Navigating with Precision: How Kuhl's Pipistrelle Bats Use Acoustic Maps and Vision
Echolocating bats have long captivated scientists with their remarkable ability to navigate through complete darkness. Recent research has revealed that these bats possess an “acoustic cognitive map,” allowing them to identify their location after being displaced and travel long distances solely using echolocation. This study, conducted with Kuhl’s pipistrelle bats in Israel’s Hula Valley, uncovered that while bats rely heavily on echolocation for navigation, they also use vision to enhance their navigational abilities whenever possible. This groundbreaking discovery was recently published on October 31 in Science, challenging previous assumptions about the limitations of bats’ sensory capabilities and underscoring the complexity of their navigational strategies.
By tracking 76 Kuhl’s pipistrelle bats weighing only six grams and relocating them within a three-kilometer radius of their roosts, researchers observed the bats’ impressive navigational skills. Each bat was fitted with a lightweight reverse GPS tracking system known as ATLAS, enabling the collection of high-resolution, real-time data on their movements. Even when relying solely on echolocation, 95% of the bats returned to their roosts within minutes. The research further demonstrated that bats’ navigation improved when they incorporated vision, revealing a surprising degree of sensory adaptability. Through detailed observations and a 3D model of the valley, it was found that bats prefer flying near environmental features offering richer acoustic information—areas with higher “echoic entropy”—to orient themselves and make informed navigational decisions.
We had the privilege to interview Dr. Aya Goldshtein, a key researcher from the Max Planck Institute of Animal Behavior and the Cluster of Excellence Centre for the Advanced Study of Collective Behaviour at the University of Konstanz. In our conversation, Dr. Goldshtein provided insights into the study’s methodology, the significance of its findings, and how these discoveries deepen our understanding of bat navigation and cognitive mapping. Her perspective highlighted the remarkable navigational skills of bats and the sophisticated interplay of sensory information they use to traverse their environment.
Q: What is your academic journey that brought you to study bat navigation?
A: I completed my PhD in Zoology at Tel Aviv University, where I focused extensively on foraging and navigation in bats. Currently, I’m conducting my postdoctoral studies at the Max Planck Institute of Animal Behavior in Konstanz and the University of Konstanz, at the collective behavior department, led by Iain Couzin. This study is a collaborative effort between our institutes, and Yossi Yovel and Xing Chen from Tel Aviv University. Ran Nathan from the Hebrew University and Sivan Toledo from Tel Aviv University also contributed significantly by developing the ATLAS system we used. Tracking such small bats, each weighing about six grams, proved challenging. The collaborative support we received was invaluable in overcoming these obstacles.
Q: Could you explain how bats develop their ‘acoustic cognitive maps’ and how often they need to visit a location to build these mental maps of their environment?
A: Acoustic cognitive mapping differs fundamentally from visual mapping due to the distinct range of perception each relies on. While bats can visually perceive their environment up to roughly two kilometers away, their echolocation range is limited to tens of meters. For instance, detecting a mountain might only be possible from about 30 meters away—depending on the species and the frequencies of their echolocation calls. This contrast in perception ranges significantly impacts how bats construct their internal maps. Visual mapping allows an animal to identify distant landmarks without physically visiting each location, much like humans can locate a grocery store from afar. However, acoustic mapping demands that bats physically explore various areas to build a comprehensive environmental map. We assume that bats need to have previously visited a location to recognize it later using echolocation, but it is currently unclear how many visits in an area might suffice to gather the necessary information. This is why we specifically released bats within three kilometers of their home range. Within this familiar territory, bats can effectively orient themselves. Beyond their known range, they likely lack the acoustic cognitive mapping needed to navigate in unfamiliar areas because they haven’t physically visited and mapped those spaces through echolocation.
Q: What inspired you to investigate whether bats use a cognitive map for navigation, and what initial hypotheses did you have?
A: During my PhD research, I found that Egyptian fruit bats—significantly larger than Kuhl’s pipistrelles—rely primarily on vision to navigate, employing what we refer to as a visual cognitive map to find their way. This discovery led me to explore navigation under more constrained conditions, specifically using echolocation. The idea that an animal could traverse large distances using such a limited sensory modality intrigued me and motivated this study. As I delved deeper into this subject, I became increasingly interested in understanding how bats can successfully navigate in total darkness over potentially vast distances. There remains much to learn about bat navigation, especially on larger scales. Over time, technological advancements like smaller GPS devices have allowed researchers to track bats more closely and gather data on their navigation and foraging behaviors. This growing body of information continues to reveal extraordinary and sometimes unexpected aspects of bat navigation.
Q: In your study, Kuhl’s pipistrelle bats were shown to use vision along with echolocation. Was this an unexpected finding, and how might this discovery change our understanding of bat navigation?
A: The discovery that these bats use vision in addition to echolocation was indeed unexpected. Initially, we hypothesized that echolocation would be their primary means of navigation, given their relatively small eyes. Finding out that vision also plays a role in their navigation was a surprise. Echolocation involves the bats emitting sounds—mainly through their mouths, but some species use their noses—and interpreting the returning echoes to understand the distance, size, and texture of objects. This process helps them navigate and hunt, whether they are catching an insect or avoiding obstacles like trees and mountains. The frequency and pattern of their echolocation calls vary depending on their activities. When pursuing prey, bats emit calls more rapidly and at higher frequencies to achieve a detailed “image” of their moving target. When just flying around to avoid collisions, they call less frequently. Humans typically cannot hear these high-frequency calls, but researchers use special devices that lower the frequency into an audible range, enabling them to locate and monitor bat populations. The finding that bats can also rely on vision enhances our understanding of their adaptability and indicates that their navigational abilities are even more sophisticated than previously thought.
Q: Could you tell us more about the field experiments in the Hula Valley? How did relocating the bats within a three-kilometer radius help demonstrate their navigational abilities?
A: The Hula Valley, being primarily agricultural, provides an open landscape with distinct features such as crop fields, tree lines, a swamp, and a river. These varied landmarks likely serve as navigational aids for bats. In our study, we tracked bats after relocating them to points within a three-kilometer radius of their roosts, ensuring they stayed within their known home range. This controlled displacement allowed us to observe whether bats could navigate back to their roosts using the available environmental cues. The open fields and minimal obstructions in the valley facilitated accurate tracking of their flight paths using the ATLAS system. This setup helped illustrate that bats can effectively recognize specific landmarks and use these features to orient themselves and return home successfully within a few kilometers. By maintaining them within their known range, we established that bats rely on environmental cues to navigate and that these cues form part of their acoustic cognitive map.
Q: How does the ATLAS tracking system work, and what made it particularly suited for this study?
A: When using the ATLAS tracking system, we attached a tiny, lightweight radio transmitter to each bat. Receivers installed around the perimeter of the Hula Valley, often on elevated terrains such as mountaintops, detect these signals. Since Kuhl’s pipistrelle bats generally stay within the valley, the network of receivers can track their movements in real-time as long as they remain within range. The ATLAS device’s lightweight nature ensured that it didn’t hinder the bats’ natural flight behaviors, making it ideal for studying their navigation. Additionally, ATLAS provided precise positional information, similar in resolution to a GPS device, which was critical for analyzing the bats’ flight paths and navigation strategies in detail. The open landscape of the Hula Valley also contributed to the system’s effectiveness, as it minimized interference that could disrupt the tracking signals. This method, combined with the bats’ movement patterns and the distinctive features of the valley, allowed the researchers to validate whether bats use an acoustic cognitive map in their home environment.
Q: The research showed that bats tend to fly near environmental features with higher ‘echoic entropy.’ Could you explain what ‘echoic entropy’ is and how it influences bats’ navigational choices? What are some examples of “richer acoustic information”?
A: Echoic entropy is a metric that describes the complexity of the echoes bats receive when they use echolocation. We created a 3D model of the Hula Valley and used echolocation simulations to determine how bats perceive their surroundings. Simple or uniform environments, such as a flat crop field, produce relatively consistent echoes, leading to lower echoic entropy. In contrast, complex environments with diverse features—trees, mountains, or a swamp—produce more varied and intricate echoes, resulting in higher echoic entropy. Bats appear to prefer these areas with richer acoustic information because they provide more detailed cues about the environment. For instance, a distinctively large tree will reflect sound differently compared to a smaller tree or open field, offering a strong acoustic landmark. By navigating near features that create complex echoes, bats can better identify their location and find their way home. Essentially, variations in echo patterns from these different landmarks allow bats to construct and refine their acoustic cognitive map, aiding in navigation.
Q: How did you discover that bats also rely on vision for navigation?
A: To investigate the role of vision, we conducted experiments where we temporarily blindfolded some bats. By comparing the navigation performance of blindfolded bats to those that could see, we found that both groups were able to navigate, but bats that retained their vision did so much more quickly. This indicates that while bats can rely solely on echolocation to find their way, their ability to see significantly enhances their efficiency in navigation. However, it’s essential to remember that bats are nocturnal animals, often flying under conditions with little to no moonlight. During these times, they can’t rely solely on vision and must use echolocation and other senses to navigate. The discovery that bats use vision when available underscores their sensory adaptability and the complexity of their navigation strategies.
Q: When you observed bats’ flight patterns, how did you interpret the shift from meandering to directed flight? What does this suggest about their spatial awareness?
A: We observed that bats initially engaged in a meandering, or search, flight when they were uncertain of their location. During this phase, they flew near environmental features with higher echoic entropy to gather more detailed acoustic information and effectively scan their surroundings for distinctive cues. For example, a bat might start flying along a crop field but then turn and fly back toward a more complex area, such as a road or a patch of trees, to gain richer echoes. This behavior suggests that the bats were actively trying to locate themselves. Once they recognized their position, they shifted to a more direct flight path straight toward their destination. This transition from meandering to directed flight indicates that bats have a form of spatial awareness akin to an acoustic cognitive map. Using echolocation, they appear able to piece together their location in the valley and determine the direction and distance to their roost. Such understanding implies that they possess a mental representation of their environment, rather than relying solely on simple navigation strategies like route-following or heading straight towards a visible landmark. Once they identify their location using various acoustic cues, bats can navigate directly home, even in complete darkness, demonstrating the sophistication of their spatial awareness and the pivotal role their acoustic cognitive maps play in guiding their flight patterns.
Q: Does wind or rain affect or complicate bats’ flight and navigation?
A: Wind and rain can significantly impact bats’ flight and navigation decisions. If strong winds are present while the bats are active, they may alter their usual flight paths, perhaps seeking shelter along tree lines to avoid gusts. Rain’s effect on bats is less understood, particularly concerning echolocation. We know that some bat species delay leaving their roosts when it’s raining, possibly because rainfall interferes with their ability to navigate or hunt using echolocation. Extremely strong winds can also be dangerous or even deadly for bats. In some instances, unexpected gusts have been observed to harm bats significantly. While bats are adaptable, environmental conditions like wind and rain can complicate their flight and potentially influence both their navigation strategies and overall survival.
Q: How does echolocation for wayfinding differ from echolocation used for hunting?
A: Wayfinding and hunting echolocation serve very different purposes and use distinct patterns. When bats use echolocation for navigation, they emit louder and longer calls, at lower frequencies, with longer pauses between calls.
In contrast, when hunting, bats switch to a more intense pattern – they use weaker and shorter signals at higher frequencies, with very brief pauses between calls. The bat needs to rapidly process the echoes bouncing back from the insect to pinpoint its location. It’s a more challenging task since the prey is significantly smaller and mobile, and even with their sophisticated hunting echolocation, bats don’t always manage to catch their prey.
Q: What were some of the biggest challenges in conducting this research, especially in tracking such small and fast-moving animals?
A: The most significant challenge was finding the right bat colony that would work with our existing Atlas tracking system. The system itself was immobile – the product of years of development by the Atlas team – so we needed to locate bats that would operate within its range. This created very specific requirements: we needed a species that reliably flew at low altitudes, which proved difficult because we lack detailed behavioral information about many bat species. Our knowledge has historically been limited to larger species due to technological constraints. The breakthrough came when we finally identified a colony and their flight route that matched our system’s capabilities. Only after finding this perfect match between the colony location, species behavior, and our tracking system could we actually begin our research.
Q: Do these findings imply that bats might have similar spatial cognitive abilities to other animals known for long-distance navigation, like birds?
A: It’s difficult to make direct comparisons between bat and bird navigation abilities, particularly regarding long-distance travel. Our study focused on local navigation within the bats’ home range, while bats and birds that navigate across vast migration routes probably use different sensory systems and strategies.
This rapid navigation ability in bats likely stems from their foraging behavior. Since they spend entire nights flying and searching for insects, which are unpredictable and widely dispersed food sources, they develop extensive knowledge of their home range. The navigation capabilities really depend on each species’ specific ecological niche, as well as on the individuals’ experience.
Q: What implications do your findings have for understanding animal behavior and sensory integration more broadly?
A: Our findings open up fascinating questions about bat social behavior and sensory processing. A key area for future research is understanding how bats manage their echolocation in social situations, particularly during mass emergencies from their roosts. We need to investigate how they process multiple echoes simultaneously – how they can detect their own echoes while avoiding collisions with other bats in a crowded airspace. Another intriguing direction is exploring how bats use echolocation for social communication within their roosts. We want to understand if and how they interpret the echolocation calls of other bats, similar to how they process echoes during hunting. These questions about sensory processing and social interaction could significantly advance our understanding of how animals integrate multiple sensory inputs in complex social environments.
Q: How might this research impact conservation efforts or the study of other nocturnal or echolocating animals?
A: Our research highlights the critical importance of landscape stability for bat survival and navigation. Bats develop detailed mental maps of their environment, and any significant changes to the landscape – even removing a single tree – can disrupt their navigation abilities. This has important conservation implications beyond just protecting roosting sites. While we’ve long understood the importance of preserving trees as roosting habitats, we now need to consider how landscape alterations affect bats’ ability to navigate effectively. Animals use environmental features not just for shelter but as essential reference points for movement and orientation. This understanding should inform conservation strategies, emphasizing the need to preserve not only direct habitat but also the broader landscape features that animals rely on for navigation.
Q: What are the next steps in your research? Are there other sensory or cognitive mechanisms in bats that you plan to investigate further?
A: Our research is increasingly focused on understanding echolocation in greater detail, particularly by leveraging new technological capabilities. The emergence of AI has revolutionized our ability to analyze bat data, opening up entirely new research possibilities that were previously unattainable. These advanced analytical tools are allowing us to ask unprecedented questions about bat behavior and process data in ways that weren’t possible before. We’re excited to use these technologies to extract even more insights about bat behavior and sensory capabilities.
Q: Finally, what was the most surprising or rewarding aspect of this research for you and your team?
A: The most rewarding part was demonstrating that bats can use acoustic cognitive mapping for navigation. After working with echolocation for so long, successfully proving this capability was incredibly satisfying. The most surprising element was to realize that these bats also use vision for navigation.
Conclusion
The discovery that echolocating bats use acoustic cognitive maps to navigate long distances in complete darkness underscores the sophistication of their sensory capabilities. This research has revealed that bats not only rely heavily on echolocation to find their way but also use vision when available to enhance their navigational efficiency. These findings challenge previous assumptions about the limitations of bats’ sensory systems and shed light on the complex interplay between acoustic cues and cognitive mapping in these animals. Through tracking efforts using innovative technology like the ATLAS system and collaborations across multiple research institutes, scientists have gained valuable insights into how bats create mental maps of their environments and adjust their flight paths based on various environmental cues. This deeper understanding of bat navigation and spatial awareness not only advances our knowledge of these remarkable creatures but also has potential implications for ecology, conservation, and even the development of new technologies inspired by bats’ sonar capabilities.