Whereas echolocation in horseshoe bats is well studied, virtually nothing is known about characteristics and function of their communication calls. Therefore, the communication calls produced by a group of captive adult greater horseshoe bats were recorded during various social interactions in a free-flight facility. Analysis revealed that this species exhibited an amazingly rich repertoire of vocalizations varying in numerous spectro-temporal aspects. Calls were classified into 17 syllable types (ten simple syllables and seven composites). Syllables were combined into six types of simple phrases and four combination phrases. The majority of syllables had durations of more than 100 ms with multiple harmonics and fundamental frequencies usually above 20 kHz, although some of them were also audible to humans. Preliminary behavioral observations indicated that many calls were emitted during direct interaction with and in response to social calls from conspecifics without requiring physical contact. Some echolocation-like vocalizations also appeared to clearly serve a communication role. These results not only shed light upon a so far widely neglected aspect of horseshoe bat vocalizations, but also provide the basis for future studies on the neural control of the production of communicative vocalizations in contrast to the production of echolocation pulse sequences.

Rodents' ultrasonic vocalizations (USVs) provide useful information for assessing their social behaviors. Despite previous efforts in classifying subcategories of time-frequency patterns of USV syllables to study their functional relevance, methods for detecting vocal elements from continuously recorded data have remained sub-optimal. Here, we propose a novel procedure for detecting USV segments in continuous sound data containing background noise recorded during the observation of social behavior. The proposed procedure utilizes a stable version of the sound spectrogram and additional signal processing for better separation of vocal signals by reducing the variation of the background noise. Our procedure also provides precise time tracking of spectral peaks within each syllable. We demonstrated that this procedure can be applied to a variety of USVs obtained from several rodent species. Performance tests showed this method had greater accuracy in detecting USV syllables than conventional detection methods. OPEN ACCESSCitation: Tachibana RO, Kanno K, Okabe S, Kobayasi KI, Okanoya K (2020) USVSEG: A robust method for segmentation of ultrasonic vocalizations in rodents. PLoS ONE 15(2): e0228907. https://doi.org/10.

Acoustic signalling is one of the most common communication mediums in a broad range of social animals, and it often encodes attributes of the signaller such as sex, kin relatedness and dominance rank. Particularly, antiphonal vocalization has been regarded to have an important function in animals living in an environment where visual cues are unreliable. Antiphony enables to acknowledge that one's signal was received with certainty. We show the first evidence of such acoustic signals among rodents: the naked mole‐rat. The society of this eusocial subterranean species is organized hierarchically according to body size. Naked mole‐rats are functionally blind, and rely highly on acoustic communication. We focused on one of their vocalizations: the soft chirp (SC). SCs are the most frequent sounds, and are often emitted upon physical contact. We expected the SC to be antiphonal, and if so, SC may function to distinguish colony members from intruders, and/or identify social rank and individuality. To examine our predictions, we placed pairs of individuals of different size together, and recorded their vocal behaviour. The intervals between the SCs of two individuals were shorter than expected intervals which were based on the assumption that animals vocalized without reference of the preceding SC. The acoustic properties of SCs varied among individuals according to body weight and colony of origin. The emission rate was positively related to the relative difference in body weight. Therefore, SCs have an antiphonal nature and may function as expected. These characteristics of SC were highly similar to those of antiphonal sounds in other social species.

Mammalian vocalizations require the precise coordination of separate laryngeal and respiratory motor pathways. Precisely how and where in the brain vocal motor patterns interact with respiratory rhythm control is unknown. The parabrachial nucleus (PB) is known to mediate key respiratory reflexes and is also considered a principle component of the mammalian vocal motor pathway, making it a likely site for vocal-respiratory interactions, yet a specific role for the PB in vocalizing has yet to be demonstrated. To investigate the role of the PB in vocal-respiratory coordination, we pharmacologically manipulated synaptic activity in the PB while spontaneously vocalizing horseshoe bats were provoked to emit either short, single syllable or long, multisyllabic vocal motor patterns. Iontophoresis of the GABA A agonist muscimol (MUS) into the lateral PB extended expiratory durations surrounding all vocalizations and increased mean call durations. Alternatively, application of the GABA A antagonist bicuculline methiodide (BIC) shortened expirations and call durations. In addition, BIC eliminated the occurrence of multisyllabic vocalizations. BIC caused a mild increase in quiet breathing rates, whereas MUS tended to slow quiet breathing. The results indicate that GABA A receptor-mediated inhibition in the lateral PB modulates the time course of respiratory phase switching during vocalizing, and is needed for proper coordination of calling and breathing in mammals. We hypothesize that vocal-respiratory rhythm entrainment is achieved at least in part via mechanisms similar to other forms of locomotorrespiratory coupling, namely somatosensory feedback influences on respiratory phase-switching in the lateral PB.

The Mongolian gerbil (Meriones unguiculatus) has been an important model system in auditory physiology, but its natural sounds are not well known. Vocalizations produced by colonies of adult gerbils were recorded during various social interactions in a standard laboratory animal-rearing facility. Sound recordings were made continuously for 24 h. This species exhibited a rich repertoire of vocalizations that varied in spectrotemporal structure. Calls were classified into 13 distinct syllable types. These syllables were further categorized into eight simple syllables and five composite syllables, which could be described by combinations of two to three simple syllables. The durations of individual syllables ranged from 30 to 330 ms with fundamental frequencies of 5 to 50 kHz. Those with lower fundamental frequencies typically contained more harmonic components (up to nine). Analysis of syllable sequences indicated that syllables may be combined into three types of simple phrases. These results provide a basis for future studies not only of the behavioral significance of vocalization, but also of the neural basis of vocal communication in the Mongolian gerbil.

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Estrildid finches have two song types: directed (courtship) and undirected (solo). These are acoustically identical and differ only in social context. Recent studies have shown that undirected singing is accompanied by strong activation of the basal ganglia pathway, whereas directed singing is not, which suggests a different degree of feedback control between the two. We examined whether the magnitude of the Lombard effect, i.e., vocal amplitude regulation in response to environmental noise, differed based on the song context. Our results indicate that Bengalese finches change the amplitude of undirected song based on background noise levels, but do not do so for directed song. This is the first behavioral evidence suggesting that feedback control of song output vary by social context.

Echolocating bats need to solve the problem of signal jamming by conspecifics when they are in a group. However, while several mechanisms have been suggested, it remains unclear how bats avoid confusion between their own echoes and interfering sounds in a complex acoustic environment. Here, we fixed on-board microphones onto individual frequency-modulating bats flying in groups. We found that group members broaden the inter-individual differences in the terminal frequencies of pulses, thereby decreasing the similarity of pulses among individuals. To understand what features most affect similarity between pulses, we calculated the similarity of signals mimicking pulses. We found that the similarity between those artificial signals was decreased most by manipulation of terminal frequency. These results demonstrate that the signal jamming problem is solved by this simple strategy, which may be universally used by animals that use active sensing, such as echolocating bats and electric fish, thereby transcending species and sensory modalities.