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.     

Sound production evoked by electrical stimulation of the forebrain in the oyster toadfish

In mammals, birds and amphibians the neural pathways controlling sound production descend from higher centers in the forebrain, whereas in fishes only brainstem and spinal centers have been explicitly implicated in sound production. We now report that electrical stimulation of the forebrain of the oyster toadfish (Opsanus tau) readily evokes both the agonistic grunt and the courtship boatwhistle. Boatwhistles are more realistic than ones previously evoked from lower centers. Positive stimulation sites are localized in the preoptic area (nucleus preopticus parvocellularis anterior) and the supracommissural nucleus of the ventral telencephalon, a likely homologue of the amygdala. Both sites contain gonadal steroid-concentrating neurons and play a central role in fish courtship behavior. Evoked sounds form a continuum from knock grunts, burst grunts, transition boatwhistles to complete boatwhistles; sound pressure level (SPL), fundamental frequency and duration increase consistently within the continuum. For all sound types, SPLs exhibit the smallest variation (coefficients of variation of 2.7 to 5.7%), fundamental frequency is intermediate (5 to 13%) and durations vary most widely (18 to 60%). Boatwhistles, with the smallest variation and greatest amplitude, are likely generated by a maximal output of the CNS and sonic muscles. Grunt SPLs however, vary over a range of 26 dB for all fish and by as much as 18 dB in an individual, suggesting recruitment of variable numbers of motor units despite electrical coupling within the sonic motor nucleus.Abbreviations AC anterior commissure - CNS central nervous system - DHT dihydrotestosterone - Dm medial nucleus of dorsal telenecphalon - DTAM dorsal tegmental area of medulla - E estrogen - HRP horseradish peroxidase - PM nucleus praeopticus magnocellularis - POA preoptic area - PPa nucleus praeopticus parvocellularis anterior - SMA sonic motor area - SMN sonic motor nucleus - SPL sound pressure level - T testosterone - VS supracommissural nucleus of ventral telencephalon - Vv ventral nucleus of ventral telencephalon     

Rapid elevations in both steroid hormones and vocal signaling during playback challenge: a field experiment in Gulf toadfish

It is well known that plasma androgens are rapidly released in response to aggressive or sexual stimuli in a broad array of vertebrates. However, experimental work on behavioral functions of rapid androgen elevation is rare. A combination of field-based behavioral experiments and lab-based neuroendocrinological approaches is beginning to show how steroid hormones rapidly regulate the expression of vocal communication signals in Gulf toadfish (Opsanus beta). Male toadfish emit multiharmonic "boatwhistles" and shorter-duration, broadband "grunts" during intraspecific communication. Neurophysiology experiments demonstrate that androgens and glucocorticoids rapidly modify vocal motor patterning in male toadfish. In this study, we simulated territorial intrusions (vocal "challenges") with acoustic playbacks to toadfish in the field, and observed simultaneous, rapid (within 5-20 min) changes in vocalizations and steroid hormones. Both plasma androgens and vocal activity increased following the presentation of pure tones that mimic the duration of natural boatwhistles (275 ms), while they remained unchanged following playbacks of tone stimuli that mimic the duration of grunts (75 ms) or the upper-range of boatwhistles (475 ms). Circulating glucocorticoids were elevated in calling vs. non-calling males but were unaffected by playback stimuli, suggesting a role in the energetics of vocalization. These results strongly suggest that one function of rapid androgen elevation in response to social challenge is to mediate similarly rapid changes in territorial vocal signaling. Given the conserved organization of neuroendocrine and vocal motor systems, rapid steroid action on vocalization mechanisms may be true of other vocal vertebrates as well, including birds and mammals.     

Seasonal variation of sound production in the Lusitanian toadfish Halobatrachus didactylus

Seasonal variation of sound production, which includes boatwhistles, grunts, croaks and double croaks, was studied in the Lusitanian toadfish Halobatrachus didactylus . Boatwhistles were emitted during the mating season in contrast with the other sound types, which were emitted all year round.     

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.     

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.     

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。     

Vocal Behavior During Territorial Intrusions in the Lusitanian Toadfish: Boatwhistles Also Function as Territorial ‘Keep‐Out’ Signals

Male signals are frequently studied in a single behavioral context, but in some cases they may assist multiple functions, namely for both male–male competition and female mate choice. Boatwhistles are known as the mate attraction calls of toadfishes typically produced during the breeding season. However, recent observations with the Lusitanian toadfish Halobatrachus didactylus (Batrachoididae) indicate that the emission of boatwhistles is not restricted to this period, which suggests a function in other behavioral contexts such as agonistic territorial interactions. We experimentally manipulated the social context of toadfish males to investigate whether boatwhistles are produced during territorial defense, by introducing ‘intruders’ in an experimental tank containing nesting ‘resident’ males. Furthermore, we examined whether parental care (eggs in the nest) affected the behavioral responses of resident males during territorial defense. Resident males defended their shelters producing sounds, mostly boatwhistles, towards intruders. Parental males revealed higher aggression levels, exhibiting additional threatening and attack behaviors. Boatwhistles registered during agonistic events were compared with the mate advertising boatwhistles recorded from small aggregations of nesting males in a natural breeding intertidal area. Agonistic boatwhistles were produced in lower and variable calling rates comparing with the advertising ones that were typically emitted in long series of calls. Agonistic boatwhistles were similar in duration and frequency harmonic structure (with a middle tonal phase) to the advertising calls, but presented less amplitude modulation, and lower dominant and fundamental frequencies. These acoustic differences were probably related to differences in calling rates and broadcast demands associated to the distance to the intended receiver. We provide first evidence that, apart from attracting mates, the toadfish boatwhistles also function as active ‘keep‐out’ signals during territorial defense.     

Vocalizations and Behaviour of Pacific Humpback Dolphins Sousa chinensis

Very little is known about the acoustic repertoire of the Pacific humpback dolphin Sousa chinensis . This study, off eastern Australia, used concurrent observations of surface behaviour and acoustic recordings to gain an insight into the behavioural significance of humpback dolphin vocalizations. Humpback dolphins exhibit five different vocalization categories: broad band clicks; barks; quacks; grunts; and whistles. Broad band clicks were high in frequency (8 kHz to > 22 kHz), were directly related to foraging behaviour and may play a role in social behaviour. Barks and quacks were burst pulse sounds (frequency: 0.6 kHz to > 22 kHz, duration: 0.1–8 s) and were associated with both foraging and social behaviour. The grunt vocalization is a low frequency narrow band sound (frequency 0.5–2.6 kHz, duration 0.06–2 s) and was only heard during socializing. There were 17 different types of whistles, ranging widely in frequency (0.9–22 kHz) and vocal structure (n=329). The predominant whistle types used by the groups were type 1 (46%) and type 2 (17%). Most whistles were heard during both socializing and foraging. The number of whistles recorded in a group increased significantly as the number of mother–calf pairs increased, suggesting that whistles may be used as contact calls. Few vocalizations were heard during either travelling or milling behaviours. Broad band clicks, barks and whistle type 1 were the only vocalizations recorded during either travelling or milling.     

Sound production in <Emphasis Type="Italic">Etheostoma oophylax</Emphasis> (Percidae) and call characteristics correlated to body size

Sound production in fishes is common in marine and freshwater species, however there are still many vocal species for which sound production has not been documented. This paper is the first account of sound production in the Guardian Darter (Etheostoma oophylax). Laboratory recordings revealed that males produced several vocalizations, including single pulse knocks, multi-pulsed purrs, and tonal drums. All vocalizations were documented during agonistic and courtship encounters, including spawning. We also investigated possible correlations between call characteristics and male size. Male standard length was found to be correlated to inter-pulse interval of purrs, as well as the slope of the drum vocalizations. Determining a link between male size and acoustic characteristics could be the first step in documenting mate or male-male assessment by acoustic communication in darters.     

Wild Female Olive Baboons Adapt their Grunt Vocalizations to Environmental Conditions

Sound propagates differently and visibility varies according to the habitat type. Animals should therefore adapt the acoustic structure and the usage of their vocal signals to the environment. In the present study, we examined the influence of the habitat on the vocal behaviour of wild olive baboons ( Papio hamadryas anubis ) in two populations: one living in Gashaka-Gumti National Park, Nigeria, and the other in Budongo Forest, Uganda. We investigated whether female baboons modified the acoustic structure of their grunts and their rate of grunting when they wandered between closed and open habitat types. As an adaptation to the environmental conditions, baboons might utter calls with a longer duration, a lower fundamental frequency and/or energy concentrated in lower frequencies in a closed habitat like forest than in an open habitat. Baboons should also grunt more frequently in the closed habitat. Analyses showed that in both populations grunts uttered in forest were significantly longer than in open habitat. Additionally, baboons from Uganda showed a significantly higher grunt rate in forest than in open habitat. These results revealed a certain degree of plasticity in vocal production and call usage with regard to the habitat type. However, results in Nigeria suggested that, besides habitat structure, other proximate factors like the context of calling and the proximity between group members could also have an influence on the actual communication patterns.     

ADAPTATION TO SEVERE CONDITIONS OF PROPAGATION: LONG-DISTANCE DISTRESS CALLS; AND COURTSHIP CALLS OF A COLONIAL SEABIRD

ABSTRACT

The boatwhistle sound produced by male toadfish during the reproductive season attracts females to the nest site. Boatwhistles consist of a series of rapidly produced, amplitude modulated ‘pulses’ of sound that are generated by specific muscles of the gas bladder. Previous studies have shown that boatwhistle characteristics vary with temperature and geographic location. This study investigated the normal range of variation in boatwhistles produced by males in a northern population of O. tau. Multiple boatwhistles were recorded from individuals at different sites around Waquoit Bay, Massachusetts. Multiple boatwhistles were recorded at different sites to assess the range of variation in boatwhistle production from this population. Pulse repetition rates varied from a low of 125 pulses/sec at 16 °C to a high of 219 pulses/sec at 21 °C. Careful examination of recordings from different sites indicated that individuals vary in the durations of their boatwhistles as well as in the pulse repetition rates during the very consistently produced second segment of the call. In particular, pulse repetition rate (PRR) varied significantly (p < 0.001) among most individuals recorded at the same temperatures. Psychophysical testing as well as behavioral choice experiments are needed to assess the relative importance of PRR and spectral cues in species recognition and/or mate choice.     

Ontogeny of Acoustic and Feeding Behaviour in the Grey Gurnard, Eutrigla gurnardus

Although sound production in teleost fish is often associated with territorial behaviour, little is known of fish acoustic behaviour in other agonistic contexts such as competitive feeding and how it changes during ontogeny. The grey gurnard, Eutrigla gurnardus, frequently emits knock and grunt sounds during competitive feeding and seems to adopt both contest and scramble tactics under defensible resource conditions. Here we examine, for the first time, the effect of fish size on sound production and agonistic behaviour during competitive feeding. We have made sound (alone) and video (synchronized image and sound) recordings of grey gurnards during competitive feeding interactions. Experimental fish ranged from small juveniles to large adults and were grouped in four size classes: 10–15, 15–20, 25–30 and 30–40 cm in total length. We show that, in this species, both sound production and feeding behaviour change with fish size. Sound production rate decreased in larger fish. Sound duration, pulse duration and the number of pulses increased whereas the peak frequency decreased with fish size, in both sound types (knocks and grunts). Interaction rate and the frequency of agonistic behaviour decreased with increasing fish size during competitive feeding sessions. The proportion of feeding interactions accompanied by sound production was similar in all size classes. However, the proportion of interactions accompanied by knocks (less aggressive sounds) and by grunts (more aggressive) increased and decreased with fish size, respectively. Taken together, these results suggest that smaller grey gurnards compete for food by contest tactics whereas larger specimens predominantly scramble for food, probably because body size gives an advantage in locating, capturing and handling prey. We further suggest that sounds emitted during feeding may potentially give information on the motivation and ability of the individual to compete for food resources.     

Saccular potentials of the vocal plainfin midshipman fish, <Emphasis Type="Italic">Porichthys notatus</Emphasis>

The plainfin midshipman fish, Porichthys notatus, is a vocal species of teleost fish that generates acoustic signals for intraspecific communication during social and reproductive behaviors. All adult morphs (females and males) produce single short duration grunts important for agonistic encounters, but only nesting males produce trains of grunts and growls in agonistic contexts and long duration multiharmonic advertisement calls to attract gravid females for spawning. The midshipman fish uses the saccule as the main acoustic endorgan for hearing to detect and locate vocalizing conspecifics. Here, I examined the response properties of evoked potentials from the midshipman saccule to determine the frequency response and auditory threshold sensitivity of saccular hair cells to behaviorally-relevant single tone stimuli. Saccular potentials were recorded from the rostral, medial and caudal regions of the saccule while sound was presented by an underwater speaker. Saccular potentials of the midshipman, like other teleosts, were evoked greatest at a frequency that was twice the stimulus frequency. Results indicate that midshipman saccular hair cells of non-reproductive adults had a peak frequency sensitivity that ranged from 75 (lowest frequency tested) to 145 Hz and were best suited to detect the low frequency components (≤105 Hz) of midshipman vocalizations.     

Variability in the mating calls of the Lusitanian toadfish Halobatrachus didactylus: cues for potential individual recognition

The mating sounds (boatwhistles) of nesting batrachoidid Halobatrachus didactylus males were recorded in the Tagus Estuary from piers. Thirteen males with 16 boatwhistles per fish were analysed for 20 acoustic features. All variables showed larger between‐male than within‐male variation and differed significantly among individuals. Discriminant function analyses (DFA) considering seven of these variables assigned 90–100% of boatwhistles to the correct individual, depending on the number of males and number of sounds per male included in the model. The acoustic features that consistently best discriminated individuals were the dominant frequency of the middle tonal segment of the boatwhistle (P₂) and dominant frequency modulation, followed by P₂ pulse period, amplitude modulation and sound duration. These results suggest the possibility of individual recognition based on acoustic cues.     

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.     

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.     

Nonlinear acoustic complexity in a fish 'two-voice' system

Acoustic signals play essential roles in social communication and show a strong selection for novel morphologies leading to increased call complexity in many taxa. Among vertebrates, repeated innovations in the larynges of frogs and mammals and the syrinx of songbirds have enhanced the spectro-temporal content, and hence the diversity of vocalizations. This acoustic diversification includes nonlinear characteristics that expand frequency profiles beyond the traditional categorization of harmonic and broadband calls. Fishes have remained a notable exception to evidence for such acoustic innovations among vertebrates, despite their being the largest group of living vertebrates that also exhibit widespread evolution of sound production. Here, we combine rigorous acoustic and mathematical analyses with experimental silencing of the vocal motor system to show how a novel swim bladder mechanism in a toadfish enables it to generate calls exhibiting nonlinearities like those found among frogs, birds and mammals, including primates. By showing that fishes have evolved nonlinear acoustic signalling like all other major lineages of vocal vertebrates, these results suggest strong selection pressure favouring this mechanism to enrich the spectro-temporal content and complexity of vocal signals.     

Sound production during competitive feeding in the grey gurnard

The acoustic repertoire of captive grey gurnard Eutrigla gurnardus during competitive feeding consisted of three types of sound: knocks, grunts and growls. Knocks were audible as a single sound, whereas grunts and growls were perceived as longer, pulsed sounds to the human ear. Typically, knocks were composed of 1–2 pulses, grunts of 4–8 pulses and growls >10 pulses. Growls were longer and had shorter pulse periods than grunts. All sound types had peak frequencies of c . 500 Hz. The sequences of behaviours observed during feeding interactions suggest that grey gurnard obtain food both by scramble and contest tactics. Competing fish emitted knocks mainly while grasping a food item and also during other non‐agonistic behaviour, suggesting that knock production may reflect a state of feeding arousal but could also serve as a warning of the forager's presence to nearby competitors. Grunts were mainly emitted during frontal displays, which were the most frequent behavioural act preceding grasps, suggesting that they may play a role in deterring other fish from gaining access to disputed food items.