Seasonal variation in the whistles of the Starling Sturnus vulgaris

Observations of sedentary male Starlings at two sites in Brittany from December 1979 to December 1980 showed that the amount of whistled song varies during the year, principally from March to July during the reproductive season. Whistles are not numerous in summer but increase from September. These results suggest a link between whistled songs and testosterone titers. The different whistle types present different evolutions of their relative frequencies. Some are abundant during the nest building phase, others during the feeding phase. The curves were similar at the two sites for a given theme, showing that each theme constitutes an entity and that the different themes are influenced differently by environmental factors. The significance to the learning process in young birds is discussed.     

Delphinid whistle production and call matching during playback of simulated military sonar

In 2007 and 2008, controlled exposure experiments were performed in the Bahamas to study behavioral responses to simulated mid‐frequency active sonar (MFA) by three groups of odontocetes: false killer whales, Pseudorca crassidens; short‐finned pilot whales, Globicephala macrorhynchus; and melon‐headed whales, Peponocephala electra. An individual in each group was tagged with a Dtag to record acoustic and movement data. During exposures, some individuals produced whistles that seemed similar to the experimental MFA stimulus. Statistical tests were thus applied to investigate whistle‐MFA similarity and the relationship between whistle production rate and MFA reception time. For the false killer whale group, overall whistle rate and production rate of the most MFA‐like whistles decreased with time since last MFA reception. Despite quite low whistle rates overall by the melon‐headed whales, statistical results indicated minor transient silencing after each signal reception. There were no apparent relationships between pilot whale whistle rates and MFA sounds within the exposure period. This variability of responses suggests that changes in whistle production in response to acoustic stimuli depend not only on species and sound source, but also on the social, behavioral, or environmental contexts of exposure.     

Quantitative Comparison of Whistle Repertoires from Captive Adult Bottlenose Dolphins (Delphinidae,Tursiops truncatus): a Re-evaluation of the Signature Whistle Hypothesis

The prevailing view among researchers of dolphin communication is that bottlenose dolphins possess an individualized whistle contour; known as the ‘signature whistle’, it accounts for 74–95 % of a dolphin's whistle repertoire and functions to signal the individual identity of the whistler. This study used a new quantitative technique, termed the contour similarity technique (CS technique), and reports on the quantitative comparison of whistles from the individuals of three different social groups of bottlenose dolphins in socially interactive contexts. Results suggest that captive adult dolphins share several different whistle types including one predominant whistle type shared by all individuals across three different social groups. These analyses suggest a different interpretation of the dolphin whistle repertoire than has previously been proposed by proponents of the signature whistle hypothesis. In addition, results from our study support the results of early studies, published before the advent of the signature whistle hypothesis, in which investigators reported a large whistle repertoire within socially interactive captive and free-ranging groups and a predominant whistle type similar to that found in our study. Our results, combined with the results from earlier studies of dolphin vocal behaviour, suggest that the signature whistle hypothesis is incomplete and that dolphin whistle repertoires need to be analysed with respect to behavioural context and social relationships. In addition, these results suggest that contour discrimination and other acoustic features of whistles need to be tested in perception and categorization experiments.     

Playback experiment to test maternal responses of Japanese macaques (Macaca fuscata) to their own infant's call when the infants were four to six months old

Calls emitted by infants when the infant loses sight of its parents are useful to estimate the infant's requirement for parental care. When an Old World monkey infant loses sight of its mother it emits whistles. Therefore, it would be interesting to determine whether mothers could distinguish their own infant's whistles from the whistles of other infants. The response of each of seven Japanese macaque (Macaca fuscata) mothers to her own infant's whistle was compared with their responses to another infant's whistle. Matched control playback experiments were performed when the infants were four to six months old. The results showed that each mother could distinguish her own infant's whistle from that of another infant when the infants were four to six months old. Although a stricter experimental plan is required to further examine the issue, we found that the dominance rank of the infant's mother was another important factor in the female response to the infant's call. The finding suggests that females can associate a call emitted by an infant with its mother's rank, even before the infant begins to wander far from its mother.     

Signature whistles in free‐ranging populations of Indo‐Pacific bottlenose dolphins,Tursiops aduncus

Common bottlenose dolphins (Tursiops truncatus) use individually distinctive signature whistles which are highly stereotyped and function as contact calls. Here we investigate whether Indo‐Pacific bottlenose dolphins (T. aduncus) use signature whistles. The frequency trace of whistle contours recorded from three genetically distinct free‐ranging populations was extracted and sorted into whistle types of similar shape using automated categorization. A signature whistle identification method based on the temporal patterns in signature whistle sequences of T. truncatus was used to identify signature whistle types (SWTs). We then compared the degree of variability in SWTs for several whistle parameters to determine which parameters are likely to encode identity information. Additional recordings from two temporarily isolated T. aduncus made during natural entrapment events in 2008 and 2009 were analyzed for the occurrence of SWTs. All populations were found to produce SWTs; 34 SWTs were identified from recordings of free‐ranging T. aduncus and one SWT was prevalent in each recording of the two temporarily isolated individuals. Of the parameters considered, mean frequency and maximum frequency were the least variable and therefore most likely to reflect identity information encoded in frequency modulation patterns. Our results suggest that signature whistles are commonly used by T. aduncus.     

A New Quantitative Technique for Categorizing Whistles Using Simulated Signals and Whistles from Captive Bottlenose Dolphins (Delphinidae,Tursiops truncatus)

A widespread problem in the study of animal vocalizations is evaluating the acoustic similarity of signals both between individuals of a social group and between social groups. This problem becomes especially salient when classifying the narrow-band frequency-modulated signals, such as whistles, found in many avian and mammalian species. Whistles are usually characterized by their relative change in frequency over time, known as whistle ‘contour’. Measuring such a characteristic is difficult as it is not a single measurement, such as the mean frequency or duration of a signal, but several associated measurements of frequency across time. This paper reports on a new quantitative technique for determining whistle types based on whistle contour similarity and an application of this technique to the whistles of bottlenose dolphins to demonstrate its utility. This ‘contour similarity’ technique (CS technique) uses cluster analysis to group the correlation coefficients of frequency measurements from a data set of signals. To demonstrate the efficacy of this CS technique, three data sets were analysed, two using computer-generated signals and a third using adult bottlenose dolphin whistles, to (1) examine the efficacy of correlation coefficients for grouping signals by their similarity in whistle contour and (2) determine the viability of this technique for categorizing bottlenose dolphin whistles. Measured actual frequencies and correlation matrices from the four simulated signal types and a correlation matrix from the whistles of five captive adult bottlenose dolphins were each subjected to K-means cluster analysis and the resulting signal types were evaluated. Results indicated that the technique grouped actual frequencies according to the amount of shared actual frequencies and grouped correlation coefficients successfully according to signal contour. This result endured even if contours differed in overall duration or actual frequency or were expanded or compressed with respect to frequency or time. The results suggest that this approach is a viable method for assigning whistle contours to categories in bottlenose dolphins or any other species with narrow-band, frequency-modulated signals.     

非洲蝼蛄(G.africana Palisot de Beauvois)的鸣声特点

本文对北京非洲蝼蛄(G.africana.)的鸣声特点进行了分析.非洲蝼蛄的鸣声类似由调幅单音节组成的哨声.单音节的频谱特性基本相一致,其载波的主峰频率(MPF)调谐度(Q_(3dB))和MPF下降20dB的带宽分别为2539Hz、17.3和479Hz.但是哨声和单音节的周期是不均一的.在由302个哨声组成的鸣声段中,哨声周期和每个哨声内单音节平均周期的主要分布区分别为115-225ms和12.90-15.75ms.这些结果可能为蝼蛄声诱捕装置的生物原型和数学模型的研究提供某些依据.     

Whistle discrimination and categorization by the Atlantic bottlenose dolphin (Tursiops truncatus): a review of the signature whistle framework and a perceptual test

Dolphin whistles vary by frequency contour, changes in frequency over time. Individual dolphins may broadcast their identities via uniquely contoured whistles, "signature whistles." A recent debate concerning categorization of these whistles has highlighted the on-going need for perceptual studies of whistles by dolphins. This article reviews research on dolphin whistles as well as presenting a study in which a captive, female, adult bottlenose dolphin performed a conditional matching task in which whistles produced by six wild dolphins in Sarasota Bay were each paired with surrogate producers, specific objects/places. The dolphin subject also categorized unfamiliar exemplars produced by the whistlers represented by the original stimuli. The dolphin successfully discriminated among the group of whistles, associated them with surrogate producers, grouped new exemplars of the same dolphin's whistle together when the contour was intact, and discriminated among same-contour whistles produced by the same dolphin. Whistle sequences that included partial contours were not categorized with the original whistlers. Categorization appeared to be based on contour rather than specific acoustic parameters or voice cues. These findings are consistent with the perceptual tenets associated with the signature whistle framework which suggests that dolphins use individualized whistle contours for identification of known conspecifics.     

Postpartum whistle production in bottlenose dolphins

Despite much research on bottlenose dolphin signature whistles, few have investigated the role of maternal whistles in early calf development. We investigated maternal whistle use in the first weeks postpartum for captive dolphins. The overall whistling rate increased by a factor of ten when the calves were born and then decreased again in the third week of the one surviving calf. Adult whistles were distinguished from calf whistles based on the extent of frequency modulation and were further classified into signature and non-signature whistles by comparison to a dictionary of known whistles. The average rate of maternal signature whistle production increased significantly from 0.02 whistles per dolphin-minute before the calves were born to 0.2 and 0.3 whistles in weeks 1 and 2, decreasing again to 0.06 in week 3 for the mother of the surviving calf. Percent maternal signature whistles changed similarly. Signature whistle production by non-mothers did not change when the calves were born. A likely function of this increase in maternal signature whistle production is that it enables the calf to learn to identify the mother in the first weeks of life.     

Identifying signature whistles from recordings of groups of unrestrained bottlenose dolphins (Tursiops truncatus)

Bottlenose dolphins (Tursiops truncatus) have individually distinctive signature whistles. Each individual dolphin develops its own unique frequency modulation pattern and uses it to broadcast its identity. However, underwater sound localization is challenging, and researchers have had difficulties identifying signature whistles. The traditional method to identify them involved isolating individuals. In this context, the signature whistle is the most commonly produced whistle type of an animal. However, most studies on wild dolphins cannot isolate animals. We present a novel method, SIGnature IDentification (SIGID), that can identify signature whistles in recordings of groups of dolphins recorded via a single hydrophone. We found that signature whistles tend to be delivered in bouts with whistles of the same type occurring within 1–10 s of each other. Nonsignature whistles occur with longer or shorter interwhistle intervals, and this distinction can be used to identify signature whistles in a recording. We tested this method on recordings from wild and captive bottlenose dolphins and show thresholds needed to identify signature whistles reliably. SIGID will facilitate the study of signature whistle use in the wild, signature whistle diversity between different populations, and potentially allow signature whistles to be used in mark‐recapture studies.     

Song Differentiation and Population Structure: the Example of the Whistled Songs in an Introduced Population of European Starlings Sturnus vulgaris in Australia

Whistled songs of male starlings were studied in Australia and results compared with previous ones in Europe. Starling whistle sonograms can be divided into general classes according to certain criteria. All or most males sing five whistled types (“species-specific” themes), plus other (“individual”) themes. The basic repertoire of species-specific themes is almost the same in Europe and Australia with the same characteristics and similar variation ranges. In both continents each male has a certain number of individual themes, but Australian repertoires tend to be smaller, with two species-specific themes less and fewer individual themes. In all study areas dialects were based on local variations in species-specific theme structure, but the Australian dialectal system is simpler than in Europe. Therefore basic characteristics seem to have been similarly transmitted across generations in both continents. But some of the differences (individual characteristics, repertoire size, frequencies) may stem from different habitat characteristics and also social structure, which could have greatly affected song differentiation.     

Cues for Early Discrimination of Conspecific Song in the White-Crowned Sparrow (Zonotrichia leucophrys)

In song learning, white-crowned sparrows ( Zonotrichia leucophrys ) begin memorizing conspecific song models at around 20 d of age. Even prior to song memorization, however, between 10 and 20 d of age, these birds respond differently to playbacks of conspecific and heterospecific songs. To investigate the acoustic cues underlying this early song discrimination, we measured the vocal responses of newly fledged young to playbacks of modified conspecific and heterospecific songs. Fledgling white-crowned sparrows responded more strongly to songs containing conspecific notes than to songs containing notes from other species. In contrast, the presence or placement of an introductory whistle, present in all white-crowned sparrow songs, did not affect response levels. A whistle has previously been shown to serve as an acoustic cue for song memorization and production in this species. Such different responses to the species-typical introductory whistle at different stages suggests that developmental changes occur in the template system underlying song learning, the factors governing song recognition, or both.     

Identification and Characteristics of Signature Whistles in Wild Bottlenose Dolphins (Tursiops truncatus) from Namibia

A signature whistle type is a learned, individually distinctive whistle type in a dolphin''s acoustic repertoire that broadcasts the identity of the whistle owner. The acquisition and use of signature whistles indicates complex cognitive functioning that requires wider investigation in wild dolphin populations. Here we identify signature whistle types from a population of approximately 100 wild common bottlenose dolphins (Tursiops truncatus) inhabiting Walvis Bay, and describe signature whistle occurrence, acoustic parameters and temporal production. A catalogue of 43 repeatedly emitted whistle types (REWTs) was generated by analysing 79 hrs of acoustic recordings. From this, 28 signature whistle types were identified using a method based on the temporal patterns in whistle sequences. A visual classification task conducted by 5 naïve judges showed high levels of agreement in classification of whistles (Fleiss-Kappa statistic, κ = 0.848, Z = 55.3, P<0.001) and supported our categorisation. Signature whistle structure remained stable over time and location, with most types (82%) recorded in 2 or more years, and 4 identified at Walvis Bay and a second field site approximately 450 km away. Whistle acoustic parameters were consistent with those of signature whistles documented in Sarasota Bay (Florida, USA). We provide evidence of possible two-voice signature whistle production by a common bottlenose dolphin. Although signature whistle types have potential use as a marker for studying individual habitat use, we only identified approximately 28% of those from the Walvis Bay population, despite considerable recording effort. We found that signature whistle type diversity was higher in larger dolphin groups and groups with calves present. This is the first study describing signature whistles in a wild free-ranging T. truncatus population inhabiting African waters and it provides a baseline on which more in depth behavioural studies can be based.     

Dolphin whistles: a functional misnomer revealed by heliox breathing

Delphinids produce tonal whistles shaped by vocal learning for acoustic communication. Unlike terrestrial mammals, delphinid sound production is driven by pressurized air within a complex nasal system. It is unclear how fundamental whistle contours can be maintained across a large range of hydrostatic pressures and air sac volumes. Two opposing hypotheses propose that tonal sounds arise either from tissue vibrations or through actual whistle production from vortices stabilized by resonating nasal air volumes. Here, we use a trained bottlenose dolphin whistling in air and in heliox to test these hypotheses. The fundamental frequency contours of stereotyped whistles were unaffected by the higher sound speed in heliox. Therefore, the term whistle is a functional misnomer as dolphins actually do not whistle, but form the fundamental frequency contour of their tonal calls by pneumatically induced tissue vibrations analogous to the operation of vocal folds in terrestrial mammals and the syrinx in birds. This form of tonal sound production by nasal tissue vibrations has probably evolved in delphinids to enable impedance matching to the water, and to maintain tonal signature contours across changes in hydrostatic pressures, air density and relative nasal air volumes during dives.     

Passive Acoustic Monitoring of the Temporal Variability of Odontocete Tonal Sounds from a Long-Term Marine Observatory

The developments of marine observatories and automatic sound detection algorithms have facilitated the long-term monitoring of multiple species of odontocetes. Although classification remains difficult, information on tonal sound in odontocetes (i.e., toothed whales, including dolphins and porpoises) can provide insights into the species composition and group behavior of these species. However, the approach to measure whistle contour parameters for detecting the variability of odontocete vocal behavior may be biased when the signal-to-noise ratio is low. Thus, methods for analyzing the whistle usage of an entire group are necessary. In this study, a local-max detector was used to detect burst pulses and representative frequencies of whistles within 4.5–48 kHz. Whistle contours were extracted and classified using an unsupervised method. Whistle characteristics and usage pattern were quantified based on the distribution of representative frequencies and the composition of whistle repertoires. Based on the one year recordings collected from the Marine Cable Hosted Observatory off northeastern Taiwan, odontocete burst pulses and whistles were primarily detected during the nighttime, especially after sunset. Whistle usage during the nighttime was more complex, and whistles with higher frequency were mainly detected during summer and fall. According to the multivariate analysis, the diurnal variation of whistle usage was primarily related to the change of mode frequency, diversity of representative frequency, and sequence complexity. The seasonal variation of whistle usage involved the previous three parameters, in addition to the diversity of whistle clusters. Our results indicated that the species and behavioral composition of the local odontocete community may vary among seasonal and diurnal cycles. The current monitoring platform facilitates the evaluation of whistle usage based on group behavior and provides feature vectors for species and behavioral classification in future studies.     

Variation in and Meaning of Alarm Calls in a Social Desert Rodent Rhombomys opimus

The great gerbil (Rhombomys opimus), a social rodent that lives in family groups, emits three different alarm vocalizations in the presence of predators: a rhythmic call; a faster more intense call; and a single whistle. We tested the hypothesis that the alarm calls communicate risk of predation. We quantified the relationship between predator distance and type of alarm call via human approaches to gerbils. We also tested responses of focal adults in family groups to playback broadcasts of the different calls and controls of bird song and tape noise. Results showed that alarm calls were related to distance from a predator. Gerbils gave the rhythmic call when the predator was farthest away, the more intense call as the predator moved closer; and a short whistle when startled by a close approach of the predator. Gerbils stopped feeding and stood vigilant in a frozen alert posture in response to playbacks of all three alarm calls. They decreased non‐vigilant behavior to the alarm vocalizations more than to the controls and decreased non‐vigilant behavior significantly more in response to the intense alarm and whistle compared with the rhythmic alarm. We conclude that one function of gerbil alarm calls is to communicate response urgency to family members. The rhythmic alarm communicates danger at a distance, whereas the intense alarm and whistle signal the close approach of a predator.     

Whistle variation in Mediterranean common bottlenose dolphin: The role of geographical,anthropogenic, social,and behavioral factors

The studies on the variation of acoustic communication in different species have provided insight that genetics, geographic isolation, and adaptation to ecological and social conditions play important roles in the variability of acoustic signals. The dolphin whistles are communication signals that can vary significantly among and within populations. Although it is known that they are influenced by different environmental and social variables, the factors influencing the variation between populations have received scant attention. In the present study, we investigated the factors associated with the acoustic variability in the whistles of common bottlenose dolphin (Tursiops truncatus), inhabiting two Mediterranean areas (Sardinia and Croatia). We explored which factors, among (a) geographical isolation of populations, (b) different environments in terms of noise and boat presence, and (c) social factors (including group size, behavior, and presence of calves), were associated with whistle characteristics. We first applied a principal component analysis to reduce the number of collinear whistle frequency and temporal characteristics and then generalized linear mixed models on the first two principal components. The study revealed that both geographic distance/isolation and local environment are associated with whistle variations between localities. The prominent differences in the acoustic environments between the two areas, which contributed to the acoustic variability in the first principal component (PC1), were found. The calf's presence and foraging and social behavior were also found to be associated with dolphin whistle variation. The second principal component (PC2) was associated only with locality and group size, showing that longer and more complex tonal sound may facilitate individual recognition and cohesion in social groups. Thus, both social and behavioral context influenced significantly the structure of whistles, and they should be considered when investigating acoustic variability among distant dolphin populations to avoid confounding factors.     

Whistle Convergence among Allied Male Bottlenose Dolphins (Delphinidae, Tursiops sp.)

Dolphins are adept at learning new vocalizations (whistles) throughout life, an ability thus far demonstrated in few nonhuman mammals. In dolphins, this ability is well documented in captivity but poorly studied in the wild, and little is known of its role in natural social behavior. This study documents the previously unknown phenomenon of whistle convergence among habituated free-living male bottlenose dolphins ( Tursiops sp.). Over a 4 yr study period, three male subjects formed an alliance, spending most of their time together and cooperating to herd females. Within individuals, whistle repertoires were more variable than expected based on previous studies, mostly performed with captive dolphins, but became less so during the course of the study. Among individuals, the distinctiveness of individual repertoires decreased such that the three males were virtually indistinguishable by the end of the study. Initially, some whistle types were shared. By the end of the study, the three males had formed a close alliance, and had all converged on one particular shared whistle form which they had rarely produced before forming the alliance. The results are discussed in terms of their implications for the prevailing 'signature whistle' hypothesis, as well as possible mechanisms and functional significance of whistle convergence among cooperating males.     

Differences in stress reactivity of laboratory macaques measured by heart period and respiratory sinus arrhythmia

Some laboratory primates are more likely than others to react to anxiety-provoking stressors. Individuals that overreact to stressors may experience diminished psychological well-being and would be inappropriate for some experiments. The differences between reactive and nonreactive individuals may be reflected in heart period and respiratory sinus arrhythmia (RSA). Using surface electrodes and radio telemetry, we measured these two cardiac variables in seven male and ten female singly caged longtailed macaques (Macaca fascicularis) when they were exposed to two stressors, a sudden noise (whistle test) and an unfamiliar technician wearing capture gloves (glove test). Behavior was videotaped during both tests. For the whistle test, cardiac data were recorded before, during, and after two 1 min whistle blasts separated by 90 min. For the glove test, data were recorded in 1 min blocks every 8 min over 96 min before, during, and after 1 min exposure to the gloved technician. Heart period was decreased and RSA was suppressed during both the whistle and glove exposures. After the whistle test, the cardiac activity of most subjects returned to baseline levels within 10 min. The glove test produced more extended suppression, with greater individual differences, than the whistle test. There were greater individual differences in RSA than in heart period. These enhanced individual differences were used to define stress reactors that differed from nonreactors in their cardiac data profiles. Of 16 subjects that completed the glove test, five were identified as reactors. Am. J. Primatol. 45:245–261, 1998. © 1998 Wiley-Liss, Inc.     

Whistle characteristics of common dolphins (Delphinus sp.) in the Hauraki Gulf,New Zealand

Quantifying the vocal repertoire of a species is critical for subsequent analysis of signal functionality, geographic variation, and social relevance. However, the vocalizations of free‐ranging common dolphins (Delphinus sp.) have not previously been described from New Zealand waters. We present the first quantitative analysis of whistle characteristics to be undertaken on the New Zealand population. Acoustic data were collected in the Hauraki Gulf, North Island from 28 independent dolphin group encounters. A total of 11,715 whistles were collected from 105.1 min of recordings. Seven whistle contours were identified containing 29 subtypes. Vocalizations spanned from 3.2 to 23 kHz, with most whistles occurring between 11 and 13 kHz. Whistle duration ranged from 0.01 to 4.00 s (mean ± SD; 0.27 ± 0.32). Of the 2,663 whistles analyzed, 82% have previously been identified within U.K. populations. An additional six contours, apparently unique to New Zealand Delphinus were also identified. Data presented here offer a first insight into the whistle characteristics of New Zealand Delphinus. Comparisons with previously studied populations reveal marked differences in the whistle frequency and modulation of the New Zealand population. Interpopulation differences suggest behavior and the local environment likely play a role in shaping the vocal repertoire of this species.