Study reveals how bats use echolocation and vision to navigate over long distances

A new study published in the journal Science reveals that Kuhl's pipistrelle bats can navigate over long distances using echolocation and vision. The research describes how these bats can identify their location even after being displaced or having moved. The study was conducted by a team of researchers from the Max Planck Institute of Animal Behavior, the Cluster of Excellence Center for the Advanced Study of Collective Behavior at the University of Konstanz in Germany, Tel Aviv University, and the Hebrew University of Jerusalem in Israel.

Scientists conducted experiments with 76 Kuhl's pipistrelle bats, tracking them near their roosts and relocating them within a three-kilometer radius. 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.

The research team aimed to isolate echolocation as a potential navigation tool. To achieve this, they first had to find the right bat species. They chose to study Kuhl's pipistrelle bats, which weigh six grams and are common in the Hula Valley in Israel. These bats are known for their ability to stitch together thousands of sound signatures into acoustic maps.

Remarkably, even with echolocation alone, 95 percent of the Kuhl's pipistrelle bats returned to their roosts within minutes, demonstrating their ability to conduct kilometer-scale navigation using only echolocation. The bats use environmental features with distinctive acoustic signals as reference points and landmarks. They can use acoustic information to distinguish between environmental features such as a tree and a road, and thus use them as acoustic landmarks.

During the localization phase after being displaced, Kuhl's pipistrelle bats perform a winding flight that, at a certain point, changes to directional flight towards their destination, suggesting they already know where they are. The model revealed that they tend to fly near environmental features with higher "echoic entropy," which are areas that provide richer acoustic information that can complement what they can see with their echolocation.

In addition to the field experiments, the team created a detailed map of the entire Hula Valley to understand what each bat experienced during flight and how they used acoustic information to navigate. The research shows that bats can use echolocation to perform map-based navigation over long distances, with a sound map aiding navigation over distances of up to 1.8 miles.

The study also found that when vision is available, Kuhl's pipistrelle bats improve their navigation performance by combining both senses. Aya Goldshtein, a researcher at the Max Planck Institute of Animal Behavior in Konstanz, Germany, said, "We were surprised to discover that these bats also use vision. 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," according to ScienceDaily.

Bats have long been known for their use of echolocation to avoid obstacles and orient themselves, using this technique to find food and their roosts. Echolocation is the ability of some animals to know their environment by emitting sounds and interpreting the echoes they generate. Many species of bats use echolocation to avoid obstacles like tree branches and to hunt small insects while flying through the dark.

However, navigation via echolocation wasn't obvious because echolocation is limited in range. Bats can use echolocation to sense objects that are at most a few dozen meters away. Echolocation is not omnidirectional; the cone of coverage bats get from echolocation is usually a maximum of 120 degrees. Despite these limitations, Kuhl's pipistrelle bats can navigate several kilometers using echolocation alone, as shown by experiments where nearly 100 bats were relocated three kilometers away from their roosts.

The bats' ability to create acoustic maps suggests they possess an acoustic mental map of their home range. They use these acoustic maps to successfully navigate several kilometers over their hunting grounds. Kuhl's pipistrelle bats fly near environmental features with more acoustic information and make navigation decisions. They use environmental agents with distinctive acoustic signals as reference points.

The study concludes that Kuhl's pipistrelle bats can navigate over several kilometers using echolocation alone. When they have vision available, they improve navigation performance by combining both senses. After being displaced, the bats first identify their new location and then fly home, using environmental features with distinctive acoustic cues as landmarks.

Echolocating bats face the challenge of recognizing their location and finding their way home from any random point within a three-kilometer radius in complete darkness, using only echolocation. The research team has shown that bats can use echolocation to know where they are and how to move over distances of several kilometers, demonstrating navigational capabilities even after being displaced. This study reveals that echolocation for bats is much more than just a short-range obstacle-avoidance and prey-targeting system.

Sources: Página/12, Ars Technica, ScienceDaily

This article was written in collaboration with generative AI company Alchemiq