Frequency-modulated second elements of two-element alarm calls do not enhance discrimination of callers in three Eurasian ground squirrels

Alarm calls of the European Spermophilus citellus (EGS), Taurus S. taurensis (TGS) and Anatolian S. xanthoprymnus (AGS) ground squirrels share the same basic structure. They are tonal sounds consisting primarily of two different elements. The first element, often produced without the second element, has limited frequency modulation, while the second element is more frequency modulated. The present study examined whether this frequency-modulated element enhances the individual distinc- tiveness of calls, allowing calls to be ascribed with greater confidence to individual callers of the three species. Cross-validated discriminant function analysis (DFA) based on five acoustic parameters of the first element successfully classified calls to correct individuals (EGS: 90%, TGS: 98%, AGS: 96%). Cross-validated DFA based on five acoustic parameters of the second element was also successful in classifications (EGS: 88%, TGS: 86%, AGS: 96%), though discrimination of callers based on parameters of the second versus first element was the same for the AGS, lower for the EGS and significantly lower for the TGS. Cross-validated DFA based on five acoustic parameters of two-element calls also successfully classified calls to correct individu- als (EGS: 93%, TGS: 98%, AGS: 97%), though did not improve the extent to which calls could be classified to individuals be- yond that based on the first element alone. Thus, the second element does not enhance the individual distinctiveness of calls, but may convey other information such as the location of the caller (Current Zoology 58 (5): 749−757, 2012).  Alarm call, Ground squirrel, Individual recognition, Spermophilus citellus, Spermophilus taurensis, Spermophilus xanthoprymnus

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title: Golden-marmot alarm calls. I: The production of situationally specific vocalizations
abstract: Many species of animals produce alarm calls that vary according to the situation. There are at least three different ways to communicate variation in situation : 1. Produce acoustically different call types ; 2. Vary the rate or number of times that a single call type is produced ; and/or 3. Vary the overall intensity in a single call. Combinations of these three mechanisms are also possible. I studied the production of alarm calls in free-living golden marmots (Marmota caudata aurea). Marmots emitted alarm calls when they encountered predators and startling stimuli. In the field these calls did not appear associated with predator type, but, rather, varied according to the degree of risk the caller perceived when it vocalized. Marmots produced calls with fewer notes when in higher risk situations, and calls with more notes when in lower risk situations. Thus, by varying the number of repeated notes in a single call type, marmots produced situationally specific alarm vocalizations.

title: Habitat structure and alarm call dialects in Gunnison's prairie dog (Cynomys gunnisoni)
abstract: We examined the relationship between habitat structure and alarm call characteristics in six colonies of Gunnison's prairie dogs (Cynomys gunnisoni) near Flagstaff, Arizona, before and after a mid-summer vegetation change. We found significant differences in alarm call characteristics between colonies, confirming the existence of alarm call dialects. Differences in frequency components but not temporal components of calls were associated with differences in habitat structure. Playback experiments revealed that differences in alarm call structure affected acoustic transmission of calls through the local habitat. Thus, we identify habitat structure as one factor that may contribute to alarm call differences between colonies of Gunnison's prairie dogs. Relationships between call characteristics and habitat structure changed over seasons. Playback experiments suggested that this changing relationship could reflect a change in the purpose of the alarm call between early and late summer. Some components of alarm calls seem tailored for attenuation over short distances in the early summer but for long-distance transmission at summer's end. These differences might arise because pups stay close to their natal burrows in the early summer and disperse throughout a colony in late summer. Alternatively, these differences in alarm call transmission between seasons could be caused by the increase in vegetation in the mid-summer. At the end of the summer prairie dogs could be more dependent on long-distance antipredator calls to offset the loss of visibility caused by the increase in vegetation in the late summer.

title: Referential specificity in the alarm calls of the black-tailed prairie dog
abstract: In this study, we show that black-tailed prairie dogs (Cynomys ludovicianus) have a referential system of communication, i.e., their alarm calls have specificity for different characteristics of humans. In a series of experiments, we tested the ability of black-tailed prairie dogs to encode information into their alarm calls about the color of clothes and general shape of humans who were potential predators. We also assessed the information encoded into the alarm calls elicited after a human fed the prairie dogs, and after a human shot a weapon within the colony. The results show that black-tailed prairie dogs have a referential communication system similar to that described for Gunnison's prairie dogs, with qualitatively and quantitatively different alarm calls for different predator characteristics.

title: The potential to encode sex, age, and individual identity in the alarm calls of three species of Marmotinae
abstract: In addition to encoding referential information and information about the sender’s motivation, mammalian alarm calls may encode information about other attributes of the sender, providing the potential for recognition among kin, mates, and neighbors. Here, we examined 96 speckled ground squirrels (Spermophilus suslicus), 100 yellow ground squirrels (Spermophilus fulvus) and 85 yellow-bellied marmots (Marmota flaviventris) to determine whether their alarm calls differed between species in their ability to encode information about the caller’s sex, age, and identity. Alarm calls were elicited by approaching individually identified animals in live-traps. We assume this experimental design modeled a naturally occurring predatory event, when receivers should acquire information about attributes of a caller from a single bout of alarm calls. In each species, variation that allows identification of the caller’s identity was greater than variation allowing identification of age or sex. We discuss these results in relation to each species’ biology and sociality.

title: Alarm Calls of California Ground Squirrels (Spermophilus beecheyi)
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title: Alarm Calling in Richardson's Ground Squirrels (Spermophilus richardsonii)
abstract: and Summary 
 
A three-year field-study of Richardson's ground squirrels was conducted to assess whether alarm calling functions to warn close relatives (“kin selection” hypothesis) or manipulate conspecifics (a “selfish” hypothesis). S. richardsonii had distinct calls for terrestrial and aerial predators, and the responses of squirrels varied appropriately according to the context of calls, implying that calling conveyed correct information concerning the nature of the danger. Alarm calling elicited by naturally occurring encounters with potential predators during 454 h of observation, and by a thrown frisbee in 70 experimental trials, was not equally probable for all age/sex classes. Squirrels were most likely to call when they had offspring or siblings nearby, which is supportive of the hypothesis that alarm calling is maintained by kin selection. Adult males, residing in the vicinity of either their probable progeny or their nonlittermate half-siblings, were the most likely age/sex class to call during the lactation period when young were below ground and were most vulnerable. I conclude that alarm calling by Richardson's ground squirrels is nepotistic rather than manipulative.

title: The Evolution, Function, and Meaning of Marmot Alarm Communication
abstract: Publisher Summary This chapter discusses the evolution, function, and meaning of marmot alarm communication. Alarm calls are a system in which one can study the dynamics of altruism. Calls can contain potentially referential information about the specific type of predator and information about the degree of risk that the caller faces while calling. Moreover, alarm‐calling systems may offer some unique insights into the adaptive significance of individuality. The chapter focuses on alarm communication; marmots obtain other information about risk acoustically. Many species respond to the sounds that their predators make. A phylogenetic reconstruction of the ability to respond to the sound of predators predicts that yellow‐bellied marmots should respond to predators. Recent experiment suggests that marmots have an innate ability to respond to the sounds of locally extinct predators. Future work can focus on the specific acoustic cues that marmots use, which enable them to respond to novel predators.

title: Generic Revision in the Holarctic Ground Squirrel Genus Spermophilus
abstract: The substantial body of research on Holarctic ground squirrels amassed over the past century documents considerable variability in morphological, cytogenetic, ecological, and behavioral attributes in the genus Spermophilus F. Cuvier, 1825. Recent molecular phylogenetic studies suggest that the traditionally recognized genera Marmota Blumenbach, 1779 (marmots), Cynomys Rafinesque, 1817 (prairie dogs), and Ammospermophilus Merriam, 1892 (antelope ground squirrels) render Spermophilus paraphyletic, potentially suggesting that multiple generic-level lineages should be credited within Spermophilus. Herein, we recognize 8 genera formerly subsumed in Spermophilus, each of which is morphologically diagnosable, craniometrically distinctive, and recovered as a monophyletic clade in phylogenetic analyses utilizing the mitochondrial gene cytochrome b. Generic-level names are available for each of these ground squirrel assemblages, most of which are exclusively or predominantly North American in distribution (Notocitellus A. H. Howell, 1938; Otospermophilus Brandt, 1844; Callospermophilus Merriam, 1897; Ictidomys ; Poliocitellus A. H. Howell, 1938; Xerospermophilus Merriam, 1892; and Urocitellus Obolenskij, 1927). Only Spermophilus sensu stricto is restricted to Eurasia. Generic subdivision of Spermophilus more aptly illuminates the taxonomic relationships, ecomorphological disparity, and biogeographic history of Holarctic ground squirrels.

title: Acoustic analysis of the alarm call of the Anatolian ground squirrel Spermophilus xanthoprymnus: a description and comparison with alarm calls of the Taurus S. taurensis and European S. citellus ground squirrels
abstract: The Anatolian ground squirrel Spermophilus xanthoprymnus like other ground-dwelling sciurids, emits alarm calls in the presence of predators. In this study, we provide a description of the acoustic structure of alarm call of this species and compare it to those of two closely related species, the Taurus ground squirrel Spermophilus taurensis and the European ground squirrel Spermophilus citellus. The alarm call of S. xanthoprymnus is a tonal sound mostly consisting of two different elements—the first element has low frequency modulation while the second element is highly frequency modulated. A similar basic structure can be found in the alarm calls of some other old world ground squirrel species of the genus Spermophilus, including S. taurensis and S. citellus. Despite this similarity, we found that these three species can be clearly distinguished on the basis of their alarm calls. Differences in the acoustic structure of S. xanthoprymnus and S. taurensis calls are especially remarkable, as these two species were considered to be conspecific until 2007. S. xanthoprymnus and S. taurensis were also demonstrated to have closer acoustic similarity, which is in contrast to results based on molecular data indicating that S. taurensis is most closely related to S. citellus.

title: Functional morphology of Richardson's ground squirrel, Spermophilus richardsonii, alarm calls: the meaning of chirps, whistles and chucks
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title: Juvenile Richardson's ground squirrels,
 Spermophilus richardsonii
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title: Individual, age and sex-specific information is contained in yellow-bellied marmot alarm calls
abstract: Individuals produce distinctive vocalizations that may contain considerable potential information about a signaller. Simply finding significant covariation between call structure and some individual attribute does not itself mean that there has been selection on callers to produce individually distinctive calls, nor on receivers to discriminate between them. Moreover, acoustic variation may degrade while being transmitted through the environment, making it potentially difficult for receivers to extract potential information. We focused on the individually distinctive calls of yellow-bellied marmots, Marmota flaviventris, to describe attributes of individuals encoded in calls. Using discriminant function analysis, we found significant potential information about identity, age and sex encoded in calls. When calls were broadcast and rerecorded over 10 m and 40 m, identity, age and sex remained statistically discriminatable. Key variables that enabled discrimination were repeatable (they had high intraclass correlation coefficients), whereas those that did not enable discrimination were less repeatable. Finally, statistics developed to describe, in a standardized and comparative way, the information about individual signallers contained in vocalizations, revealed that marmot alarm calls contained at least 3.37 bits of information about identity. When compared to other species for which the information content of signals has been calculated, marmots may have not undergone strong selection for individually distinctive vocalizations. The fact that receivers discriminate between individuals suggests that receivers benefit by doing so.

title: Social Group Size Predicts the Evolution of Individuality
abstract: Discriminating among individuals is a critical social behavior in humans and many other animals and is often required for offspring and mate recognition, territorial or coalitional behaviors, signaler reliability assessment, and social hierarchies. Being individually discriminated is more difficult in larger groups, and large group size may select for increased individuality-signature information-in social signals, to facilitate discrimination. Small-scale studies suggest that more social species have greater individuality in their social signals, such as contact calls. However, this relationship has not been evaluated in a broader-scale evolutionary context or in social signals other than contact calls. It is not yet known whether social group size may be viewed as a general evolutionary driver of individuality. Here we show a strong positive evolutionary link between social group size in sciurid rodents and individuality in their social alarm calls. Social group size explained over 88% of the variation in vocal individuality in phylogenetic independent contrasts. Species living in larger groups, but not in more complex groups, had more signature information in their calls. Our results suggest that social group size may promote the evolution of individual signatures and that the sociality-individuality relationship may be a general phenomenon in nature.

title: The squirrel that cried wolf: reliability detection by juvenile Richardson's ground squirrels (Spermophilus richardsonii)
abstract: Where alarm signals function to warn others of the presence of threat, variation is likely to exist in the reliability of alarm signalers. Some signalers, with too low a threshold of excitation, will issue false alarms and should be ignored if potential alarm recipients are to maximize energy gains. We exposed juvenile Richardson's ground squirrels to reliable signalers, whose alarm calls were paired with the presentation of a predator model, and unreliable signalers, whose alarm calls were played when no potential predator was present. Call recipients discriminated among individual alarm callers, and reduced responsiveness to callers that had been unreliable. Thus, like primates, squirrels are capable of forming a concept of reliability by associating an individual's identity with that individual's past performance.

title: The More the Scarier: Adult Richardson’s Ground Squirrels (Spermophilus richardsonii) Assess Response Urgency Via the Number of Alarm Signallers
abstract: Richardson’s ground squirrels (RGS) produce alarm calls that warn conspecifics of potential predators. We presented free-living adult and juvenile RGS with playbacks of repetitive alarm calls from one vs. two juvenile callers broadcast sequentially through two spatially separated loudspeakers. Adult RGS spent a greater proportion of time vigilant in response to two vs. one calling squirrel, whereas juvenile RGS did not respond differentially to two vs. one caller. Apparently then, the relative inexperience of juvenile RGS with alarm calls and the context in which such calls are emitted precludes their enumeration of alarm callers. Taken together with our earlier finding that adult but not juvenile RGS ignore information regarding response urgency encoded in the rate of juvenile produced repetitive calls, our present results suggest a developmental shift in response-urgency perception. Adult RGS selectively extract information regarding response urgency via discrimination of the number of callers, ignoring less reliable information encoded in the rate of repetitive calls issued by inexperienced juvenile signallers.

title: Short-Term and Long-Term Individuality in Speckled Ground Squirrel Alarm Calls
abstract: Apart from the alerting function of alarm calls, selection may favor cues that help individuals to distinguish between reliable and unreliable callers. However, this mechanism for selective response to real and false alarms may act only if the individual characteristics of the call are stable at least for some time. Here we test this implicit assumption for the caller's reliability hypothesis, studying individuality of alarm calls in a colony of free-living, individually marked speckled ground squirrels (Spermophilus suslicus). We recorded each of 20 study animals 4 times during repeated captures when calling from a live trap toward a human, with spans of 1 day, 2 weeks, and 1 year from the 1st capture. Ten alarm call notes per animal per capture were analyzed. Individual alarm call notes showed high similarity within captures but differed strongly between captures. Both multivariate analysis of variance and discriminant function analysis showed that vocal individuality decreased rapidly with an increase of the time span between recordings. However, vocal individuality always remained higher than expected random value. Examination of our data suggests that alarm calls are unstable, which contradicts the caller reliability hypothesis, because its implicit assumption of stable individual identity is not fulfilled. However, short-term stability still may be sufficient to ensure short-term individual recognition between kin and neighbors. Also, even if the alarm calls change structurally, because group members meet up daily, they can update their knowledge of the call structure of individuals, and this would likely allow them to distinguish between reliable and unreliable individuals.

title: Neighbourhood watch: multiple alarm callers communicate directional predator movement in Richardson’s ground squirrels, Spermophilus richardsonii

abstract: Richardson's ground squirrels are social animals that warn conspecifics of a predator's presence through the production of alarm vocalizations. Their ability to discriminate among individual alarm callers and to identify the location of those callers may allow receivers to track predator movement from acoustic information in multiple-caller bouts. Observations of encounters with live terrestrial and avian predators revealed that squirrels were significantly more likely to produce a multiple-caller bout that tracked predator movement when avian predators were airborne than when predators remained on the ground. To test whether receivers perceived such differences, squirrels were presented with playbacks of multiple-caller bouts composed of either chirps (commonly issued in response to airborne predators), or whistles (commonly issued in response to predators on the ground) from callers that were either unfamiliar or familiar to the receiver. In response to unfamiliar chirps, but not unfamiliar whistles, receivers were significantly more vigilant when call bouts progressively increased in proximity than when call bouts progressively decreased in proximity. Thus, Richardson's ground squirrels use multiple alarm callers to track airborne avian but not terrestrial predators, presumably owing to the more immediate threat that airborne predators pose, but also because of the relative paucity of directional information in bouts of whistle calls associated with potential threats on the ground. Squirrels were more responsive to calls from familiar neighbours, however, and despite our relatively small sample of familiar caller playbacks, receivers showed limited evidence of differential response to approaching versus receding bouts of whistle calls when they were familiar with callers.

title: Pre‐screening acoustic and other natural signatures for use in noninvasive individual identification
abstract: Common ecological tasks, such as wildlife monitoring, adaptive management, and behavioural study, often make use of natural signatures (e.g. animal calls or visual markings) to identify individual animals noninvasively. However, there is no accepted method for pre-screening candidate natural signatures to select which signatures are the best-suited for this purpose. In this paper, we suggest a pre-screening checklist and focus on the challenge of assessing a candidate signature’s individuality. 2. Individuality is critical, as the use of low-individuality natural signatures can lead to misidentification of individuals and therefore bias estimation of population parameters and population response to management actions. An information-based metric of individuality could assist researchers with selecting suitable signatures by allowing comparison among candidate signatures and providing an estimate of how many individuals may be reliably discriminated using a particular signature. 3. Before an individuality metric can be used to pre-screen natural signatures, the metric must first be calculated from preliminary sampling and must be robust to typical sampling concerns. We used field-collected animal vocalizations as well as simulations to test how robust the metric is to variation in sampling design. 4. We found that the metric is fairly robust to the number of animals sampled and the number of sessions (e.g. calling bouts) analysed, but that it is sensitive to the number of observations per session. 5. Synthesis and applications. Managers and researchers could save time and energy and improve the accuracy of estimates (such as abundance, survival, or population response) based on individual identification by first pre-screening candidate natural signatures for their individuality. As long as the number of observations per session is controlled, the relative values of the individuality metric can be meaningfully compared. The metric can thus be used as a tool to estimate relative individuality and so facilitates a difficult step in choosing a natural signature for noninvasive individual identification. We include instructions on how to calculate and interpret the individuality metric.

title: Stability of acoustic individuality in the alarm calls of wild yellow ground squirrels Spermophilus fulvus and contrasting calls from trapped and free-ranging callers
abstract: The questions of individuality and stability of cues to identity in vocal signals are of considerable importance from theoretical and conservation perspectives. While individuality in alarm calls has been reported for many sciurids, it is not well-documented that the vocal identity encoded in the alarm calls is stable between different encounters with predators. Previous studies of two obligate hibernating rodents, speckled ground squirrels Spermophilus suslicus, and yellow ground squirrels Spermophilus fulvus demonstrated that, after hibernation, most individuals could not be identified reliably by their alarm calls. Moreover, in most speckled ground squirrels, individual patterns of alarm calls changed progressively over as little as 2 weeks. However, these previous data have been obtained using the collection of alarm calls from trapped animals. Here, we examined ten free-ranging dye-marked yellow ground squirrels to determine whether their alarm calls retain the cues to individuality between two encounters of surrogate predators (humans), separated on average by 3 days. Discriminant function analysis showed that the alarm calls of individual yellow ground squirrels were very similar within a recording session, providing very high individual distinctiveness. However, in six of the ten animals, the alarm calls were unstable between recording sessions. Also, we examined ten dye-marked individuals for consistency of acoustic characteristics of their alarm calls between the encounters of humans, differing in techniques of call collection, from free-ranging vs trapped animals. We found differences only in two variables, both related to sound degradation in the environment. Data are discussed in relation to hypotheses explaining the adaptive utility of acoustic individuality in alarm calls.

title: ALARM CALLS OF THE EUROPEAN GROUND SQUIRREL SPERMOPHILUS CITELLUS AND THE TAURUS GROUND SQUIRREL S. TAURENSIS ENCODE INFORMATION ABOUT CALLER IDENTITY
abstract: Vocalizations of many mammalian species have been reported to encode information about caller identity. In this study, we analyzed 300 alarm calls from 10 free-living European Ground Squirrels Spermophilus citellus (30 per individual) and 300 alarm calls from 10 free-living Taurus Ground Squirrels S. taurensis (30 per individual), and tested the potential of these calls to encode information about the callers' identities. Discriminant analysis including all 10 European Ground Squirrel individuals correctly classified 98% of calls, and cross-validation reached a classification success of 97%. Correct classification of 98% and cross-validation of 98% was assigned when the analysis included only those individuals producing calls consisting of both elements (eight individuals). For the Taurus Ground Squirrel, correct classification was 95% and cross-validation 94% for all 10 animals. When only those individuals producing calls consisting of both elements were included (eight individuals), discriminant analysis led to 94% correct classification and cross-validation produced a classification success of 93%. These analyses demonstrate that the structure of alarm calls in these two closely related species is highly variable and that it has significant potential to encode information about caller identity.

title: Responses to alarm calls by California ground squirrels: Effects of call structure and maternal status
abstract: Summary1.The purposes of this study were to assess the response eliciting properties of five structural variants of the California ground squirrel alarm call system, and to compare the responsiveness of females with and without young to the vocalizations. Tape recordings of alarm calls and control sounds were played back in the field to adult female ground squirrels. The squirrels responded very little to control sounds. Following alarm calls, however, posture height and running increased; feeding, walking and non-locomotion movements decreased. None of the playbacks elicited vocalizations from the squirrels.2.The four chatter-chat calls evoked patterns of response that were distinctly different from reactions to the whistle. The immediate running response to chatter-chats was followed quickly by upright posturing, which subsequently declined throughout the 3-min period following the call. Feeding was suppressed throughout the 3-min post-chatter-chat interval, but movement increased after initial inhibition. After the initial running response to whistles, walking was common and upright posturing was delayed until the second post-call minute. Feeding and nonlocomotion movement were initially suppressed but increased monotonically over time. We proposed that these differences were adaptively related to the fact that chatter-chats typically follow detection of terrestrial predators, whereas whistles usually signal flying raptors.3.The responses to the four chatter-chat calls were graded in intensity, reaching higher levels in response to calls with more notes and lower noise content. The chat, a one-note call with high noise content, evoked the weakest reaction. We proposed that these two dimensions of calling (number of notes and noise content), in conjunction with several other semi-independent parameters, provide a sufficient diversity of signals to permit specification of the referent of the call (conspecific or predator) as well as the arousal level of the caller.4.We hypothesized that kin selection was responsible for the greater responsiveness of parous than of nonparous females to the alarm calls, and we discussed some implications of this difference.

title: Principles of Animal Communication
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title: Evening bat isolation calls provide evidence for heritable signatures
abstract: . Vocalizations of infant evening bats, Nycticeius humeralis, have unique characteristics that contain sufficient information for a mother to distinguish her offspring from other offspring in a colony. Using seven acoustic variables, all 306 isolation calls recorded from 39 pups in one attic nursery colony at 2-5 days of age were classified to the correct pup without error. Studies of captive bats reveal that the amount of among-bat variation in call variables remains constant from birth through to at least the next 14 days. Though several variables change as pups grow, an individually distinctive pattern of frequency modulation can be recognized at all ages. Isolation calls also contain information about family identity, as expected when call characteristics arc heritable: calls of wild pup twins were assigned to the correct family 68% of the time and three variables had significant heritabilities between 0·61 and 0·85. Factor analysis indicates that infant isolation calls exhibit independent variation in at least four dimensions. Consequently, over 1800 pups could produce calls without overlap in any dimension of acoustic space.

title: INDIVIDUALITY IN THE VOICE OF FUR SEAL FEMALES: AN ANALYSIS STUDY OF THE PUP ATTRACTION CALL IN ARCTOCEPHALUS TROPICALIS
abstract: Like most otariids species, the Subantarctic fur seal breeds on land in large, dense colonies. Pups are confronted by the long and repetitive absences of their mother throughout lactation. At each mother’s return, pups have to find her among several hundreds of congeners. This recognition process mainly relies on acoustic signals. We performed an acoustic analysis on 125 calls from 20 females recorded during the 1999-2000 breeding season on Amsterdam Island (Indian Ocean). Ten variables were measured in both temporal and frequency domains. To find the acoustic parameters supporting individual signature, we assessed the differences between individuals using Kruskall-Wallis univariate analysis of variance. For each variable, we also calculated the potential of individuality coding (PIC) as the ratio between the between-individual coefficient of variation and the mean value of the within-individual coefficients of variation. We found that the frequency spectrum, the characteristics of the frequency modulation of the initial and middle part of the call and the call duration exhibit an important individual stereotypy (PIC values ranging between 1.5 and 3), whereas features relative to amplitude and the frequency modulation

title: INDIVIDUAL VOCAL IDENTITY IN MOTHER AND PUP AUSTRALIAN SEA LIONS (NEOPHOCA CINEREA)
abstract: Individual vocal recognition between mothers and pups has been widely observed in pinnipeds, especially otariids. Otariids are colonial breeders; mothers suckle only their own offspring, aggressively attacking nonrelated young. Mothers alternate foraging trips with periods ashore, and at each return to the colony, mothers and pups must find each other among all the individuals of the colony. In the Australian sea lion (Neophoca cinerea), the need for a finely tuned mechanism of recognition is exacerbated by their habit of changing the nursing location over the course of lactation. We investigated potential acoustic parameters used in mother–pup recognition in Australian sea lions. We measured 11 acoustic parameters on calls of mothers and pups and found that several parameters (fundamental frequency, energy spectrum, amplitude, and frequency modulation) were highly individually specific. Discriminant analysis correctly assigned calls to individual mothers or pups with an average classification rate of 65% and 77%, respectively. Spectral features and frequency modulation were the most important features distinguishing individuals. Lastly, principal component analysis showed that calls of pups and mothers were easily distinguishable using energy spectrum and frequency modulation. Comparison with other pinniped species suggests that individual vocal identity is likely to be selected through ecological constraints such as density of the colony, degree of polygyny, likelihood of allosuckling or fostering, and degree of maternal absence during lactation.

title: Signature whistle shape conveys identity information to bottlenose dolphins.
abstract: Bottlenose dolphins (Tursiops truncatus) develop individually distinctive signature whistles that they use to maintain group cohesion. Unlike the development of identification signals in most other species, signature whistle development is strongly influenced by vocal learning. This learning ability is maintained throughout life, and dolphins frequently copy each other's whistles in the wild. It has been hypothesized that signature whistles can be used as referential signals among conspecifics, because captive bottlenose dolphins can be trained to use novel, learned signals to label objects. For this labeling to occur, signature whistles would have to convey identity information independent of the caller's voice features. However, experimental proof for this hypothesis has been lacking. This study demonstrates that bottlenose dolphins extract identity information from signature whistles even after all voice features have been removed from the signal. Thus, dolphins are the only animals other than humans that have been shown to transmit identity information independent of the caller's voice or location.

title: Iberian Wolf Howls: Acoustic Structure, Individual Variation, and a Comparison with North American Populations
abstract: We present a detailed description of the acoustic structure of howls emitted by Iberian wolves and a comparison with published descriptions of North American wolf howls. We recorded and analyzed 176 howls emitted by 11 wolves held in captivity in social groups of 1–5 individuals. Our sample included solo howls as well as howls included in choruses. Iberian wolf howls are long (1.1- to 12.8-s) harmonic sounds, with a mean fundamental frequency between 270 and 720 Hz. Our results revealed striking similarities between Iberian and North American wolf howls in all variables analyzed except for the number of discontinuities in the frequency of the howl, which was lower for Iberian wolves. Using discriminant function analysis we could assign 84.7% of howls to the correct individual. Variables related to fundamental frequency (mean and maximum) and the coefficient of fundamental modulation best discriminate individuals. We suggest that Iberian wolves could use howls for individual recognition.

title: Mother–Calf vocal communication in Atlantic walrus: a first field experimental study
abstract: In all colonial pinnipeds studied, mother–young vocal recognition exists and allows rapid and reliable meetings in spite of the confusing environment of the breeding colony. The efficiency of this recognition process guarantees pup survival, especially in species where females alternate foraging sea trips and lactation periods on land. The Atlantic Walrus (Odobenus rosmarus rosmarus) is a highly gregarious pinniped with females attending their calves for an extended period of time (2–3 years). Although we expect mother–calf vocal recognition to occur in this species due to the high density of individuals packed in herds, it has never been experimentally demonstrated. Here, we assessed the individual stereotypy of both mother and calf barks recorded in the wild by measuring frequency and temporal acoustic parameters. Both discriminant function and artificial neural network analyses resulted in high correct classification rates, underlying a well-defined individual stereotypy in parameters related to frequency modulation and frequency values. Playback experiments showed that mothers were more responsive to the barks of their own calf than to those of unrelated young. Finally, propagation experiments revealed that barks propagate at greater distances over water surface than over ice, acoustic features such as frequency modulation and frequency spectrum being highly resistant to degradation during propagation. Thus, acoustic analysis and propagation experiments suggest that these frequency parameters might be the key acoustic features involved in the individual identification process. This experimental study clearly demonstrates that Atlantic walrus has developed a highly reliable mother–calf vocal communication allowing such strong social bond.

title: Individual acoustic variation in Belding's ground squirrel alarm chirps in the High Sierra Nevada.
abstract: The acoustic structure of calls within call types can vary as function of individual identity, sex, and social group membership and is important in kin and social group recognition. Belding’s ground squirrels (Spermophilus beldingi) produce alarm chirps that function in predator avoidance but little is known about the acoustic variability of these alarm chirps. The purpose of this preliminary study was to analyze the acoustic structure of alarm chirps with respect to individual differences (e.g., signature information) from eight Belding’s ground squirrels from four different lakes in the High Sierra Nevada. Results demonstrate that alarm chirps are individually distinctive, and that acoustic similarity among individuals may correspond to genetic similarity and thus dispersal patterns in this species. These data suggest, on a preliminary basis, that the acoustic structure of calls might be used as a bioacoustic tool for tracking individuals, dispersal, and other population dynamics in Belding’s ground squirrels, and perhaps other vocal species.

title: Acoustic analysis of alarm calls of the European ground squirrel (Spermophilus citellus) and the Taurus ground squirrel (S. taurensis) (Mammalia: Sciuridae)
abstract: In comparison to some other species of ground squirrels, little is known about alarm calls of the European ground squirrel Spermophilus citellus, occurring in some parts of Central Europe and the Balkans, and essentially nothing is known about alarm calls of the Taurus ground squirrel S. taurensis, recently described from a small area in Taurus Mountains in southern Anatolia, Turkey. In this study, we performed a detailed analysis, description and comparison of alarm calls in these closely related species. We recorded 20 free-living individuals (10 per species) spontaneously vocalizing toward human in their natural colonies, and analyzed a total of 600 alarm calls (30 per individual). In both species, alarm calls in this context are tonal sounds usually consisting of two different elements. There is almost no frequency modulation in the first element, while the second element is highly modulated in frequency. In spite of the similar basic structure, the calls of each species differed significantly in most of temporal and spectral parameters. Our results support the assumption that vocalizations in sciurids are useful features supporting species identification. The potential factors that might be important in shaping the acoustic structure of alarm calls in S. citellus and S. taurensis remain a fruitful area for future research.

title: Applied Discriminant Analysis
abstract: Partial table of contents: Discriminant Analysis in Research. PREDICTION. Basic Ideas of Classification. Multivariate Normal Rules.   Nonnormal Rules. Reporting Results of a PDA. Applications of PDA.  Group Separation. Assessing Effects. Describing Effects. Selecting and Ordering Variables. Reporting Results of a DDA. Applications of DDA. ISSUES AND PROBLEMS.

title: Individuality in the voice of the emperor penguin Aptenodytes forsteri: adaptation to a noisy environment
abstract: The extreme coloniality in emperor penguins (Aptenodytes forsteri) demands that (1) individual recognition by the mutual display call must be supremely adapted to the total absence of nest sites — landmarks that would facilitate partner reunion, and (2) birds must transmit a precise message through an obstructed and noisy environment. A computerized sound analysis and subsequent data were submitted to univariate and multivariate statistics to determine individual-specific cues of the call. Temporal patterning of syllables, variables of the power spectrum (frequency and timbre features) and variables of a beat generated by two acoustic sources were analyzed (58 calls from 7 animals). Number and duration of syllables, fundamental frequencies and period of the beat were highly individual, with inter- significantly greater then intra-individual variation, enabling correct classification of the 58 calls. The respective relevance of temporal and spectral cues for individual recognition is discussed. In the acoustically hostile and noisy environment, beat was peculiarly emphasized, as it allowed great precision in the production of an amplitude modulation that was unlikely to be degraded by the environment.

title: Prairie dog alarm calls encode labels about predator colors
abstract: Some animals have the cognitive capacity to differentiate between different species of predators and generate different alarm calls in response. However, the presence of any addition information that might be encoded into alarm calls has been largely unexplored. In the present study, three similar-sized human females walked through a Gunnison’s prairie dog (Cynomys gunnisoni) colony wearing each of three different-colored shirts: blue, green, and yellow. We recorded the alarm calls and used discriminant function analysis to assess whether the calls for the different-colored shirts were significantly different. The results showed that the alarm calls for the blue and the yellow shirts were significantly different, but the green shirt calls were not significantly different from the calls for the yellow shirt. The colors that were detected, with corresponding encoding into alarm calls, reflect the visual perceptual abilities of the prairie dogs. This study suggests that prairie dogs are able to incorporate labels about the individual characteristics of predators into their alarm calls, and that the complexity of information contained in animal alarm calls may be greater than has been previously believed.

title: Pups crying bass: vocal adaptation for avoidance of age-dependent predation risk in ground squirrels?
abstract: In most mammals, larger adult body size correlates with lower fundamental frequency and more closely spaced formants in vocalizations relative to juveniles. In alarm whistles of two free-living rodents, the speckled ground squirrel Spermophilus suslicus and yellow ground squirrel S. fulvus, these cues to body size were absent despite prominent differences in body weight and skull and larynx sizes between juveniles and adults. No significant correlations were found between the individual maximum fundamental frequency and body weight, both within age classes and for pooled samples of all animals within species. Furthermore, the mean alarm whistle maximum fundamental frequencies did not differ significantly between age classes (juvenile versus adult) in the speckled squirrel and were even significantly lower in juvenile yellow squirrels. We discuss the hypothesis that the obfuscation of vocal differences between juvenile and adult squirrels may represent a special adaptation of pup vocal behaviour—a form of “vocal mimicry,” resulting in imitation of adult vocal pattern to avoid infanticide and age-dependent predation risk.

title: Signaler and Receiver Ages do not Affect Responses to RIchardson's Ground Squirrel Alarm Calls
abstract: Alarm calls alert receivers to the presence and/or nature of a predatory threat. Studies of alarm communication in Richardson's ground squirrels (Spermophilus richardsonii) have focused on juvenile signalers and receivers; however, adult and juvenile receivers may tailor their response to alarm calls based on different underlying signal parameters and attend differentially to alarm calls broadcast by adult versus juvenile signalers. To examine the potential influence of signaler and receiver age on the perception of response urgency, we presented free-living juvenile and adult S. richardsonii with alarm calls produced by juveniles and adults. Behavioral responses of call recipients were videotaped and analyzed to determine the influence of signaler and receiver age-class. No differences in vigilance response after juvenile- and adult-produced calls were detected for either adult or juvenile receivers. At the proximate level, the absence of any detectable difference in the acoustic attributes of juvenile- versus adult-produced calls may account for the lack of differential response. The absence of any age-dependent productional difference also is consistent with the recently advanced notion of young concealing information regarding their age in their alarm signals.