ABSTRACT Felids are top predators with a significant impact on ecosystems worldwide. Yet many species are endangered, and their behaviour remains poorly studied. Felids rely on acoustic signals to convey a wide range of information over long distances and sometimes dense habitats. These signals reflect key behavioural contexts, such as mating, cub-rearing, and territorial defence – aspects relevant for conservation and habitat management. Our systematic literature review provides an overview of current knowledge on the structure and function of acoustic signals in undomesticated felids, evaluates their potential for acoustic monitoring and outlines future applications of acoustic methods in conservation, research and management. In January 2025, we searched Scopus and Web of Science for English and German publications on acoustic signals in all 40 undomesticated felid species, excluding only the domestic cat (Felis catus), identifying 51 relevant publications. Most studies focused on large-sized felids such as lions and cheetahs. For 32 of the 40 felid species researched, no species-specific studies were found. Felids share a basic acoustic repertoire, but exhibit species-specific variations that suggest adaptive functions. Most call types studied in detail encode information such as caller’s age, sex, or identity, suggesting high potential for acoustic monitoring and implications in conservation.

ABSTRACT Environmental factors shape animal signals by influencing how sound propagates through natural habitats. The acoustic adaptation hypothesis predicts that signal features promoting effective propagation should be favoured, yet the role of habitat-mediated propagation in shaping song-type prevalence remains unclear. In songbird populations with multiple song types, some are commonly shared while others are rare. We tested the hypothesis that common song types in a population of Bachman’s Sparrows possess acoustic features that enhance propagation relative to rare song types. We quantified the acoustic features of common and rare song types and conducted sound propagation experiments. Common song types had shorter inter-syllable gaps, higher peak frequency, broader frequency bandwidth, and higher maximum frequency than rare song types. Consistent with predictions, common song types propagated more effectively for two of five propagation metrics, exhibiting higher amplitude envelope correlation and lower tail-to-signal ratios. Tree density showed a non-significant trend in which common song types exhibited higher amplitude envelope correlation as tree density increased, whereas wind speed and signal height did not influence propagation. Together, these results provide partial support for the hypothesis that propagation efficiency contributes to song-type prevalence, yet social processes during song learning likely play an equal or greater role.

ABSTRACT Male túngara frogs appear in choruses and have well-defined vocal cords at a size of 19 mm snout-vent length (SVL), but they do not begin producing advertisement calls until they reach approximately 24 mm SVL. Is this because the larynx is not fully mature until the latter point, or is it because the calls of small-bodied adults would not be attractive enough to outweigh the costs (energy, predation and parasitism) of producing them? We investigate this question by tuning bond graph models of the túngara frog larynx with parameter values across this critical body size range. Simulations were informed by a new set of diceCT-based measurements of key laryngeal morphological features from an ontogenetic series. Models produce sustained oscillations in airflow through the larynx (sound) with species-typical spectral features across the full range of the ontogenetic ‘silent zone’, suggesting that muteness during this period is facultative and not physically enforced. This result illuminates the morphological and behavioural consequences of an interplay of natural and sexual selection. Sexual selection and developmental constraints may lead the early development of laryngeal vibratory tissues, while natural selection (energetic costs and predation avoidance) and sexual selection (reduced call attractiveness) act to mute smaller adult frogs.

ABSTRACT Marine conservation has benefited from Passive Acoustic Monitoring Systems, though processing the recorded signals remains time-consuming and resource-intensive. This paper evaluates the potential of You Only Look Once v8 (YOLOv8) to automatically detect dolphin whistles. Despite being primarily designed for detecting high-level features in real-world objects, YOLOv8 effectively identifies dolphin whistles in spectrograms. The paper details the conversion of acoustic signals into spectrograms for YOLOv8 analysis and outlines an experimental methodology in three phases. First, it compares model performance with and without additional labels on a three-hour dataset. Second, cross-dataset transferability is assessed by testing the model on historical and critical datasets. Finally, a general model is trained using all datasets to evaluate overall performance. Introducing additional labels improves the model’s average precision by 12% and recall by 19%, better distinguishing whistles from non-whistles. However, temporal transferability presents challenges, with recall dropping by 3–36% and precision improving by 3–17%. In the final phase, the model achieves a precision of 84% and recall of 70%, demonstrating YOLOv8’s potential for automated detection and labelling of dolphin whistles in spectrograms, even with small datasets.

ABSTRACT The vocal repertoire of anurans can be categorised according to the social context, especially during the reproductive season, when acoustic communication is fundamental. It is known that some factors can influence these calling variations, such as the chytrid fungus, Batrachochytrium dendrobatidis (Bd), as studies show that some anurans infected with Bd have differences in calls when compared to healthy males. This study is focused on Dendropsophus minutus, a small treefrog whose reproductive cycle takes place during rainy seasons. It is possible that infection by Bd can affect their reproductive success, by affecting the vocalisation of males. Previously recorded call data and analyses, as well as skin swabs and qPCR experiments from D. minutus, were compiled to test the relationship between calling variables and Bd infection. We found no difference between infected and uninfected male’s calls. However, among infected individuals, Bd load was positively correlated to the number of notes and call duration. In this study, we propose that two hypotheses may explain the observed patterns: the terminal investment hypothesis and the Hamilton–Zuk hypothesis. The terminal investment hypothesis suggests that individuals with poor health may increase their current calling effort as a last attempt to reproduce. On the other hand, the Hamilton–Zuk hypothesis takes into account that D. minutus is resistant to the infection, and those with higher Bd loads may display enhanced call performance, as more intense vocalisations suggests that these individuals possess traits associated with Bd resistance. With these results, we advocate for further investigations on how Bd impacts the mating behaviour and female preferences of D. minutus, and how the infection alters their reproductive success.

ABSTRACT Acoustic indices are promising tools for ecoacoustic studies and may be useful in zoos for passive acoustic monitoring of enclosures and their inhabitants. To validate their suitability for these applications, it is important to understand how different sounds in the environment affect them. Zoos have unique soundscapes with anthropogenic sounds such as human voices and mechanical noises often prevalent alongside high levels of animal-produced sounds; however, the influence of these sounds on acoustic indices in zoos has yet to be studied. This study investigates how different sound types recorded in aviaries at Chester Zoo in 2019 and 2020 affected three widely used acoustic indices: the Sonic Heterogeneity Index (SHI), the Acoustic Entropy Index (H), and the Normalised Difference Soundscape Index (NDSI). All three indices increased with avian vocalisations; H and SHI increased with human voices; only H increased with non-vocal anthropophonic sounds; SHI and NDSI increased with non-vocal biophonic sounds; and SHI increased but H decreased with the sound of wind. Because each index captures sound types in different ways, using all three in conjunction may provide researchers and practitioners with a more detailed understanding of the acoustic environments in zoos and other anthropogenically dominated environments.

ABSTRACT Bioacoustics is a non-invasive method and an important complementary tool because, in combination with other methods such as mist nets, it allows us to characterise more completely the assemblage of bats in a given place. However, a description of echolocation calls in local conditions is required to use it. This study presents the acoustic characterisation of bat species from northwestern Argentina using different recording techniques. Between April 2022 and November 2023, surveys were carried out with mist nets in different locations in the province of Tucumán (Argentina). The captured specimens were recorded with an Echo Meter Touch 2 device using four techniques: hand release, zip-line, flight cage, and emergence recordings. A total of 209 echolocation calls were recorded from 13 species belonging to the families Phyllostomidae, Molossidae, and Vespertilionidae. The phyllostomid species showed frequency-modulated calls (FM) of low intensity with multiple harmonics; molossids calls exhibited quasi-constant frequency, long duration, and narrow bandwidth; while in vespertilionid bats the calls have pulses with descendent FM (FMd), short duration, and greater bandwidth. This research provides the first acoustic reference data for bats from Argentina, helping to facilitate the acoustic identification of bats in the region.

ABSTRACT Insects are known for communicating via sounds created by rubbing body parts, a behaviour referred to as stridulation. Red Wood ants (Formica rufa group) are not known to possess stridulatory organs and have historically been categorised as a non-stridulating species. In this exploratory study, we report that Red Wood ants generate stridulation-like sounds, being about 0.7 ± 0.2 seconds-long (mean ± standard deviation), rattling sounds that were repeatedly generated in our laboratory setting (about 0.6 productions h-1 individual-1). In addition, we assess Red Wood ant behavioural responses to playbacks of this stridulation-like sound. Our playback experiments show that the stridulation-like sound initiates a reduced locomotory speed among conspecifics, an effect not seen when the ants were exposed to silence. However, this response was not different from that generated by an artificial pure tone, making the use of this stridulation-like sound uncertain. We hypothesise that the stridulation-like sound is produced by rubbing the leg against a ridge structure located on the anterior margin of the pronotum, a structure that we describe using X-ray micro-tomography. Our exploratory study suggests that the recorded sound may be part of Formica ant communication that is hard to detect and easily missed in behavioural assays.

ABSTRACT Solitary dolphins occurring outside their normal range provide a unique opportunity to study acoustic signals in the complete absence of conspecifics, drawing insights into their communicative functions. In this study, we analysed the acoustic behaviour of a solitary bottlenose dolphin residing in the Baltic Sea. We expected that he would produce few, if any, communicative sounds in the absence of potential recipients. Contrary to this expectation, we found the dolphin to be highly vocal, emitting burst-pulse and tonal sounds in rhythmic bouts. The sounds did not co-occur with echolocation trains, indicating that they were not produced during feeding activities, despite the presence of bray calls previously identified as feeding-associated in this population. The dolphin produced three different types of stereotyped whistles, deviating from the typical pattern of one individually distinctive signature whistle per dolphin. Additionally, three different biphonic sound categories were identified: combinations of two whistle components, a whistle and a low-frequency tonal component, and two burst-pulse components. In conclusion, the production of vocalisations in the absence of conspecifics suggests that these sounds may be emitted unintentionally as emotional signals, serve functions other than direct communication, or simply be a byproduct of dolphins’ intrinsic need for social interaction.

ABSTRACT Marine fishes use sound for critical functions, including foraging, competition, and reproductive activities. Despite the biological significance of these sounds, research on the applicability of sound profiles to discriminate between fish species is limited. This study aimed to characterise and differentiate the vocalisations of Haemulon aurolineatum, Haemulon parra, and Haemulon squamipinna off the northeastern Brazilian coast. Seventy-two individuals were recorded, with 140 vocalisations per species. The analyses revealed a grunt profile with significant variation in time parameters across all species, characterised by irregular pulses with variable frequencies (1.8 to 5.9 kHz) and a dominant frequency of approximately 0.75 kHz. Differences among species were observed, with H. aurolineatum showing the highest values in most parameters. Cross-validation tests indicated an overall rate of 69.5% of single sounds correctly assigned to species. Haemulon squamipinna was the most discernible species, while H. parra had the lowest prediction accuracy, showing intermediate sound parameter values. The analysis of pharyngeal jaws revealed minor differences in morphology and tooth distribution in H. parra, but these could not be linked to sound differentiation. Our results indicate that it is feasible to distinguish Haemulon species using the sound characteristics of their vocalisations, offering new insights into their sound communication.