Neophoca cinerea otariid pinniped vocal communication Vocalizing by males plays an important role... more Neophoca cinerea otariid pinniped vocal communication Vocalizing by males plays an important role in the reproductive activities of many species. Geographical variation in the characteristics of male vocalization is well studied in birds, but largely unexplored in mammals. This study quantified the extent of geographical variation in male Australian sea lion, Neophoca cinerea, barking calls and examined what drives vocal differences in this species. We recorded male barking calls from seven breeding colonies separated by ca. 5e2700 km enabling us to investigate acoustic differences on both micro-and macrogeographical scales. Our results revealed significant nonuniform geographical variation across colonies. Neither genetic nor geographical distances between colonies fully explained the observed acoustic variation. We suggest that environmental or morphological factors are likely to further contribute to differences in vocal characteristics.
In many gregarious mammals, mothers and offspring have developed the abilities to recognise each ... more In many gregarious mammals, mothers and offspring have developed the abilities to recognise each other using acoustic signals. Such capacity may develop at different rates after birth/parturition, varying between species and between the participants, i.e., mothers and young. Differences in selective pressures between species, and between mothers and offspring, are likely to drive the timing of the onset of mother-young recognition. We tested the ability of Australian sea lion mothers to identify their offspring by vocalisation, and examined the onset of this behaviour in these females. We hypothesise that a rapid onset of recognition may reflect an adaptation to a colonial lifestyle. In a playback study maternal responses to own pup and non-filial vocalisations were compared at 12, 24 and every subsequent 24 hours until the females' first departure post-partum. Mothers showed a clear ability to recognise their pup's voice by 48 hours of age. At 24 hours mothers called more, ...
The acoustic channel is important for communication in otariids (fur seals and sea lions). Discri... more The acoustic channel is important for communication in otariids (fur seals and sea lions). Discrimination between species, sex or individuals is essential in communication; therefore insight into the role of vocalisations in recognition is vital to understanding otariid social interactions. We measured vocalisations and their use in discriminating sex and species in male Australian sea lions (Neophoca cinerea). Barking calls of mature males were recorded and analysed based on five acoustic parameters. A discriminant function analysis classified calls to the correct individual at a classification rate of 56%, suggesting that male barking calls are individually distinctive with the potential to facilitate individual vocal recognition. Playback experiments were used to assess the role of vocalisations in sex and species recognition both in and out of the breeding season. Males showed significantly stronger reactions to both conspecific and heterospecific males than they did to conspecific females and were most responsive during the breeding season. Australian sea lion males have the most depauperate vocal repertoire of any otariid. This simple repertoire may reflect the ecological circumstances in which these animals breed, with very low colony densities, asynchronous breeding and low levels of polygyny. Yet even in this simple system, males are able to discriminate between males and females of their own species, and distinguish the calls of conspecifics from other species. The barking calls of male Australian sea lions have sufficient information embedded to provide the potential for individual discrimination and this ability will be assessed in future studies.
Proceedings of the Royal Society B: Biological Sciences, 2004
Offspring solicit food from their parents by begging behaviours. Studies on birds suggest that th... more Offspring solicit food from their parents by begging behaviours. Studies on birds suggest that these displays are 'honest signals of need' and adults provide food according to the begging level. However, siblings may compete for parental resources and the begging intensity is expected to change with brood size. Here, we show that in the black-headed gull (Larus ridibundus) an increase of the numbers of siblings can result in a decrease of individual begging cost through nestlings' synchronized signalling. This is in accordance with some mathematical models. As parents respond to the total solicitation emerging from the nest, the probability to get food increases with the number of chicks begging together. The more siblings there are, the more they coordinate their begging while decreasing the number of individual begging bouts. Intra-brood synchronization of begging enables chicks to reduce their effort and hence exerting an important role in parental-offspring negotiation.
In colonial birds, acoustic communication is essential for mate recognition. The South Polar skua... more In colonial birds, acoustic communication is essential for mate recognition. The South Polar skua (Catharacta maccormicki) lives in loose colonies and is highly territorial for feeding and breeding. We studied the potential of individual identity coding in the three main calls of the South Polar skua repertoire: the courtship, the contact and the alarm calls. We investigated parameters in both temporal and frequencial domains, i.e. amplitude modulation, frequency modulation and power spectrum density. For each parameter, the intra-and inter-individual variabilities were calculated. The ratio between these values represents the potential of individuality coding (PIC) of the considered feature. Low values of PICs for amplitude and frequency modulations show that both parameters may not be used for individual recognition. In contrast, high values of PIC for the power spectrum density indicate that the energy distribution among the frequency spectrum is likely to be an individual marker. PIC also varies according to the call type. Both courtship and contact calls have a higher potentiality of individual identity coding than the alarm call. The two former calls may allow individual recognition whereas the latter may not, and this last result can be extrapolated to many other species.
Australian fur seals breed on thirteen islands located in the Bass Strait, Australia. Land access... more Australian fur seals breed on thirteen islands located in the Bass Strait, Australia. Land access to these islands is restricted, minimising human presence but boat access is still permissible with limitations on approach distances. Thirty-two controlled noise exposure experiments were conducted on breeding Australian fur seals to determine their behavioural response to controlled in-air motor boat noise on Kanowna Island (39u109S, 146u189E). Our results show there were significant differences in the seals' behaviour at low (64-70 dB) versus high (75-85 dB) sound levels, with seals orientating themselves towards or physically moving away from the louder boat noise at three different sound levels. Furthermore, seals responded more aggressively with one another and were more alert when they heard louder boat noise. Australian fur seals demonstrated plasticity in their vocal responses to boat noise with calls being significantly different between the various sound intensities and barks tending to get faster as the boat noise got louder. These results suggest that Australian fur seals on Kanowna Island show behavioural disturbance to high level boat noise. Consequently, it is recommended that an appropriate level of received boat sound emissions at breeding fur seal colonies be below 74 dB and that these findings be taken into account when evaluating appropriate approach distances and speed limits for boats.
In pinnipeds and especially in otariids, mothers and pups develop the capacity to recognize each ... more In pinnipeds and especially in otariids, mothers and pups develop the capacity to recognize each other's voices. Pups become able to discriminate their mother's voice a few days after birth. For females, this discrimination seems to occur earlier, probably during the few hours after parturition. However, during lactation, mothers are confronted with a major problem: the change of the characteristics of their pup's calls. To investigate this problem, we first performed an acoustic analysis of pups' calls from birth to weaning to identity the successive different versions of these calls. Secondly, we performed playback experiments just before weaning to test if females retain these different versions over a long time period. The acoustic analysis of pups' calls reveals that several characteristics of their vocalizations change with age. Playback experiments demonstrate that females still recognize all the successive immature and mature versions of their pup's calls. In our opinion, this long-term memorization seems to be a by-product of the permanent pups' voice learning from birth to weaning since no apparent adaptive benefit seems to arise from this capacity.
Like most otariids species, the Subantarctic fur seal breeds on land in large, dense colonies. Pu... more 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 161 162 MARINE MAMMAL SCIENCE, VOL. 19, NO. 1, 2003 of the final part of the call are weakly individualized (PIC values between 1 and 1.2).
Mammalian Biology - Zeitschrift für Säugetierkunde, 2011
Walrus are highly gregarious pinnipeds that can form herds of several hundreds or thousands of in... more Walrus are highly gregarious pinnipeds that can form herds of several hundreds or thousands of individuals when hauling out on ice or on land. They produce vocalisations in almost all social interactions, from aggressive vocalisations, contact calls involved in mother-calf bond to adult-adult communication to stereotyped courtship display during the mating season. The knowledge on walrus' vocal behaviour and its perceptual abilities is limited due to the extreme difficulty of studying these animals in their natural environment. In the present study, we reported the results of a pilot experimental work on group/social vocal communication in captive Pacific Walruses (Odobenus rosmarus divergens). By analysing the main vocalisations produced by females and males during social interactions, we found some differences in their call characteristics compared to the Atlantic subspecies. In a second step, we experimentally demonstrated the abilities of females and mature males to discriminate between vocalizations of individuals from their own group and those of unknown individuals. In spite of the low sample size of animals, these findings on captive walruses improved knowledge of the cognitive abilities of this endemic Arctic species.
Mammalian Biology - Zeitschrift für Säugetierkunde, 2011
a b s t r a c t Frequent mother-pup separations and reunions occurring in the South American sea ... more a b s t r a c t Frequent mother-pup separations and reunions occurring in the South American sea lion Otaria flavescens require a well-developed individual recognition system. Individuality in mothers' and pups' calls of this species has been found in Península Valdés (PV), Argentina (with individuality rates of 95% and 89%, respectively). In order to test the hypotheses of ecological constraints (i.e., population density, habitat) and geographic variation affecting the characteristics and/or the individuality of vocalizations, we studied another population at Isla de Lobos (IL), Uruguay, separated by approx. 1200 km from PV. DFAs showed classification rates of 63.2% in mothers and 53.3% in pups. This lower degree of individuality can be explained by differences in population density. Differences in acoustic characteristics were also found: at IL mother and pup calls tended to be shorter in duration and mother calls lower-pitched. This can be explained by an adaptation to the local environment: at IL sea lions breed in sympatry with South American fur seals in an obstructed habitat whereas PV sea lions are the unique species in the colony constituted by an open habitat. Finally, the acoustic differences can also be a consequence of the genetic isolation that has been found between these two colonies of O. flavescens.
The Journal of the Acoustical Society of America, 2006
The "chick-a-dee" call of the black-capped chickadee ͑Poecile atricapillus͒ contains four note ty... more The "chick-a-dee" call of the black-capped chickadee ͑Poecile atricapillus͒ contains four note types, A, B, C, and D that have important functional roles. This provides strong motivation for studying the classification of acoustic components of the call into different note types. In this paper, the spectrograms from a sample of A, B, and C notes ͑370 in total͒ were each described as a set of 9 summary features. An artificial neural network was trained to identify note type on the basis of these features, and was able to obtain better than 98% accuracy. An internal analysis of this network revealed a distributed code in which different hidden units generated high activities to different subsets of notes. By combining these different sensitivities, the network could discriminate all three types of notes. The performance of this network was compared to a discriminant analysis of the same data. This analysis also achieved a high level of performance ͑95%͒. A comparison between the two approaches revealed some striking similarities, but also some intriguing differences. These results are discussed in terms of two related issues: developing a research tool for note classification, and developing a theory of how birds themselves might classify notes.
The Journal of the Acoustical Society of America, 2009
For some time, the Sturdy laboratory group has been studying chickadee vocal production and perce... more For some time, the Sturdy laboratory group has been studying chickadee vocal production and perception using a variety of approaches. These include, among others, bioacoustic analyses of vocalizations, operant conditioning studies, and, more recently, artificial neural networks ...
The Journal of the Acoustical Society of America, 2013
ABSTRACT Northern elephant seals (Mirounga angustirostris) have a polygynous breeding system in w... more ABSTRACT Northern elephant seals (Mirounga angustirostris) have a polygynous breeding system in which adult males establish dominance hierarchies that determine access to females. Acoustic signaling plays an important role in settling fights between males, as stereotyped displays elicit appropriate behavioral responses from individuals without contact during an energetically demanding breeding season. To determine whether reliable differences exist in the acoustic displays of individuals and whether these differences function to convey identity, we behaviorally and acoustically sampled male seals during the breeding season. Vocalizations were recorded during competitive interactions and analyzed for spectral, temporal, and amplitude characteristics. A cross-validated discriminant function analysis revealed small differences within-and significant differences between-the calls produced by 17 adult males of known dominance status. To determine whether acoustic displays serve as individual signatures that males learn to recognize during the breeding season, we conducted playback experiments to test if having prior experience with a particular caller would influence the approach or avoidance response of the listener. Our findings reveal that these unique acoustic signals serve as individual vocal signatures, and males likely remember the identity of their rivals based on call features that have been associated with the outcome of previous competitive interactions.
Individual vocal recognition between mothers and pups has been widely observed in pinnipeds, espe... more 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.
Neophoca cinerea otariid pinniped vocal communication Vocalizing by males plays an important role... more Neophoca cinerea otariid pinniped vocal communication Vocalizing by males plays an important role in the reproductive activities of many species. Geographical variation in the characteristics of male vocalization is well studied in birds, but largely unexplored in mammals. This study quantified the extent of geographical variation in male Australian sea lion, Neophoca cinerea, barking calls and examined what drives vocal differences in this species. We recorded male barking calls from seven breeding colonies separated by ca. 5e2700 km enabling us to investigate acoustic differences on both micro-and macrogeographical scales. Our results revealed significant nonuniform geographical variation across colonies. Neither genetic nor geographical distances between colonies fully explained the observed acoustic variation. We suggest that environmental or morphological factors are likely to further contribute to differences in vocal characteristics.
In many gregarious mammals, mothers and offspring have developed the abilities to recognise each ... more In many gregarious mammals, mothers and offspring have developed the abilities to recognise each other using acoustic signals. Such capacity may develop at different rates after birth/parturition, varying between species and between the participants, i.e., mothers and young. Differences in selective pressures between species, and between mothers and offspring, are likely to drive the timing of the onset of mother-young recognition. We tested the ability of Australian sea lion mothers to identify their offspring by vocalisation, and examined the onset of this behaviour in these females. We hypothesise that a rapid onset of recognition may reflect an adaptation to a colonial lifestyle. In a playback study maternal responses to own pup and non-filial vocalisations were compared at 12, 24 and every subsequent 24 hours until the females' first departure post-partum. Mothers showed a clear ability to recognise their pup's voice by 48 hours of age. At 24 hours mothers called more, ...
The acoustic channel is important for communication in otariids (fur seals and sea lions). Discri... more The acoustic channel is important for communication in otariids (fur seals and sea lions). Discrimination between species, sex or individuals is essential in communication; therefore insight into the role of vocalisations in recognition is vital to understanding otariid social interactions. We measured vocalisations and their use in discriminating sex and species in male Australian sea lions (Neophoca cinerea). Barking calls of mature males were recorded and analysed based on five acoustic parameters. A discriminant function analysis classified calls to the correct individual at a classification rate of 56%, suggesting that male barking calls are individually distinctive with the potential to facilitate individual vocal recognition. Playback experiments were used to assess the role of vocalisations in sex and species recognition both in and out of the breeding season. Males showed significantly stronger reactions to both conspecific and heterospecific males than they did to conspecific females and were most responsive during the breeding season. Australian sea lion males have the most depauperate vocal repertoire of any otariid. This simple repertoire may reflect the ecological circumstances in which these animals breed, with very low colony densities, asynchronous breeding and low levels of polygyny. Yet even in this simple system, males are able to discriminate between males and females of their own species, and distinguish the calls of conspecifics from other species. The barking calls of male Australian sea lions have sufficient information embedded to provide the potential for individual discrimination and this ability will be assessed in future studies.
Proceedings of the Royal Society B: Biological Sciences, 2004
Offspring solicit food from their parents by begging behaviours. Studies on birds suggest that th... more Offspring solicit food from their parents by begging behaviours. Studies on birds suggest that these displays are 'honest signals of need' and adults provide food according to the begging level. However, siblings may compete for parental resources and the begging intensity is expected to change with brood size. Here, we show that in the black-headed gull (Larus ridibundus) an increase of the numbers of siblings can result in a decrease of individual begging cost through nestlings' synchronized signalling. This is in accordance with some mathematical models. As parents respond to the total solicitation emerging from the nest, the probability to get food increases with the number of chicks begging together. The more siblings there are, the more they coordinate their begging while decreasing the number of individual begging bouts. Intra-brood synchronization of begging enables chicks to reduce their effort and hence exerting an important role in parental-offspring negotiation.
In colonial birds, acoustic communication is essential for mate recognition. The South Polar skua... more In colonial birds, acoustic communication is essential for mate recognition. The South Polar skua (Catharacta maccormicki) lives in loose colonies and is highly territorial for feeding and breeding. We studied the potential of individual identity coding in the three main calls of the South Polar skua repertoire: the courtship, the contact and the alarm calls. We investigated parameters in both temporal and frequencial domains, i.e. amplitude modulation, frequency modulation and power spectrum density. For each parameter, the intra-and inter-individual variabilities were calculated. The ratio between these values represents the potential of individuality coding (PIC) of the considered feature. Low values of PICs for amplitude and frequency modulations show that both parameters may not be used for individual recognition. In contrast, high values of PIC for the power spectrum density indicate that the energy distribution among the frequency spectrum is likely to be an individual marker. PIC also varies according to the call type. Both courtship and contact calls have a higher potentiality of individual identity coding than the alarm call. The two former calls may allow individual recognition whereas the latter may not, and this last result can be extrapolated to many other species.
Australian fur seals breed on thirteen islands located in the Bass Strait, Australia. Land access... more Australian fur seals breed on thirteen islands located in the Bass Strait, Australia. Land access to these islands is restricted, minimising human presence but boat access is still permissible with limitations on approach distances. Thirty-two controlled noise exposure experiments were conducted on breeding Australian fur seals to determine their behavioural response to controlled in-air motor boat noise on Kanowna Island (39u109S, 146u189E). Our results show there were significant differences in the seals' behaviour at low (64-70 dB) versus high (75-85 dB) sound levels, with seals orientating themselves towards or physically moving away from the louder boat noise at three different sound levels. Furthermore, seals responded more aggressively with one another and were more alert when they heard louder boat noise. Australian fur seals demonstrated plasticity in their vocal responses to boat noise with calls being significantly different between the various sound intensities and barks tending to get faster as the boat noise got louder. These results suggest that Australian fur seals on Kanowna Island show behavioural disturbance to high level boat noise. Consequently, it is recommended that an appropriate level of received boat sound emissions at breeding fur seal colonies be below 74 dB and that these findings be taken into account when evaluating appropriate approach distances and speed limits for boats.
In pinnipeds and especially in otariids, mothers and pups develop the capacity to recognize each ... more In pinnipeds and especially in otariids, mothers and pups develop the capacity to recognize each other's voices. Pups become able to discriminate their mother's voice a few days after birth. For females, this discrimination seems to occur earlier, probably during the few hours after parturition. However, during lactation, mothers are confronted with a major problem: the change of the characteristics of their pup's calls. To investigate this problem, we first performed an acoustic analysis of pups' calls from birth to weaning to identity the successive different versions of these calls. Secondly, we performed playback experiments just before weaning to test if females retain these different versions over a long time period. The acoustic analysis of pups' calls reveals that several characteristics of their vocalizations change with age. Playback experiments demonstrate that females still recognize all the successive immature and mature versions of their pup's calls. In our opinion, this long-term memorization seems to be a by-product of the permanent pups' voice learning from birth to weaning since no apparent adaptive benefit seems to arise from this capacity.
Like most otariids species, the Subantarctic fur seal breeds on land in large, dense colonies. Pu... more 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 161 162 MARINE MAMMAL SCIENCE, VOL. 19, NO. 1, 2003 of the final part of the call are weakly individualized (PIC values between 1 and 1.2).
Mammalian Biology - Zeitschrift für Säugetierkunde, 2011
Walrus are highly gregarious pinnipeds that can form herds of several hundreds or thousands of in... more Walrus are highly gregarious pinnipeds that can form herds of several hundreds or thousands of individuals when hauling out on ice or on land. They produce vocalisations in almost all social interactions, from aggressive vocalisations, contact calls involved in mother-calf bond to adult-adult communication to stereotyped courtship display during the mating season. The knowledge on walrus' vocal behaviour and its perceptual abilities is limited due to the extreme difficulty of studying these animals in their natural environment. In the present study, we reported the results of a pilot experimental work on group/social vocal communication in captive Pacific Walruses (Odobenus rosmarus divergens). By analysing the main vocalisations produced by females and males during social interactions, we found some differences in their call characteristics compared to the Atlantic subspecies. In a second step, we experimentally demonstrated the abilities of females and mature males to discriminate between vocalizations of individuals from their own group and those of unknown individuals. In spite of the low sample size of animals, these findings on captive walruses improved knowledge of the cognitive abilities of this endemic Arctic species.
Mammalian Biology - Zeitschrift für Säugetierkunde, 2011
a b s t r a c t Frequent mother-pup separations and reunions occurring in the South American sea ... more a b s t r a c t Frequent mother-pup separations and reunions occurring in the South American sea lion Otaria flavescens require a well-developed individual recognition system. Individuality in mothers' and pups' calls of this species has been found in Península Valdés (PV), Argentina (with individuality rates of 95% and 89%, respectively). In order to test the hypotheses of ecological constraints (i.e., population density, habitat) and geographic variation affecting the characteristics and/or the individuality of vocalizations, we studied another population at Isla de Lobos (IL), Uruguay, separated by approx. 1200 km from PV. DFAs showed classification rates of 63.2% in mothers and 53.3% in pups. This lower degree of individuality can be explained by differences in population density. Differences in acoustic characteristics were also found: at IL mother and pup calls tended to be shorter in duration and mother calls lower-pitched. This can be explained by an adaptation to the local environment: at IL sea lions breed in sympatry with South American fur seals in an obstructed habitat whereas PV sea lions are the unique species in the colony constituted by an open habitat. Finally, the acoustic differences can also be a consequence of the genetic isolation that has been found between these two colonies of O. flavescens.
The Journal of the Acoustical Society of America, 2006
The "chick-a-dee" call of the black-capped chickadee ͑Poecile atricapillus͒ contains four note ty... more The "chick-a-dee" call of the black-capped chickadee ͑Poecile atricapillus͒ contains four note types, A, B, C, and D that have important functional roles. This provides strong motivation for studying the classification of acoustic components of the call into different note types. In this paper, the spectrograms from a sample of A, B, and C notes ͑370 in total͒ were each described as a set of 9 summary features. An artificial neural network was trained to identify note type on the basis of these features, and was able to obtain better than 98% accuracy. An internal analysis of this network revealed a distributed code in which different hidden units generated high activities to different subsets of notes. By combining these different sensitivities, the network could discriminate all three types of notes. The performance of this network was compared to a discriminant analysis of the same data. This analysis also achieved a high level of performance ͑95%͒. A comparison between the two approaches revealed some striking similarities, but also some intriguing differences. These results are discussed in terms of two related issues: developing a research tool for note classification, and developing a theory of how birds themselves might classify notes.
The Journal of the Acoustical Society of America, 2009
For some time, the Sturdy laboratory group has been studying chickadee vocal production and perce... more For some time, the Sturdy laboratory group has been studying chickadee vocal production and perception using a variety of approaches. These include, among others, bioacoustic analyses of vocalizations, operant conditioning studies, and, more recently, artificial neural networks ...
The Journal of the Acoustical Society of America, 2013
ABSTRACT Northern elephant seals (Mirounga angustirostris) have a polygynous breeding system in w... more ABSTRACT Northern elephant seals (Mirounga angustirostris) have a polygynous breeding system in which adult males establish dominance hierarchies that determine access to females. Acoustic signaling plays an important role in settling fights between males, as stereotyped displays elicit appropriate behavioral responses from individuals without contact during an energetically demanding breeding season. To determine whether reliable differences exist in the acoustic displays of individuals and whether these differences function to convey identity, we behaviorally and acoustically sampled male seals during the breeding season. Vocalizations were recorded during competitive interactions and analyzed for spectral, temporal, and amplitude characteristics. A cross-validated discriminant function analysis revealed small differences within-and significant differences between-the calls produced by 17 adult males of known dominance status. To determine whether acoustic displays serve as individual signatures that males learn to recognize during the breeding season, we conducted playback experiments to test if having prior experience with a particular caller would influence the approach or avoidance response of the listener. Our findings reveal that these unique acoustic signals serve as individual vocal signatures, and males likely remember the identity of their rivals based on call features that have been associated with the outcome of previous competitive interactions.
Individual vocal recognition between mothers and pups has been widely observed in pinnipeds, espe... more 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.
Many territorial species have the ability to recognise neighbours from stranger individuals. If t... more Many territorial species have the ability to recognise neighbours from stranger individuals. If the neighbouring individual is assumed to pose less of a threat, the territorial individual responds less and avoids unnecessary confrontations with familiar individuals at established boundaries, thus avoiding the costly energy expenditure associated with fighting. Territorial male Australian fur seals respond more to strangers than to neighbouring males. The present study evaluated which acoustic features were important in the neighbour–stranger recognition process in male Australian fur seals. The results reveal that there was an increase in response strength or intensity from males when they heard more bark units, indicating the importance of repetition to detect a caller. However, lengthening and shortening the inter-unit spaces, (i.e. changing the rhythm of the call) did not appear to significantly affect an animal's response. In addition, the whole frequency spectrum was considered important to recognition with results suggesting that they may vary in their importance. A call containing the dominant and surrounding harmonics was considered important to a male's ability to recognise its neighbour. Furthermore, recognition occurs even with a partial bark, but males need to hear between 25 and 75% of each bark unit from neighbouring seals. Our study highlights which acoustic features induce stronger or weaker responses from territorial males, decoding the important features in neighbour–stranger recognition.
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Papers by Isabelle Charrier