Contextual Information and Differential Responses to Alarm Whistles in California Ground Squirrels

In the field, we videotaped the reactions of squirrels to playbacks of 1, 3 and 5 whistle vocalizations at two sound intensities differing by 10 dB. The squirrels reacted by running to boulders or burrows and freezing. As time progressed following playbacks, freezing declined and squirrels resumed feeding, locomotion and grooming. With increasing numbers of whistles, squirrels were more likely to run and less likely to mount a boulder. With more high intensity whistles, squirrels froze quadrupedally more and bipedally less. Freezing postures did not vary as a function of the number of low-intensity whistles. Walking was suppressed least by 1 and 3 whistles at low intensity, and inhibited most by all high-intensity whistles as well as by the low-intensity 5-whistle playback. When the squirrel was on a boulder, quadrupedal freezing was more common than bipedal freezing. Off the boulder, the two freezing postures were equally likely. We propose that squirrels assessed risk from information encoded in the whistle(s) and contextual to it, and varied their reactions as a function of apparent risk.     

Signature whistles in wild bottlenose dolphins: long-term stability and emission rates

Whistles are key elements in the acoustic repertoire of bottlenose dolphins. In this species, the frequency contours of whistles are used as individual signatures. Assessing the long-lasting stability of such stereotyped signals, and the abundant production of non-stereotyped whistles in the wild, is relevant to a more complete understanding of their biological function. Additionally, studying the effects of group size and activity patterns on whistle emission rate may provide insights into the use of these calls. In this study, we document the decades-long occurrence of whistles with stereotyped frequency contours in a population of wild bottlenose dolphins, resident in the region of the Sado estuary, Portugal. Confirmed stereotypy throughout more than 20 years, and positive identification using the signature identification (SIGID) criteria, suggests that the identified stereotyped whistles are in fact signature whistles. The potential roles of non-stereotyped whistles, which represent 68 % of all whistles recorded, are still unclear and should be further investigated. Emission rates were significantly higher during food-related events. Finally, our data show a comparatively high overall whistle production for this population, and no positive correlation between group size and emission rates, suggesting social or environmental restriction mechanisms in vocal production.     

Calling and vigilance in california ground squirrels: a test of the tonic communication hypothesis

Owings & Hennessy (1984) proposed that repetitive calling by ground squirrels, i.e. long bouts of calling wherein the same vocalization is uttered repeatedly, might act as a tonic signal to promote vigilance in perceivers. This idea was tested by comparing the effect of naturally occurring repetitive and nonrepetitive calls on the behaviour of California ground squirrels, Spermophilus beecheyi. Both types of calls increased the amount of time spent vigilant by perceivers, especially in bipedal postures. More time was spent vigilant after repetitive than non-repetitive calls, thus supporting the tonic communication hypothesis. However, longer bouts of repetitive calling did not promote proportionately increased vigilance over that evoked by shorter calls. In fact, the reverse was true and the increase in vigilance to repetitive calls began to wane during the later stages of a calling bout. Repetitive calling may represent a case of ‘persuasion’, in which the signaller continues signalling in an attempt to maintain some state in resistant perceivers.     

Age Differences in the Response of California Ground Squirrels (Spermophilus beecheyi) to Conspecific Alarm Calls

Juvenile California ground squirrel responses to adult alarm calls and juvenile alarm calling may be modified during development to achieve adult form. Adult conspecific chatter and whistle alarm calls were played back to juvenile and adult ground squirrels at an agricultural field site. In response to chatter playbacks, adults spent more time visually orienting to the environment and less time out of view and in covered habitats than juveniles; the converse was true in response to whistle playbacks. To test the evocativeness of juvenile calling, a subset of adult subjects received juvenile chatter and whistle playbacks. Adults spent less time out of view to juvenile call types than to adult calls, and showed more similar responses to juvenile chatters and whistles than to adult chatters and whistles. Age differences in the ground squirrel's alarm call system may reflect adjustments to changing risks during development.     

Vocalizations of Belding's ground squirrels (Spermophilus beldingi)

Vocalizations of Belding's ground squirrels (Spermophilus beldingi) were recorded during the summer of 1982 near Tioga Pass in the central Sierra Nevada of California. Sonagrams were made and call parameters were measured. Discriminant function analyses revealed that multiple-note calls (‘trills’) differed acoustically depending on whether they occurred in response to a predator, or were given by males following copulations. The post-copulatory trills of males were individually distinctive. Among anti-predator trills there was no evidence of predator-specificity within the narrow range of predators tested: trills given to two species of (stuffed) weasels (Mustela), to dogs and to humans were statistically indistinguishable. Sonagrams of trills occurring in agonistic contexts suggest that a third general category of trills may exist, but agonistic trills were more variable than either anti-predator or post-copulatory trills. The ground squirrels also gave single-note calls in the three contexts described above, either repetitively (‘chirps’) or singly (‘whistles’). Neither chirps nor whistles encoded any obvious situation-specific information, except that whistles were typically associated with rapidly-moving predators, usually raptors. The post-copulatory chirps of males were individually distinctive. Vocalizations of Belding's ground squirrels may not vary among contexts as much as do the analogous calls of California ground squirrels (S. beecheyi).     

Differences in oscillatory whistles produced by spinner (Stenella longirostris) and pantropical spotted (Stenella attenuata) dolphins

Acoustic recordings of two closely related species, spinner dolphin (Stenella longirostris) and pantropical spotted dolphin (Stenella attenuata), were investigated from four different geographic locations: two in the Central Tropical Pacific, one in the Eastern Tropical Pacific and one in the Indian Ocean. The two delphinid species occur in tropical and warm temperate waters, with overlapping ranges. They produce very similar vocalizations, but at the same time their calls exhibit a certain degree of intraspecific variation among different geographic locations as has been observed in other delphinid species. Oscillatory whistles (whistles with at least two oscillations in their frequency contours) were identified and manually extracted from the recordings. Whistles with four or more maxima (oscillations) occurred only in spinner dolphins and they were present in all geographic regions investigated. In addition, the oscillatory whistles with two and three maxima were significantly more frequent in spinner than in spotted dolphins. The differences in oscillatory whistles for these two species seem to be consistent across study areas and therefore, could be used in addition to other whistle features to help distinguish between them.     

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.     

Alarm calls elicit predator-specific physiological responses

Glucocorticoids regulate glucose concentrations and responses to unpredictable events, while also modulating cognition. Juvenile Belding''s ground squirrels (Urocitellus beldingi) learn to respond to whistle and trill alarm calls, warning of aerial and terrestrial predators, respectively, shortly after emerging from natal burrows at one month of age. Alarm calls can cause physiological reactions and arousal, and this arousal, coupled with watching adult responses, might help juveniles learn associations between calls and behavioural responses. I studied whether young show differential cortisol responses to alarm and non-alarm calls, using playbacks of U. beldingi whistles, trills, squeals (a conspecific control vocalization) and silent controls. Trills elicited very high cortisol responses, and, using an individual''s response to the silent control as baseline, only their response to a trill was significantly higher than baseline. This cortisol increase would provide glucose for extended vigilance and escape efforts, which is appropriate for evading terrestrial predators which hunt for long periods. Although whistles do not elicit a cortisol response, previous research has shown that they do result in bradycardia, which enhances attention and information processing. This is a novel demonstration of two physiological responses to two alarm calls, each appropriate to the threats represented by the calls.     

Variability and context specificity of narwhal (Monodon monoceros) whistles and pulsed calls

The behavioral and environmental context of animal calls provides insights into their functions. Narwhals are a highly vocal species and, like other social cetaceans, rely on acoustic signals to communicate. We characterize and categorize narwhal whistles and pulsed calls, as well as investigate variation in these calls under different contexts (behavior, herd, and year) using recordings made during the month of August 2006–2008, in Koluktoo Bay (72°04′N, 80°32′W). We detected similarities among whistles but not pulsed calls that were produced under a similar behavioral context. Both whistles and pulsed calls recorded within the same herd were more similar than whistles and pulsed calls recorded within different herds. We did not find any type of whistle to be associated with a specific behavior although some acoustical features might be behavior specific. Both whistles and pulsed calls show properties that are consistent with the hypothesis that narwhals produce group‐ or individual‐specific calls.     

Communication in bottlenose dolphins: 50 years of signature whistle research

Bottlenose dolphins (Tursiops truncatus) produce individually distinctive signature whistles that broadcast the identity of the caller. Unlike voice cues that affect all calls of an animal, signature whistles are distinct whistle types carrying identity information in their frequency modulation pattern. Signature whistle development is influenced by vocal production learning. Animals use a whistle from their environment as a model, but modify it, and thus invent a novel signal. Dolphins also copy signature whistles of others, effectively addressing the whistle owner. This copying occurs at low rates and the resulting copies are recognizable as such by parameter variations in the copy. Captive dolphins can learn to associate novel whistles with objects and use these whistles to report on the presence or absence of the object. If applied to signature whistles, this ability would make the signature whistle a rare example of a learned referential signal in animals. Here, we review the history of signature whistle research, covering definitions, acoustic features, information content, contextual use, developmental aspects, and species comparisons with mammals and birds. We show how these signals stand out amongst recognition calls in animals and how they contribute to our understanding of complexity in animal communication.     

Signature-whistle production in undisturbed free-ranging bottlenose dolphins (Tursiops truncatus)

Data from behavioural observations and acoustic recordings of free-ranging bottlenose dolphins (Tursiops truncatus) were analysed to determine whether signature whistles are produced by wild undisturbed dolphins, and how whistle production varies with activity and group size. The study animals were part of a resident community of bottlenose dolphins near Sarasota, Florida, USA. This community of dolphins provides a unique opportunity for the study of signature-whistle production, since most animals have been recorded during capture-release events since 1975. Three mother-calf pairs and their associates were recorded for a total of 141.25 h between May and August of 1994 and 1995. Whistles of undisturbed dolphins were compared with those recorded from the same individuals during capture-release events. Whistles were conservatively classified into one of four categories: signature, probable signature, upsweep or other. For statistical analyses, signature and probable signature whistles were combined into a 'signature' category; upsweep and other whistles were combined into a 'non-signature' category. Both 'signature' and 'non-signature' whistle frequencies significantly increased as group size increased. There were significant differences in whistle frequencies across activity types: both 'signature' and 'non-signature' whistles were most likely to occur during socializing and least likely to occur during travelling. There were no significant interactions between group size and activity type. Signature and probable signature whistles made up ca. 52% of all whistles produced by these free-ranging bottlenose dolphins.     

SHORT COMMUNICATION UNDERWATER SOUND PRODUCTION IN A NEOTROPICAL ANURAN,PHYSALAEMUS PUSTULOSUS (LEPTODACTYLIDAE)

ABSTRACT

Underwater vocalisations of Weddell seals Leptonychotes weddellii were recorded approximately 1400 km apart at Casey and Davis, Antarctica. Recordings were made during the 1992 and 1997 breeding seasons at Davis and during the 1997 season at Casey. Two observers independently analysed four attributes (start and end frequency, duration and number of elements) of narrow bandwidth calls from each location and time. There were few observer differences when the calls were grouped into four broad types (Trills, Descending Whistles, Ascending Whistles and Mews). Ascending Whistles and Mews were rare at Casey but common at Davis. Descending Whistles occurred significantly more often at Davis. Except for Trills, discriminant function analyses indicated less variation between the call attributes at Davis in 1992 and 1997 than between either of the Davis data sets and that from Casey. Vocalisation differences between Weddell seals from different areas can be detected by measuring common attributes of narrow bandwidth calls.     

ACOUSTIC IDENTIFICATION OF NINE DELPHINID SPECIES IN THE EASTERN TROPICAL PACIFIC OCEAN

Acoustic methods may improve the ability to identify cetacean species during shipboard surveys. Whistles were recorded from nine odontocete species in the eastern tropical Pacific to determine how reliably these vocalizations can be classified to species based on simple spectrographic measurements. Twelve variables were measured from each whistle ( n = 908). Parametric multivariate discriminant function analysis (DFA) correctly classified 41.1% of whistles to species. Non-parametric classification and regression tree (CART) analysis resulted in 51.4% correct classification. Striped dolphin whistles were most difficult to classify. Whistles of bottlenose dolphins, false killer whales, and pilot whales were most distinctive. Correct classification scores may be improved by adding prior probabilities that reflect species distribution to classification models, by measuring alternative whistle variables, using alternative classification techniques, and by localizing vocalizing dolphins when collecting data for classification models.     

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.     

The Sound of Arousal: The Addition of Novel Non-linearities Increases Responsiveness in Marmot Alarm Calls

Vocal structure should reflect vocal function. While much attention has focused on quantifying attributes of harmonic vocalizations, the vocalizations of many species also may contain non-linear phenomena such as warbles, subharmonics, biphonation, and deterministic chaos or noise. The function of these non-linearities remains enigmatic. In some species, harmonic vocalizations abruptly become 'noisy' when individuals are physiologically aroused and the sudden onset of these non-linearities could signal arousal or fear to receivers. One untested functional hypothesis is that vocalizations containing non-linearities are more variable from one rendition to the next, and thus are harder to habituate to. In some situations, reducing the likelihood of habituation could be important. Signals that are highly evocative are more difficult to habituate to. Thus, we conducted playback experiments to foraging yellow-bellied marmots ( Marmota flaviventris ) to determine whether the addition of white noise (a non-linear acoustic phenomenon) to alarm calls elicited a greater response than control calls without the non-linearity or control calls with silence, rather than noise, added to them. Marmots spent less time foraging after hearing calls that included noise than after normal or control calls. This result is consistent with the unpredictability hypothesis and suggests that the adaptive value of non-linearities is to prevent habituation.     

Description of whistles of Irrawaddy dolphins (Orcaella brevirostris) from the waters of Matang,Peninsular Malaysia

The whistles of Irrawaddy dolphins (Orcaella brevirostris) from the waters of Matang, western Peninsular Malaysia are described. Duration, frequency and frequency modulation variables were measured from 163 whistles recorded using a broadband towed hydrophone. Irrawaddy dolphins produced whistles with a mean duration of 0.366 s (S.D. ± 0.217 s). The fundamental frequency of whistles extended from 3040 to 17,123 Hz with low levels of frequency modulation. These dolphins produced whistles that were comparable to those of conspecifics recorded from the waters of Kalimantan, but were generally different from the related Australian snubfin dolphin (O. heinsohni). They also differed from the whistles of the sympatric Indo-Pacific humpback dolphin (Sousa chinensis). Characteristics of Irrawaddy dolphin whistles may be useful in future passive acoustic monitoring studies to investigate differences in sympatric species and their habitat.     

Species-specific and shared features in vocal repertoires of three Eurasian ground squirrels (genus <Emphasis Type="Italic">Spermophilus</Emphasis>)

Along to alarm calls, Eurasian ground squirrels of the genus Spermophilus also produce other call types toward potential predators and rival conspecifics. Individually identified 50 speckled (Spermophilus suslicus), 18 European (S. citellus) and 59 yellow (S. fulvus) ground squirrels were examined for interspecies differences in their vocal repertoires. A separate sample of 116 (90 adult and 26 juvenile) S. suslicus was examined for presence of ultrasound in their alarm calls. In addition, all tonal calls in all the three species were checked for presence of nonlinear phenomena. Calls were elicited by approaching animals in live-traps or near burrows; some types of vocalizations were also recorded during handling. Eight call types, three tonal and five wideband ones, were described. Vocal repertoires were remarkably similar between species, excluding the alarm calls, which were species-specific. Alarm calls with ultrasonic components were found in two individuals of S. suslicus. Concerning nonlinear phenomena, biphonation in alarm calls of S. suslicus, frequency jumps and sidebands in screams of S. citellus, frequency jumps and subharmonics in screams of S. fulvus were found. Results are discussed with literature evidence on audible and ultrasonic vocalizations in ground squirrels.     

Ultrasonic Vocalizations Emitted by Flying Squirrels

Anecdotal reports of ultrasound use by flying squirrels have existed for decades, yet there has been little detailed analysis of their vocalizations. Here we demonstrate that two species of flying squirrel emit ultrasonic vocalizations. We recorded vocalizations from northern (Glaucomys sabrinus) and southern (G. volans) flying squirrels calling in both the laboratory and at a field site in central Ontario, Canada. We demonstrate that flying squirrels produce ultrasonic emissions through recorded bursts of broadband noise and time-frequency structured frequency modulated (FM) vocalizations, some of which were purely ultrasonic. Squirrels emitted three types of ultrasonic calls in laboratory recordings and one type in the field. The variety of signals that were recorded suggest that flying squirrels may use ultrasonic vocalizations to transfer information. Thus, vocalizations may be an important, although still poorly understood, aspect of flying squirrel social biology.