Biology subjects

Hiryu, S.

Publications and source records attributed to Hiryu, S..

12 recordsLinked to original sources

bioRxiv2026

Avoidance of simultaneous patch use in Japanese large-footed bats

Group foraging can enhance prey detection, but depending on resource availability, it may also generate conflicts among conspecifics. To understand how animals balance these benefits and costs, foraging performance must be evaluated together with inter-individual interactions. However, under fully natural conditions, it remains challenging to quantify both simultaneously. Here, we investigated how individual foraging efficiency and pairwise interactions are shaped when more than one individuals simultaneously exploit the same foraging patch, using the Japanese large-footed bat (Myotis macrodactylus) as a model system. We monitored an entire pond functioning as a natural foraging patch using two thermal cameras and an eight-channel microphone array, and reconstructed the arrival, prey-attack, and exit times of individual bats. Using a Poisson generalized linear mixed model (GLMM), we found that prey-attack rates were approximately 25% lower during paired flights than during solitary flights. We then constructed a null model in which arrival, attack, and departure events followed independent Poisson processes parameterized from the empirical data. Compared with null-model predictions, both the total duration and the duration of individual paired flights in the empirical data were significantly shorter, indicating that bats limited the time spent co-using the same patch relative to solitary foraging. In addition, the probability that the first exiting individual was the one that arrived earlier or later did not deviate from chance levels, providing no evidence for a prior residence advantage. Together, these results demonstrate that simultaneous patch use avoidance occurs independently of arrival order and coincides with reduced prey-attack rate, suggesting that bats leave shared patches and move to alternative foraging sites to mitigate losses in prey-attack efficiency. Our findings highlight bats as an excellent model system for non-invasively linking individual behavior and foraging performance via echolocation, and for elucidating the dynamics of foraging behavior and sensory interference in the wild.

animal behavior and cognition↗

bioRxiv2026

Tactile pup loss and acoustic signal enhance selective maternal retrieval behavior in echolocating bats, Pipistrellus abramus

Pup retrieval is a critical maternal behavior ensuring pup survival. Its mechanisms have been studied mainly in rodents, where mothers tolerate brief pup separation. In contrast, in species for which even short separation is life-threatening, mothers maintain constant physical contact, reinforcing anti-separation behavior. Studying such species may uncover maternal strategies under survival-critical extremes. Among these species, echolocating bats provide an ideal model for acoustic-based decision-making, as they rely heavily on sound. In bats, pup isolation calls (ICs) are essential signals in mother-pup communication. To assess their motivation in retrieval based on ICs, we conducted behavioral experiments: (1) pup retrieval test, and (2) playback test using ICs from own vs. non-own pups. Each was conducted under three maternal conditions: holding (a) no-pup, (b) one-pup, and (c) two-pup, to assess tactile influence on maternal motivation. In pup retrieval tests, mothers showed selective responsiveness to their own pups, and it is decreased with their pup development. Playback tests showed that acoustic signals alone were sufficient to elicit maternal responses, and their latencies were negatively correlated to pup vocalization rates. These maternal responses were strongly suppressed under condition (c), but robustly expressed under conditions (a) and (b). These findings suggest that maternal motivation is context-dependent responsiveness, which is enhanced by tactile pup loss and ICs, providing insight into instinctive maternal behavior in mammals. Summary statementThis study demonstrates that in the Pipistrellus abramus, maternal motivation is context-dependent responsiveness, which is enhanced by tactile pup loss and vocalizations, providing insight into a flexible multimodal mechanism underlying instinctive maternal behavior.

animal behavior and cognition↗

bioRxiv2025

Bats create a silent frequency band to detect prey through Doppler shift compensation

Acquiring information efficiently through sensory inputs is essential for animal survival. Animals with active sensory systems that emit their own signals often optimize the design and use of these signals according to context and purpose1-6. In this study, we reveal a previously unrecognized function of Doppler shift compensation (DSC) in bats. During flight, bats actively lower the frequency of their echolocation calls so that echoes remain stable at a reference frequency (fref) despite Doppler shifts caused by movement7-12. We demonstrate that DSC does not simply serve, as previously thought, to align echoes with the acoustic fovea--a narrow band of maximal auditory sensitivity13,14--but in addition, suppresses background noise for detecting prey-derived signals. Using phantom echo playbacks and on-board microphone recordings, we show that bats selectively compensate for the highest-frequency echoes rather than the most intense ones. This process shifts all clutter echoes below fref, leaving the spectral band above fref free of stationary-object echoes and secures a "quiet frequency band". Recordings during prey capture and noise playback experiments revealed that spectral glints from fluttering moth wings appear in this "quiet frequency band" and are exploited for prey detection. This mechanism enhances the high-fidelity detection of prey echoes even in cluttered environments. Such findings reveal a sensory strategy in which animals actively create silence in a critical frequency range. It represents a conceptual advance in active sensing and auditory scene analysis, highlighting how evolution shapes sensory systems to extract reliable information under noisy natural conditions.

animal behavior and cognition↗

bioRxiv2025

Mothers respond to biological pup calls with heart rate changes in Japanese house bats, Pipistrellus abramus

Maternal care is essential for offspring survival in mammals, especially in colonial species where mothers must recognize their own young among many. In the Japanese house bat, Pipistrellus abramus, mothers identify their pups using acoustic cues, particularly isolation calls (ICs) produced by newborns. However, the physiological mechanisms underlying such maternal recognition remain largely unknown. Here, we investigated maternal emotional responses of mother bats to pup calls by measuring heart rate (HR) changes during controlled playback experiments. We recorded ICs from 2-day-old pups and echolocation calls (ECs) from 30-day-old pups, then presented these sounds to mothers after their pups had become independent. HR significantly increased in response to calls from the mothers own pups--both ICs and ECs--but not to calls from non-family pups. Among all stimuli, ECs from their own older pups evoked the largest HR increase, indicating strong physiological arousal and suggesting sustained maternal responsiveness despite developmental changes in call structure. In contrast, ECs from an unfamiliar adult also induced HR elevation, possibly reflecting general social arousal rather than maternal recognition. These findings demonstrate that P. abramus mothers exhibit selective physiological arousal to their own pups vocalizations, and that HR provides a sensitive physiological index of maternal motivation and recognition based on dynamic acoustic information.

animal behavior and cognition↗

bioRxiv2025

Flight trajectory modeling reveals species-specific obstacle avoidance policies in echolocating bats

Echolocating bats routinely navigate complex wild environments with remarkable agility, yet it remains unclear whether their flight trajectories reflect reproducible internal control strategies or are merely the result of improvised reactive behavior. To address this question, we recorded flight paths and pulse emissions of Rhinolophus nippon and Miniopterus fuliginosus as they navigated seven obstacle-rich arenas in complete darkness. Using a machine learning model--a variational recurrent neural network (VRNN)--we show that bat flight is governed by a consistent internal policy. Trained on only part of each trajectory, our model accurately predicted future flight paths across arenas and individuals, preserving key features such as turning direction, obstacle-avoidance arcs, and velocity profiles. The models ability to faithfully reproduce species-specific strategies despite differences in sonar and flight morphology supports the existence of structured internal control in bat navigation. Our approach reveals that bat flight, while appearing improvisational, is in fact guided by internal policies that can be directly inferred from trajectory data, without relying on hand-crafted assumptions. Furthermore, the data-driven model developed here enables a priori testing of flight-path reorganization by virtually imposing environmental changes and analysing the resulting predicted trajectories, providing a powerful tool for biomimetic robotic design and for forecasting ecological responses to landscape transformation.

ecology↗

bioRxiv2024

Self-organized acoustic behavior in bats arises from simple rules

Although self-organized behavior has been extensively studied in the movement of group-behaving animals, such as fish or birds, far less attention has been paid to vocal behavior in animal groups, especially in mammals. Here, by testing the vocal response of echolocating bats (Miniopterus fuliginosus) to the playback of jamming stimuli in the lab, we discovered a mathematical model that can well describe vocal frequency control by bats in response to jamming stimuli mimicking echolocation sounds emitted in a group of bats. We then extended the model to a group of flying bats and observed frequency-adjusting behavior by which the frequency differences for the group increased overall, similar to a previous observation on group-flying bats. Further, we showed the frequency-adjusting behavior led to less potential misdetections by echolocation in a group. Our findings suggest this frequency-adjusting behavior is a self-organized vocal behavior that mitigates conflicts within a group, one achieved via simple behavioral rules, as in other types of collective animal behavior.

animal behavior and cognition↗

bioRxiv2023

The distress context of social calls evokes a fear response in the bat Pipistrellus abramus

Bats primarily use sound information, including echolocation, for social communication. Bats under stressful conditions, for example when confronted by a predator, will emit aggressive social calls. The presentation of aggressive social calls, including distress calls (DCs), is known to increase heart rate (HR), but how this change in HR is related to the bats sound perception and how this evokes behaviors such as the fear response is unknown. Herein, we show that the perception of a distress context induces freezing behavior as a fear response in bats. We found that bats responded by freezing and displayed increased HRs when they were presented with a conspecific donor bat in a distress situation evoked by gentle poking with a cotton swab. In addition, when we presented two types of auditory oddball paradigms with different probabilities of DCs and echolocation calls (ECs), the bats HRs increased when DCs were presented as deviant or control stimuli within standard ECs but did not increase when DCs were presented as standard stimuli. These results suggest that the situational context created by the frequency of sound presentation, rather than simply a single sound feature, induces HR increases and freezing as fear responses in bats. Summary statementWe investigated the electrocardiograms of captive Pipistrellus abramus and found that their heart rate increased as a fear response when the bats heard sounds with a distress context.

animal behavior and cognition↗

bioRxiv2023

Laser-induced auditory perception: transtympanic laser irradiation of the cochlea from the outer ear evokes an auditory-related neural and behavioral response

Brain-machine interfaces are emerging devices that act as a medium for communication between the neural system and external software and hardware. Over the last decade, there has been a discussion on applying infrared laser stimulation to the brain-machine interfaces, including cochlear implants. Infrared lasers can selectively activate neural populations without introducing exogenous agents to tissues. This study presents the first demonstration that laser irradiation of the cochlea, a peripheral sensory organ, can elicit a clear behavioral auditory response. Mongolian gerbils (Meriones unguiculatus) were divided into two groups, each subjected to classical conditioning where a reward water delivery was predicted by either cochlear laser stimulation or sound stimulus. Laser-conditioned animals successfully learned licking behavior, with conditioned responses and behavioral properties comparable to auditory-conditioned animals. The laser-evoked response was significantly inhibited by auditory masking, and auditory-conditioned animals demonstrated stimulus generalization to laser stimulation. In a subsequent experiment, simultaneous presentation of auditory and laser stimulation induced nonlinear amplification in both auditory cortical and behavioral responses, suggesting that combining auditory and laser stimulation can enhance auditory perception beyond the effects of each stimulus alone. These findings indicate that infrared laser irradiation of the cochlea can potentially evoke and enhance auditory perception, making it a promising candidate for implementation in auditory prostheses.

neuroscience↗

bioRxiv2022

Safety margin evaluations for transtympanic laser stimulation of the cochlea from the outer ear in Mongolian gerbils (Meriones unguiculatus)

Infrared laser cochlear stimulation has been suggested as an alternative to traditional auditory prostheses. Previous research has mainly examined the short-term effects of laser stimulation, but to effectively use this technique, it is necessary to study whether prolonged laser exposure can safely and sustainably induce cochlear responses. This study assessed the effect of laser-induced cochlear damage using classically-conditioned Mongolian gerbils. The white noise was presented as a conditioned stimulus, and reward licking was recorded as a conditioned response. After training, the subjects cochlea was exposed to a continuous pulsed laser for 15 h. The licking rate drastically decreased after the exposure of 26.4 W/cm2, while it did not change after 6.6 W/cm2 or weaker. These findings showed, for the first time, that the safety margin of long-term, at least several hours, cochlear laser stimulation exists and will contribute to the safe and effective delimitation of laser parameters in future research.

bioengineering↗

bioRxiv2021

Feasibility evaluation of transtympanic laser stimulation of the cochlea from the outer ear

Infrared laser stimulation has been studied as an alternative approach to auditory prostheses. This study evaluated the feasibility of infrared laser stimulation of the cochlea from the outer ear bypassing the middle ear function. An optic fiber was inserted into the ear canal and a laser was used to irradiate the cochlea through the tympanic membrane in Mongolian gerbil. A pulsed infrared laser (10.1 mJ/cm2) and clicking sound (70 peak-to-peak equivalent sound pressure level) were presented to the animals. The amplitude of the laser-evoked cochlear response was systematically decreased following insertion of a filter between the tympanic membrane and cochlea; however, the auditory-evoked cochlear response did not decrease. The filter was removed and the laser-evoked response returned to around the original level. The amplitude ratio and the relative change in response amplitude before and during filter insertion significantly decreased as the absorbance of the infrared filter increased. These results indicate that laser irradiation could bypass the function of the middle ear and directly activate the cochlea. Therefore, an auditory prosthesis based on laser stimulation represents a possible noninvasive alternative to conventional auditory prostheses requiring surgical implants.

neuroscience↗

bioRxiv2021

Discriminating predation attempt outcomes during natural foraging using the post-buzz pause in Japanese large-footed bat Myotis macrodactylus

Bats emit a series of echolocation calls with an increasing repetition rate (the terminal buzz), when attempting to capture prey. This is often used as an acoustic indicator of prey-capture attempts. However, because it is directly linked to foraging efficiency, predation success is a more useful measure than predation attempts in ecological research. The characteristics of echolocation calls that consistently signify predation success across different situations have not been identified. Due to additional influencing factors, identification of these characteristics is particularly challenging for wild bats foraging in their natural environment compared to those in flight chambers. This study documented the natural foraging behavior of wild Japanese large-footed bat Myotis macrodactylus using synchronized acoustic and video recordings. From the video recordings, we could assign 137 attacks to three outcome categories: prey captured (51.8%), prey dropped (29.2%), and failed attempt (19%). Based on previous indications from laboratory studies that the length of the silent interval following the terminal buzz (post-buzz pause) might reflect the prey capture outcome, we compared post-buzz pause durations among categories of attack outcomes. The post-buzz pause was longest in the case of successful capture, suggesting that the length of the post-buzz pause is a useful acoustic indicator of predation success during natural foraging in M. macrodactylus. Our finding will advance the study of bat foraging behavior using acoustic data, including estimations of foraging efficiency and analyses of feeding habitat quality. Summary statementWe investigated the natural foraging behavior of wild Myotis macrodactylus and found that the length of the post-buzz pause is a useful acoustic indicator of predation success.

animal behavior and cognition↗

bioRxiv2017

Experience-dependent modulation of behavioral features in sensory navigation of nematodes and bats revealed by machine learning

Animal behavior is the final and integrated output of the brain activity. Thus, recording and analyzing behavior is critical to understand the underlying brain function. While recording animal behavior has become easier than ever with the development of compact and inexpensive devices, detailed behavioral data analysis requires sufficient previous knowledge and/or high content data such as video images of animal postures, which makes it difficult for most of the animal behavioral data to be efficiently analyzed to understand brain function. Here, we report a versatile method using a hybrid supervised/unsupervised machine learning approach to efficiently estimate behavioral states and to extract important behavioral features only from low-content animal trajectory data. As proof of principle experiments, we analyzed trajectory data of worms, fruit flies, rats, and bats in the laboratories, and penguins and flying seabirds in the wild, which were recorded with various methods and span a wide range of spatiotemporal scales--from mm to 1000 km in space and from sub-seconds to days in time. We estimated several states during behavior and comprehensively extracted characteristic features from a behavioral state and/or a specific experimental condition. Physiological and genetic experiments in worms revealed that the extracted behavioral features reflected specific neural or gene activities. Thus, our method provides a versatile and unbiased way to extract behavioral features from simple trajectory data to understand brain function.

neuroscience↗