Feature weighting in "chick-a-dee" call notes of Poecile atricapillus

Artificial neural networks were trained to discriminate between different note types from the black-capped chickadee (Poecile atricapillus) "chick-a-dee" call. Each individual note was represented as a vector of summary features taken from note spectrograms and networks were trained to respond to exemplar notes of one type and to fail to respond to exemplar notes of another type. Following initial network training, the network was presented novel notes in which individual acoustic features had been modified. The strength of the response of the network to each novel and shifted note was recorded. When network responses were plotted as a function of the degree of acoustic feature modification and training context, it became clear that modifications of some acoustic features had significant effects on network responses, while others did not. Moreover, the training context of the network also played a role in the responses of networks to manipulated test notes. The implications of using artificial neural networks to generate testable hypotheses for animal research and the role of context are discussed.     

Artificial neural network discrimination of black-capped chickadee (Poecile atricapillus) call notes

Artificial neural networks were trained to discriminate between two different notes from the "chick-a-dee" call of the black-capped chickadee (Poecile atricapillus). An individual note was represented as a vector of nine summary features taken from note spectrograms. A network was trained to respond to exemplar notes of one type (e.g., A notes) and to fail to respond to exemplar notes of another type (e.g., B notes). After this training, the network was presented novel notes of the two different types, as well as notes of the same two types that had been shifted upwards or downwards in frequency. The strength of the response of the network to each novel and shifted note was recorded. When network responses were plotted as a function of the degree of frequency shift, the results were very similar to those observed in birds that were trained in an analogous task [Charrier et al., J. Comp. Psychol. 119(4), 371-380 (2005)]. The implications of these results to simulating behavioral studies of animal communication are discussed.     

Development of a contact call in black-capped chickadees (Poecile atricapillus) hand-reared in different acoustic environments

The tseet contact call, common to black-capped (Poecile atricapillus) and mountain chickadees (P. gambeli), is the most frequently produced vocalization of each species. Previous work has characterized the tseet call of black-capped and mountain chickadees from different geographic locations in terms of nine acoustic features. In the current study, using similar methods, the tseet call of black-capped chickadees that were hand reared with either conspecifics, heterospecifics (mountain chickadees), or in isolation from adult chickadees are described. Analysis of call features examined which acoustic features were most affected by rearing environment, and revealed that starting frequency and the slope of the descending portion of the tseet call differed between black-capped chickadees reared with either conspecific or heterospecific adults. Birds reared in isolation from adults differed from the other hand-reared groups on almost every acoustic feature. Chickadee tseet calls are more individualized when they are reared with adult conspecifics or heterospecifics compared to chickadees that are reared in isolation from adults. The current results suggest a role of learning in this commonly used contact call.     

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.     

Tonal vocalizations in the red wolf (Canis rufus): potential functions of nonlinear sound production

The purpose of this study is to further understanding of the function of nonlinear vocalizations in red wolves (Canis rufus) by examining the acoustic, structural, and contextual characteristics of nonlinear sounds as compared to linear sounds. Video recordings of captive wolves from a breeding facility were analyzed. The acoustic nature of sound units was consistent with that of other social canids. The sound units included high-frequency squeaks (2600-9500 Hz) and low-frequency wuhs (160-1600 Hz) occurring either as separate units or in combination as nonlinear units (squeak-wuh frequency jumps, biphonations, squeaks with sidebands) and frequency jumps within squeaks. These low-amplitude sounds occurred in trains of 1-30 units that were classified as squeak vocalizations (49%), wuh vocalizations (19%), and nonlinear vocalizations (any combination including one or more nonlinear units, 32%). Nonlinear vocalizations transitioned directionally from high-frequency units to mixed-frequency units which has implications for the study of sound production and function. Wolves squeaked most often when oriented toward others, implying a solicitation function, while wuh vocalizations were more common during social interactions. Nonlinear vocalizations occurred most often during penmate-play or when oriented toward neighbors, indicating that nonlinear sound production may signal an increase in arousal.     

Seismic properties of Asian elephant (Elephas maximus) vocalizations and locomotion

Seismic and acoustic data were recorded simultaneously from Asian elephants (Elephas maximus) during periods of vocalizations and locomotion. Acoustic and seismic signals from rumbles were highly correlated at near and far distances and were in phase near the elephant and were out of phase at an increased distance from the elephant. Data analyses indicated that elephant generated signals associated with rumbles and "foot stomps" propagated at different velocities in the two media, the acoustic signals traveling at 309 m/s and the seismic signals at 248-264 m/s. Both types of signals had predominant frequencies in the range of 20 Hz. Seismic signal amplitudes considerably above background noise were recorded at 40 m from the generating elephants for both the rumble and the stomp. Seismic propagation models suggest that seismic waveforms from vocalizations are potentially detectable by instruments at distances of up to 16 km, and up to 32 km for locomotion generated signals. Thus, if detectable by elephants, these seismic signals could be useful for long distance communication.     

Automatic classification and speaker identification of African elephant (Loxodonta africana) vocalizations

A hidden Markov model (HMM) system is presented for automatically classifying African elephant vocalizations. The development of the system is motivated by successful models from human speech analysis and recognition. Classification features include frequency-shifted Mel-frequency cepstral coefficients (MFCCs) and log energy, spectrally motivated features which are commonly used in human speech processing. Experiments, including vocalization type classification and speaker identification, are performed on vocalizations collected from captive elephants in a naturalistic environment. The system classified vocalizations with accuracies of 94.3% and 82.5% for type classification and speaker identification classification experiments, respectively. Classification accuracy, statistical significance tests on the model parameters, and qualitative analysis support the effectiveness and robustness of this approach for vocalization analysis in nonhuman species.     

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.     

Dynamics of communal vocalizations in a social songbird, the zebra finch (Taeniopygia guttata)

Colonies or communities of animals such as fishes, frogs, seabirds, or marine mammals can be noisy. Although vocal communication between clearly identified sender(s) and receiver(s) has been well studied, the properties of the noisy sound that results from the acoustic network of a colony of gregarious animals have received less attention. The resulting sound could nonetheless convey some information about the emitting group. Using custom-written software for automatic detection of vocalizations occurring over many hours of recordings, this study reports acoustic features of communal vocal activities in a gregarious species, the zebra finch (Taeniopygia guttata). By biasing the sex ratio and using two different housing conditions (individual versus communal housing), six groups of zebra finches were generated, with six different social structures that varied both in terms of sex-composition and proportion of paired individuals. The results showed that the rate of emission and the acoustic dynamic both depended on the social structure. In particular, the vocal activity of a group of zebra finches depended mainly on the number of unpaired birds, i.e., individuals not part of a stably bonded pair.     

Effects of noise levels and call types on the source levels of killer whale calls

Accurate parameter estimates relevant to the vocal behavior of marine mammals are needed to assess potential effects of anthropogenic sound exposure including how masking noise reduces the active space of sounds used for communication. Information about how these animals modify their vocal behavior in response to noise exposure is also needed for such assessment. Prior studies have reported variations in the source levels of killer whale sounds, and a more recent study reported that killer whales compensate for vessel masking noise by increasing their call amplitude. The objectives of the current study were to investigate the source levels of a variety of call types in southern resident killer whales while also considering background noise level as a likely factor related to call source level variability. The source levels of 763 discrete calls along with corresponding background noise were measured over three summer field seasons in the waters surrounding the San Juan Islands, WA. Both noise level and call type were significant factors on call source levels (1-40 kHz band, range of 135.0-175.7 dB(rms) re 1 [micro sign]Pa at 1 m). These factors should be considered in models that predict how anthropogenic masking noise reduces vocal communication space in marine mammals.     

Variation in chick-a-dee calls of tufted titmice, Baeolophus bicolor: note type and individual distinctiveness

The chick-a-dee call of chickadee species (genus Poecile) has been the focus of much research. A great deal is known about the structural complexity and the meaning of variation in notes making up calls in these species. However, little is known about the likely homologous "chick-a-dee" call of the closely related tufted titmouse, Baeolophus bicolor. Tufted titmice are a prime candidate for comparative analyses of the call, because their vocal and social systems share many characteristics with those of chickadees. To address the paucity of data on the structure of chick-a-dee calls of tufted titmice, we recorded birds in field and aviary settings. Four main note types were identified in the call: Z, A, D(h), and D notes. Several acoustic parameters of each note type were measured, and statistical analyses revealed that the note types are acoustically distinct from one another. Furthermore, note types vary in the extent of individual distinctiveness reflected in their acoustic parameters. This first step towards understanding the chick-a-dee call of tufted titmice indicates that the call is comparable in structure and complexity to the calls of chickadees.     

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.     

MPEG-2先进音频编码(AAC)的研究和软件仿真

ＭＰＥＧ－２ＡＡＣ是ＩＳＯ／ＩＥＣ ＭＰＥＧ组织继 ＭＰＥＧ－１、ＭＰＥＧ－２音频编解码标准后,制定 的最新国际标准（ＩＳＯ／ＩＥＣ １３８１８－７）,在６４ｋｂｐｓ／每声道低码率时能提供全透明音质。本文对其编 解码算法进行了简要介绍。论文作者对ＭＰＥＧ－２ＡＡＣ进行了软件仿真,文中介绍了仿真结果,仿 真时对ＡＡＣ标准所附编码范例中的一些不妥之处,作了改进,文中列举了６方面的修正。     

MPEG-2先进音频编码(AAC)的研究和软件仿真

ＭＰＥＧ－２３ＡＡＣ是ＩＳＯ／ＩＥＣＭＰＥＧ组织继ＭＰＥＧ－１,ＭＰＥＧ－２音频编解码标准后,制定的最新国际标准（ＩＳＯ／ＩＥＣ１３８１８－７）在６４ｋｂｐｓ／每声道低码率时能提供全透明音质,本文对其编解码算法进行了简要介绍,论文作者对ＭＰＥＧ－２ＡＡＣ进行了软件仿真,文中介绍了仿真结果,仿真时对ＡＡＣ标准所附编码范 中的一些不妥之处,作了改进,文中列举了６方面的修正。     

Note on the spring region of Gacka River (Croatia)

We present the first results of a study of the Gacka River spring area, an important Croatian drinking water resource. Stable isotope data (obtained at the Stable Isotope Laboratory SILab in Rijeka) are used in combination with hydrological and meteorological data. The delta18O values give information on the mean catchment altitudes of the three main springs of Gacka River (Majerovo vrelo, Tonkovica vrelo and Pecina). Hydrological, meteorological and stable isotope data indicate good mixing of infiltrated and ground waters. The precipitation d-excess shows a seasonally varying influence of continental and maritime air masses.     

Sources of acoustic variation: implications for production specificity and call categorization in chacma baboon (Papio ursinus) grunts

Elucidating the information content of vocal signals is fundamental to the understanding of animal communication. Acoustically distinct calls produced in specific contexts allow listeners to predict future events and choose adequate responses. However, the vocal repertoires of most terrestrial mammals consist of a limited number of call types that vary within and between categories. These "graded signaling systems" are thought to be rich in information, at the cost of increasing uncertainty regarding call categorization. In this study, patterns of acoustic variation in grunts of wild chacma baboons (Papio ursinus) were assessed in relation to different contexts, callers' arousal, the presence of listeners, and individual identity. Although overall production specificity was low, and sensitive to the number of contexts under consideration, grunts given in three contexts could be statistically distinguished from each other. Contextual differences remained when controlling for caller arousal, suggesting that these differences cannot be explained by variation in arousal. No audience effect was detected, but individual identity was found to have an influence on acoustic structure. Overall, these results support the view that, in comparison to other signaling systems associated with hazardous conditions, lower production specificity might evolve under relaxed circumstances where unambiguous signaling is less important.     

A Note on Spin of Skyrmions in the (2+1)-DO(3) Non-Linear σ Model

It is shown that, by usual definition about the Hopf term, the Skyrmions in the (2+1)-DO(3) non-linear σ model with this term have only integer spin. A modified definition about the term is suggested to make the Skyrmiona have probability to poaaeas fractional spin.