Echolocating bats use an acoustic cognitive map for navigation

Would you be able to instantly recognize your location and find your way home from any random point within a three-kilometer radius, in complete darkness, with only a flashlight to guide you? Echolocating bats face a similar challenge, with a local and directed beam of sound -- their echolocation -- to guide their way. Bats have long been known for their use of echolocation to avoid obstacles and orient themselves. However, the research team, led by Aya Goldshtein from Iain Couzin's group at 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, has now shown that bats can identify their location even after being displaced and use echolocation to perform map-based navigation over long distances.

Study with 6-gram light bats

To explore this, the team conducted experiments with Kuhl's pipistrelle (Pipistrellus kuhlii), a bat species weighing only 6 grams, in Israel's Hula Valley. Over several nights, the researchers tracked 76 bats near their roosts and relocated them to various points within a three-kilometer radius, but still within their home range. Each bat was tagged with an innovative lightweight reverse GPS tracking system called ATLAS, which provided high-resolution, real-time tracking.

Some bats were fitted solely with the ATLAS system, while others were additionally manipulated to assess how their vision, sense of smell, magnetic sense, and echolocation influenced their ability to navigate back to their roosts. Remarkably, even with echolocation alone, 95 percent of the bats returned to their roosts within minutes, demonstrating that bats can conduct kilometer-scale navigation using only this highly directional, and relatively local, mode of sensing. However, it was also shown that, when available, bats improve their navigation using vision. "We were surprised to discover that these bats also use vision," notes Aya Goldshtein. "That was not what we expected. It was incredible to see that, even with such small eyes, they can rely on vision under these conditions."

Modulation of each bat's flight

In addition to the field experiments, the team created a detailed map of the entire valley. "We wanted to visualize what each bat experienced during flight and understand how they used acoustic information to navigate," explains Xing Chen, from Yossi Yovel's lab at Tel Aviv University, who developed the valley's reconstruction.

The model revealed that bats tend to fly near environmental features with higher 'echoic entropy' -- areas that provide richer acoustic information. "During the localization phase, bats conduct a meandering flight that, at a certain point, changes to a directional flight toward their destination, suggesting they already know where they are," says Goldshtein. "Bats fly near environmental features with more acoustic information and make navigation decisions." Bats can use this acoustic information to distinguish between environmental features such as a tree and a road, and thus use them as acoustic landmarks.

Bats have an acoustic mental map

The study concludes that Kuhl's pipistrelles can navigate over several kilometers using echolocation alone. However, when vision is available, they enhance their navigation performance by combining both senses. After being displaced, these small bats first identify their new location and then fly home, using environmental features with distinctive acoustic cues as landmarks. This behavior suggests they possess an acoustic mental map of their home range.