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ABSTRACT Male frogs emit stereotypical advertisement calls to attract mates and deter conspecific rivals. The evolution of these calls is thought to be linked to anatomical constraints and the acoustic characteristics of their surroundings. The acoustic adaptation hypothesis (AAH) posits that species evolve calls that maximize propagation distance and reduce signal degradation in the environment where they are emitted. We applied phylogenetic comparative analyses to study the association of body size, vegetation density, type of aquatic ecosystem, and calling site on the evolution of acoustic traits in Cophomantini, a large radiation of Neotropical treefrogs (Hylidae). We obtained and analyzed body size, acoustic, and habitat data from a total of 112 species (58% of Cophomantini), using the most inclusive available phylogeny. We found a significant negative correlation between peak frequency, body size, and calling site, but contrary to the predictions of the AAH, we did not find support for associations among call traits and environmental characteristics. Although spectral allometry is explained by an anatomical constraint, it could also be maintained by female choice. We recommend that future studies strive to incorporate factors such as female mate preferences, eavesdropping by predators or parasites, and genetic drift. [ABSTRACT FROM AUTHOR]

Studying intraspecific geographic variation in communication signals represents a good approach to understand the evolution of species diversification in animals. The poison frog Andinobates bombetes (Dendrobatidae) exhibits intraspecific geographic variation in the spectral traits of its advertisement call. However, it is still unknown whether there is concomitant variation in temporal call traits, and whether call variation is somehow linked to differences in warning coloration (red and yellow morphs). We analyzed spectral and temporal traits of the advertisement calls recorded from 100 males belonging to twelve populations of A. bombetes: nine bearing the red coloration, and three bearing the yellow one. After controlling for eventual effects of temperature and body size of males in call traits, we found geographic variation in both spectral and temporal call traits, yet such variation was unrelated to differences in warning coloration between populations. Previous research indicated that geographic variation in the spectral properties of this species advertisement call can be explained by concomitant differences in the acoustic abiotic environment. Nonetheless, a positive relationship between geographic distance and call divergence also supports the role of genetic drift in the evolution of acoustic signaling of A. bombetes. [ABSTRACT FROM AUTHOR]

Predatory interactions result in strong selection pressures acting on multiple aspects of animal behaviour. Anti‐predator strategies are therefore common in most animals, typically signalling at various stages of a predation event. Many species of caprimulgids perform conspicuous anti‐predator displays, including stereotyped behaviours and vocal signals. Here, we described distress calls of red‐necked nightjars (Caprimulgus ruficollis), produced when birds are trapped and unable to escape during a predatory interaction. Distress calls are harsh, low‐frequency guttural vocalisations with irregular amplitude modulations. The age and sex of birds partially explained the acoustic variation observed, whereas size‐related morphological features were poor predictors of the acoustic structure. Age‐sex differences in distress calls may respond to physiological constraints associated with sexual dimorphism and/or developmental variation. Alternatively, directional selection associated with differential predation risk on each age‐sex class may have resulted in the observed differences in distress calls. The extremely deep voice and the harsh quality of distress calls fit the structure of aggressive signals and may resemble those produced by a larger animal. We propose that these calls serve as a last resort strategy to reduce post‐encounter risk of predation, either as a startling effect to facilitate escape or to attract other predators that could intimidate the captor. [ABSTRACT FROM AUTHOR]

Ultrasound‐driven triboelectric nanogenerators (US‐TENGs) offer an innovative solution for transcutaneous power transfer, with the potential to enable battery‐free, permanently implantable electronics. However, research to date has primarily demonstrated only fragmentary functionalities for these applications. This work presents the simultaneous transmission of acoustic power and precise acoustic information using a double‐electrode US‐TENG, enabling a battery‐free implant controlled via ultrasound. High and sustained output from a US‐TENG is crucial for operating the versatile system; therefore, a novel triboelectric membrane with a top electrode incorporating a gold‐polymer intermixing layer has been designed. Reversible micro‐cracks form in the intermixing layer, ensuring electrical connectivity under high‐frequency strain. In vivo experiments confirm that the system is biocompatible and can be reliably operated inside living rats. These achievements represent a significant step toward realizing multifunctional implantable electronics that can be reliably powered and controlled by ultrasound. [ABSTRACT FROM AUTHOR]

ABSTRACT Acoustic communication plays a prominent role in various ecological and evolutionary processes involving social interactions. The properties of acoustic signals are thought to be influenced not only by the interaction between signaller and receiver but also by the acoustic characteristics of the environment through which the signal is transmitted. This conjecture forms the core of the so‐called “acoustic adaptation hypothesis” (AAH), which posits that vegetation structure affects frequency and temporal parameters of acoustic signals emitted by a signaller as a function of their acoustic degradation properties. Specifically, animals in densely vegetated “closed habitats” are expected to produce longer acoustic signals with lower repetition rates and lower frequencies (minimum, mean, maximum, and peak) compared to those inhabiting less‐vegetated “open habitats”. To date, this hypothesis has received mixed results, with the level of support depending on the taxonomic group and the methodology used. We conducted a systematic literature search of empirical studies testing for an effect of vegetation structure on acoustic signalling and assessed the generality of the AAH using a meta‐analytic approach based on 371 effect sizes from 75 studies and 57 taxa encompassing birds, mammals and amphibians. Overall, our results do not provide consistent support for the AAH, neither in within‐species comparisons (suggesting no overall phenotypically plastic response of acoustic signalling to vegetation structure) nor in among‐species comparisons (suggesting no overall evolutionary response). However, when considering birds only, we found weak support for the AAH in within‐species comparisons, which was mainly driven by studies that measured frequency bandwidth, suggesting that this variable may exhibit a phenotypically plastic response to vegetation structure. For among‐species comparisons in birds, we also found support for the AAH, but this effect was not significant after excluding comparative studies that did not account for phylogenetic non‐independence. Collectively, our synthesis does not support a universal role of vegetation structure in the evolution of acoustic communication. We highlight the need for more empirical work on currently under‐studied taxa such as amphibians, mammals, and insects. Furthermore, we propose a framework for future research on the AAH. We specifically advocate for a more detailed and quantitative characterisation of habitats to identify frequencies with the highest detection probability and to determine if frequencies with greater detection distances are preferentially used. Finally, we stress that empirical tests of the AAH should focus on signals that are selected for increased transmission distance. [ABSTRACT FROM AUTHOR]

Simple Summary: Males in many species of animals congregate to produce calls that attract females for reproduction. Such choruses are often limited to particular times of day, and, in some cases, the rhythm of calls is synchronized among males, suggesting advantages at the collective level to calling at the same time. However, synchronized calling may also represent the outcome of competitive interactions among males without the need to invoke advantages at the collective level. I investigated chorus organization in one species of Neotropical forest cicada in southern Belize to explore these issues. Choruses of calling males occurred at dawn and dusk and occasionally during the daytime. I found no evidence of synchronization in the rhythm of calls by males, as bouts of calling occurred after variable rather than fixed quiet intervals. In this species, synchronized calling by males thus probably emerged from competitive interactions among males to attract females. The degree of temporal overlap in the calls of males during a chorus varied as a function of chorus phase and time of day, suggesting flexibility in chorus organization, perhaps in relation to variation in the environmental factors, such as the number of predators present or ambient temperature during a chorus. In many species of animals, males aggregate in particular locations and produce calls to attract searching females for reproduction. One striking feature of such choruses is synchronization. On a scale of hours, choruses are often concentrated at particular times of day, such as dawn or dusk. On a scale of seconds, males may also synchronize the rhythm of their calls with one another. While synchronized calling at this scale suggests benefits acting at the collective level, competitive interactions between males to attract females can also lead to synchronized calling as an epiphenomenon. Why males in some species synchronize the rhythm of their calls is still debated, and more work is needed to understand the evolution of this behavior. I investigated chorus organization in the Emerald cicada (Zammara smaragdula), a Neotropical forest cicada in southern Belize, to explore these issues. Choruses in this species occurred at dawn and dusk and, occasionally, during daytime. There was no evidence for synchronization in the rhythm of calls among males, as bouts of collective calling occurred after quiet intervals of variable rather than fixed durations. The temporal aggregation of calls in this species thus probably emerged from competitive interactions among males to attract females. The degree of temporal overlap in the calls of males during a chorus varied as a function of chorus phase and time of day, suggesting flexibility in chorus organization, perhaps in relation to temporal variations in factors such as the number of calling cicadas, the number of predators present or ambient temperature during a chorus. [ABSTRACT FROM AUTHOR]

This study investigates the effects of individuality and harem‐holding status on the acoustic parameters of rutting calls (bugles) of 14 stags of Siberian wapiti Cervus canadensis sibiricus. The stags competed for mating with hinds in a large herd, free ranging inside a fenced area with complex landscape. We considered as harem‐holders the stags, which kept a harem of 5 or more hinds for at least 2 days. Of the 15 days of observations enveloping the most active rutting period, during 3 days there was only one harem in the enclosure, during 9 days two harems, during 2 days three harems and during 1 day four harems. Stag bugles displayed both individual and status‐related variation. Harem‐holders compared with peripheral stags had shorter bugles with higher minimum fundamental frequency. After winning a harem and changing status from harem‐candidate to harem‐holder, stags shortened the duration of their bugles, lowered the beginning and maximum fundamental frequency and increased the minimum fundamental frequency. Significantly higher than the levels expected by chance, discriminant analysis classified 78.9% of bugles by the correct stag status and 53.2% of bugles by the correct individual callers. Different acoustic parameters encoded the status and individuality of the bugles. Status was encoded by the duration of the start and end parts and by the beginning and end fundamental frequencies. Individuality was encoded by the maximum fundamental frequency. We discuss that rutting calls of Siberian wapiti, although individualized, do not represent vocal signatures. However, these calls reliably mark stag harem‐holding status. [ABSTRACT FROM AUTHOR]

Auditory streaming underlies a receiver's ability to organize complex mixtures of auditory input into distinct perceptual "streams" that represent different sound sources in the environment. During auditory streaming, sounds produced by the same source are integrated through time into a single, coherent auditory stream that is perceptually segregated from other concurrent sounds. Based on human psychoacoustic studies, one hypothesis regarding auditory streaming is that any sufficiently salient perceptual difference may lead to stream segregation. Here, we used the eastern grey treefrog, Hyla versicolor, to test this hypothesis in the context of vocal communication in a non-human animal. In this system, females choose their mate based on perceiving species-specific features of a male's pulsatile advertisement calls in social environments (choruses) characterized by mixtures of overlapping vocalizations. We employed an experimental paradigm from human psychoacoustics to design interleaved pulsatile sequences (ABAB...) that mimicked key features of the species' advertisement call, and in which alternating pulses differed in pulse rise time, which is a robust species recognition cue in eastern grey treefrogs. Using phonotaxis assays, we found no evidence that perceptually salient differences in pulse rise time promoted the segregation of interleaved pulse sequences into distinct auditory streams. These results do not support the hypothesis that any perceptually salient acoustic difference can be exploited as a cue for stream segregation in all species. We discuss these findings in the context of cues used for species recognition and auditory streaming. [ABSTRACT FROM AUTHOR]

Understanding why females prefer exaggerated male mating displays, when males offer little more than sperm in lek mating systems, has been an important challenge in behavioral ecology and evolutionary biology. The Hamilton-Zuk hypothesis proposes that the expression of mating displays is limited by parasitism and females choose parasite-resistant males that can produce costly, exaggerated displays. We used Pacific treefrogs (Pseudacris regilla) and natural infections by the fungal pathogen Batrachochytrium dendrobatidis (Bd), to test predictions of the Hamilton-Zuk hypothesis. Specifically, we predicted that (i) call properties, especially those that are more likely under selection by female choice, correlate with parasitic infection, and (ii) females discriminate against highly infected males based on the properties of their mating call. We found that energetically costly call properties that are likely under selection by female choice, like call rate and call effort, were not influenced by Bd infection. However, males with high levels of Bd infection produced calls with faster pulse rates than males with lower levels of infection. In two-choice tests, females did not show a preference between calls that resemble males with either high or low levels of Bd infection. Our results provide little support for the Hamilton-Zuk hypothesis and suggest that Bd infection may have little effect on female choice in natural settings. We discuss our results in terms of the effects of Bd and other parasites in anuran mating behavior. Significance statement: This study shows that infection by a fungal pathogen responsible for world-wide amphibian loss may influence the expression of male mating displays in Pacific treefrogs. Importantly, we also show that females do not discriminate against mating calls typical of highly infected males. These results suggest that asymptomatic levels of infection may have little effect on mating behavior in natural settings. Furthermore, our study offers little support for the influential hypothesis that parasitism limits the expression of mating displays and females choose parasite-resistant males that can produce exaggerated displays. [ABSTRACT FROM AUTHOR]

The rapid growth of marine industries has emphasized the focus on environmental impacts for all industries, as well as the influence of key environmental parameters on, for instance, offshore wind or aquaculture performance, animal welfare and structural integrity of different constructions. Development of automatized sensors together with efficient communication and information systems will enhance surveillance and monitoring of environmental processes and impact. We have developed a modular Smart Ocean observatory, in this case connected to a large-scale marine aquaculture research facility. The first sensor rigs have been operational since May 2022, transmitting environmental data in near real-time. Key components are Acoustic Doppler Current Profilers (ADCPs) for measuring directional wave and current parameters, and CTDs for redundant measurement of depth, temperature, conductivity and oxygen. Communication is through 4G network or cable. However, a key purpose of the observatory is also to facilitate experiments with acoustic wireless underwater communication, which are ongoing. The aim is to expand the system(s) with demersal independent sensor nodes communicating through an "Internet of Underwater Things (IoUT)", covering larger areas in the coastal zone, as well as open waters, of benefit to all ocean industries. The observatory also hosts experiments for sensor development, biofouling control and strategies for sensor self-validation and diagnostics. The close interactions between the experiments and the infrastructure development allow a holistic approach towards environmental monitoring across sectors and industries, plus to reduce the carbon footprint of ocean observation. This work is intended to lay a basis for sophisticated use of smart sensors with communication systems in long-term autonomous operation in remote as well as nearshore locations. [ABSTRACT FROM AUTHOR]

Estimating repeatability allows a first approximation that may indicate a potential response to selection of sexual traits. Acoustic sexual signals comprise spectral and temporal variables, where the former generally have lower intra‐individual variation and higher repeatability values. Studies of repeatability in anurans have been conducted mainly in natural conditions, but the stability of laboratory settings allows extended recording intervals, favoring measurement accuracy. We conducted a study of variation and repeatability of the calls of males of Batrachyla taeniata, a frog from the South American temperate forest to evaluate under homogeneous environmental and social conditions: (i) the extent of variation in acoustic properties of calls within and among days, (ii) the extent of temporal variation in the repeatability of call properties, and (iii) differences in repeatability among call variables. Variation of acoustic properties differed within and across days of recording, call rate generally increased within and throughout days, suggesting sensitization processes. Call duration decreased during these time spans, yielding constant calling effort. In contrast, the dominant frequency decreased within days but increased across days. Overall repeatability differs significantly among variables: dominant frequency, call rate, and call duration having the highest, intermediate, and lowest values, respectively. The high repeatability of call rate relative to call duration contrasts with an opposing general tendency in previous studies in anurans. The repeatability of the three variables analyzed increases within days, and the repeatability of call rate also increases throughout days, highlighting the relevance of this variable for individual identity over different time ranges. [ABSTRACT FROM AUTHOR]

The birth of a baby or the hatching of an egg are moments when the risk of predation is particularly high. In oviparous species where clutches contain many eggs, one strategy for limiting predation is based on mechanisms that synchronise hatching, which reduces the individual risk of being targeted and may allow hatchlings to emerge under parental protection. These mechanisms involve communication signals between eggs and between eggs and parents. While previous studies in various species have shown the importance of sound and vibration signals in these exchanges, how embryos integrate this information remains poorly understood. Here we show that crocodile embryos respond differently to calls emitted by siblings (hatching calls) and to vibrations mimicking parental intervention (rubbing and scratching the shell) or the presence of a predator, suggesting that these two stimuli carry different information. Through playback experiments, we confirm that hatching calls elicit vocal responses and synchronous hatching in mature embryos, while embryos hatch earlier when they perceive vibrations. Our study underlines that the control of hatching by external factors can rely on differential apprehension of multiple sensory inputs by embryos. [ABSTRACT FROM AUTHOR]

Recent research on bird calls has unearthed a striking result: birds sometimes react to the calls of other species that are neither geographically nor phylogenetically close. One mechanism explaining this response may be the recognition of specific acoustic features, also present in their own vocalizations, rather than the recognition of complete notes, with the result that unfamiliar calls may be understood if they contain the critical feature. Parids and other passerines produce mobbing calls with similar properties that are responded to across species (i.e. noisy, large frequency range notes reaching low frequencies and with numerous harmonics) that are therefore good candidates for recognition based on features. In a playback experiment, we explored the featural interpretation hypothesis by testing the response of free-ranging great tits, Parus major , to artificial mobbing calls with varying acoustic properties. We first confirmed that they respond to artificial calls sharing all the targeted spectral properties (large frequency range, low frequency, noise and harmonics). In contrast, great tits did not respond to calls with the same rhythmicity but without the targeted features. We then tested whether great tits respond to calls that possess only one of the four above-mentioned properties. We show that great tits did not respond to any of the four treatments, and therefore no single specific spectral feature seems likely to explain great tits' response to unknown calls. We discuss alternative mechanisms for decoding novel calls, notably through a similarity threshold. • How do birds recognize relevant mobbing calls? • One hypothesis is that they focus on specific acoustic features, not whole notes. • Great tits respond to artificial mobbing calls that have four crucial features. • Great tits do not respond to mobbing calls with only one feature. • More sophisticated hypotheses, beyond simple featural decoding, are posited. [ABSTRACT FROM AUTHOR]

In recent years, acoustic metamaterials, as a sort of novel artificial composite materials, have demonstrated the ability to surpass the limitations of traditional materials through their exceptional acoustic parameter manipulation capabilities. Thus, acoustic metamaterials have shown promising applications in numerous areas such as underwater detection, underwater target identification, acoustic imaging, navigation, and underwater communication. The advancements in metamaterial-based underwater acoustic communication were reviewed, focusing primarily on multiplex communication based on acoustic orbital angular momentum, underwater acoustic communication between specific transmitter and receiver based on beam steering of acoustic metasurface, and water-air trans-medium acoustic communication. The key technologies were summarized, and the current challenges and future prospects of metamaterial-based underwater acoustic communication were outlined.

Abstract Emotionally expressive vocalizations can elicit approach-avoidance responses in humans and non-human animals. We investigated whether artificially generated sounds have similar effects on humans. We assessed whether subjects' reactions were linked to acoustic properties, and associated valence and intensity. We generated 343 artificial sounds with differing call lengths, fundamental frequencies and added acoustic features across 7 categories and 3 levels of biological complexity. We assessed the hypothetical behavioural response using an online questionnaire with a manikin task, in which 172 participants indicated whether they would approach or withdraw from an object emitting the sound. (1) Quieter sounds elicited approach, while loud sounds were associated with avoidance. (2) The effect of pitch was modulated by category, call length and loudness. (2a) Low-pitched sounds in complex sound categories prompted avoidance, while in other categories they elicited approach. (2b) Higher pitch in loud sounds had a distancing effect, while higher pitch in quieter sounds prompted approach. (2c) Longer sounds promoted avoidance, especially at high frequencies. (3) Sounds with higher intensity and negative valence elicited avoidance. We conclude that biologically based acoustic signals can be used to regulate the distance between social robots and humans, which can provide an advantage in interactive scenarios.

Anthropogenic disturbance, including noise, is a major cause of biodiversity decline worldwide. Especially in anurans, the effect of noise pollution is known to have major consequences on their reproduction since acoustic communication is an essential part of this process. In this study, we tested the effect of three levels of traffic noise (55 dB, 65 dB, and 75 dB) corresponding to three different distances from the road (200, 100, and 50 m, respectively) on the Brazilian Mundo Novo treefrog (Boana marginata). The results of the playback experiments showed an effect on call type B. More specifically, there was a decrease in the advertisement call rate, a reduction in the number of pulses, and a lengthening of the interval between pulses, particularly at 65 dB. These findings suggest that at distances of up to 100 m, the masking effect significantly influences acoustic communication on the species. However, a 55 dB stimulus—equal to 200 m from the road edge—did not change the call in this species, suggesting a minimal distance to implement noise-inflicting infrastructures. We recommend that new studies adopt sampling methods from this distance to refine the threshold of the traffic noise effect. [ABSTRACT FROM AUTHOR]

The matched filter hypothesis proposes a close match between senders and receivers and is supported by several studies on variation in signal properties and sensory-processing mechanisms among species and populations. Importantly, within populations, individual variation in sensory processing may affect how receivers perceive signals. Our main goals were to characterize hearing sensitivity of Pacific treefrogs (Pseudacris regilla), assess patterns of individual variation in hearing sensitivity, and evaluate how among-individual variation in hearing sensitivity and call frequency content affect auditory processing of communication signals. Overall, males and females are most sensitive to frequencies between 2.0 and 2.5 kHz, which matches the dominant frequency of the call, and have a second region of high sensitivity between 400 and 800 Hz that does not match the fundamental frequency of the call. We found high levels of among-individual variation in hearing sensitivity, primarily driven by subject size. Importantly, patterns of among-individual variation in hearing differ between males and females. Cross-correlation analyses reveal that among-individual variation in hearing sensitivity may lead to differences on how receivers, particularly females, perceive male calls. Our results suggest that individual variation in sensory processing may affect signal perception and influence the evolution of sexually selected traits. [ABSTRACT FROM AUTHOR]

Details in birdsong parameters convey information about fitness, quality and motivational state of the signaller. Perception of these song details may affect decision making of receivers in territorial defence and mate choice. Whether the message in the song is perceived or not may have major consequences for the birds' reproductive success. Consequently, birds may suffer fitness consequences from masking by other sounds in the environment. We conducted two different playback experiments to test whether song consistency, a sexually selected performance trait expressed in the temporal and spectral parameters of song, is perceived under different noise conditions. In the first experiment, we found that blue tits, Cyanistes caeruleus , are less able to assess the performance levels of song, but still detect the song stimuli under experimentally high broadband noise levels. Blue tits also responded with more songs overall, independent of song stimulus variation to playback of song stimuli under noisy conditions. When song stimulus variants were exposed simultaneously with a narrow band of noise in the second experiment, blue tits showed reduced capacity to discriminate only when the band of noise overlapped in frequency with the song. Results from this experiment support the notion that it is indeed the masking, rather than nonauditory effects of noise that cause the change in behaviour. Overall, our results show that there are noisy conditions that do not affect detection but still affect perception of information in the detailed structure of songs. Not being able to respond appropriately to songs that differ in performance level is likely to have negative fitness consequences and contribute to a detrimental impact of anthropogenic noise on individuals and populations. • Blue tits were exposed to white noise and narrow-band noise conditions. • Detection of conspecific songs was not affected under any noise conditions. • Discrimination of variation in song performance was affected by high noise levels. • Discrimination of song performance was reduced only by spectrally overlapping noise. • Blue tits showed a stronger territorial response under higher noise levels. [ABSTRACT FROM AUTHOR]

The increasing expansion of urban areas leads to the emergence of new noisy environments that can affect animal communication. Calls play a crucial role in the mating displays of anurans, and the negative impact of anthropogenic noise-induced auditory masking has been reported in several species. We investigated the acoustic variation in 96 males (n =  971 calls) of the treefrog Boana pulchella across acoustically undisturbed sites and different noise conditions, associated with urban areas (URBAN) and roads (ROAD), in Central Argentina. We analyzed the effect of anthropogenic noise conditions on 6 temporal (call duration [CD], intercall interval, first and second note duration, internote interval, and call rate) and 3 spectral (dominant frequency of first and second note, frequency difference between them) call properties. The effects of temperature and size on acoustical variables were controlled. We observed differences in all call attributes among the noise conditions, except for intercall interval. Males exposed to URBAN and ROAD exhibited significant changes in CD, dominant frequency of the second note, and frequency difference between them. URBAN males had longest internote interval, while ROAD individuals displayed increased first and second note duration and call rates. Interestingly, ROAD males exhibited immediate changes in call rate in direct response to passing heavy vehicles. Our study emphasizes the impact of anthropogenic noise on the acoustic characteristics of B. pulchella calls. Understanding how animals adapt to noisy environments is crucial in mitigating the adverse effects of urbanization on their communication systems. Future investigations should explore whether the observed call adjustments are effective in avoiding or mitigating the negative consequences of anthropogenic noise on reproductive success. [ABSTRACT FROM AUTHOR]

Acoustic communication in animals can be affected by multiple biotic (intra and interspecific) and abiotic (e.g., wind and rain) natural noises. In addition, human beings produce additional novel sources of noise, which can reduce or inhibit the reception of acoustic signals by conspecifics, leading to behavioral changes. In this study, we investigated whether sound of conspecifics and road noise additively affect the acoustic parameters of the advertisement call of males of a Yellow Heart‐tongued Frog (Phyllodytes luteolus). We hypothesized that males that vocalize in choruses (males calling nearby) and in areas close to highways (anthropic noise) will increase their temporal and spectral acoustic parameters, respectively, to avoid acoustic signal masking. We recorded the vocalizations of 38 males in environments close (N = 18) to and distant (N = 20) from highways in different social contexts (many or few individuals calling nearby). Contrary to our expectation, the results indicated that males calling in areas close to highways had lower dominant frequency calls than those from natural areas (far from highways), and that the density of males in the chorus had no influence on the acoustic parameters. Furthermore, we found a positive relationship between body size and intensity, indicating that larger individuals can emit calls that can reach greater distances. The advertisement call of Phyllodytes luteolus has a high dominant frequency, with little overlap with the frequency of anthropic noises (roads), which may explain its presence and reproductive success of this species in bromeliads from urbanized areas. [ABSTRACT FROM AUTHOR]

Recently, an acoustic individual identification (AIID) approach based on recognition of dolphins by individually distinctive calls such as "signature whistles" has been applied to bottlenose dolphins Tursiops truncatus. Some other Odontoceti species can also have individually specific calls: e.g., in beluga whales Delphinapterus leucas, these are so-called "contact calls". In this pilot study, we have tested the possibility of using the presumed contact calls of belugas to obtain the data on occurrence, number, and individual composition of their local aggregations in the natural environment. We have concluded that the diversity of contact calls can serve as an acceptable indicator of the number of individuals in the research area; in addition, these calls are potentially applicable for individual acoustic identification in belugas. [ABSTRACT FROM AUTHOR]

Simple Summary: Grasshopper species of the Stenobothrini tribe are known by the wide diversity of their premating traits, such as acoustic behavior and morphological characters. However, the phylogenetic relationships, divergence time, and phylogeography of these species inferred with the mtDNA markers (the control region and the COI gene) did not reflect the species divergence. The analysis of interspecific and intraspecific variability in the control region in two hybridizing species of this genus, S. eurasius and S. hyalosuperficies, supports the hypothesis of putative hybridization between the species and shows the direction of the mtDNA introgression. The two cryptic grasshopper species of the genus Stenobothrus, S. eurasius and S. hyalosuperficies, demonstrate different acoustic behavior despite a strong similarity in morphology. A hybridization between these species is possible in the contact zone; however, there are little molecular data about the relationships of these species. The analysis of the mtDNA control region (CR) reveals that haplotypes of S. hyalosuperficies have more in common with the more distant Stenobothrus species than with the closely related S. eurasius. In the contact zone, S. eurasius has mt-haplotypes shared with S. hyalosuperficies, which might indicate an introgression of mtDNA from S. hyalosuperficies to the S. eurasius gene pool. We also analyze the structure and evolutionary rate of the mtDNA CR for the Stenobothrus genus and estimate the time of divergence of the species within the genus. The phylogenetic tree of the tribe Stenobothrini reconstructed with either the CR or COI gave the same four groups. The phylogenetic tree of the Stenobothrus genus has a star-like topology with each mtDNA haplotype found in any analyzed species, except S. eurasius, which forms a separate branch. The maximum degree of incomplete lineage sorting can demonstrate either ancestral polymorphism or introgression. [ABSTRACT FROM AUTHOR]

In this study, we describe the acoustic structure of ultrasonic alarm calls of Mongolian gerbils Meriones unguiculatus in the wild and verify these calls as belonging to Mongolian gerbils by comparison of their acoustic parameters with alarm calls recorded in captivity. Both in captivity and in the wild, the alarm calls of Mongolian gerbils represented prolonged calls with an average duration of 118 ms and a flat contour and an average maximum fundamental frequency of 26.84 kHz. We found that alarm calls of captive Mongolian gerbils were shorter and higher in fundamental frequency and followed in a quicker succession than in the wild. Although the dataset size is not sufficient to determine significant acoustic variation between the populations, we discuss the potential reasons of the acoustic differences between the ultrasonic alarm calls produced in the wild and in captivity in our study and between the alarm calls reported in literature for different captive populations. We propose a method for non-invasive estimation of occupancy of the burrows by Mongolian gerbils in fragmented colonies at very low population density, by presence of the ultrasonic alarm calls. [ABSTRACT FROM AUTHOR]

Noise from human activity is a global concern that threatens wildlife, including by disrupting acoustic communication. This disruption is often assumed to be caused by masking, where signals are difficult to hear in the presence of noise of similar frequency to the signals. However, other mechanisms can also lead to reduced responses to signals: animals may be distracted by noise and so miss the signal, or noise may increase their vigilance and so lead them to use personal information instead of responding to signals from others. Previous experimental work on superb fairy-wrens, Malurus cyaneus , found evidence that masking disrupted responses to conspecific alarm calls but could not rule out distraction. We therefore designed experiments using responses to heterospecific alarm calls to distinguish masking from distraction. We tested responses to low- and high-frequency heterospecific alarm calls during low- and high-frequency noise. Fairy-wrens responded to both heterospecific alarm calls during nonoverlapping noise, but not during overlapping noise, regardless of noise frequency, and vigilance was similar during the two types of noise. We conclude that the alarm call response was compromised by masking, not distraction or increased vigilance. Overall, the assessment of mechanisms helps predict the consequences of noise pollution and provides suggestions on managing anthropogenic noise at the community level, such as avoiding noise whose frequency overlaps either conspecific or heterospecific calls. • Noise might stop animals responding to calls via masking, distraction or vigilance. • We tested mechanisms using playback of heterospecific bird alarm calls and noise. • Masking stopped response during noise that overlapped calls in frequency. • Neither distraction nor changes in vigilance affected responses. • Masking could affect community function by stopping response to critical signals. [ABSTRACT FROM AUTHOR]

The vocal behavior of Neotropical birds has received less attention compared to birds in Northern temperate regions. Many bird species rely on acoustic communication to establish and maintain territories and to interact with conspecifics. For this reason, the growing threat of noise pollution in their habitats is a cause for concern. Birds perform behavioral adjustments when confronted with atypical environmental situations (e.g. urban noises, artificial light, human voice or vegetation loss). The aim of this study was to investigate vocal adjustments of Masked Gnatcatcher (Polioptila dumicola) males in environments located near a route with varying level of traffic noise (measured in decibels) and differing percentage of cover vegetation. Linear mixed models (LMMs) were used to analyze the effects of both environmental parameters in P. dumicola song. Results reveal that P. dumicola increases the amplitude of its songs in response to higher levels of traffic noise. Cover vegetation did not show any effect on song parameters. The model with the highest significance demonstrates a positive linear relationship between amplitude and traffic noise. These findings underscore the importance of studying communication alterations in noisy environments and understanding the ecological consequences of such effects on bird populations. [ABSTRACT FROM AUTHOR]

Communication takes place within a network of multiple signallers and receivers. Social network analysis provides tools to quantify how an individual's social positioning affects group dynamics and the subsequent biological consequences. However, network analysis is rarely applied to animal communication, likely due to the logistical difficulties of monitoring natural communication networks. We generated a simulated communication network to investigate how variation in individual communication behaviours generates network effects, and how this communication network's structure feeds back to affect future signalling interactions. We simulated competitive acoustic signalling interactions among chorusing individuals and varied several parameters related to communication and chorus size to examine their effects on calling output and social connections. Larger choruses had higher noise levels, and this reduced network density and altered the relationships between individual traits and communication network position. Hearing sensitivity interacted with chorus size to affect both individuals' positions in the network and the acoustic output of the chorus. Physical proximity to competitors influenced signalling, but a distinctive communication network structure emerged when signal active space was limited. Our model raises novel predictions about communication networks that could be tested experimentally and identifies aspects of information processing in complex environments that remain to be investigated. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'. [ABSTRACT FROM AUTHOR]

Acoustic communication plays an important role in coordinating group dynamics and collective movements across a range of taxa. However, anthropogenic disturbance can inhibit the production or reception of acoustic signals. Here, we investigate the effects of noise and light pollution on the calling and collective behaviour of wild jackdaws (Corvus monedula), a highly social corvid species that uses vocalizations to coordinate collective movements at winter roosting sites. Using audio and video monitoring of roosts in areas with differing degrees of urbanization, we evaluate the influence of anthropogenic disturbance on vocalizations and collective movements. We found that when levels of background noise were higher, jackdaws took longer to settle following arrival at the roost in the evening and also called more during the night, suggesting that human disturbance may cause sleep disruption. High levels of overnight calling were, in turn, linked to disruption of vocal consensus decision-making and less cohesive group departures in the morning. These results raise the possibility that, by affecting cognitive and perceptual processes, human activities may interfere with animals' ability to coordinate collective behaviour. Understanding links between anthropogenic disturbance, communication, cognition and collective behaviour must be an important research priority in our increasingly urbanized world. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'. [ABSTRACT FROM AUTHOR]

Because of the diverging needs of individuals, group life can lead to disputes and competition, but it also has many advantages, such as reduced predation risk, information sharing and increased hunting success. Social animals have to maintain group cohesion and need to synchronize activities, such as foraging, resting, social interactions and movements, in order to thrive in groups. Acoustic signals are highly relevant for social dynamics, some because they are long-ranging and others because they are short-ranging, which may serve important within-group functions. However, although there has been an increase in studies concentrating on acoustic communication within groups in the past decade, many aspects of how vocalizations relate to group dynamics are still poorly understood. The aim of this review is to present an overview of our current knowledge on the role of vocalizations in regulating social group dynamics, identify knowledge gaps and recommend potential future research directions. We review the role that vocalizations play in (i) collective movement, (ii) separation risk and cohesion maintenance, (iii) fission–fusion dynamics, and (iv) social networks. We recommend that future studies aim to increase the diversity of studied species and strengthen the integration of state-of-the-art tools to study social dynamics and acoustic signals. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'. [ABSTRACT FROM AUTHOR]

In both terrestrial and marine ecosystems, prey species exhibit various reactions to predators, including avoidance, fighting and freezing. Acoustic communication associated with mobbing has been depicted in numerous tetrapod species. This sonic behaviour remains however largely unknown in fish although mobbing has been shown in different coral reef fish as a response to predation risk. This study focused on the communication strategy of prey species in the presence of predators. We tested the reaction of the holocentrid Sargocentron caudimaculatum when facing a moray eel and compared the sounds they produced against the predator with sounds produced when the fish are hand-held, recorded in standardized conditions. When introduced in mesocosms to a moray eel, S. caudimaculatum produced distinct distress sounds, resembling staccato calls, and swam towards the predator with their heads pointed in its direction and their dorsal fin erected. This observation supports a mobbing behaviour with specimens shifting from an escape behaviour to an aggressive response in presence of predator. Moreover, these sounds are different from those emitted during manual handling. This difference in acoustic signal suggests the coexistence of multiple warning/alarm sounds in this species. Holocentrids can produce different kinds of sounds witnessing their ability to provide graded information based on the perceived predation risk. We suggest that species of this family would be a suitable and promising group with which to test the hypothesis of acoustic coordination where individuals could inform their conspecifics about an increase in the immediate predation risk through appropriate alarm calls and trigger an escape response of the group if needed. [ABSTRACT FROM AUTHOR]

Underwater Wireless Sensor Networks (UWSNs) have emerged for various tasks in marine environments. Routing Protocols (RPs) in UWSNs face challenges such as high propagation delay, Energy Consumption (EC), low bandwidth, and low throughput compared to Terrestrial WSNs (TWSNs). UWSNs operate autonomously without human intervention, and the limited energy of sensor batteries poses a significant challenge. Uneven energy resource utilization reduces network longevity, which is a major issue in UWSNs. To combat these issues, a promising approach involves the design of RPs employing clusters for efficient packet routing from source to destination. This paper systematically reviews recent Cluster-oriented RPs (CRPs) in UWSNs, organizing them chronologically. It assesses their merits, drawbacks, and overall network performance, offering insights into future directions for improvement in this domain. [ABSTRACT FROM AUTHOR]

In many bird species, nestling begging signals play a key role in the interaction between parents and their offspring during development. The information conveyed by begging calls can be disrupted by anthropogenic noise, which is one of the major threats to biodiversity in increasingly urbanized landscapes. Here, we describe the developmental change in acoustic structure of begging calls in nestling Eurasian Blue Tits Cyanistes caeruleus; begging calls are pure‐tone, low‐frequency, soft calls during the first days of development and gradually turn into white‐noise, hiss‐like, powerful calls of broadband frequency. This strong developmental variation highlights the importance of an extended sampling scheme in developmental studies. Furthermore, we pinpoint two phases where begging calls could be most vulnerable to masking by anthropogenic noise. First, during early development, begging calls are very soft and low‐pitched, closer to high‐intensity noise bands of traffic noise. Secondly, around day 11, begging calls show reduced tonality, which implies higher degradation, and relatively low amplitude, which implies reduced signal range. We encourage future research to describe acoustic development of begging calls in other species, to provide a robust foundation that will make noise mitigation policies more effective. [ABSTRACT FROM AUTHOR]

Environmental monitoring and disaster mitigation are critical applications of underwater acoustic sensor networks (UASNs). However, UASNs face significant challenges, including high latency, limited bandwidth, and energy constraints. This study introduces an Internet of Things (IoT)-driven location-aware framework (ILAF) designed to enhance UASN performance by utilizing non-GPS geographic coordinates for determining the location of sensor and sink nodes, identifying their neighbors based on coordinates and transmission range, and optimizing node placement and routing without the need for GPS modems. The framework is compared with several state-of-the-art protocols, including Bald Eagle Search inspired optimized energy efficient routing protocol (BES-OEERP) and IoT-enabled depth-based routing technique (IDBR), demonstrating superior performance. Specifically, ILAF achieved a packet delivery ratio (PDR) of 99%, which outperforms energy-efficient region-based source distributed routing algorithm (EERSDRA) (98%) and energy-efficient geo-opportunistic routing protocols (EEGORP) (96%). Additionally, ILAF reduced energy consumption by 20% compared to these existing protocols. These improvements result in a more energy-efficient network with fewer dead nodes (12 after 1,000 rounds) and higher throughput (5.7 kbps at 1,000 rounds), making ILAF suitable for real-time underwater applications. Future research will explore integrating lightweight IoT protocols like Message Queue Telemetry Transport (MQTT) and Constrained Application Protocol (CoAP) to enhance the framework’s performance and reliability further.

BackgroundBiological invasions pose a critical threat to biodiversity, affecting ecological balance and native species’ communication. Eleutherodactylus johnstonei, an exotic anuran in São Paulo, vocalizes at intensities that could interfere with native anuran species, potentially causing acoustic masking.MethodsWe evaluated the effects of E. johnstonei's calls on the vocalizations of two native species, Scinax imbegue and Physalaemus cuvieri, both with and without spectral overlap with the invasive species. Field playbacks were conducted using six versions of stimuli, including E. johnstonei's calls, the native Boana bischoffi (as a control), and white noise. We recorded response calls and behavioral changes of S. imbegue and P. cuvieri males.ResultsThe calls of E. johnstonei did not affect the spectral or temporal parameters of the native species’ announcement calls. However, S. imbegue males displayed behavioral responses such as cessation of vocalization or movement away from the noise source. Additionally, B. bischoffi's calls and white noise influenced native species’ call parameters.DiscussionOur findings reveal that exotic species’ vocalizations may disrupt native anurans’ acoustic behavior. This impact varies with species and context, underlining the need for further research on anuran acoustic interactions across different frequencies and acoustic environments to fully understand the effects of exotic acoustic interference.

Abstract Examples of symbiotic relationships often include cleaning mutualisms, typically involving interactions between cleaner fish and other fish, called the clients. While these cleaners can cooperate by removing ectoparasites from their clients, they can also deceive by feeding on client mucus, a behavior usually referred to as “cheating behavior” that often leads to a discernible jolt from the client fish. Despite extensive studies of these interactions, most research has focused on the visual aspects of the communication. In this study, we aimed to explore the role of acoustic communication in the mutualistic relationship between cleaner fishes and nine holocentrid client species across four regions of the Indo-Pacific Ocean: French Polynesia, Guam, Seychelles, and the Philippines. Video cameras coupled with hydrophones were positioned at various locations on reefs housing Holocentridae fish to observe their acoustic behaviors during interactions. Our results indicate that all nine species of holocentrids can use acoustic signals to communicate to cleaner fish their refusal of the symbiotic interaction or their desire to terminate the cooperation. These sounds were predominantly observed during agonistic behavior and seem to support visual cues from the client. This study provides a novel example of acoustic communication during a symbiotic relationship in teleosts. Interestingly, these vocalizations often lacked a distinct pattern or structure. This contrasts with numerous other interspecific communication systems where clear and distinguishable signals are essential. This absence of a clear acoustic pattern may be because they are used in interspecific interactions to support visual behavior with no selective pressure for developing specific calls required in conspecific recognition. The different sound types produced could also be correlated with the severity of the client response. There is a need for further research into the effects of acoustic behaviors on the quality and dynamics of these mutualistic interactions.

In base-station-based underwater wireless acoustic networks (B-UWANs), effective handover mechanisms are necessary to ensure seamless data services for mobile nodes such as autonomous underwater vehicles (AUVs). Unlike terrestrial base stations (BSs), moored buoy BSs in B-UWANs experience motion responses due to wave loads under environmental conditions, posing unique challenges to the handover process. This study examines how BS motion affects handover decision errors, which arise when AUVs incorrectly initiate handovers to unintended BSs due to BS motion. By utilizing the AUV–BS distance as a handover triggering parameter, our analysis reveals a significant increase in decision errors within the overlapping regions when both the current and target BSs are in motion, especially when moving in the same direction. In addition, these errors intensify with the magnitude of BS motion and are exacerbated by smaller BS network radii. Based on these simulation results, we present an analytical framework that not only measures the influence of BS motion on the AUV–BS distance but also provides strategic insights for refining underwater handover protocols, thereby enhancing operational reliability and service continuity in B-UWANs. [ABSTRACT FROM AUTHOR]

Research on urban noises affecting acoustic communication of animals is a growing area of study and conservation concern. However, the consequences of aircraft noise on anuran acoustic communication have been explored on a restricted basis to date. In this study, we investigated the impact of aircraft overflights on the individual and chorus performance of acoustic signalling in the Pedregal frog (Eleutherodactylus grandis), a microendemic and threatened species from Mexico City. During the summer of 2021, we recorded acoustic signals from male individuals and conducted acoustic monitoring to analyse how chorus social interactions change due to aircraft overflights. For this purpose, we evaluated acoustic properties of the call, including call duration, dominant frequency, call amplitude, and call repetition rate. Additionally, we measured the amplitude of environmental noises and signals by means of two types of complementary methodological approaches. Our results show changes in the individual performance of acoustic signals with longer call duration, lower dominant frequency, and higher call amplitude due to aircraft overflights, while individual call repetition rate did not vary. Furthermore, a decrease in the number of calls within the chorus was observed during aircraft overflight. Overall, these results show that aircraft noise causes plastic changes in the acoustic signals of the Pedregal frog and that social interactions between conspecifics decrease, thus adding a new disturbance to this species that already suffers from other anthropogenic noises, and habitat fragmentation. [ABSTRACT FROM AUTHOR]

Radio frequency electromagnetic, acoustics, optics, and near field magnetic induction are the primary wireless communication carriers that are employed for underwater and underground communication. Radio waves are preferred for shallow-water and underground communication because of their high data rate over other communication carriers. This inherently motivated our research to find new capabilities with radio wave communication in conducting mediums, including underwater and underground regions. The focus of our research aims at experimentally reducing path loss for radio waves. Proposed communication model involves a communicating node present in the terrestrial region with air as the medium; and a receiving node either buried underneath soil or submerged underwater. The research focuses on assessing the impact of the incidence angle of the signal affecting path loss when the transmitting signal travels through air–water and air-ground interface. The simulation results show that path loss becomes more with the increase in angle of incidence of the propagating signal. [ABSTRACT FROM AUTHOR]

The rapid advancement toward smart cities has accelerated the adoption of various Internet of Things (IoT) devices for underground applications, including agriculture, which aims to enhance sustainability by reducing the use of vital resources such as water and maximizing production. On-farm IoT devices with above-ground wireless nodes are vulnerable to damage and data loss due to heavy machinery movement, animal grazing, and pests. To mitigate these risks, wireless Underground Sensor Networks (WUSNs) are proposed, where devices are buried underground. However, implementing WUSNs faces challenges due to soil heterogeneity and the need for low-power, small-size, and long-range communication technology. While existing radio frequency (RF)-based solutions are impeded by substantial signal attenuation and low coverage, acoustic wave-based WUSNs have the potential to overcome these impediments. This paper is the first attempt to review acoustic propagation models to discern a suitable model for the advancement of acoustic WUSNs tailored to the agricultural context. Our findings indicate the Kelvin–Voigt model as a suitable framework for estimating signal attenuation, which has been verified through alignment with documented outcomes from experimental studies conducted in agricultural settings. By leveraging data from various soil types, this research underscores the feasibility of acoustic signal-based WUSNs. [ABSTRACT FROM AUTHOR]

Vocal complexity is central to many evolutionary hypotheses about animal communication. Yet, quantifying and comparing complexity remains a challenge, particularly when vocal types are highly graded. Male Bornean orangutans (Pongo pygmaeus wurmbii) produce complex and variable "long call" vocalizations comprising multiple sound types that vary within and among individuals. Previous studies described six distinct call (or pulse) types within these complex vocalizations, but none quantified their discreteness or the ability of human observers to reliably classify them. We studied the long calls of 13 individuals to: (1) evaluate and quantify the reliability of audio-visual classification by three well-trained observers, (2) distinguish among call types using supervised classification and unsupervised clustering, and (3) compare the performance of different feature sets. Using 46 acoustic features, we used machine learning (i.e., support vector machines, affinity propagation, and fuzzy c-means) to identify call types and assess their discreteness. We additionally used Uniform Manifold Approximation and Projection (UMAP) to visualize the separation of pulses using both extracted features and spectrogram representations. Supervised approaches showed low inter-observer reliability and poor classification accuracy, indicating that pulse types were not discrete. We propose an updated pulse classification approach that is highly reproducible across observers and exhibits strong classification accuracy using support vector machines. Although the low number of call types suggests long calls are fairly simple, the continuous gradation of sounds seems to greatly boost the complexity of this system. This work responds to calls for more quantitative research to define call types and quantify gradedness in animal vocal systems and highlights the need for a more comprehensive framework for studying vocal complexity vis-à-vis graded repertoires. [ABSTRACT FROM AUTHOR]

Geographic variation in acoustic characteristics of anuran advertisement calls could be an important indicator of species divergence due to its importance for species recognition. In this study, we evaluated the hypotheses of morphological by-product, local adaptation, and genetic drift to explain the geographic variation of the calls of the frog Eleutherodactylus nitidus. We compared six acoustic variables using ANOVA and linear discriminant analyses, as well as inter- and intra-population and intra-individual variation estimates to understand E. nitidus call variation. Recorded calls were corrected for temperature and body size to rule out the influence of these factors on call variation. The advertisement call of E. nitidus is a short whistle with an oscillating amplitude modulation that forms pulses. In total, we analysed 1676 advertisement calls from 66 individuals. We find that call duration, call amplitude, dominant frequency, pulses per call and highest pulse differ between populations, and such differences were independent of body size and temperature variation, ruling out the morphological by-product and local adaptation hypotheses. Additionally, the linear discriminant analysis indicates that geographic call variation depends principally on call amplitude. We suggest that the geographic distance between populations of E. nitidus yields genetic differences that account for differences in advertisement calls. [ABSTRACT FROM AUTHOR]