricted variability in fundamental frequency and robustness of the source signal gave rise to the formant patterns observed in Diana monkey alarm calls, used to convey predator information.     

Acoustic detection of North Atlantic right whale contact calls using the generalized likelihood ratio test

This paper addresses the problem of passive acoustic detection of contact calls produced by the highly endangered North Atlantic right whale Eubalaena glacialis. The proposed solution is based on using a generalized likelihood ratio test detector of polynomial-phase signals with unknown amplitude and polynomial coefficients observed in the presence of locally stationary Gaussian noise. The closed form representation for a minimal sufficient statistic is derived and a realizable detection scheme is developed. The receiver operation characteristic curves are calculated using empirical data recordings containing known right whale calls. The curves demonstrate that the proposed detector provides superior detection performance as compared with other known detection techniques for northern right whale contact calls.