Acoustic characteristics and variations in grunt vocalizations in the oyster toadfish <Emphasis Type="Italic">Opsanus tau</Emphasis>

Acoustic communication is critical for reproductive success in the oyster toadfish Opsanus tau. While previous studies have examined the acoustic characteristics, behavioral context, geographical variation, and seasonality of advertisement boatwhistle sound production, there is limited information on the grunt or other non-advertisement vocalizations in this species. This study continuously monitored sound production in toadfish maintained in an outdoor habitat for four months to identify and characterize grunt vocalizations, compare them with boatwhistles, and test for relationships between the incidence of grunt vocalizations, sound characteristics and environmental parameters. Oyster toadfish produced grunts in response to handling, and spontaneous single (70% of all grunts), doublet (10%), and trains of grunts (20%) throughout the May to September study period. Grunt types varied in pulse structure, duration, and frequency components, and were shorter and of lower fundamental frequency than the pulse repetition rate of boatwhistles. Higher water temperatures were correlated with a greater number of grunt emissions, higher fundamental frequencies, and shorter sound durations. The number of grunts per day was also positively correlated with daylength and maximum tidal amplitude differences (previously entrained) associated with full and new moons, thus providing the first demonstration of semilunar vocalization rhythms in the oyster toadfish. These data provide new information on the acoustic repertoire and the environmental factors correlated with sound production in the toadfish, and have important implications for seasonal acoustic communication in this model vocal fish.     

Selection for acoustic individuality within the vocal repertoire of wild chimpanzees

Individual primates typically produce acoustically distinct calls. To investigate the factors that facilitate the evolution of individual vocal signatures, we examined two components of the call repertoire of chimpanzees: the pant hoot and pant grunt. Pant hoots are long-distance signals whose recipients can be several hundred meters away, while pant grunts are short-range calls given to conspecifics within close visual range. Given their markedly different contexts of emission, we predicted that natural selection would favor the elaboration of individually distinctive acoustic features in pant hoots compared with pant grunts. Analyses of nine acoustic features revealed that pant hoots are more stereotyped within-individuals and variable between-individuals than pant grunts. These data are consistent with the hypothesis that selection may act to encode varying degrees of individuality in different components of the vocal repertoire of a single species.     

Acoustic cues to caller identity in lemurs: a case study

This study investigated the acoustic structure of grunt vocalizations in red-bellied lemurs (Eulemur rubriventer) and its potential for individual discrimination. Acoustic analyses were performed on 1,605 grunts recorded from seven lemurs belonging to two captive groups. From the perspective of sound-filter theory, we described the acoustic structure of grunts, measuring two sets of parameters: fundamental frequency characteristics as larynx-related variables and four formant frequencies as filter-related features. Formants were effective in assigning 80.5% of the vocalizations to the correct emitter against 24.9% scored by the model based on larynx-related variables. We concluded that vocal tract resonances might potentially provide conspecifics with individual cues.     

Expression of Emotional Arousal in Two Different Piglet Call Types

Humans as well as many animal species reveal their emotional state in their voice. Vocal features show strikingly similar correlation patterns with emotional states across mammalian species, suggesting that the vocal expression of emotion follows highly conserved signalling rules. To fully understand the principles of emotional signalling in mammals it is, however, necessary to also account for any inconsistencies in the way that they are acoustically encoded. Here we investigate whether the expression of emotions differs between call types produced by the same species. We compare the acoustic structure of two common piglet calls—the scream (a distress call) and the grunt (a contact call)—across three levels of arousal in a negative situation. We find that while the central frequency of calls increases with arousal in both call types, the amplitude and tonal quality (harmonic-to-noise ratio) show contrasting patterns: as arousal increased, the intensity also increased in screams, but not in grunts, while the harmonicity increased in screams but decreased in grunts. Our results suggest that the expression of arousal depends on the function and acoustic specificity of the call type. The fact that more vocal features varied with arousal in scream calls than in grunts is consistent with the idea that distress calls have evolved to convey information about emotional arousal.     

The study of vocal communication of wild mandrills in Cameroon in relation to their social structure

The vocal repertoire of the mandrill (Mandrillus sphinx), a forest living baboon, is described, and their vocal communication analyzed quantitatively. Although the vocal repertoire of mandrills corresponds well to that of savanna living baboons,Papio, some characteristics differed, such as the development of long-distance calls and differentiation of vocalizations between age-sex classes. Vocal communication within a group was closely related to changes in the spatial distribution of group members, and the two most common vocalizations, crowing and 2PG, appear to function as contact calls. Based on the wide dispersion of food trees, a group of mandrills divided into several feeding groups (subgroups). The two types of contact call were given in different and in some senses complementary contexts, and helped to facilitate and maintain group integration. According to their acoustic structure, these calls are long distance calls. Influenced by the high-level of attenuation of vocalization on the forest floor, the mandrill has developed them as contact calls, instead of using the contact “grunt,” which is common to the savanna living baboons. Comparing the patterns of vocal exchanges of mandrills with those of gelada and hamadryas baboons which have a multi-levelled society, the social structure of the mandrill is discussed. From the analysis of the spatial distribution of vocal emission, a number of clusters of vocalizations were obtained. These clusters correspond to subgroups. The frequent female-female and female-male vocal exchange between subgroups of mandrills suggest that the relationships between subgroups are less closed than between the one-male units of gelada and hamadryas baboons. Furthermore some of these clusters include more than two vocalizing adult males, while in other clusters there are no vocalizing adult males. Thus, the social structure of mandrills is suggested to be multi-male rather than a multilevelled type. The absence of contact calls specific for short distance and the functional replacement of the grunting of all group members by persistent emission of a loud call (2PG) by usually just one adult male suggests that the social structure of mandrills is not exactly equivalent to that of the multimale troop of savanna living baboons. Usually the use of 2PG is monopolized by one adult male travelling in the rear part of the group. Such monopolization of 2PG emission and the pattern of 2PG-2PG or 2PG-roar exchanges by adult males in some cases indicate the existence of strong dominance relationships among adult males, and especially the existence of a leader male within a multi-male group of mandrills.     

Social stressors and coping mechanisms in wild female baboons (Papio hamadryas ursinus)

We examined the social correlates of fecal glucocorticoid (GC) levels in wild female baboons during a period of social and demographic stability. Females' GC levels were not affected by individual attributes such as number of kin or dominance rank, nor could we detect any significant seasonal effects. Instead, GC levels were influenced by behavioral attributes that varied between individuals and within individuals across time. Pregnant and cycling females who received high rates of aggression had higher GC levels than others. In contrast, pregnant and cycling females who received grunts - vocal signals of benign intent - at high frequencies from dominant females had lower GC levels than females who received grunts at lower frequencies. Lactating females showed the opposite trend, apparently as a consequence of the high rate of grunting and intense, unsolicited attention that their infants received from others. All females experienced lower GC levels in months when they concentrated their grooming among a small number of partners than when their grooming was more evenly distributed among many partners. Although GC levels in female baboons are most strongly influenced by events that directly affect their reproductive success, subtle social factors associated with the loss of predictability and control also seem to exert an effect. Loss of control may be mitigated if a female is able to predict others' intentions - for example, if others grunt to her to signal their intentions - and if she is able to express some preference over the timing and identities of her grooming partners.     

Weak genetic structure indicates strong dispersal limits: a tale of two coral reef fish

The extent of dispersal by pelagic larvae in marine environments, including coral reefs, is central for understanding local population dynamics and designing sustainable marine reserves. We present here the first example of a clear stepping-stone genetic structure throughout the Caribbean basin for a common coral reef species, the French grunt (Haemulon flavolineatum). Analysis of microsatellite DNA markers indicated that French grunt population structure may be characterized by overlapping populations throughout the Caribbean, influenced by independent population dynamics but with no fixed geographical boundaries. In addition, different spatial genetic patterns were found in different oceanographic regions. A second species, the bluehead wrasse (Thalassoma bifasciatum), has a much longer pelagic larval duration than French grunts and showed no explicit spatial pattern of genetic variation. This finding is concordant with the hypothesis of a positive relationship between larval dispersal and duration in the plankton. While the magnitude of the genetic signal of population structure in French grunts was very low (F(ST) approximately 0.003), the pattern of isolation-by-distance throughout the Caribbean indicated considerable population structure with important ecological and conservation significance.     

Structural Classification of Wild Boar (Sus scrofa) Vocalizations

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.     

Vocal convergence in a multi-level primate society: insights into the evolution of vocal learning

The extent to which nonhuman primate vocalizations are amenable to modification through experience is relevant for understanding the substrate from which human speech evolved. We examined the vocal behaviour of Guinea baboons, Papio papio, ranging in the Niokolo Koba National Park in Senegal. Guinea baboons live in a multi-level society, with units nested within parties nested within gangs. We investigated whether the acoustic structure of grunts of 27 male baboons of two gangs varied with party/gang membership and genetic relatedness. Males in this species are philopatric, resulting in increased male relatedness within gangs and parties. Grunts of males that were members of the same social levels were more similar than those of males in different social levels (N = 351 dyads for comparison within and between gangs, and N = 169 dyads within and between parties), but the effect sizes were small. Yet, acoustic similarity did not correlate with genetic relatedness, suggesting that higher amounts of social interactions rather than genetic relatedness promote the observed vocal convergence. We consider this convergence a result of sensory–motor integration and suggest this to be an implicit form of vocal learning shared with humans, in contrast to the goal-directed and intentional explicit form of vocal learning unique to human speech acquisition.     

The meaning and function of grunt variants in baboons

Wild baboons Papio cynocephalus ursinus, give tonal, harmonically rich vocalizations, termed grunts, in at least two distinct, behavioural contexts: when about to embark on a move across an open area ('move' grunts); and when approaching mothers and attempting to inspect or handle their young infants ('infant' grunts). Grunts in these two contexts elicit different responses from receivers and appear to be acoustically distinct (Owren et al. 1997 Journal of the Acoustical Society of America101 2951-2963). Differences in responses to grunts in the two contexts may, then, be due to acoustic differences, reflecting at least a rudimentary capacity for referential signalling. Alternatively, responses may differ simply due to differences in the contexts in which the grunts are being produced. We conducted playback experiments to test between these hypotheses. Experiments were designed to control systematically the effects of both context and acoustic features so as to evaluate the role of each in determining responses to grunts. In playback trials, subjects differentiated between putative move and infant grunts. Their responses based only on the acoustic features of grunts were functionally distinct and mirrored their behaviour to naturally occurring move and infant grunts. However, subjects' responses were in some cases also affected by the context in which grunts were presented, and by an interaction between the context and the acoustic features of the grunts. Furthermore, responses to grunts were affected by the relative rank difference between the caller and the subject. These results indicate that baboon grunts can function in rudimentary referential fashion, but that the context in which grunts are produced and the social identity of callers can also affect recipients' responses. Copyright 1999 The Association for the Study of Animal Behaviour.     

Acoustic communication in the Bocon toadfish (<Emphasis Type="Italic">Amphichthys cryptocentrus</Emphasis>)

The soundscapes of many coastal habitats include vocalizations produced by species of the family Batrachoididae (toadfish and midshipman). We describe the calling and grunting behavior of male Amphichthys cryptocentrus, a tropical toadfish, and predict how these vocalizations are influenced by conspecifics. We recorded individual males, which produced broadband grunts and multi-note, harmonic “boatwhistle” calls. Grunts were either in combination with calls or stand-alone. We used a null model to test if these latter grunts were produced at random or in response to calls from conspecifics. The model supports the hypothesis that grunts were in response to calls from neighboring males, suggesting acoustic competition. Using the most conservative estimate of hearing abilities we predict that males responded to the second harmonic of neighbor’s calls (230 Hz) at amplitudes of approximately 100–125 dB re 1μPa²/Hz. We also observed that call and grunt rates increased when males were exposed to higher rates of acoustic activity from neighboring fish. Fish used grunts to respond to background calls that occurred at different amplitudes, suggesting they responded to the calls of multiple neighboring fish and not just the highest amplitude neighbor. This communication with multiple fish within hearing range suggests a communication network in which the spatial distribution of individual toadfish relative to one another will impact their vocal behavior. Thus, the density and distribution, and not just abundance, of these toadfish at a given site will influence the characteristics of the chorus and the role of this species in the local soundscape.     

Vocal divergence between two disjunct populations of Giant Antshrike (Batara cinerea) is related to environmental conditions

Variation in the avian vocal signals emitted may have a significant impact on species evolution. Vocal divergence in suboscine species like Giant Antshrike (Batara cinerea) may be associated with selective adaptation, since learning has little influence on vocal development and variation in acoustic structure cannot be attributed to learning deviation. Consequently, tracheophone suboscine species are ideal subjects to explore vocal variation, since cultural evolution does not seem to influence vocal variation in this group. Environmental conditions may determine the selection of vocal features because acoustic transmission could be attenuated under certain conditions of temperature, humidity and vegetation cover. Here, we examined vocalizations of Giant Antshrike and assessed possible acoustic variations between two disjunct groups (Andean and Atlantic), correlating the differences to the environmental structure. Univariate and multivariate analysis show temporal and spectral differences between both groups. Andean individuals produce vocalizations with longer duration, faster trill rates, shorter syllable duration and higher frequencies. Environmental features are different between the two populations, and they are correlated to the acoustic structure of vocalizations. Temporal variations arise directly from climatic influence, while spectral divergence could be a secondary effect of morphological adaptation to habitat structure.     

How vervet monkeys perceive their grunts: Field playback experiments

Free-ranging vervet monkeys grunt to each other in a variety of social situations: when approaching a dominant or subordinate individual, when moving into a new area of their range, or when observing another group. Like other non-human primate vocalizations, these grunts have traditionally been interpreted as a single, highly variable call that reflects the arousal state of the signaller. Field playback experiments suggest, however, that what humans initially perceive as one grunt the monkeys perceive as at least four. Each grunt carries a specific meaning that seems to depend more on its acoustic properties than on the context in which it occurs. Results suggest that the vocalizations given by monkeys during social interactions may function in a rudimentary representational manner, as if to designate objects or events in the external world.     

Kin-mediated reconciliation substitutes for direct reconciliation in female baboons

It has been hypothesized that group-living mammals engage in reconciliation (post-conflict affiliation between former opponents) to reduce the disruptive costs of aggression and restore opponents' tolerance to baseline levels. Recipients of aggression are sometimes reluctant to tolerate the proximity of a recent opponent, however, in apparent fear that aggression will be renewed. In such cases, reconciliatory behaviour by the aggressor's close kin may substitute for direct reconciliation. We describe a playback experiment with free-ranging baboons (Papio hamadryas ursinus) that examines whether friendly behaviour by the aggressor's kin can substitute for direct reconciliation by the aggressor herself. In the test condition, female subjects who had recently been threatened heard the friendly grunt of one of their aggressor's relatives, mimicking kin-mediated vocal reconciliation. In the control condition, subjects heard the grunt of a dominant female from a different matriline. Subjects responded significantly more strongly in test than in control trials. Moreover, in the next hour they were significantly more likely to tolerate the proximity of both their aggressor and the relative whose grunt they had heard. In contrast, subjects' behaviour towards both control females and other members of their aggressor's matriline was unaffected. We conclude that kin-mediated vocal reconciliation can substitute for direct reconciliation in baboons.     

饲养状态真鲂(鱼弗)发声的昼夜与季节变化

本文研究了受水温和光周期等自然变化影响的饲养状态真鲂鮄发声的昼夜与季节变化,并研究了实验鱼活动(鱼类游泳次数)的日变化。声音信号的昼夜节律记录发声活动的日常水平(摄食之外的时期),但是每月变化的记录(季节性式型)则在摄食期间进行,因为摄食时声音信号增加,而日常发声活动较不频繁。实验鱼包括雌雄两性,且未达性成熟。真鲂鮄在白天发声多一些,也更活跃。声音为阵发式的,较不频繁(平均值=0.04发声/min每鱼每天)。最少的发声活动出现在晚上,凌晨和黄昏居中(声音的阵发更频繁,但是声音更少),最多的发声活动出现在白天(声音的阵发更频繁,并且含更多数目的声音)。竞争摄食时声音信号的比率不呈现季节性变化(平均值=3.98发声/min每鱼),与温度也不相关,显示出竞争摄食时声音的发出以最大比率进行。敲击声和呼噜声的某些声学特征与温度相关,特别是在较高的温度下呼噜声的节拍间隔急剧下降。敲击声和呼噜声的声音参数中的季节性变化,多数可以解释为发声肌肉和中央声音控制回路的温度效应。     

Playbacks of food-associated calls attract chimpanzees towards known food patches in a captive setting

Food-associated calls have received much research attention due to their potential to refer to discovered food in a word-like manner. Studies have found that in many species, food-associated calls attract receivers to the food patch, suggesting these calls play roles in food sharing, cooperation and competition. Additionally, in various species, these calls play a role that has received much less attention: mediating social interactions among foragers that are already nearby or within the food patch, independently of whether they attract outside foragers. In order to increase understanding of the function of the chimpanzee (Pan troglodytes) food-associated rough grunt, we conducted captive playback studies testing whether rough grunt playbacks attract, repel or have no effect on the proximity of foragers already familiarized with the presence of food. We tested how acoustic playbacks of rough grunts (or control calls) from one of two known, identical feeding sites affected receivers’ approach and feeding behaviors. More often than expected, participants first approached the feeding site from which rough grunts, but not control calls, were broadcast. However, neither condition increased the likelihood that participants fed first from a given site. Our results support the hypothesis that rough grunts elicit an approach response in receivers, while providing no evidence that they repel. In addition, our study provides evidence that receivers may approach rough grunts even if they do not intend to feed. We discuss the information rough grunts may convey to receivers beyond information about discovered food and the potential benefits signalers may gain from this calling behavior.

     

Nocturnal foraging habitats of French and bluestriped grunts,Haemulon flavolineatum and H. sciurus,at Tobacco Caye,Belize

Synopsis Nocturnal foraging habitats of Haemulon flavolineatum and H. sciurus were investigated in the backreef habitat around Tobacco Caye, Belize. Grunts leave the reef at dusk to forage in the grass beds and sand flats surrounding the reef. The hypothesis that French and bluestriped grunts use separate foraging habitats was examined by following tagged fishes from their diurnal territories or schooling sites to nocturnal foraging grounds. The tag consisted of a small, glowing Cyalume light stick sutured to the dorsal musculature of the fish, next to the first dorsal fin. Surveys of foraging habitats were done to support the tracking study. Large quadrats (225 m²) were set out over the sand flats and grass beds during the day. The numbers of French and bluestriped grunts feeding in each habitat were counted one hour after dark. Foraging French grunts used sand flats, whereas bluestriped grunts usually fed in grass beds. Repeated sightings of two French grunts and one bluestriped grunt in the same individual night-time locations support the hypothesis that nocturnal foraging sites may be used repeatedly by the same individuals.     

Acoustic Repertoire of Spawning Cod, Gadus morhua

We examine the vocal repertoire of spawning cod, Gadus morhua. Fish captured in northern Norway were allowed to spawn in tanks and we recorded sound during the spawning period. The cod's grunt repertoire contained more variation than previously suggested. Half of the grunts lasted more than 200ms including one grunt lasting nearly 1s and consisting of 52 pulses, which is far beyond previous reports. Moreover, increasing repetition period and increasing duration of pulses within a grunt from the first pulse towards pulses at the end of the grunt, has previously not been described. On the other hand, no knocks or series of knocks, and on average only one grunt per hour suggest that cod are less versatile vocalists than closely related gadid species, such as haddock, Melanogrammus aeglefinus.     

The use of Vocalizations of the Sambirano Mouse Lemur (<Emphasis Type="Italic">Microcebus sambiranensis</Emphasis>) in an Acoustic Survey of Habitat Preference

Primate vocalizations convey a variety of information to conspecifics. The acoustic traits of these vocalizations are an effective vocal fingerprint to discriminate between sibling species for taxonomic diagnosis. However, the vocal behavior of nocturnal primates has been poorly studied and there are few studies of their vocal repertoires. We compiled a vocal repertoire for the Endangered Sambirano mouse lemur, Microcebus sambiranensis, an unstudied nocturnal primate of northwestern Madagascar, and compared the acoustic properties of one of their call types to those of M. murinus and M. rufus. We recorded vocalizations from radio-collared individuals using handheld recorders over 3 months. We also conducted an acoustic survey to measure the vocal activity of M. sambiranensis in four forest habitat types at the study site. We identified and classified five vocalization types in M. sambiranensis. The vocal repertoires of the three Microcebus species contain very similar call types but have different acoustic properties, with one loud call type, the whistle, having significantly different acoustic properties between species. Our acoustic survey detected more calls of M. sambiranensis in secondary forest, riparian forest, and forest edge habitats, suggesting that individuals may prefer these habitat types over primary forest. Our results suggest interspecific differences in the vocal repertoire of mouse lemurs, and that these differences can be used to investigate habitat preference via acoustic surveys.     

Temporal variation and characterization of grunt sounds produced by Atlantic cod Gadus morhua and pollack Pollachius pollachius during the spawning season

Fine‐scale temporal patterning in grunt production and variation in grunt attributes in Atlantic cod Gadus morhua and pollack Pollachius pollachius was examined. Pollachius pollachius produced only a single sound type, the grunt, similar to that previously described for G. morhua. Sound production and egg production were correlated in P. pollachius but not in G. morhua. Only G. morhua displayed a strongly cyclical pattern, producing more grunts at night. Finer‐scale temporal patterning in grunt production was observed in both species which produced significantly fewer grunts following a period of high grunt production. These quieter periods lasted up to 45 min for P. pollachius and up to 1 h in G. morhua. Grunts were not always produced in isolation but organized into bouts in both species. Longer bouts were more frequent during periods of increased sound activity and were linked with changes in grunt characteristics including increased grunt duration, pulse duration and repetition period of each pulse combined with decreased dominant frequency. This study provides the first evidence of acoustic signalling being used by spawning P. pollachius and presents the most detailed analysis of the complexity of gadoid sound production.