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Boucher AJ, Weladji RB, Holand Ø, Kumpula J. Modelling reindeer rut activity using on-animal acoustic recorders and machine learning. Ecol Evol 2024; 14:e11479. [PMID: 38932958 PMCID: PMC11199844 DOI: 10.1002/ece3.11479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Revised: 04/24/2024] [Accepted: 05/13/2024] [Indexed: 06/28/2024] Open
Abstract
For decades, researchers have employed sound to study the biology of wildlife, with the aim to better understand their ecology and behaviour. By utilizing on-animal recorders to capture audio from freely moving animals, scientists can decipher the vocalizations and glean insights into their behaviour and ecosystem dynamics through advanced signal processing. However, the laborious task of sorting through extensive audio recordings has been a major bottleneck. To expedite this process, researchers have turned to machine learning techniques, specifically neural networks, to streamline the analysis of data. Nevertheless, much of the existing research has focused predominantly on stationary recording devices, overlooking the potential benefits of employing on-animal recorders in conjunction with machine learning. To showcase the synergy of on-animal recorders and machine learning, we conducted a study at the Kutuharju research station in Kaamanen, Finland, where the vocalizations of rutting reindeer were recorded during their mating season. By attaching recorders to seven male reindeer during the rutting periods of 2019 and 2020, we trained convolutional neural networks to distinguish reindeer grunts with a 95% accuracy rate. This high level of accuracy allowed us to examine the reindeers' grunting behaviour, revealing patterns indicating that older, heavier males vocalized more compared to their younger, lighter counterparts. The success of this study underscores the potential of on-animal acoustic recorders coupled with machine learning techniques as powerful tools for wildlife research, hinting at their broader applications with further advancement and optimization.
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Affiliation(s)
| | | | - Øystein Holand
- Department of Animal and Aquacultural SciencesNorwegian University of Life SciencesÅsNorway
| | - Jouko Kumpula
- Natural Resources Institute of Finland (Luke), Reindeer Research StationHelsinkiFinland
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Diversity of Underwater Vocalizations in Chinese Soft-Shelled Turtle ( Pelodiscus sinensis). Animals (Basel) 2023; 13:ani13050812. [PMID: 36899669 PMCID: PMC10000088 DOI: 10.3390/ani13050812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 02/11/2023] [Accepted: 02/21/2023] [Indexed: 02/26/2023] Open
Abstract
Sound communication is important for underwater species. The wild population of the Chinese soft-shelled turtle (Pelodiscus sinensis) is listed as vulnerable. However, its vocalization, which can serve as the basis for ecological and evolutionary research, has not been studied. Here, we performed underwater recordings of 23 Chinese soft-shelled turtles of different ages and sexes and identified 720 underwater calls. The turtle calls were manually divided into 10 call types according to visual and aural inspection properties. The similarity test indicated that the manual division was reliable. We described the acoustic properties of the calls and the statistical analysis showed that the peak frequency of calls was significantly different between adult females and males, and also between subadults and adults. Similar to other aquatic turtles that prefer to live in deep water, Chinese soft-shelled turtles have a high vocal diversity and many harmonic calls, indicating that this highly aquatic species developed a variety of vocalizations to enhance their underwater communication, which helped them adapt to the complex and dim underwater environment. Furthermore, the turtles showed a tendency for vocalization to become more diverse with age.
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Zhou L, Lei J, Zhai X, Shi H, Wang J. Chinese striped-neck turtles vocalize underwater and show differences in peak frequency among different age and sex groups. PeerJ 2023; 11:e14628. [PMID: 36655045 PMCID: PMC9841902 DOI: 10.7717/peerj.14628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Accepted: 12/02/2022] [Indexed: 01/15/2023] Open
Abstract
Background Turtle vocalizations play an important role throughout their lives by expressing individual information (position, emotion, or physiological status), reflecting mating preferences, and synchronizing incubation. The Chinese striped-neck turtle (Mauremys sinensis) is one of the most widely distributed freshwater turtles in China, whose wild population is critically endangered. However, its vocalization has not been studied, which can be the basis for behavioral and ecological studies. Methods Five different sex-age groups of turtles were recorded underwater in a soundproof room. Cluster analysis and principal component analysis for classification of Chinese striped-neck turtle calls were unreasonable. The turtle calls were manually sought using visual and aural inspection of the recordings in Raven Pro 1.5 software and classified according to differences perceived through auditory inspection and the morphological characteristics of the spectrograms. The results of similarity analysis verified the reliability of manual classification. We compared the peak frequency of the calls among different age and sex groups. Results We identified ten M. sinensis call types, displayed their spectra and waveforms, and described their auditory characteristics. Most calls produced by the turtles were low-frequency. Some high-frequency call types, that are common in other turtle species were also produced. Similar to other turtles, the Chinese striped-neck turtle generates harmonic vocalizations. Courtship behaviors were observed when one of the call types occurred in the mixed-sex group. Adult females produced more high-frequency call types, and subadult males had higher vocalizations than other groups. These results provide a basis for future research on the function of vocalizations, field monitoring, and conservation of this species.
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Affiliation(s)
- Lu Zhou
- Ministry of Education Key Laboratory for Ecology of Tropical Islands, Key Laboratory of Tropical Animal and Plant Ecology of Hainan Province, College of Life Sciences, Hainan Normal University, Haikou, China
| | - Jinhong Lei
- Ministry of Education Key Laboratory for Ecology of Tropical Islands, Key Laboratory of Tropical Animal and Plant Ecology of Hainan Province, College of Life Sciences, Hainan Normal University, Haikou, China
| | - Xiaofei Zhai
- Ministry of Education Key Laboratory for Ecology of Tropical Islands, Key Laboratory of Tropical Animal and Plant Ecology of Hainan Province, College of Life Sciences, Hainan Normal University, Haikou, China
| | - Haitao Shi
- Ministry of Education Key Laboratory for Ecology of Tropical Islands, Key Laboratory of Tropical Animal and Plant Ecology of Hainan Province, College of Life Sciences, Hainan Normal University, Haikou, China
| | - Jichao Wang
- Ministry of Education Key Laboratory for Ecology of Tropical Islands, Key Laboratory of Tropical Animal and Plant Ecology of Hainan Province, College of Life Sciences, Hainan Normal University, Haikou, China
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Zhou L, Zhao LH, Li H, Wang T, Shi H, Wang J. Underwater vocalizations of Trachemys scripta elegans and their differences among sex–age groups. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.1022052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The aim of this study was to identify underwater vocalizations in red-eared turtles (Trachemys scripta elegans) and assess differences between sexes and ages. We recorded the underwater vocalizations of the red-eared sliders and identified 12 call types through manual visual and aural inspection of the recordings. Similarity analysis verified that manual classification was relatively reliable. The call types of the turtle were described and displayed as spectrograms and waveforms. The turtles produced fewer high-frequency call types than low-frequency types in all recordings. Statistical analysis revealed significant differences in the frequencies and duration of the calls of red-eared turtles between different sexes and ages. Males vocalized pulse calls very frequently, whereas a high proportion of high-frequency call types was emitted by the female adult group. The male subadult group emitted higher frequencies of Type A, B, and C calls, which is in accordance with the phenomenon that vocal frequency is often inversely proportional to the turtle size. Some call types produced by red-eared turtles were above the frequency range of their known hearing range. This may have been a by-product of the sound production mechanism or it may have adaptive value in mitigating interference to communication from low-frequency noise common in natural waters in communication The behavioral implications of these vocalizations and whether turtles can hear such high sounds warrant further study.
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Frey R, Wyman MT, Johnston M, Schofield M, Locatelli Y, Reby D. Roars, groans and moans: Anatomical correlates of vocal diversity in polygynous deer. J Anat 2021; 239:1336-1369. [PMID: 34342877 PMCID: PMC8602020 DOI: 10.1111/joa.13519] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Revised: 06/15/2021] [Accepted: 07/06/2021] [Indexed: 02/01/2023] Open
Abstract
Eurasian deer are characterized by the extraordinary diversity of their vocal repertoires. Male sexual calls range from roars with relatively low fundamental frequency (hereafter fo ) in red deer Cervus elaphus, to moans with extremely high fo in sika deer Cervus nippon, and almost infrasonic groans with exceptionally low fo in fallow deer Dama dama. Moreover, while both red and fallow males are capable of lowering their formant frequencies during their calls, sika males appear to lack this ability. Female contact calls are also characterized by relatively less pronounced, yet strong interspecific differences. The aim of this study is to examine the anatomical bases of these inter-specific and inter-sexual differences by identifying if the acoustic variation is reflected in corresponding anatomical variation. To do this, we investigated the vocal anatomy of male and female specimens of each of these three species. Across species and sexes, we find that the observed acoustic variability is indeed related to expected corresponding anatomical differences, based on the source-filter theory of vocal production. At the source level, low fo is associated with larger vocal folds, whereas high fo is associated with smaller vocal folds: sika deer have the smallest vocal folds and male fallow deer the largest. Red and sika deer vocal folds do not appear to be sexually dimorphic, while fallow deer exhibit strong sexual dimorphism (after correcting for body size differences). At the filter level, the variability in formants is related to the configuration of the vocal tract: in fallow and red deer, both sexes have evolved a permanently descended larynx (with a resting position of the larynx much lower in males than in females). Both sexes also have the potential for momentary, call-synchronous vocal tract elongation, again more pronounced in males than in females. In contrast, the resting position of the larynx is high in both sexes of sika deer and the potential for further active vocal tract elongation is virtually absent in both sexes. Anatomical evidence suggests an evolutionary reversal in larynx position within sika deer, that is, a secondary larynx ascent. Together, our observations confirm that the observed diversity of vocal behaviour in polygynous deer is supported by strong anatomical differences, highlighting the importance of anatomical specializations in shaping mammalian vocal repertoires. Sexual selection is discussed as a potential evolutionary driver of the observed vocal diversity and sexual dimorphisms.
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Affiliation(s)
- Roland Frey
- Department of Reproduction ManagementLeibniz Institute of Zoo and Wildlife Research (IZW)BerlinGermany
| | - Megan Tompkins Wyman
- Department of Evolutionary Biology and Environmental ScienceUniversity of ZurichZurichSwitzerland
| | - Malcolm Johnston
- Clinical Imaging Sciences CentreUniversity of SussexBrightonUK
- Department of RadiologyBrighton and Sussex University HospitalsBrightonUK
| | - Michael Schofield
- Genome Damage and Stability CentreSchool of Life SciencesUniversity of SussexBrightonUK
| | - Yann Locatelli
- Réserve de la Haute ToucheMuséum National d’Histoire NaturelleObterreFrance
| | - David Reby
- Equipe de Neuro‐Ethologie Sensorielle (ENES)/Centre de Recherche en Neurosciences de Lyon (CRNL)University of Saint‐Étienne, CNRS UMR5292, INSERM UMR_S 1028Saint‐ÉtienneFrance
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Muller MN. Testosterone and reproductive effort in male primates. Horm Behav 2017; 91:36-51. [PMID: 27616559 PMCID: PMC5342957 DOI: 10.1016/j.yhbeh.2016.09.001] [Citation(s) in RCA: 93] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Revised: 09/06/2016] [Accepted: 09/07/2016] [Indexed: 10/21/2022]
Abstract
Considerable evidence suggests that the steroid hormone testosterone mediates major life-history trade-offs in vertebrates, promoting mating effort at the expense of parenting effort or survival. Observations from a range of wild primates support the "Challenge Hypothesis," which posits that variation in male testosterone is more closely associated with aggressive mating competition than with reproductive physiology. In both seasonally and non-seasonally breeding species, males increase testosterone production primarily when competing for fecund females. In species where males compete to maintain long-term access to females, testosterone increases when males are threatened with losing access to females, rather than during mating periods. And when male status is linked to mating success, and dependent on aggression, high-ranking males normally maintain higher testosterone levels than subordinates, particularly when dominance hierarchies are unstable. Trade-offs between parenting effort and mating effort appear to be weak in most primates, because direct investment in the form of infant transport and provisioning is rare. Instead, infant protection is the primary form of paternal investment in the order. Testosterone does not inhibit this form of investment, which relies on male aggression. Testosterone has a wide range of effects in primates that plausibly function to support male competitive behavior. These include psychological effects related to dominance striving, analgesic effects, and effects on the development and maintenance of the armaments and adornments that males employ in mating competition.
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Affiliation(s)
- Martin N Muller
- Department of Anthropology, University of New Mexico, United States.
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Fedurek P, Slocombe KE, Enigk DK, Emery Thompson M, Wrangham RW, Muller MN. The relationship between testosterone and long-distance calling in wild male chimpanzees. Behav Ecol Sociobiol 2016; 70:659-672. [PMID: 27182103 PMCID: PMC4864005 DOI: 10.1007/s00265-016-2087-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Long-distance calling is a common behaviour in animals that has various important social functions. At a physiological level, calling is often mediated by gonadal hormones such as testosterone (T), particularly when its function is linked to intra-sexual competition for mates or territory. T also plays an important role in the development of vocal characteristics associated with dominance in humans. However, the few available studies of T and vocal behaviour in non-human primates suggest that in primates T has less influence on call production than in other animals. We tested this hypothesis by studying the relationship between T concentrations and pant hooting in wild male chimpanzees (Pan troglodytes schweinfurthii) of the Kanyawara community in the Kibale National Park, Uganda. We found three kinds of correlation. Hourly T averages were positively associated with hourly rates of pant-hooting. Monthly T levels were likewise correlated with monthly rates of pant hooting after controlling for other influences such as fission-fusion rates. Finally, males with high T levels had higher peak frequency at the start of the call climax. These results suggest that T affects the production of pant-hoots in chimpanzees. This implies that the pant-hoot call plays a role in male-male competition. We propose that even in cognitively sophisticated species, endocrine mechanisms can contribute to regulating vocal production.
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Affiliation(s)
- Pawel Fedurek
- Institute of Biology, University of Neuchâtel, Switzerland
| | | | - Drew K. Enigk
- Department of Anthropology, University of New Mexico
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Bergman TJ, Cortés-Ortiz L, Dias PAD, Ho L, Adams D, Canales-Espinosa D, Kitchen DM. Striking differences in the loud calls of howler monkey sister species (Alouatta pigra and A. palliata). Am J Primatol 2016; 78:755-66. [PMID: 26950654 DOI: 10.1002/ajp.22539] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Revised: 02/08/2016] [Accepted: 02/09/2016] [Indexed: 11/10/2022]
Abstract
Comparing vocalizations across species is useful for understanding acoustic variation at mechanistic and evolutionary levels. Here, we take advantage of the divergent vocalizations of two closely related howler monkey species (Alouatta pigra and A. palliata) to better understand vocal evolution. In addition to comparing multiple acoustic and temporal features of roars and the calling bouts in which they are produced, we tested several predictions. First, A. pigra should have roars with lower fundamental frequency and lower formant dispersion because they are larger than A. palliata and have a larger hyoid apparatus. Second, A. pigra should have faster calling rates, longer roars, longer bouts, and exaggerated call features linked to vocal effort (e.g., nonlinear phenomena and emphasized frequencies) because they are the more aggressive species during intergroup encounters. We found significant interspecific differences supporting our predictions in every tested parameter of roars and bouts, except for roar duration and barking rate. Stepwise discriminant function analyses identified the best features for differentiating roars (acoustic features: formant dispersion followed by highest frequency; temporal features: longest syllable duration followed by number of syllables). Although resembling each other more than they resemble South American howler monkeys, our comparison revealed striking differences in the vocalizations of the two Mesoamerican species. While we cannot completely rule out the influence of body size or the environmental conditions in which the two species evolved, vocal differences were likely influenced by sexual selection. The exaggerated roars and intense calling patterns in A. pigra seem more suitable for intergroup competition, whereas A. palliata calls may be better suited for mate attraction and competition within groups. With interspecific acoustic differences quantified, we will now be able to examine how vocalizations contribute to the evolutionary dynamics of the A. palliata × A. pigra hybrid zone in southern Mexico. Am. J. Primatol. 78:755-766, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Thore J Bergman
- Department of Psychology, University of Michigan, Ann Arbor, Michigan.,Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan
| | - Liliana Cortés-Ortiz
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan
| | - Pedro A D Dias
- Laboratorio de Ecología del Comportamiento de Primates, Instituto de Neuroetología, Universidad Veracruzana, Xalapa, Veracruz, Mexico
| | - Lucy Ho
- Department of Psychology, University of Michigan, Ann Arbor, Michigan
| | - Dara Adams
- Department of Anthropology, The Ohio State University, Mansfield, Ohio
| | - Domingo Canales-Espinosa
- Laboratorio de Ecología del Comportamiento de Primates, Instituto de Neuroetología, Universidad Veracruzana, Xalapa, Veracruz, Mexico
| | - Dawn M Kitchen
- Department of Anthropology, The Ohio State University, Mansfield, Ohio.,Department of Anthropology, The Ohio State University, Columbus, Ohio.,Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, Ohio
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Garcia M, Gingras B, Bowling DL, Herbst CT, Boeckle M, Locatelli Y, Fitch WT. Structural Classification of Wild Boar ( Sus scrofa) Vocalizations. Ethology 2016; 122:329-342. [PMID: 27065507 PMCID: PMC4793927 DOI: 10.1111/eth.12472] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Revised: 07/20/2015] [Accepted: 12/28/2015] [Indexed: 11/28/2022]
Abstract
Determining whether a species' vocal communication system is graded or discrete requires definition of its vocal repertoire. In this context, research on domestic pig (Sus scrofa domesticus) vocalizations, for example, has led to significant advances in our understanding of communicative functions. Despite their close relation to domestic pigs, little is known about wild boar (Sus scrofa) vocalizations. The few existing studies, conducted in the 1970s, relied on visual inspections of spectrograms to quantify acoustic parameters and lacked statistical analysis. Here, we use objective signal processing techniques and advanced statistical approaches to classify 616 calls recorded from semi‐free ranging animals. Based on four spectral and temporal acoustic parameters—quartile Q25, duration, spectral flux, and spectral flatness—extracted from a multivariate analysis, we refine and extend the conclusions drawn from previous work and present a statistically validated classification of the wild boar vocal repertoire into four call types: grunts, grunt‐squeals, squeals, and trumpets. While the majority of calls could be sorted into these categories using objective criteria, we also found evidence supporting a graded interpretation of some wild boar vocalizations as acoustically continuous, with the extremes representing discrete call types. The use of objective criteria based on modern techniques and statistics in respect to acoustic continuity advances our understanding of vocal variation. Integrating our findings with recent studies on domestic pig vocal behavior and emotions, we emphasize the importance of grunt‐squeals for acoustic approaches to animal welfare and underline the need of further research investigating the role of domestication on animal vocal communication.
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Affiliation(s)
- Maxime Garcia
- Department of Cognitive Biology University of Vienna Vienna Austria
| | - Bruno Gingras
- Department of Cognitive Biology University of Vienna Vienna Austria
| | - Daniel L Bowling
- Department of Cognitive Biology University of Vienna Vienna Austria
| | - Christian T Herbst
- Voice Research Lab Department of Biophysics Faculty of Science Palacký University Olomouc Czech Republic
| | - Markus Boeckle
- Department of Cognitive Biology University of Vienna Vienna Austria; Department of Psychotherapy and Biopsychosocial Health Danube University Krems Krems Austria
| | - Yann Locatelli
- Réserve de la Haute Touche Muséum National d'Histoire Naturelle Obterre France; Equipe Interactions Cellulaires et Fertilité UMR0085 Physiologie de la Reproduction et des Comportements Institut National de la Recherche Agronomique Nouzilly France
| | - W Tecumseh Fitch
- Department of Cognitive Biology University of Vienna Vienna Austria
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Vocal Production by Terrestrial Mammals: Source, Filter, and Function. VERTEBRATE SOUND PRODUCTION AND ACOUSTIC COMMUNICATION 2016. [DOI: 10.1007/978-3-319-27721-9_8] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Intrasexual selection drives sensitivity to pitch, formants and duration in the competitive calls of fallow bucks. BMC Evol Biol 2015; 15:149. [PMID: 26279584 PMCID: PMC4538740 DOI: 10.1186/s12862-015-0429-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Accepted: 07/16/2015] [Indexed: 11/10/2022] Open
Abstract
Background Mammal vocal parameters such as fundamental frequency (or pitch; fo) and formant dispersion often provide information about quality traits of the producer (e.g. dominance and body size), suggesting that they are sexually selected. However, little experimental evidence exists demonstrating the importance of these cues in intrasexual competition, particularly fo. Male Fallow deer (bucks) produce an extremely low pitched groan. Bucks have a descended larynx and generate fo well below what is expected for animals of their size. Groan parameters are linked to caller dominance, body size and condition, suggesting that groans are the product of sexual selection. Using a playback experiment, we presented bucks with groans that had been manipulated to alter vocal cues to these male characteristics and compared the response to the same, non-modified (natural) groans. Results We experimentally examined the ability of bucks to utilise putative cues to dominance (fo), body size (formant frequencies) and condition (groan duration), when assessing competitors. We found that bucks treated groans with lowered fo (more dominant), and lowered formant frequencies (larger caller) as more threatening. By contrast, groans with raised formant frequencies (smaller caller), and shorter durations (more fatigued caller) were treated as less threatening. Conclusions Our results indicate that intrasexual selection is driving groans to concurrently convey caller dominance, body size and condition. They represent the first experimental demonstration of the importance of fo in male competition in non-human mammals, and show that bucks have advanced perception abilities that allow them to extract information based on relatively small changes in key parameters. Electronic supplementary material The online version of this article (doi:10.1186/s12862-015-0429-7) contains supplementary material, which is available to authorized users.
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Response of red deer stags (Cervus elaphus) to playback of harsh versus common roars. Naturwissenschaften 2014; 101:851-4. [PMID: 25119193 DOI: 10.1007/s00114-014-1217-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2014] [Revised: 07/08/2014] [Accepted: 07/23/2014] [Indexed: 10/24/2022]
Abstract
Red deer stags (Cervus elaphus) give two distinct types of roars during the breeding season, the "common roar" and the "harsh roar." Harsh roars are more frequent during contexts of intense competition, and characterized by a set of features that increase their perceptual salience, suggesting that they signal heightened arousal. While common roars have been shown to encode size information and mediate both male competition and female choice, to our knowledge, the specific function of harsh roars during male competition has not yet been studied. Here, we investigate the hypothesis that the specific structure of male harsh roars signals high arousal to competitors. We contrast the behavioral responses of free ranging, harem-holding stags to the playback of harsh roars from an unfamiliar competitor with their response to the playback of common roars from the same animal. We show that males react less strongly to sequences of harsh roars than to sequences of common roars, possibly because they are reluctant to escalate conflicts with highly motivated and threatening unfamiliar males in the absence of visual information. While future work should investigate the response of stags to harsh roars from familiar opponents, our observations remain consistent with the hypothesis that harsh roars may signal motivation during male competition, and illustrate how intrasexual selection can contribute to the diversification of male vocal signals.
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