Japanese Horseshoe Bat Research Articles

Nasal Bone Variability in two Japanese Horseshoe Bats Revealed by 3-Dimensional Geometric Morphometrics

Nasal Bone Variability in two Japanese Horseshoe Bats Revealed by 3-Dimensional Geometric Morphometrics

Seasonal diets of two rhinolophid bats, Rhinolophus nippon and Rhinolophus cornutus, in the southern Japanese Alps

Abstract Knowledge of diets is important for understanding species ecology and the mechanism of coexistence of multiple closely related species. Two rhinolophid bats, the greater Japanese horseshoe bat (Rhinolophus nippon) and the little Japanese horseshoe bat (Rhinolophus cornutus), occur in Japan, but little is known about their diets and interspecific interactions regarding food resources. In this study, we examined the fecal contents of these two species in the Southern Japanese Alps by microscopic analysis over multiple seasons. R. cornutus, which have more skillful flight, consumed nonvolant insects (caterpillars and spiders), whereas R. nippon did not; this indicates that R. cornutus can glean prey better than R. nippon. The larger-bodied R. nippon more frequently consumed hard-bodied beetles, whereas the smaller-bodied R. cornutus more frequently consumed soft-bodied dipterans and neuropterans. Body size differences influenced flight ability and bite force, which resulted in food resource partitioning and enabled multispecies coexistence of these closely related bats. A R. nippon nursery colony consumed a wider variety of insects, such as beetles, moths, and dipterans, during the pregnancy and lactation periods; however, after lactation, they showed a beetle-dependent diet, and before hibernation they again consumed various food resources. A R. cornutus non-nursery colony frequently consumed dipterans and moths in spring; dipterans, moths, and neuropterans in autumn; and moths and neuropterans in winter. These seasonal changes in diet seemed to be related to food supply or reproductive status.

Horseshoe bats use not changes in echo delay but Doppler shift to perceive approaching objects

Echolocating bats use echo delay for target ranging and Doppler shift information for relative velocity recognition. However, how they perceive moving objects remains unclear. To investigate this question, we played back echolocation pulses in real-time as virtual echoes to Japanese horseshoe bats (Rhinolophus ferrumequinum nippon) on a perch in a flight room. Since echoes coming back from an approaching object are theoretically characterized by both changes in echo delay and the presence of Doppler shift, we reproduced an artificial approaching object by encoding these two acoustic parameters in the virtual echoes. As a result, only Doppler shift evoked bats flight reaction, showing that they use only Doppler shift and not change in echo delay to perceive approaching objects. Also, we played back only constant frequency (CF) component and confirmed that they use the CF component to detect Doppler shift. Furthermore, as a response to the Doppler shift in the perceived echo, bats increased the bandwidth of the terminal component of their pulse. Surprisingly, this response occurred in the very first pulse after Doppler shift, which indicates bats can adapt their echolocation pulse characteristics to changing situations within a pulse. [This work was supported by JSPS KAKENHI Grant Nos. 18H03786 and 16H06542.]

Echo reception in group flight by Japanese horseshoe bats, Rhinolophus ferrumequinum nippon.

The ability to detect behaviourally relevant sensory information is crucial for survival. Especially when active-sensing animals behave in proximity, mutual interferences may occur. The aim of this study was to examine how active-sensing animals deal with mutual interferences. Echolocation pulses and returning echoes were compared in spaces of various sizes (wide and narrow) in Rhinolophus ferrumequinum nippon flying alone or in a group of three bats. We found that in the narrow space, the group-flying bats increased the duration and bandwidth of the terminal frequency-modulated component of their vocalizations. By contrast, the frequency of the returning echoes did not differ in the presence of conspecifics. We found that their own echo frequencies were compensated within the narrow frequency ranges by Doppler shift compensation. By contrast, the estimated frequencies of the received pulses emitted by the other bats were much more broadly distributed than their echoes. Our results suggest that the bat auditory systems are sharply tuned to a narrow frequency to filter spectral interference from other bats.

Analysis of bats’ gaze and flight control based on the estimation of their echolocated points with time-domain acoustic simulation

Bats detect objects by echolocation. With those echoes, they can describe the shape of objects as well as position, and then approach or avoid them. To reveal which part of objects bats gaze at, we simulated the echoes that bats hear, and estimate the bats’ echolocated points by time-domain 2D-acoustic-simulation based on the behavioral data during obstacle-avoiding flight. First, we constructed a microphone array system in an experimental chamber and attached telemetry-microphones to Japanese horseshoe bats. With that measurement system, we obtained the timing, positions and directions of emitted pulses during obstacle-avoiding flight. Using these data, we simulated the echoes returning from the obstacles (acrylic boards) and investigated how the bats show spatial and temporal changes in the echolocated points of objects as they became familiar with the space. In a comparison between before and after the habituation in same obstacle layout, there are differences in the wideness of echolocated points on objects. By flying same layout repeatedly, their echolocating field become narrower. This study suggests the help of acoustic simulation to understand the way bats see the world. [This research was supported by Scientific Research on Innovative Areas of JSPS, and the JST PRESTO program.]

Obstacle avoidance navigation by echolocating bat: Compared relationships between acoustic guidance and flight control in unfamiliar space and familiar space

Echolocating bats can fly without colliding with obstacles by synchronizing acoustic guidance and flight control. To research how bats adapt echolocation as they became familiar with the spaces, we made CF-FM bats (Japanese horseshoe bat) exhibit S-sharp flight repeatedly in a chamber arranged acoustically transparent chains. We found (1) flight path was changed continuously to reduce its curvature as the bats repeated the flights, resulting that the maximum flight speed increased from 2.7 to 3.0 m/s in the 1st trial to 3.2 to 3.8 m/s in the 12th (last) trial for all three bats, (2) pulse emission was reduced by 45% (66/148 pulses) from the first to the last trial, (3) they shifted the pulse direction dynamically relative to their flight direction in the 1st flight whereas the pulse direction was shifted smoothly, the bats emitted more intense pulses toward the intended flight direction as they became familiar with the space. When acrylic boards were arranged, the bats could not pass through the obstacle course until they learned the space. These suggest echolocation is changed between unfamiliar and familiar space flight and the bats adapt their echolocation to feedforward-dominant control for perceiving more at distance for path planning when they have a spatial map.

How flying CF-FM echolocating bats adapt to acoustically jammed environments: Quantitative evaluation

Echolocating bats face the acoustical interferences from sounds of other conspecifics; they can fly without colliding each other and avoid surrounding obstacles. The purpose of this study was to reveal how CF-FM bats extract their own echoes in acoustically jammed environments. The Japanese horseshoe bats (Rhinolophus ferrumequinum nippon) were flown with conspecifics in the flight chamber. As the number of flying bats increased from one to seven, the duration of constant frequency (CF) components decreased, whereas the terminal frequency modulated (TFM) components were extended in both time and frequency ranges. In order to quantitatively evaluate behavioral responses under jamming conditions, a flying bat was exposed by artificially synthesized CF-FM pulses. As a result, the bats also changed the CF and TFM components as observed in the group flight experiment. This shows that the bats modify the characteristics of pulses to adapt to acoustical jamming and not to adapt to spatial jamming owing to other flying bats. These results suggest that TFM component was more important than CF component in extracting their own echoes during flight in acoustically jammed conditions. We will examine echolocation behavior when we manipulate CF components in context of jamming avoidance during Doppler-shift compensation.

Prey pursuit strategy of Japanese horseshoe bats during an in-flight target-selection task

The prey pursuit behavior of Japanese horseshoe bats (Rhinolophus ferrumequinum nippon) was investigated by tasking bats during flight with choosing between two tethered fluttering moths. Echolocation pulses were recorded using a telemetry microphone mounted on the bat combined with a 17-channel horizontal microphone array to measure pulse directions. Flight paths of the bat and moths were monitored using two high-speed video cameras. Acoustical measurements of returning echoes from fluttering moths were first collected using an ultrasonic loudspeaker, turning the head direction of the moth relative to the loudspeaker from 0° (front) to 180° (back) in the horizontal plane. The amount of acoustical glints caused by moth fluttering varied with the sound direction, reaching a maximum at 70°-100° in the horizontal plane. In the flight experiment, moths chosen by the bat fluttered within or moved across these angles relative to the bat's pulse direction, which would cause maximum dynamic changes in the frequency and amplitude of acoustical glints during flight. These results suggest that echoes with acoustical glints containing the strongest frequency and amplitude modulations appear to attract bats for prey selection.

Group B betacoronavirus in rhinolophid bats, Japan.

We report group B Betacoronavirus infection in little Japanese horseshoe bats in Iwate prefecture. We then used reverse-transcription PCR to look for the coronavirus RNA-dependent RNA polymerase gene in fecal samples collected from 27 little Japanese horseshoe bats and found eight were provisionally positive. We had a success in the nucleotide sequencing of six of the eight positive samples and compared them with those of authentic coronaviruses. We found that these six samples were positive in coronavirus infection, and they belonged to the group B Betacornavirus by phylogenetic analysis. Virus isolation using the Vero cell culture was unsuccessful. Pathogenic trait of these bat coronaviruses remained unexplored.

Qualitative and Quantitative Analyses of the Echolocation Strategies of Bats on the Basis of Mathematical Modelling and Laboratory Experiments

Prey pursuit by an echolocating bat was studied theoretically and experimentally. First, a mathematical model was proposed to describe the flight dynamics of a bat and a single prey. In this model, the flight angle of the bat was affected by angles related to the flight path of the single moving prey, that is, the angle from the bat to the prey and the flight angle of the prey. Numerical simulation showed that the success rate of prey capture was high, when the bat mainly used the angle to the prey to minimize the distance to the prey, and also used the flight angle of the prey to minimize the difference in flight directions of itself and the prey. Second, parameters in the model were estimated according to experimental data obtained from video recordings taken while a Japanese horseshoe bat (Rhinolphus derrumequinum nippon) pursued a moving moth (Goniocraspidum pryeri) in a flight chamber. One of the estimated parameter values, which represents the ratio in the use of the angles, was consistent with the optimal value of the numerical simulation. This agreement between the numerical simulation and parameter estimation suggests that a bat chooses an effective flight path for successful prey capture by using the angles. Finally, the mathematical model was extended to include a bat and prey. Parameter estimation of the extended model based on laboratory experiments revealed the existence of bat’s dynamical attention towards prey, that is, simultaneous pursuit of prey and selective pursuit of respective prey. Thus, our mathematical model contributes not only to quantitative analysis of effective foraging, but also to qualitative evaluation of a bat’s dynamical flight strategy during multiple prey pursuit.

Prey pursuit strategy of Japanese horseshoe bats, Rhinolophus ferrumequinum Nippon, during target selection task

We investigated prey pursuit behavior of Japanese horseshoe bats, while they were tasked to make a choice between two tethered fluttering moths during flight. Echolocation pulses were recorded by a telemetry microphone mounted on the bat, combined with a 17-ch horizontal microphone array to measure pulse directions. Flight paths of the bat and moths were monitored by using two high-speed video cameras. Acoustical measurements of CF echoes from fluttering moths (67 kHz : CF2 frequency) was conducted using an ultrasonic loudspeaker, turning the head direction of the moth to the loudspeaker from 0° to 180° in the horizontal plane. Amount of acoustical glints caused by moth fluttering varied with the sound direction, showing the maximum between 70° and 100°. In the flight experiment, moths chosen by the bat fluttered within or moved across these angles to the bat’s pulse direction, which would cause dynamic changes in frequency and amplitude of acoustical glints during flight. This result suggests that dynamic changes in acoustical glints appear to attract the bats for prey selection. Furthermore, mathematical modeling implied that the bats possibly took the optimum flight path for capturing a target, which the bat selected based on the acoustical cues in the echoes.

Echolocation behavior of the Japanese horseshoe bat in pursuit of fluttering prey

Echolocation sounds of Rhinolophus ferrumequinum nippon as they approached a fluttering moth (Goniocraspidum pryeri) were investigated using an on-board telemetry microphone (Telemike). In 40% of the successful moth-capture flights, the moth exhibited distinctive evasive flight behavior, but the bat pursued the moth by following its flight path. When the distance to the moth was approximately 3-4 m, the bats increased the duration of the pulses to 65-95 ms, which is 2-3 times longer than those during landing flight (30-40 ms). The mean of 5.8 long pulses were emitted before the final buzz phase of moth capture, without strengthening the sound pressure level. The mean duration of long pulses (79.9 ± 7.9 ms) corresponded to three times the fluttering period of G. pryeri (26.5 × 3 = 79.5 ms). These findings indicate that the bats adjust the pulse duration to increase the number of temporal repetitions of fluttering information rather than to produce more intense sonar sounds to receive fine insect echoes. The bats exhibited Doppler-shift compensation for echoes returning from large static objects ahead, but not for echoes from target moths, even though the bats were focused on capturing the moths. Furthermore, the echoes of the Telemike recordings from target moths showed spectral glints of approximately 1-1.5 kHz caused by the fluttering of the moths but not amplitude glints because of the highly acoustical attenuation of ultrasound in the air, suggesting that spectral information may be more robust than amplitude information in echoes during moth capturing flight.

Paradoxical reference frequency shifts during paired flights in Japanese horseshoe bats evaluated with a Telemike.

In order to examine vocal behaviors for the echolocating bats to improve extraction of jammed echolocation signals, group flight experiments were conducted where two Japanese horseshoe bats were flown simultaneously in a flight chamber. Horseshoe bats are known to conduct Doppler-shift compensation, keeping their echo CF2 frequency constant to which their auditory system is sharply tuned. It was hypothesized that bats shifted their reference frequencies apart to avoid overlapping the reference frequencies. Echolocation sounds during sequential flights were recorded with an onboard wireless microphone, Telemike. Reference frequencies were investigated by measuring Doppler-shift compensated CF2 frequencies of the bats’ own echoes. Recorded data show that the bats kept their echo CF2 frequency constant with a standard deviation (SD) of 50–80 Hz, indicating that they exhibited Doppler-shift compensation with the same accuracy as that used for flying alone (SD = 83.2 Hz). However, the bats did not shift their reference frequency toward increasing the frequency difference even when the initial difference in the reference frequencies between individuals was less than 100 Hz. Rather, the bats tended to make their reference frequencies closer during group flight compared to those for single flights. These findings suggest that multiple bats may squeeze their echo CF2 frequencies into a narrow frequency range. In addition, horseshoe bats may adapt to acoustic interference without expanding the frequency difference between individuals. [Work supported by ONR grant.]

Echolocation-like pulse emission for communication by Japanese horseshoe bats, Rhinolophus ferrumequinum nippon

It has been reported that the bats communicate with conspecifics by various types of vocalizations, which are different from echolocation pulses. However, we have found pulses used for communication, which were emitted when a bat walked to another individual, appeared to be very similar to those for echolocation. Data have shown two evidences. First, the bats never approached another one without emitting pulses. Second, the bats emitted echolocation-like pulses whose CF2 frequency sequentially changed during the approaching behavior. Such pulses were never emitted by an isolated bat. The changes in CF2 frequency were clearly different from Doppler-shift compensation. If this frequency shift was caused by Doppler-shift compensation, the bat should be moving as fast as 1-5 m/s in the cage. Thus, we suggest that these CF2 frequency shifts may play an important role for communication during the approaching behavior to a conspecific animal. [The research supported by a grant to RCAST at Doshisha Univ. from MEXT and by the Innovative Cluster Creation Project promoted by MEXT.]

Distribution of oxytocin and vasopressin neurons in the diencephalon of the Japanese horseshoe bat, Rhinolophus ferrumequinum. An immunohistochemical study.

The distribution of oxytocin (OXT) and vasopressin (VP) neurons in the diencephalon of the hibernating Japanese horseshoe bat, Rhinolophus ferrumequinum, was immunohistochemically investigated by the avidin-biotin complex method. Magnocellular OXT and VP neurons were localized mainly in the paraventricular nucleus and the supraoptic nucleus. In addition to these main nuclei, both kinds of magnocellular neurons were also found in the periventricular nucleus, perifornical area and lateral hypothalamic area. Extensively distributed parvocellular neurons containing only VP were observed in the rostral and middle portions of the suprachiasmatic nucleus. The size of OXT and VP magnocellular neurons was almost equal in the paraventricular and ventromedial supraoptic nuclei, whereas VP neurons were significantly larger than OXT neurons in the dorsolateral supraoptic nucleus. The OXT and VP cells in the ventral supraoptic nucleus showed a distinctive elliptical shape. Both OXT and VP fibers were distributed in the lateral habenular nucleus, stria medullaris thalami, lateral preoptic area, stria terminalis, and medial and supracapsular part of the bed nucleus of the stria terminalis. Moreover, OXT fibers were found in the substantia nigra, and VP fibers were noted in the nucleus reunions and the paraventricular nucleus of the thalamus.

Echolocation sounds and hearing of the greater Japanese horseshoe bat (Rhinolophus ferrumequinum nippon)

The relationship between the orientation sounds and hearing sensitivity in the greater Japanese horseshoe bat,Rhinolophus ferrumequinum nippon was studied.