Bats could help the development of AI robots

Rolf Müller –
X (twitter): @UBDVTLab
Instagram: @ubdvtcenter
Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia, 24061, United States

Popular version of 4aAB7 – Of bats and robots
Presented at the 186th ASA Meeting
Read the abstract at

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

Given the ongoing revolution in AI, it may appear that all humanity can do now is wait for AI-powered robots to take over the world. However, while stringing together eloquently worded sentences is certainly impressive, AI is still far from dealing with many of the complexities of the real world. Besides serving the sinister goal of world-domination, robots that have the intelligence to accomplish demanding missions in complex environments could transform humanity’s ability to deal with fundamental key challenges to its survival, e.g., production of food and regrowable materials as well as maintaining healthy ecosystems.

To accomplish the goal of having a robot operate autonomously in complex real-world environments, a variety of methods have been developed – typically with mixed results at best. At the basis of these methods are usually two related concepts: The creation of a model for the geometry of an environment and the use of deterministic templates to identify objects. However, both approaches have already proven to be limited in their applicability, reliability, as well as due to their often prohibitively high computational cost.

Bats navigating dense vegetation – such as in rainforests of Southeast Asia, where our fieldwork is being carried out – may provide a promising alternative to the current approaches: The animals sense their environments through a small number of brief echoes to ultrasonic pulses. The comparatively large wavelengths of these pulses (millimeter to centimeter) combined with the fact that the ears of the bats fall not too far above from these wavelengths on the size scale condemns bat biosonar to poor angular resolution. This prevents the animals from resolving densely packed scatterers such as leave in a foliage. Hence, the echoes that bats navigating under such conditions have to deal with inputs that can be classified as “clutter”, i.e., signals that consists of contributions from many unresolvable scatterers that must be treated as random due to lack of knowledge. The nature of the clutter echoes makes it unlikely that bats having to deal with complex environments rely heavily on three-dimensional models of their surroundings and deterministic templates.

Hence, bats must have evolved sensing paradigms to ensure that the clutter echoes contain the relevant sensory information and that this information can be extracted. Coupling between sensing and actuation could very well play a critical role in this. Hence, robotics might be of pivotal importance in replicating the skills of bats in sensing and navigating their environments. Similarly, the deep-learning revolution could bring a previously unavailable ability to extract complex patterns from data to bear on the problem of extracting insight from clutter echoes. Taken together, insights from these approaches could lead to novel acoustics-based paradigms for obtaining relevant sensory information on complex environment in a direct and highly parsimonious manner. These approaches could then enable autonomous robots that can learn to navigate new environments in a fast and highly efficient manner and transform the use of autonomous systems in outdoor tasks.

batsBiomimetic robots designed to reproduce the (a) biosonar sensing and (b) flapping-flight capabilities of bats. Design renderings by Zhengsheng Lu (a) and Adam Carmody (b).

As pilot demonstration for this approach, we present a twin pair of bioinspired robots, one to mimic the biosonar sensing abilities of bats and the other to mimic the flapping flight of the animals. The biosonar robot has been used successfully to identify locations and find passageways in complex, natural environments. To accomplish this, the biomimetic sonar has been integrated with deep-learning analysis of clutter echoes. The flapping-flight line of biomimetic robots has just started to reproduce some of the many degrees of freedom in the wing kinematics of bats. Ultimately, the two robots are to be integrated into a single system to investigate the coupling of biosonar sensing and flight.

The Evolution of Bat Robots: A Spooky Tale of Echo Location

As Halloween approaches, it’s the perfect time to dive into the mysterious world of bat robots in this Acoustics Today article, “The Evolution of Bat Robots.” The ability of bats to navigate their environment using ultrasound has fascinated scientists for decades, and the mystery of how they process this information has drawn researchers from various fields. It’s no wonder that engineers have been lured into this world, attempting to replicate the biosonar capabilities of bats through a variety of “bat robots.”

Despite decades of research, the intricacies of bat biosonar remain mostly uncharted. Continuous advancements in recording and data analytics technologies promise to unlock more insights into the world of bat robots. These insights will likely drive further evolution in the field. Researchers are on the cusp of developing more integrated systems that combine encoding and extraction of sensory information. These mechanical marvels, inspired by the eerie elegance of bats, may hold the key to autonomous drones capable of navigating the dark forests, just like their natural counterparts.

The Acoustics Today article weaves together a captivating story of technological evolution, highlighting the challenges, breakthroughs, and intriguing possibilities that lie ahead. If you’re curious about how bats’ extraordinary biosonar abilities are inspiring cutting-edge drones and robotic systems, read the full article for free at It’s a journey that promises to leave you in awe of both nature and human ingenuity. Happy Halloween!

AT Winter 2020 cover - bat robots

2pAB8 – Blind as a bat? Evidence suggests bats use vision to supplement echolocation in presence of ambient light

Kathryn A. McGowan –
Saint Mary’s College
Le Mans Hall, 149
Notre Dame, IN 46556

Presented Tuesday afternoon, November 6, 2018
176th ASA Meeting, Victoria, British Columbia

Bats use echolocation, or biological sonar, to make an auditory picture of their environment when foraging and avoiding obstacles in flight (1). To echolocate, bats emit a loud, high-pitched sound using their mouth or nose. The sound bounces off an object and returns to the bat as an echo, providing each individual with information about the object characteristics and location. While echolocation allows for the detection and discrimination of targets, the high-pitched frequency sounds that bats emit when echolocating provide a limited range of information (2). Despite being known for flying at night, some bats spend only a part of their time flying in complete darkness, suggesting that they may also rely on vision to supplement their echolocation in environments that have more light (2, 3). Previous studies have demonstrated that vision in bats influences flight behavior, which suggests bats may combine vision and echolocation to sense their environment (2). It is, therefore, accepted that bats are not blind, as the common phrase suggests, but little is known about how vision influences the way bats use echolocation.

Figure 1. Swarm of Brazilian free-tailed bats flying during daylight hours after emergence. Photo Credit – Dr. Laura Kloepper, 2018

The Brazilian free-tailed bat migrates annually from Mexico to form large maternal colonies in caves in the Southwestern United States (2). These bats forage for insects in flight and emerge from the cave in groups of thousands for nightly foraging. The bats return to the cave in the early hours of the morning, requiring them to navigate back to their complex cave environment across a vast, open landscape. This reentry occurs across periods of complete darkness as well as early morning hours when ambient light is present. This suggests that bats have the option of using both echolocation and visual cues to navigate their environment in hours of daylight. Our research addresses how bats change their echolocation calls from an open environment to the more complex cave edge environment, and how the presence of daylight may influence their level of echolocation when accomplishing this feat.

bat echolocation

Figure 2. Spectrogram image of a sequence of bat echolocation calls recorded at the cave environment.

Compared to the calls used over a vast landscape, bats at the cave edge used more complex calls that gathered more precise information about that environment. During hours of daylight, however, these calls collected less precise information than hours of darkness. As less information was gathered acoustically by bats during daylight hours, it is likely that bats are getting information from visual cues once daybreak occurs. This supplementing of vision for echolocation indicates that despite what the phrases say, bats are not blind.

Video 1. Bats emerging for foraging during early dusk.

  1. Moss, C. F., & Surlykke, A. 2010. Probing the natural scene by echolocation in bats. Frontiers in Behavioral Neuroscience 4: 33.
  2. Mistry, S. 1990. Characteristics of the visually guided escape response of the Mexican free-tailed bat Tadarida Brasiliensis Animal Behavior 39: 314-320.
  3. Davis, W.H., Barbour, R.W. 1965. The use of vision in flight by the bat Myotis sodalis. The American Midland Naturalist 74: 497–499.

1pAB4 – Size Matters To Engineers, But Not To Bats

Rolf Müller –
Bryan D. Todd

Popular version of paper 1pAB4, “Beamwidth in bat biosonar and man-made sonar”
Presented Monday, May 7, 2018, 1:30-3:50 PM, LAKESHORE B,
175th ASA Meeting, Minneapolis.

Bats and Navy engineers both use sonar systems. But do they worry about the same design features?

To find out, we have done an exhaustive review of both kinds of sonar systems, poring over the spec sheets of about two dozen engineered sonars for a variety of applications and using computer models to predict 151 functional characteristics of bat biosonar systems spanning eight different biological families. Crunching the numbers revealed profound differences between the way engineers approach sonar and the way bats do.

The most important finding from this analysis is related to a parameter called beamwidth. Beamwidth is a measure of the angle over which the emitted sonic power or receiver sensitivity is distributed. A small beamwidth implies a focused emission, where the sound energy is – ideally – concentrated with laser-like precision. But the ability to generate such a narrow beam is limited by the sonar system’s size: the larger the emitter is relative to the wavelength it uses, the finer the beam it can produce. Reviewing the design of man-made sonars indicates that beamwidth has clearly been the holy grail of sonar engineering — and in fact, the beamwidth of these systems hews closely to their theoretical minima.


Some of the random emission baffles made from crumpled aluminum foil that served as a reference for the scatter seen in the bat beam width data.

But when it comes to beamwidth, tiny bats are at a significant disadvantage: even the largest bat ears are barely ten times the size of the animals’ ultrasonic wavelength, while engineered systems can exceed their wavelengths by 100 or 1000 times. Remarkably, our analysis showed that bats seem to disregard beamwidth entirely. In our data set, the bats’ beamwidth scattered widely towards larger values; the scatter was even larger than that for random cone shapes we created from crumpled aluminum foil. Clearly, the bats’ sonar systems are not optimized for beamwidth. But we know that they are incredible capable when it comes to navigating complex environments — which begs the question: what criteria are influencing their design?

We don’t know yet. But the bats’ superior performance demonstrates every night that giant sonar arrays with narrow beamwidths aren’t the only and certainly not the most efficient path to success: smaller, leaner solutions exist. And those solutions will be necessary for compact modern systems like autonomous underwater or aerial vehicles. To make sonar-based autonomy in natural environments a reality, engineers should let go of their fixation on size and look at the bats.

4aAB4 – Analysis of bats’ gaze and flight control based on the estimation of their echolocated points with time-domain acoustic simulation

Taito Banda –
Miwa Sumiya –
Yuya Yamamoto –
Yasufumi Yamada –
Faculty of Life and Medical Sciences, Doshisha UniversityKyotanabe, Kyoto, Japan

Yoshiki Nagatani –
Department of Electronics, Kobe City College of Technology, Kobe, Japan.

Hiroshi Araki –
Advanced Technology R&D Center, Mitsubishi Electric Corporation, Amagaski, Japan

Kohta I. Kobayasi –
Shizuko Hiryu –
Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe, Kyoto, Japan

Popular version of paper 4aAB4 “Analysis of bats’ gaze and flight control based on the estimation of their echolocated points with time-domain acoustic simulation.”
Presented Friday morning, December 7, 2017, 8:45-9:00 AM, Salon F/G/H
174th ASA in New Orleans

Bats broadcast ultrasound and listen to the echoes to understand surrounding information. It is called echolocation. By analyzing those echoes, i.e., arrival time of echoes, bats can detect the position of objects, shape or texture [1-3]. Contrary to the way people use visual information, bats use the sound for sensing the world. How is the world different between the two by sensing? Because both senses are completely different, we cannot imagine how bats see the world.

To address this question, we simulated the echoes arriving at the bats during obstacle-avoiding flight based on the behavioral data so that we could investigate how the surrounding objects were described acoustically.

First, we arranged microphone arrays (24 microphones) and two high-speed cameras in an experimental flight chamber (Figure 1) [4]. The timing, positions and directions of emitted ultrasound as well as the flight paths were measured. A small telemetry-microphone was attached on the back of the bat so that the intensity of emitted ultrasound could be recorded accurately [5]. The bat was forced to follow a S-shaped flight pattern to avoid the obstacle acrylic boards.

Based on those behavioral data, we simulated propagation of sounds with the measured strength and direction emitted at the position of the bat in the experiment, and we could obtain echoes reaching both left and right ears from the obstacles. By using interaural time difference of echoes, we could acoustically identify the echolocated points in the space for all emissions (square plots in Fig.2). We also investigated how the bats show spatial and temporal changes in the echolocated points in the space as they became familiar with the space (top and bottom panels).

We analyzed changes in the echolocated points by using this acoustic simulation, corresponding to which part of objects the bats intended to gaze at. In a comparison between before and after the habituation in the same obstacle layout, there are differences in the wideness of echolocated points on the objects. By flying the same layout repeatedly, false detection of objects was reduced, and their echolocating fields became narrower.

It is natural for animals to pay their attention toward objects adequately and adapt both flight and sensing controls cooperatively as they became familiar with the space. These finding suggests that our approach in this paper, i.e., acoustic simulation based on behavioral experiment is one of effective ways to visualize how the object groups are acoustically structured and represented in the space for bats by echolocation during flight. We believe that it might serve a tip to the question; “What is it like to see as a bat?”

Figure 1 Diagram of bat flight experiment. Blue and red circles indicate microphones on the wall and the acrylic boards, respectively. Two high-speed video cameras are attached at the two corners of the room. Three acrylic boards are arranged to make bats follow S-shaped flight pattern to avoid the obstacles.

Figure 2 Comparison of echolocated points between before and after space habituation. The measured positions where the bat emitted the sound are shown with circle plots meanwhile the calculated echolocated points are shown with square plots. Color variation from blue to red for both circle and square plots corresponds to temporal sequence of the flight. Sizes of circle and square plots correspond to the strength of emissions and their echoes from the obstacles at the bat, respectively.

[1] Griffim D. R., Listning in the dark, Yle University, New Haven, CT, 1958

[2] Simmons J.A., Echolocation in bats: signal processing of echoes for target range, Science, vol. 171, pp.925-928., 1971

[3] Kick S. A., Target-Detection by the Echolocating Bat, Eptesicus fuscus, J Comp Physiol, A., vol. 145, pp.431-435, 1982

[4] Matsuta N, Hiryu S, Fujioka E, Yamada Y, Riquimaroux H, Watanabe Y., Adaptive beam-width control of echolocation sounds by CF-FM bats, Rhinolophus ferrumequinum nippon, during prey-capture flight, J Exp Biol., vol. 206, pp.1210-1218, 2013

[5] Hiryu S, Shiori Y, Hosokawa T, Riquimaroux H, Watanabe Y., On-board telemetry of emitted sounds from free-flying bats: compensation for velocity and distance stabilizes echo frequency and amplitude, J Comp Physiol A., vol. 194, pp.841-851, 2008