Repeated decrease in vocal repertoire size in Streptopelia doves

Most bird species produce different acoustic signals in different behavioural contexts. This intraspecific variation in signal types is thought to be the result of selection for optimal communication in each context. Doves in the genus Streptopelia have three distinct behavioural contexts in which they produce coo vocalizations. Some Streptopelia species have three acoustically similar coo vocalizations associated with the three contexts, but in others the coo vocalizations differ in acoustic structure. Using a well-resolved phylogeny, we examined whether acoustic differentiation between coo types was the ancestral state. Unexpectedly, the results showed that the common ancestor of Streptopelia had differentiated coos rather than a single coo type. This result implies that context-specific acoustic signals disappeared from the vocal repertoire independently at least two times. We further tested whether different context-dependent signal types follow different evolutionary pathways and whether they differ in rate of evolutionary change. We found that the long-range signal (perch-coo) evolves at a higher rate than the short-range signal (bow-coo). These results are discussed in relation to selection for species recognition and transmission requirements.     

Effects of proximity and behavioral context on acoustic variation in the coo calls of Japanese macaques

Acoustic features of coo calls in Japanese macaques (Macaca fuscata) show large and graded variation. To explore the relevance of acoustic variation in coo calls, I examined whether acoustic features differed by the caller's activity and proximity to group members. The subjects were five adult females from a wild, habituated group of Japanese macaques consisting of 23 individuals. Coo calls from the five females were recorded with their activity and proximity to group members. Acoustic features of 280 calls were measured with a sound spectrograph. Some of the acoustic variables differed by proximity but not by activity. The callers produced coo calls with larger frequency modulation and longer duration when they were far from group members compared to when they were near another member. The results suggest that Japanese macaques produce calls with more detectable and locatable features depending on the proximity to group members.     

Cross-Sectional and Longitudinal Studies of the Development of Group Differences in Acoustic Features of Coo Calls in Two Groups of Japanese Macaques

Japanese macaques, Macaca fuscata, frequently utter coo calls to maintain vocal contact. Cross‐sectional and longitudinal comparisons were conducted on the acoustic features of coo vocalizations of two groups of M. fuscata, Yakushima and Ohirayama groups, to explore the possibility of vocal plasticity. These two groups derive from the same local population but have been separated for more than 34 yr. The Yakushima group is non‐provisioned, while the Ohirayama group is provisioned. Initially, coo calls in the two groups were compared cross‐sectionally in females ranging from 0 to 18 yr. Mean values of the four variables studied (start, end, maximum, and minimum frequencies) were consistently lower in all age groups of the Ohirayama individuals compared with the Yakushima individuals. Secondly, longitudinal comparisons were conducted on individuals in the 1–4 yr after birth. Mean values of the five frequency variables studied (start, end, maximum, minimum and average frequencies) were again consistently lower in all age groups of Ohirayama compared with Yakushima individuals, although mean values of both groups gradually declined with an increase in age. Inter‐group differences were significant at all ages in minimum frequency and at the first, second and third years in start frequency. Longitudinal comparisons of individuals aged 4–11 mo were also conducted. Regarding the four variables that differed between the two groups in the cross‐sectional study, the mean values of minimum and start frequency did not differ significantly between the two groups at 4–5 mo, but were significantly lower in Ohirayama individuals aged 7–8 and 9–11 mo. Although provisioning may have had an effect on the weight difference between the groups, and consequently on vocalization frequency, these results suggest that the inter‐group differences in coo call features form approximately 6–7 mo after birth as a result of vocal plasticity.     

Changes In Rhesus Macaque 'Coo' Vocalizations during Early Development

In order to test whether ‘coo’ calls of young rhesus macaques, Macaca mulatta, undergo some modifications during early development, and to explore which factors may influence these changes, we studied the ontogeny of their contact call, the ‘coo’ call. Vocalizations were recorded during brief periods of social separation. Infants were either raised with their mothers and other conspecifics, or separated from their mothers at birth and housed in a nursery with other infants. We recorded calls uttered in the separation context from 20 infants. We digitized the first 50 calls of a given series and subjected them to a Fourier transform. From each frequency–time spectrum, we extracted 65 acoustic parameters using a software program (LMA 5.9). We then used a cluster analysis to separate the ‘coo’ calls from other call types. With increasing age, the ‘coos’ dropped in pitch and became more even. The course of amplitude became more constant and the call duration increased slightly. Nevertheless, we found a high intra‐individual variation throughout the 5 mo. Neither rearing condition nor sex had any apparent influence on age‐related changes in ‘coo’ structure. With one exception, all parameters that correlated with age could be explained by variation in weight. Therefore, we conclude that growth is the main factor accounting for the observed changes.     

Individual Signature in Canary Songs: Contribution of Multiple Levels of Song Structure

Through variations in features, both within and between individuals, songs of male passerines provide information on the identity of the singer. In domesticated canaries (Serinus canaria), these variations remain, for a large part, to be investigated. This led us to question whether individual identity might be coded at one or more hierarchical levels of song organization, i.e. in acoustic parameters, in the syllable repertoire and in the delivery order of syllables. A song as a whole had numerous individual distinctive acoustic features. However, the structure of its individual signature appeared to be complex. A repertoire combined syllables never sung by other individuals with those shared by other birds. But, most of the individual‐specific syllables that accounted for 16% of a repertoire did not recur frequently. Variation in sequences of multiple syllable types appeared to reflect the individual identity of a male canary. Nearly all sequences larger than three syllable types were specific to the individual that produced them. Some of these occurred recurrently in songs and differed in their acoustic structure between individuals. Focusing upon recurrent sequences might allow vocal recognition of an individual without requiring the knowledge of its full repertoire. However, acoustic parameters and repertoire composition might also serve as additional cues to limit confusion between individuals.     

The effect of isolation,fragmentation, and population bottlenecks on song structure of a Hawaiian honeycreeper

Little is known about how important social behaviors such as song vary within and among populations for any of the endemic Hawaiian honeycreepers. Habitat loss and non‐native diseases (e.g., avian malaria) have resulted in isolation and fragmentation of Hawaiian honeycreepers within primarily high elevation forests. In this study, we examined how isolation of Hawai'i ‘amakihi (Chlorodrepanis virens) populations within a fragmented landscape influences acoustic variability in song. In the last decade, small, isolated populations of disease tolerant ‘amakihi have been found within low elevation forests, allowing us to record ‘amakihi songs across a large elevational gradient (10–1800 m) that parallels disease susceptibility on Hawai'i island. To understand underlying differences among populations, we examined the role of geographic distance, elevation, and habitat structure on acoustic characteristics of ‘amakihi songs. We found that the acoustic characteristics of ‘amakihi songs and song‐type repertoires varied most strongly across an elevational gradient. Differences in ‘amakihi song types were primarily driven by less complex songs (e.g., fewer frequency changes, shorter songs) of individuals recorded at low elevation sites compared to mid and high elevation populations. The reduced complexity of ‘amakihi songs at low elevation sites is most likely shaped by the effects of habitat fragmentation and a disease‐driven population bottleneck associated with avian malaria, and maintained through isolation, localized song learning and sharing, and cultural drift. These results highlight how a non‐native disease through its influence on population demographics may have also indirectly played a role in shaping the acoustic characteristics of a species.     

Individuality but not Stability in Marmoset Long Calls

Individually distinct communication signals (‘signatures’) have been documented in a variety of taxa across signal modalities and they serve a host of important functions. However, studies have rarely examined the temporal stability of these signals. Cooperatively breeding species, such as marmosets and tamarins, are characterized by long-term group membership, complex social organization, and high levels of interindividual coordination of behaviour. These social attributes may promote complex, individually distinct and stable acoustic signals to facilitate the expression of cooperative behaviour. In this study, the long calls of socially housed individual Wied's black tufted-ear marmosets, Callithrix kuhli, were examined for a ‘signature system’ potentially important in such interactions. Vocalizations were recorded at three different times (1993, 1995, 1996), digitized, and then measured by spectrographic analysis. Acoustic and temporal features of the calls were examined, including number of syllables, length of syllables, intersyllable interval, frequency range, start/stop frequency, peak frequency, and total call duration. A number of significant intra-individual changes in acoustic parameters were identified across the recording periods. Discriminant analysis revealed that many variables contributed to differentiation among individuals, and average classification accuracy for calls within a given year was high, ranging from 91.7% to 93.5%. However, reclassification accuracy for calls between-years was much poorer, averaging less than 50%. In addition, classification confidence was higher for within-year scores in contrast to the between-year values. Thus, tufted-ear marmosets have an individually distinct vocalization which is acoustically modified across time. Our finding suggests that to the extent that the vocalization is used for individual recognition, recognition mechanisms must be modified over time as well.     

体征对灰眉岩鹀鸣唱特征的影响

声信号是鸟类交流的重要方式。鸟类的鸣声特征受到生境的塑造和性选择,也受到发声器官的影响,如种间的比较研究发现,体重大的鸟类鸣声频率低,喙短的鸟类鸣声频宽大。在种内是否也存在类似的规律,目前的结论还不一致。2012年6月,在北京小龙门地区(40°00'N,115°26'E)测量了17只灰眉岩鹀(Emberiza godlewskii)的形态参数以及鸣声的频率特征,未发现体重或喙长与鸣声的最高频率、最低频率、峰频或频宽存在显著的相关性。本研究的结果支持在小型雀形目鸟类中,体型对繁殖期鸣唱频率特征的影响不显著。     

Traffic noise differentially impacts call types in a Japanese treefrog (Buergeria japonica)

Acoustic noise from automobile traffic impedes communication between signaling animals. To overcome the acoustic interference imposed by anthropogenic noise, species across taxa adjust their signaling behavior to increase signal saliency. As most of the spectral energy of anthropogenic noise is concentrated at low acoustic frequencies, species with lower frequency signals are expected to be more affected. Thus, species with low-frequency signals are under stronger pressure to adjust their signaling behaviors to avoid auditory masking than species with higher frequency signals. Similarly, for a species with multiple types of signals that differ in spectral characteristics, different signal types are expected to be differentially masked. We investigate how the different call types of a Japanese stream breeding treefrog (Buergeria japonica) are affected by automobile traffic noise. Male B. japonica produce two call types that differ in their spectral elements, a Type I call with lower dominant frequency and a Type II call with higher dominant frequency. In response to acoustic playbacks of traffic noise, B. japonica reduced the duration of their Type I calls, but not Type II calls. In addition, B. japonica increased the call effort of their Type I calls and decreased the call effort of their Type II calls. This result contrasts with prior studies in other taxa, which suggest that signalers may switch to higher frequency signal types in response to traffic noise. Furthermore, the increase in Type I call effort was only a short-term response to noise, while reduced Type II call effort persisted after the playbacks had ended. Overall, such differential effects on signal types suggest that some social functions will be disrupted more than others. By considering the effects of anthropogenic noise across multiple signal types, these results provide a more in-depth understanding of the behavioral impacts of anthropogenic noise within a species.     

The Modulation Transfer Function for Speech Intelligibility

We systematically determined which spectrotemporal modulations in speech are necessary for comprehension by human listeners. Speech comprehension has been shown to be robust to spectral and temporal degradations, but the specific relevance of particular degradations is arguable due to the complexity of the joint spectral and temporal information in the speech signal. We applied a novel modulation filtering technique to recorded sentences to restrict acoustic information quantitatively and to obtain a joint spectrotemporal modulation transfer function for speech comprehension, the speech MTF. For American English, the speech MTF showed the criticality of low modulation frequencies in both time and frequency. Comprehension was significantly impaired when temporal modulations <12 Hz or spectral modulations <4 cycles/kHz were removed. More specifically, the MTF was bandpass in temporal modulations and low-pass in spectral modulations: temporal modulations from 1 to 7 Hz and spectral modulations <1 cycles/kHz were the most important. We evaluated the importance of spectrotemporal modulations for vocal gender identification and found a different region of interest: removing spectral modulations between 3 and 7 cycles/kHz significantly increases gender misidentifications of female speakers. The determination of the speech MTF furnishes an additional method for producing speech signals with reduced bandwidth but high intelligibility. Such compression could be used for audio applications such as file compression or noise removal and for clinical applications such as signal processing for cochlear implants.     

Acoustic divergence in two cryptic Hipposideros species: a role for social selection?

We present evidence that a relatively widespread and common bat from South East Asia comprises two morphologically cryptic but acoustically divergent species. A population of the bicoloured leaf-nosed bat (Hipposideros bicolor) from Peninsular Malaysia exhibits a bimodal distribution of echolocation call frequencies, with peaks in the frequency of maximum energy at ca. 131 and 142 kHz. The two phonic types are genetically distinct, with a cytochrome b sequence divergence of just under 7%. We consider the mechanisms by which acoustic divergence in these species might arise. Differences in call frequency are not likely to effect resource partitioning by detectable prey size or functional range. However, ecological segregation may be achieved by differences in microhabitat use; the 131kHz H. bicolor is characterized by significantly longer forearms, lower wing loading, a lower aspect ratio and a more rounded wingtip, features that are associated with greater manoeuvrability in flight that may enable it to forage in more cluttered environments relative to the 142 kHz phonic type. We suggest that acoustic divergence in these species is a consequence of social selection for a clear communication channel, which is mediated by the close link between the acoustic signal and receptor systems imposed by the highly specialized nature of the hipposiderid and rhinolophid echolocation system.     

Superfast vocal muscles control song production in songbirds

Birdsong is a widely used model for vocal learning and human speech, which exhibits high temporal and acoustic diversity. Rapid acoustic modulations are thought to arise from the vocal organ, the syrinx, by passive interactions between the two independent sound generators or intrinsic nonlinear dynamics of sound generating structures. Additionally, direct neuromuscular control could produce such rapid and precisely timed acoustic features if syringeal muscles exhibit rare superfast muscle contractile kinetics. However, no direct evidence exists that avian vocal muscles can produce modulations at such high rates. Here, we show that 1) syringeal muscles are active in phase with sound modulations during song over 200 Hz, 2) direct stimulation of the muscles in situ produces sound modulations at the frequency observed during singing, and that 3) syringeal muscles produce mechanical work at the required frequencies and up to 250 Hz in vitro. The twitch kinematics of these so-called superfast muscles are the fastest measured in any vertebrate muscle. Superfast vocal muscles enable birds to directly control the generation of many observed rapid acoustic changes and to actuate the millisecond precision of neural activity into precise temporal vocal control. Furthermore, birds now join the list of vertebrate classes in which superfast muscle kinetics evolved independently for acoustic communication.     

Sources of Acoustic Variation in Rhesus Macaque (Macaca mulatta))Vocalizations

All species in the genus Macaca produce a set of harmonically rich vocalizations known as “coos”. Extensive acoustic variation occurs within this call type, a large proportion of which is thought to be associated with different social contexts such as mother-infant separation and the discovery of food. Prior studies of these calls have not taken into account the potential contributions of individual differences and changes in emotional or motivational state. To understand the function of a call and the perceptual salience of different acoustic features, however, it is important to determine the different sources of acoustic variation. I present data on the rhesus macaques' (M. mulatta) coo vocalization and attempt to establish some of the causes of acoustic variation. A large proportion of the variation observed was due to differences between individuals and to putative changes in arousal, not to differences in social context. Specifically, results from a discriminant-function analysis indicated that coo exemplars were accurately assigned to the appropriate individual, but vocal “signatures” were more variable in some contexts than in others. Moreover, vocal signatures may not always be reliable cues to caller identity because closely related individuals sound alike. Rhesus macaque coos evidently provide sufficient acoustic information for individual recognition and possibly kin recognition, but are unlikely to provide sufficient information about an external referent.     

Individually Specific Call Feature Is Not Used to Neighbour-Stranger Discrimination: The Corncrake Case

In various contexts, animals rely on acoustic signals to differentiate between conspecifics. Currently, studies examining vocal signatures use two main approaches. In the first approach, researchers search for acoustic characteristics that have the potential to be individual specific. This approach yields information on variation in signal parameters both within and between individuals and generates practical tools that can be used in population monitoring. In the second approach, playback experiments with natural calls are conducted to discern whether animals are capable of discriminating among the vocal signatures of different individuals. However, both approaches do not reveal the exact signal characteristics that are being used in the discrimination process. In this study, we tested whether an individual-specific call characteristic – namely the length of the intervals between successive maximal amplitude peaks within syllables (PPD) – is crucial in neighbour-stranger discrimination by males of the nocturnal and highly secretive bird species, the corncrake (Crex crex). We conducted paired playback experiments in which corncrakes (n = 47) were exposed to artificial calls with PPD characteristics of neighbour and stranger birds. These artificial calls differed only in PPD structure. The calls were broadcast from a speaker, and we recorded the birds'' behavioural responses. Although corncrakes have previously been experimentally shown to discriminate between neighbours and strangers, we found no difference in the responses to the artificial calls representing neighbours versus strangers. This finding demonstrates that even if vocal signatures are individual specific within a species, it does not automatically mean that said signatures are being crucial in discrimination among individuals. At the same time, the birds'' aggressive responses to the artificial calls indicated that the information transmitted by PPDs is important in species-specific call recognition and may be used by males and/or females to evaluate sender quality, similarly like sound frequency in some insect species.     

Temporal and structural features of infant calls in relation to caregiving behaviour in common marmosets,Callithrix j. jacchus

The role of infants in the communal rearing system of marmosets and tamarins has received little attention although their demands may not be complied by inadequate helpers. As acoustic signalling plays an important role in their social communication, it is expected to be an effective way for infants to signal their demand for care. As a first approach, this study focussed on the use and quality of ‘tsik’ calls given by infants of common marmosets (Callithrix j. jacchus) in the context of caregiving. The acoustic and non-acoustic behaviour of a group of common marmosets were recorded during the first two weeks of the life of two infants (twins). Vocalizations were classified, and the structure of the infants' ‘tsik’ calls was quantified by measuring specific signal parameters. Infants gave ‘tsik’ calls in close temporal relation to caregiving behaviour. Specific parameters covaried with the subsequent behaviour of potential caretakers. Values of call duration, start frequency, peak frequency, and range were lower when infants' calls were followed by no reaction or an approach of group members, whereas these parameters showed higher values when followed by a transfer of infants. Our results suggest that the actual demand of infants is encoded in the variations of ‘tsik’ calls.     

An acoustic valve within the nose of sperm whales Physeter macrocephalus

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Factors Affecting Acoustic Variation in Barbary-macaque (Macaca sylvanus) Disturbance Calls

Semi-free-ranging Barbary macaques (Macaca sylvanus) were observed to utter distinctive calls after disturbances in the surroundings (e.g. presence of a predator, occurrence of some unusual phenomenon). These calls differed from calls given in other contexts. Most of these calls were uttered in a serial manner, some of which lasted as long as the corresponding context. The aim of this study was to determine the object-related specificity of calls and variation of acoustic parameters within a call series. The analysis revealed that acoustic features of calls varied among contexts. Within one apparently homogeneous context, both temporal and frequency characteristics shifted gradually. Furthermore, the disturbance calls clearly differed between individuals. To examine the disturbance calls' meaning, playback experiments were conducted in which alarm calls and disturbance calls were presented. After playback of an alarm call, subjects typically showed an escape response, whereas, in response to disturbance calls, they most often scanned the surroundings. Juvenile animals generally showed stronger responses than adults.     

Overview on the Diversity of Sounds Produced by Clownfishes (Pomacentridae): Importance of Acoustic Signals in Their Peculiar Way of Life

Background

Clownfishes (Pomacentridae) are brightly colored coral reef fishes well known for their mutualistic symbiosis with tropical sea anemones. These fishes live in social groups in which there is a size-based dominance hierarchy. In this structure where sex is socially controlled, agonistic interactions are numerous and serve to maintain size differences between individuals adjacent in rank. Clownfishes are also prolific callers whose sounds seem to play an important role in the social hierarchy. Here, we aim to review and to synthesize the diversity of sounds produced by clownfishes in order to emphasize the importance of acoustic signals in their way of life.

Methodology/Principal Findings

Recording the different acoustic behaviors indicated that sounds are divided into two main categories: aggressive sounds produced in conjunction with threat postures (charge and chase), and submissive sounds always emitted when fish exhibited head shaking movements (i.e. a submissive posture). Both types of sounds showed size-related intraspecific variation in dominant frequency and pulse duration: smaller individuals produce higher frequency and shorter duration pulses than larger ones, and inversely. Consequently, these sonic features might be useful cues for individual recognition within the group. This observation is of significant importance due to the size-based hierarchy in clownfish group. On the other hand, no acoustic signal was associated with the different reproductive activities.

Conclusions/Significance

Unlike other pomacentrids, sounds are not produced for mate attraction in clownfishes but to reach and to defend the competition for breeding status, which explains why constraints are not important enough for promoting call diversification in this group.     

Optimisation of the transmit beam parameters for generation of subharmonic signals in native and altered populations of a commercial microbubble contrast agent SonoVue®

The aim of this work was to establish the optimum acoustic characterisation approach and insonation transmit beam parameters for subharmonic signal generation with ‘native’ and ‘altered’ populations of a commonly-used microbubble contrast agent. Dynamic contrast-enhanced (DCE) ultrasound is a non-invasive method of imaging the microvasculature, typically implemented using harmonic imaging. Subharmonic imaging, in which echoes at half the fundamental frequency are detected, detects signals which are generated by the ultrasound contrast agents (UCAs) but not by tissue. However, optimal transmission parameters and furthermore, the optimum acoustic characterisation method have not been established. The subharmonic response of ‘native’ and ‘altered’ UCA, altered through decantation, was investigated at transmit centre frequencies 1.8–5 MHz and pulse lengths 1–8 cycles. The ‘altered’ UCA had reduced polydispersity (1–4 µm: 82% bubble volume), compared to ‘native’ (4–10 µm: 57% bubble volume). A custom-built narrow-band acoustic characterisation system was found to be more appropriate for acoustic characterisation compared to the commonly used broadband pulse-echo approach. Both UCA generated the highest subharmonic signal at pulse length of 3-cycles. The maximum ‘native’ subharmonic signal was generated at a transmit centre frequency of 1.9 MHz, corresponding to a subharmonic at 0.95 MHz. This optimal frequency increased in the ‘altered’ population to 2.3–2.5 MHz, bringing the subharmonic above 1 MHz and hence into a range amenable to clinical abdominal imaging transducers. The use of subharmonic signal detection coupled with a modified UCA size distribution has potential to significantly improve the quantification sensitivity and accuracy of DCE ultrasound imaging.     

Geographical and individual variation in echolocation calls of the intermediate leaf‐nosed bat,Hipposideros larvatus

The cause and significance of variation in echolocation call frequency within hipposiderid bats is not well understood despite an increasing number of allopatric and sympatric examples being documented. We examined variation patterns in the resting frequency (RF) of echolocation calls emitted by the intermediate leaf‐nosed bat, Hipposideros larvatus, on a broad geographical scale. Data mining technology and Kruskal–Wallis test both showed substantial variation with a longitudinal pattern in RF in H. larvatus among colonies, and this variation was associated with geographical distance and not body size. In addition, we found that a high degree of variability between individuals was hidden under the geographical variation. The results support an effect of random cultural drift, and challenge the prey detection hypothesis. Moreover, an acoustic difference among local island colonies may be indicative of a vocal dialect. We found that each colony of H. larvatus seems to maintain a ‘private bandwidth’, which could be used for colony identity and individual communication thus helping individuals and colonies to get a number of fitness benefits.