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Ecstatic display songs recorded from two penguins (a,b) over different days provided as an example of the intra-individual stereotypy of the vocal units across the song. Spectrograms were generated in Praat v. 5.4.01 sound editor window (Gaussian window shape, view range  =  0 to 8000 Hz, window length  =  0.02 s, dynamic range  =  50 dB). 

Ecstatic display songs recorded from two penguins (a,b) over different days provided as an example of the intra-individual stereotypy of the vocal units across the song. Spectrograms were generated in Praat v. 5.4.01 sound editor window (Gaussian window shape, view range = 0 to 8000 Hz, window length = 0.02 s, dynamic range = 50 dB). 

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... Although not all differences found between individuals encode information for the receiver (Townsend et al. 2010), investigation of individual vocal recognition has been demonstrated in the call types of a few species, for example, elephants (McComb et al. 2000), zebra finches (Taeniopygia guttata, Elie and Theunissen 2018), and African penguins (Spheniscus demersus, Favaro et al. 2015). Our work might offer a novel approach on the chorus howl, since regardless of the acoustic features of vocal types, it highlights the fact that wolves have individually unique vocal behaviors when they participate in a chorus howl. ...
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Wolf packs perform group vocalizations called chorus howls. These acoustic signals have a complex structure and could be involved in functions such as strengthening of social bonds, territory advertisement, or spacing between packs. We analyzed video recordings of 46 chorus howls emitted by 10 packs of wolves held in captivity, in order to investigate whether sex, age, social status, pack, or individual influence the way wolves participate in a chorus. We found that, during a chorus, wolves vocalized 63% of the time, with the howl being the most common vocalization (36% of the chorus duration), followed by woa (13.5%), other vocalizations (11.8%), and bark (1.7%). The main factor affecting the vocal behavior of wolves was age, since young wolves vocalized less and uttered shorter acoustic signals than adults. The discriminant analysis carried out with the wolves of Cañada Real pack assigned 89.3% of the cases to the correct individual, which is much better than the assignment expected by chance, suggesting that individuals could have a unique vocal usage during a chorus howl, mainly due to the use of howls and woa-woa howls. Based on our results, we propose that in the context of a chorus the woa-woa howl is important, although further research is needed to address this issue properly.
... Two acoustic features appeared to contribute the most to differentiate individuals, the Inter-Onset-Interval (related to the temporal rate of unit production) and frequency parameters during the down-movement part (Fmax for females and F0 for males). Spectral differences, such as the fundamental frequency and energy distribution in seabird vocalisations have been associated with anatomical differences in their airways [59,60] according to the source-filter theory [61]. Slight differences in vocal tract anatomy between individuals most likely explain the differences in the fundamental frequency between individuals we found in this study. ...
... Individual signatures are common in the vocalisations of nesting colonial seabirds [17,27,60], although the signatures can be carried on a variety of acoustic variables. Individual vocal signatures were found in the greeting calls of black-legged kittiwakes, on both temporal and frequency features [27]. ...
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Vocalisations play a vital role in animal communication, as they are involved in many biological functions. Seabirds often breed in large and dense colonies, making successful recognition between mates or between parents-and offspring crucial for reproductive success. Most seabird species, including Cape gannets (Morus capensis), are monomorphic and likely rely on acoustic signals for mate selection and mate recognition. This study aimed to better understand the use of vocalisations for sex and individual recognition in Cape gannets by describing the acoustic structure of their display calls at the nest. Vocalisations of nesting Cape gannets were recorded and acoustic measurements were extracted in both temporal and frequency domains. Values of the fundamental frequency and the average of Inter-Onset-Interval appeared to be the most important acoustic variables for sex determination. Both temporal and frequency parameters showed a potential for individual identity coding, with the average units Inter-Onset-Interval being the most important variable for individual identification for both sexes. This study provides the first evidence of sex-specific and individual vocal signatures in adult breeding Cape gannets. From an applied perspective, identified sex specific differences could potentially be used as a non-invasive method for field-based sex-determination in research and monitoring projects on Cape gannets.
... Morphological and structural differences between birds, as well as environmental factors, cause these distinguishable individual characteristics in acoustic cues (Morton 1975). In King Penguins, a harmonic structure is the main component determining differences between individuals (Jouventin et al. 1999) and in Corn Crakes Crex crex, the temporal pattern of the calls varies between individuals (Peake et al. 1998), but in the majority of species, individuality is a result of a complex mixture of time and frequency parameters (Mathevon 1997, Favaro et al. 2015. ...
... Extreme environmental conditions and a unique breeding system have driven the evolution of an efficient vocal coding mechanism in non-nesting penguins that ensures discrimination of mates and offspring [20][21][22][23]. However, in contrast with non-nesting penguins, like the king and emperor (Aptenodytes spp.), individual identity information encoded in the vocal calls of nesting penguins, like banded penguins, is much weaker [20,22,24,25]. This may have provided nesting penguins with the pressure to have evolved complex modality-independent representations of individuals in order to recognize other individuals reliably. ...
... Contact calls are distinctive short calls expressing isolation from groups or their mates [27]. Ecstatic display calls or mutual displays calls play important roles in long behavioural processes, like mating and bonding [24,36]. Unlike these types of calls, only very brief attention is required to locate and respond appropriately to contact calls. ...
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... Vocal individuality also contributes to acoustic parameters divergence [42][43][44]. Nevertheless, although vocal variation of call a among individuals was considered in our study (LMM), a parameter, Duration of syllable (T), was still differed significantly in different behavioral contexts, which indicates T is specifically used for expressing distinct behavioral motivation. ...
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Background Although acoustic communication plays an essential role in the social interactions of Rallidae, our knowledge of how Rallidae encode diverse types of information using simple vocalizations is limited. We recorded and examined the vocalizations of a common coot (Fulica atra) population during the breeding season to test the hypotheses that 1) different call types can be emitted under different behavioral contexts, and 2) variation in the vocal structure of a single call type may be influenced both by behavioral motivations and individual signature. We measured a total of 61 recordings of 30 adults while noting the behavioral activities in which individuals were engaged. We compared several acoustic parameters of the same call type emitted under different behavioral activities to determine how frequency and temporal parameters changed depending on behavioral motivations and individual differences. Results We found that adult common coots had a small vocal repertoire, including 4 types of call, composed of a single syllable that was used during 9 types of behaviors. The 4 calls significantly differed in both frequency and temporal parameters and can be clearly distinguished by discriminant function analysis. Minimum frequency of fundamental frequency (F0min) and duration of syllable (T) contributed the most to acoustic divergence between calls. Call a was the most commonly used (in 8 of the 9 behaviors detected), and maximum frequency of fundamental frequency (F0max) and interval of syllables (TI) contributed the most to variation in call a. Duration of syllable (T) in a single call a can vary with different behavioral motivations after individual vocal signature being controlled. Conclusions These results demonstrate that several call types of a small repertoire, and a single call with function-related changes in the temporal parameter in common coots could potentially indicate various behavioral motivations and individual signature. This study advances our knowledge of how Rallidae use “simple” vocal systems to express diverse motivations and provides new models for future studies on the role of vocalization in avian communication and behavior.
... According to this theory, calls are produced through the syrinx, which is regarded as a 'source' and located at the base of the trachea. Syringeal constriction functionally overlaps the role of the larynx in mammalian phonation, and the trachea acts as a 'filter' to remove certain frequencies or leave others unchanged (Fletcher, 1988;Beckers et al., 2003;Taylor and Reby, 2010;Favaro et al., 2015). Sourcerelated vocal features (the fundamental frequency, F 0 ), which are related to the vibrating mass in the syrinx, are stable (laying hens, F 0 : 400-2500 Hz) (Cao et al., 2014), while filter-related features (formants), which are related to the supra-syringeal vocal tract, are dependent on different vocalisations. ...
... Source-filter theory has been considered to be the commonly used theory for explaining the acoustic characteristics of bird vocalisations (Favaro et al., 2015). Williams concluded that the syrinx in birds can vary the harmonic amplitude output (Williams et al., 1989). ...
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... Furthermore, African penguin vocal signals mediate several social relationships, including mate and group member recognition and nest defence (Favaro et al. 2014). Recent studies, applying the source-filter theory of bird and mammal vocal production (Taylor and Reby 2010;Beckers 2011), have shown that acoustic cues to individual identity in the African penguin are encoded in the fundamental frequency (sound source, produced by the syrinx through membranes vibration) and formants (resonant frequencies generated by the supra-syringeal vocal tract) of the vocalisations (Favaro et al. 2015(Favaro et al. , 2016. ...
... We performed two separate leave-one-out cross-validated Discriminant Function Analyses (DFA), one for contact calls and one for ecstatic display songs. The discriminant Table 1 Abbreviations and descriptions for the acoustic parameters measured a For the ecstatic display songs, acoustic measurements were performed on the first long syllable following Favaro et al. (2015) Acoustic parameter Description We used individual identity as the grouping variable and the 14 acoustic parameters as continuous independent variables. The percentage of correct classification was adjusted according to group size, because there was an imbalance in the number of vocalisations from each penguin. ...
... The results show that individual acoustic features of both contact calls and ecstatic display songs remained stable across four consecutive breeding seasons. In addition, the results provide further support to the source-filter theory as a robust framework to identify the acoustic cues linked with the identity encoded in penguin vocal signals (Favaro et al. 2015(Favaro et al. , 2016. ...
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The stability of individual acoustic features is fundamental in social species, and more importantly in monogamous and territorial species, showing long-term fidelity both to the partner and the breeding site. In this study, the stability over time of two discrete vocal types was investigated in the African penguin (Spheniscus demersus), a monogamous and territorial seabird. Contact calls and ecstatic display songs were recorded from an ex situ colony in 2017 and in 2020. For each vocalisation, we measured 14 spectral and temporal acoustic parameters related to both source and filter components. Two separate leave-one-out cross-validated Discriminant Function Analyses (DFA) were then performed, generating the discriminant functions from the vocalisations collected in 2017 to classify those recorded in 2020. The DFA correctly classified 62% of the contact calls (10 subjects) and 80.9% of the ecstatic display songs (seven subjects) according to the correct emitter, showing that acoustic cues to individuality encoded in both vocal types remained unchanged over four consecutive breeding seasons. We suggest that, in this monogamous and territorial bird species, individual acoustic stability could be selected for to identify groupmates and neighbours over the years and to help couples to reunite in consecutive breeding seasons, increasing individual fitness.
... All rights reserved single-unit vocalisations used to mediate agonistic interactions (agonistic calls) and or maintain acoustic contact (contact calls) among group members at sea (Jouventin 1982, Favaro et al. 2014). Display songs are complex sequences of short vocal units named "syllables", given at land and characterising the breeding season (Favaro et al. 2014(Favaro et al. , 2015. Display songs can be further divided into ecstatic display songs (vocalised mostly by males to attract females and territorial defence) and mutual display songs (vocalised by established pairs within their nest, primarily for recognition when joining after one of the members comes back from a foraging trip at sea) (Jouventin 1982, Favaro et al. 2014. ...
... From a practical standpoint, the values of the H index can vary between 0 and 1, with low values indicating an acoustic scene characterised by pure tones (or noise) and high values by a scene dominated by harmonics sounds, where the acoustic energy is portioned across frequency bands (Sueur et al. 2014). Accordingly, we suggest that the acoustic structure of the African Penguins' display songs (Favaro et al., 2014;2015;, with many harmonic frequencies covering a broad portion of the spectrum (0.2 kHz to 8 kHz; Favaro et al., 2014) explains the effect of the number of vocalisations we observed within recordings and the increase of the H index values. Most importantly, our results demonstrate for the first time that the acoustic entropy can be used as a reliable indicator of the number of ecstatic display songs produced within a colony, which might reflect the number of reproductive males (Jouventin 1982, Favaro et al. 2014. ...
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African Penguins (Spheniscus demersus) are endangered and declining seabirds which make extensive use of vocal signals for intra‐specific vocal communication. Accordingly, passive acoustic monitoring tools could be developed as robust population monitoring methods that cause minimal disturbance to the birds. In this study, we collected soundscape recordings at the Stony Point penguin colony (Betty’s Bay, South Africa) during the breeding season in 2019 (i) to document the circadian rhythms of vocal activity of this species (ii) to investigate whether the magnitude of variation of three different ecoacoustic indices correlates with the number of ecstatic and mutual display songs counted in recordings, which might inform on the breeding activity of the colony. Indeed, while ecstatic display songs are produced by males during intersexual competition and territorial defence, mutual display songs are given by parents returning to the nest after foraging trips. We found that the vast majority of the display songs (>80%) occurred between 04:00‐08:00 and 17:30‐21:30. We also found that the Acoustic Entropy index was a good predictor of the number of penguins’ songs within a recording. Overall, our study shows that African penguins vocalisations have the potential to assist the monitoring of this species while minimising disturbance.
... Such difference in syllable types between the two islands could simply be explained by founder effects (Baker, 1996) and cultural drift (Lachlan & Slater, 2003;Lynch & Baker, 1993) if fewer individuals colonized the more remote Floreana Island. In Darwin's finches, song differences between populations have been shown to arise in allopatry through random selection of syllable types in the newly founded population (Grant & Grant, 1995), followed by random extinction of other syllable types and small copying errors in transmission from father to son (Grant & Grant, 1996;Grant & Grant, 1997a, b (Brumm et al., 2010;Grant & Grant, 2002;Kleindorfer et al., 2013;Podos, 2007Podos, , 2010Ratcliffe & Grant, 1985) -we found that territorial males on both islands showed a stronger response to local versus foreign songs, may be using other features of the songs not captured by spectrograms, such as the length of the inter-syllable intervals, their temporal pattern (equal or unequal) or some tonal features of the syllables (their internal structure) (Favaro et al., 2015;Grant & Grant, 2002). ...
... A study in African penguins (Spheniscus demersus), for example, showed that up to 14 acoustic parameters within a single vocalization could be used for individual recognition (Favaro et al., 2015), (Dudaniec & Kleindorfer, 2006;Fessl et al., 2018;Kleindorfer & Dudaniec, 2016;. Divergence in learned acoustic signals can rapidly restrict gene flow by promoting song divergence and thereby enhancing assortative mating (Grant & Grant, 2002;Greig & Webster, 2013;Halfwerk et al., 2016;Lipshutz et al., 2016). ...
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Empirical data that identify contemporary mechanisms of divergence shed light on how species could multiply. In this study, we measured population genetic structure, song syllable diversity, and response to simulated intruder song in Darwin’s small tree finch (Camarhynchus parvulus) on Santa Cruz and Floreana Islands, Galápagos archipelago. Our aim was to test whether the magnitude of contemporary behavioural response in resident birds was consistent with patterns of genetic or cultural differences between populations. We analysed genetic structure and the occurrence of song syllable types, and experimentally measured the response of resident birds to intruder bird song from different geographical origin (i.e., island) or syllable type. We discovered a weak signal of population genetic structure between Santa Cruz and Floreana Islands. While some song syllables occurred on both islands, others were unique to each island; Santa Cruz Island males used more unique syllables than Floreana Island males. Both Santa Cruz and Floreana resident males discriminated their response towards a simulated intruder song based on the geographical origin of the intruder song, but not on the syllable type sung by the intruder. We conclude that the populations are diverging in genetic and cultural traits and identified a signal of contemporary behavioural response that could maintain divergence upon secondary contact.
... Individual recognition mediates a wide variety of social interactions (Tibbetts & Dale, 2007;Wiley, 2013;Yorzinski, 2017), but it requires sensory signals that contain distinctive 'individual signatures' (i.e. phenotypic cues with high interindividual and low intraindividual variation, Penn et al., 2007;Favaro, Gamba, Alfieri, Pessani, & McElligott, 2015;Jornod & Roche, 2015). Many species have been found to produce vocalizations that contain individual signatures (reviewed in Shapiro, 2010;Kershenbaum et al., 2016, cited in Stowell, Petruskov a, S alek, & Linhart, 2019). ...
... To quantify the individual variation between males and determine which parameters provide candidates for individual signatures, we calculated the PIC (Favaro et al., 2015). We examined 27 USV parameters and used four different models. ...
... We conducted an analysis to quantify individual variation and to determine which parameters provide candidates for individual signatures, called PIC (potential for individual coding; Favaro et al., 2015). PIC compares variation within individuals (coefficient of variation within individuals, CVw) to between-individual variation (coefficient of variation between individuals, CVb) for each parameter, and all the parameters with a PIC > 1 are considered to be candidates for individual signatures. ...
Article
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Acoustic communication mediates many types of social interactions; however, few studies have investigated whether courtship vocalizations contain distinctive individual signatures necessary for individual recognition. Male house mice, Mus musculus, produce spectrally complex ultrasonic vocalizations (USVs) during courtship and mating, which appear to attract females and increase male reproductive success. Our goals were to (1) describe quantitative and qualitative changes in the vocalizations of wild-derived male house mice, M. m. musculus, induced by a female odour stimulus; (2) measure individual variation and consistency in male USV emission over time; (3) test whether the variation in USVs is greater between than within individuals; and (4) identify individual signatures in spectrotemporal features using univariate statistics, multivariate models and machine learning methods. We recorded males once per week for 3 weeks, used an automated method (A-MUD) to detect USVs, and manually classified them into distinct syllables. We found that most males did not vocalize until they encountered female scent, and then most males dramatically increased the number and the types of different vocalizations (repertoire size and composition). Male USVs showed high interindividual variation and most showed intraindividual consistency, and we found greater inter- than intraindividual variation for both USV count and repertoire size. Male USVs contained individual signatures in most spectrotemporal features, regardless of the method of analysis. Males sometimes produced few, if any, vocalizations when presented with female scent, but consistent nonvocalizers were rare. Our study provides the first evidence that individual signatures in USVs of male house mice are stable over time and across recording trials, although studies are still needed to investigate repeatability across social contexts and to test whether USVs mediate individual recognition.