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ABSTRACT

Australian fur seals Arctocephalus pusillus doriferus are colonial breeding animals forming dense social groups during the breeding season. During this time, males establish and defend territories through physical conflicts, stereotyped posturing and vocalisations. While vocalisations are suggested to play an important role in male recognition systems, it has received little attention. Recordings of nine adult male Australian fur seals were made during the 2000 and 2001 breeding seasons at Kanowna Island (39° 10′S, 146° 18′ E), Bass Strait, Australia. The in-air bark vocalisations of territory-holding males were used to characterise the Bark Call and to determine whether males produce individually distinct calls, which could be used as a basis for vocal recognition. Seventeen frequency and temporal variables were measured from a total of 162 barks from nine individual males. The Bark Series was more reliably classified (83%) to the correct caller compared to the Bark Unit. This was assigned with less certainty (68%), although the classification was still relatively high. Findings from this study indicate that there is sufficient stereotypy within individual calls, and sufficient variation between them, to enable vocal recognition in male Australian fur seals.     

Characterization of Australian fur seal vocalizations during the breeding season

The vocal repertoire, structure, and behavioral context of airborne vocalizations produced by Australian fur seals (Arctocephalus pusillus doriferus) are described using recordings made at a breeding colony on Kanowna Island, Bass Strait, Australia. The study identified six different call types: three produced by males (bark, guttural threat, and submissive call); five produced by females (bark, guttural threat, submissive call, growl, and pup attraction call) and the female attraction call produced by pups and yearlings. Vocalizations were compared according to age and sex classes. The overall structure and function of the pup attraction and female attraction call produced by females, yearlings, and pups, was similar. However, while similar in their overall appearance, certain call types have a lower fundamental frequency when compared with other fur seals. In addition, the male bark call alters in rate of production according to the context used, where calls are slower when males are stationary and advertising their territorial status and faster when males are involved in confrontations with other males or actively herding females. Further research is required to investigate changes in environmental conditions and their effects on shaping the call structure and communication in Australian fur seals.     

VOCAL INDIVIDUALITY OF IN-AIR WEDDELL SEAL (LEPTONYCHOTES WEDDELLII) PUP "PRIMARY" CALLS

As a result of selective pressures faced during lactation, vocal recognition may play a crucial role in maintaining the phocid mother–pup bond during the period of dependence. To investigate this possibility, we examined whether Weddell seal ( Leptonychotes weddellii ) pups produce individually distinctive "primary" calls. One temporal, nine fundamental frequency features, and two spectral characteristics were measured. A discriminant function analysis (DFA) of 15 Vestfold Hills pups correctly classified 52% of calls, while the cross-validation procedure classified 29% of calls to the correct pup. A second DFA of 10 known-age McMurdo Sound pups correctly classified 44% of "test" calls. For novel calls, the probabilities of attaining such classification rates by chance are low. The relationship between age and call stereotypy indicated that pups 2 wk and older may be more vocally distinctive. Overall, findings suggest that Weddell seal pup "primary" calls are moderately distinctive and only exhibit sufficient stereotypy to aid maternal recognition by approximately two weeks of age.     

Vocal signature recognition of mothers by fur seal pups

Subantarctic fur seals, Arctocephalus tropicalis, come ashore to breed in dense colonies and lactating females have to alternate foraging trips at sea with periods ashore during which they suckle their pups. The effectiveness of vocal recognition between mothers and pups, has been shown experimentally. To see whether the recognition abilities of females differ from those of their offspring, we investigated how pups recognize their mother's calls. We used artificially modified signals in playback experiments to determine which acoustic parameters support the recognition process. Pups used both the energy spectrum and the ascending frequency modulation occurring at the beginning of each call. However, they seemed to rely mainly on spectral analyses. The vocal identification process at a perceptual level is therefore asymmetrical, as mothers mainly use temporal structures to recognize their pup's calls. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Mother Vocal Recognition in Antarctic Fur Seal Arctocephalus gazella Pups: A Two-Step Process

In otariids, mother’s recognition by pups is essential to their survival since females nurse exclusively their own young and can be very aggressive towards non-kin. Antarctic fur seal, Arctocephalus gazella, come ashore to breed and form dense colonies. During the 4-month lactation period, females alternate foraging trips at sea with suckling period ashore. On each return to the colony, females and pups first use vocalizations to find each other among several hundred conspecifics and olfaction is used as a final check. Such vocal identification has to be highly efficient. In this present study, we investigated the components of the individual vocal signature used by pups to identify their mothers by performing playback experiments on pups with synthetic signals. We thus tested the efficiency of this individual vocal signature by performing propagation tests and by testing pups at different playback distances. Pups use both amplitude and frequency modulations to identify their mother’s voice, as well as the energy spectrum. Propagation tests showed that frequency modulations propagated reliably up to 64m, whereas amplitude modulations and spectral content greatly were highly degraded for distances over 8m. Playback on pups at different distances suggested that the individual identification is a two-step process: at long range, pups identified first the frequency modulation pattern of their mother’s calls, and other components of the vocal signature at closer range. The individual vocal recognition system developed by Antarctic fur seals is well adapted to face the main constraint of finding kin in a crowd.     

CONFERENCE ANNOUNCEMENTS

ABSTRACT

In most mammals, adults produce relatively low frequency vocalizations compared to those of juveniles. This rule is not maintained however at least in four species of ground squirrels, whose juveniles call at the adult's fundamental frequency. These findings have been obtained however with separate sets of juveniles and adults and no data is available concerning the ontogeny linked to these differences. Here we analyze the acoustic structure of alarm calls of the same Yellow Spermophilus fulvus and Speckled S. suslicus ground squirrel individuals, recorded as pups and as adults after hibernation. We found the fundamental frequencies of adults within the same frequency ranges as those of pups, in spite of the significant difference in body mass. In ground squirrels, severing the relationship between body size and call frequency removes some vocal cues to age. We discuss some functional hypotheses advanced to explain manipulations with fundamental frequencies in ground squirrels and other animals, and suggest the lack of data for discussing the mechanisms of such vocal tuning.     

Small Mammals Ignore Common Rules: A Comparison of Vocal Repertoires and the Acoustics between Pup and Adult Piebald Shrews Diplomesodon pulchellum

A common rule for mammals vocalizing in the human audible frequency range (20 Hz–20 kHz) suggests that calls are higher in fundamental frequency (f0) in the young than in adults, because of the smaller sound‐producing structures of the young. Exclusions are rare, for example the pups of Asian house shrews (Suncus murinus) make some call types of the same or higher pitch than adults. In this study, calls from 62 piebald shrews (Diplomesodon pulchellum), 37 1 to 10‐d‐old pups from 10 litters and 25 adults were acoustically investigated in captivity. We found eight call types, all within the human audible frequency range: short and long low‐frequency squeaks with nearly flat contour, high‐frequency squeaks with modulated contour, high‐frequency squeaks with fractured contour, short and long screeches, clicks and whimpers. Seven call types were shared by pups and adults, suggesting that this vocal repertoire commences at birth. Against the common rule, the f0 of squeaks was the same in pups and adults, and the f0 of clicks and screeches was even higher in adults than in pups. These results suggest a non‐descending ontogenetic pathway that not follows the common physical relationship, of the lower f0 for the larger vocal folds.     

Sex recognition in brown skuas: do acoustic signals matter?

Bird vocalisations are often essential for sex recognition, especially in species that show little morphological sex dimorphism. Brown skuas (Catharacta antarctica lonnbergi), which exhibit uniform plumage across both sexes, emit three main calls: the long call, the alarm call and the contact call. We tested the potential for sex recognition in brown skua calls of 42 genetically sexed individuals by analysing 8–12 acoustic parameters in the temporal and frequency domains of each call type. For every call type, we failed to find sex differences in any of the acoustic parameters measured. Stepwise discriminant function analysis (DFA) revealed that sexes cannot be unambiguously classified, with increasing uncertainty of correct classification from contact calls to long calls to alarm calls. Consequently, acoustic signalling is probably not the key mechanism for sex recognition in brown skuas.     

Mother-Infant Communication in the Lesser Spear-nosed Bat Phyllostomus discolor (Chiroptera,Phyllostomidae) — Evidence for Acoustic Learning

When mother-offspring couples of Phyllostomus discolor (lesser spear-nosed bat) are reunited after separation, an intensive exchange of infants' isolation calls and mothers' directive calls can be observed. The directive calls of each mother show a distinctive frequency-time structure, which appears to represent her individual vocal signature. During ontogenesis the isolation calls of the young change gradually, adapting increasingly to the mother's call type. A comparison of calls of separated pups at different ages with their mothers' directives demonstrated the individually distinct call characteristics of the mother also to be characteristic of the isolation calls of her young by about 50 days of age. This suggests that acoustic signals may be learned in Phyllostomus discolor.     

VOCAL INDIVIDUALITY IN MOTHER AND PUP SOUTH AMERICAN FUR SEALS, ARCTOCEPHALUS AUSTRALIS

South American fur seals breeding in Peru are subjected to levels of maternal aggression, and subsequent pup mortality, that are higher than has been reported for any other otariid species. For mothers and pups to maintain contact with each other, a mutual recognition system should exist to facilitate reunion and avoid misdirection of maternal effort. We recorded vocalizations of mothers and pups at Punta San Juan, Peru, during the 1994 and 1995 breeding seasons. Sixteen acoustic variables were measured from a total of 560 calls from 15 mothers and 13 pups. Multivariate analysis showed that calls were variable in several acoustic dimensions. While calls of both mothers and pups showed low variability within and high variability among individuals, mothers' calls were more individualistic. On average, discriminant-function analysis correctly assigned 60% of pup calls and 70% of mother calls to the individual that produced them. Characteristics of the fundamental frequency were most important for distinguishing among mothers, while pup calls, which typically contained less harmonic structure, could be differentiated by formant-like frequency ranges. Thus, calls of mother and pup South American fur seals appear to exhibit sufficient stereotypy to allow for recognition and discrimination among individuals.     

Vocal repertoire of cooperatively breeding Smooth‐billed Anis

Calls are functionally diverse signals that mediate behavior in a wide variety of contexts in both passerines and non‐passerines. However, the call‐based acoustic communication systems of non‐passerines have received less attention from investigators than those of passerines. We examined the vocal repertoire of Smooth‐billed Anis (Crotophaga ani), cooperatively breeding cuckoos that live in groups with multiple breeding pairs. We recorded calls from 22 groups over two breeding seasons at the Cabo Rojo National Wildlife Refuge in Puerto Rico. We identified 11 call types and one group vocalization, and used an automated sound measurement program to quantify their acoustic features. Discriminant function analysis (DFA) correctly classified 74.2% of calls based on these features. The vocal repertoire of Smooth‐billed Anis is larger than that reported for the three other species in the subfamily Crotophaginae. Smooth‐billed Anis have at least two alarm calls, two nest‐specific calls, and one nest defense call. We also identified one possible signal of aggressive intent, one possible appeasement signal, and two calls that may communicate identity. The relatively large vocal repertoire of Smooth‐billed Anis and association of distinct call types with different functions and contexts supports the main prediction of the social complexity hypothesis, i.e., species with more complex social systems will have more complex communication systems.     

Stability and change in the vocal signatures of common marmoset mobbing calls

Alarm calls that carry information about the identity of the caller may help the receiver decide how to react. We recorded the tsik calls of six captive adult marmosets (Callithrix jacchus) in two different social groups in response to snake models at two time points (summer 2014 and January 2015). We measured eight acoustic variables including duration, inter-call interval, minimum and maximum frequency, and starting, maximum and ending peak frequency. Discriminant function analyses (DFA) confirmed that calls were individually distinct at both time periods (78.88 and 79.89% correctly classified at time one and time two, respectively). Stability of the vocal signatures was assessed using the DFA model for summer 2014 to classify calls elicited in January 2015. Although the classification rates were lower in 2015, calls were still classified more than would be expected by chance (64.50%). This suggests that acoustic signatures of common marmoset tsik calls remain fairly stable over time and therefore remain recognizable by their groupmates. However, during that six-month period, at least three (out of seven) acoustic parameters changed such that they were significantly higher or lower in all six marmosets; in two marmosets six out of seven parameters changed. Changes to individual ‘voices’ of animals, despite overall stability reflected in above-chance matching of calls over time in a DFA analysis, may have implications for acoustic research.     

Geographic variation of Weddell seal (<Emphasis Type="Italic">Leptonychotes weddellii</Emphasis>) airborne mother–pup vocalisations

Geographic variation of vocal behaviour may be reflective of genetic, cultural and ecological differences between locations. Such differences have been previously reported in six pinnipeds, including Weddell seals (Leptonychotes weddellii). This study investigated whether the acoustic characteristics of airborne Weddell seal mother and pup ‘contact’ calls vary geographically between the Vestfold Hills and McMurdo Sound. From each location, 72 mother and 120 pup calls were analysed, with 11 acoustic characteristics measured. MANOVA and Discriminant function analysis (DFA) identified significant differences in several fundamental frequency characteristics. The cross-validated DFA classified greater than 60% of mother and pup vocalisations to the correct location. For novel calls, the probabilities of correctly classifying these percentages by chance are low. Additionally, ordinal logistic regression identified significant differences in the maximum energy distribution of mother and pup vocalisations. For pups, this variation is likely the result of genetic differences between the two populations. Nevertheless, results support suggestions that, when compared with underwater repertoire differences, airborne within-call differences are less efficient at identifying Weddell seal breeding populations.     

Advertising individual identity by mother and adolescent contact calls in Siberian wapiti Cervus elaphus sibiricus

Individualistic contact calls facilitate mother‐offspring reunion after separation. However, in many mammals, both the acoustic structure and individuality of contact calls differ between mother and young. In contrast, in Siberian wapiti Cervus elaphus sibiricus, contact calls are similar in the acoustics between mother and young, whereas effects of this similarity on vocal individuality were not investigated. In this study, we analyzed acoustic differences between closed‐mouth (nasal) and open‐mouth (oral) contact calls and examined individuality of the most usual oral calls of 19 Siberian wapiti (9 hinds and 10 5–6‐month adolescents) emitted in response to mother‐offspring separation. In the oral calls, the values of frequency and power variables were higher than in the nasal calls. Calls of hinds and adolescents did not differ by the maximum fundamental frequency and duration, whereas the peak frequency was higher in the young. Discriminant function analysis (DFA) based on 11 acoustic variables of oral calls accurately classified to individual 92.5% of hind calls and 96.9% of adolescent calls (chi‐square test for differences between hinds and adolescents, p = 0.19). Variables mainly contributing to vocal identity (duration, start, and maximum fundamental frequency) were the same in calls of mothers and adolescents. We conclude that similarities in the acoustics calls of mothers and adolescents mean that they do not differ in their potential for encoding individual identity, suggesting a mutual process of mother‐offspring vocal recognition in Siberian wapiti.     

DO THE SIBERIAN TITS PARUS CINCTUS IN SCANDINAVIA AND SIBERIA SPEAK THE SAME LANGUAGE?

ABSTRACT

The vocabulary of Siberian tits Parus cinctus in South Norway and East Siberia is compared by means of tape recordings and spectrograms. The species has many different calls that are greatly confused in the literature. In this paper ten main call types are examined. On the whole, the equivalent utterings are geographically so similar that a distinction is usually impossible or questionable. This similarity also applies to the contextual use of the calls. Consistent structural differences in certain calls were nevertheless found. The sit foraging call embraced on average a broader frequency range and was of a slightly longer duration in Siberia than in Norway. The complex ‘gargle’ system could at both places be divided into three main groups equally represented in the populations: (1) trilled, (2) tonal and (3) simple gargles. The tonal gargles are characterized by a terminal tonal element (T) that varies in shape. In Norway, tonal gargles terminating with an even or upslurred T dominated, in Siberia those with a chevron-formed T. Historically, the west-east distribution throughout Eurasia was apparently continuous until quite recently, allowing an effective gene flow. Considering the huge distance from Norway to East Siberia and the markedly resident behaviour of the Siberian tit, it is nevertheless somewhat unexpected that so few vocal differences have evolved. Several of the calls of the Siberian tit are structurally very similar to equivalent (most likely homologous) calls in other species belonging to the subgenus Poecile, e.g. the willow tit Parus montanus and the black-capped chickadee P. atricapillus, suggesting that the multicall repertoire of their common ancestor remained largely intact despite Poecile's differentiation into different species.     

VOCAL BEHAVIOUR AND CALL DEVELOPMENT IN THE BULLFINCH (PYRRHULA PYRRHULA)

ABSTRACT

A sonagraphic analysis of the vocalizations of bullfinches Pyrrhula pyrrhula is presented and their behavioural contexts and functions noted. The vocal repertoire of the bullfinch is compared to that of other finches with particular attention to repertoire size and sexual specificity; the repertoire of 14–17 vocal categories is comparatively greater than that of most carduelines and the majority of vocalizations were given by both sexes. The development of nestling, fledgling and some adult calls is described. Early vocal ontogeny in the bullfinch was similar to that previously described for the chaffinch. The earliest recorded calls of nestling bullfinches showed a single fundamental. The independent use of two sound sources became apparent on the second day after hatching and the major elements of the three best studied call types were all derived from the lower fundamental of the nestling begging call.     

THE SENSORY BASIS OF SEXUAL SELECTION FOR COMPLEX CALLS IN THE TÚNGARA FROG,PHYSALAEMUS PUSTULOSUS (SEXUAL SELECTION FOR SENSORY EXPLOITATION)

Male túngara frogs (Physalaemus pustulosus) vocalize to attract females, and enhance the attractiveness of their simple, whine-only call by adding chucks to produce complex calls. Complex calls contain more total energy and are of longer duration. By virtue of the greater frequency range of the chuck, complex calls also simultaneously stimulate both the amphibian papilla and the basilar papilla of the frog's inner ear. Female phonotaxis experiments using synthetic stimuli demonstrate that an increase in the call's acoustic energy is not sufficient to account for the enhanced attractiveness of the complex call. However, the stimulation of either or both of the female's sound-sensitive inner-ear organs is sufficient to elicit her preference. We suggest that the female's sensory system generates selection that equally favors at least three evolutionary alternatives for enhancing call attractiveness and that historical constraints imposed by the male's morphology determined which of the alternatives was more likely to evolve. These data are consistent with our hypothesis of sensory exploitation, which states that selection favors those traits that elicit greater stimulation from the female's sensory system and which emphasizes the nonadaptive nature of female preference.     

Discomfort-related changes in pup ultrasonic calls of fat-tailed gerbils Pachyuromys duprasi

Rodent pups vocalize when placed in social isolation. We apply a method of “joint calls” for examining discomfort in rodent pup ultrasonic (>20 kHz) calls. Previously, this method has been developed for audible calls of fur farm mammals. Using a repeated measures design to exclude effects of individual identity and age on the analysed variables, we compared the ultrasonic call variables produced by 8–40-day pups of fat-tailed gerbils Pachyuromys duprasi during two subsequent experimental stages, the Isolation Stage and the Handling Stage. We considered that discomfort-related negative emotional arousal increased towards the Handling Stage compared to the Isolation Stage because of cumulative effects of handling and time of pup isolation from the nest. At the Isolation Stage, the call rate (calls/s) was higher from 10 to 18 days of age, whereas both the maximum amplitude frequency and power quartiles of joint calls were lower than at the Handling Stage from 20 to 32 days of age. At the same time, in audible (<20 kHz) vocalizations of a wide range of mammalian species, both the higher call rate and the upward shift of the maximum amplitude frequency and power quartiles indicate the discomfort-related increase of negative emotional arousal. We discuss the advantages of the method of joint calls for express-analyses of power variables for large sequences of ultrasonic vocalizations of complex acoustic structure during experimental trials.     

Individual variation in pup vocalizations and absence of behavioral signs of maternal vocal recognition in Weddell seals (Leptonychotes weddellii)

Individually stereotyped vocalizations often play an important role in relocation of offspring in gregarious breeders. In phocids, mothers often alternate between foraging at sea and attending their pup. Pup calls are individually distinctive in various phocid species. However, experimental evidence for maternal recognition is rare. In this study, we recorded Weddell seal (Leptonychotes weddellii) pup vocalizations at two whelping patches in Atka Bay, Antarctica, and explored individual vocal variation based on eight vocal parameters. Overall, 58% of calls were correctly classified according to individual. For males (n= 12) and females (n= 9), respectively, nine and seven individuals were correctly identified based on vocal parameters. To investigate whether mothers respond differently to calls of familiar vs. unfamiliar pups, we conducted playback experiments with 21 mothers. Maternal responses did not differ between playbacks of own, familiar, and unfamiliar pup calls. We suggest that Weddell seal pup calls may need to contain only a critical amount of individually distinct information because mothers and pups use a combination of sensory modalities for identification. However, it cannot be excluded that pup developmental factors and differing environmental factors between colonies affect pup acoustic behavior and the role of acoustic cues in the relocation process.