How do bats avoid collisions in massive groups? Now we know!

Watch a video explaining how bats avoid collisions when in large groups. Image via BenMayr/ Pexels.

How do bats avoid collisions in massive groups?

It’s well known that bats use echolocation to navigate. That is, they emit a sound, and when this sound hits an object and bounces back, the bat hears the sound and knows how far away the object is. But bats live in colonies of thousands. When they emerge from their cave at dusk in a huge swarm, how do bats manage to navigate amid all the noise? A team of scientists from Tel Aviv University in Israel and the Max Planck Institute of Animal Behavior in Germany said on March 26, 2025, that they’ve solved this interesting dilemma.

The researchers tracked dozens of bats in Israel’s Hula Valley and discovered how these animals manage to perform perfect, incident-free flights. The team published its study in the peer-reviewed journal Proceedings of the National Academy of Sciences on March 31, 2025.

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Cocktail party nightmare

When bats leave their cave at dusk to stretch their wings and feed, they do so at almost the same time. This situation poses a challenge, as thousands of bats can live in a single cave.

Since all the individuals in the cave use the same navigation system — echolocation — a lot of noise is produced, and the sounds emitted by each individual mix with those of others. This hampers these animals’ ability to navigate. Scientists dubbed this massive and chaotic movement the cocktail party nightmare.

Despite all the turmoil, bats do not collide, even in colonies of hundreds of thousands of individuals leaving home through small openings. The study’s lead author, Aya Goldshtein at the Max Planck Institute of Animal Behavior, joked that bat collisions rarely happen:

You’re almost excited when you witness one.

Studying bats in their natural environment

For decades, scientists have tried to figure out how bats are able to pass through small openings so close together that they resemble a kind of flowing liquid.

Some researchers have observed small groups of bats in laboratories. They realized that each bat emitted a sound at a slightly different frequency than the others. Yet this isn’t the solution to the dilemma. This strategy works in a small group, where each bat has its own unique “voice,” but what happens when the colony is huge?

When there are so many individuals producing sounds at once, the voice they need to hear back becomes unrecognizable amid all the noise.

The study’s authors realized that to understand how they move in such large groups, they needed to observe them in their natural environment. So they analyzed the behavior of greater mouse-tailed bats in caves in Israel’s Hula Valley.

Study co-author Yossi Yovel commented:

No one had looked at this situation from the point of view of an individual bat during emergence. How can we understand a behavior if we don’t study it in action?

Bats in action

The team of scientists attached lightweight trackers to dozens of bats and monitored their locations every second for two years. Plus, the trackers had ultrasonic microphones to pick up what the bats were hearing.

Thanks to the combination of high-resolution tracking, ultrasonic recording and computer modeling, the researchers were able to put themselves in the bats’ shoes. They analyzed the bats in detail as they emerged from cave openings and flew across the landscape in search of food.

The scientists found that when bats emerged from the caves, the cacophony of sound blocked 94% of echolocations. Scientists call this loss of acoustic information “jamming.” They thought that, due to these interferences, the bats should collide. But surprisingly, this is not the case.

See bats emerging from a cave by the thousands.

Mystery solved

Just five seconds after leaving the cave, the echolocation jamming reduced significantly. This is because the first thing bats do upon leaving is move away from the colony center and disperse, but without losing their group structure.

This behavior was expected. Scientists assumed jamming would decrease as they moved quickly away from the cave. However, they also experienced another significant behavioral change. Upon leaving, the bats began to emit shorter, softer calls, but with a higher frequency.

The researchers wondered why they would shift their echolocation to a higher frequency. Wouldn’t this increase the jamming and, therefore, the risk of collision? To understand this phenomenon, the researchers had to analyze the situation from a bat’s perspective. Co-author Omer Mazar explained:

Imagine you’re a bat flying through a cluttered space. The most important object you need to know about is the bat directly in front of you. So you should echolocate in such a way that it gives you the most detailed information about only that bat. Sure, you might miss most of the available information because of jamming, but it doesn’t matter because you only need enough detail to avoid crashing into that bat.

In other words, bats adjust their echolocation to obtain more precise information about bats that are nearby, a tactic that ultimately allows them to navigate successfully and avoid collisions with each other.

Hundreds of bats flying out of a cave in Texas.

The importance of observation in nature

So a bat increases its distance from the core of the group and adjusts its echolocation to navigate safely in areas that are most densely populated.

The researchers emphasized that this finding was made possible by studying bats in their natural habitat. Although previous laboratory studies provided a solid foundation, the best way to confirm the behavior was by directly observing it in its real environment. According to Goldshtein:

Theoretical and lab studies of the past have allowed us to imagine the possibilities. But only by putting ourselves, as closely as possible, into the shoes of an animal will we ever be able to understand the challenges they face and what they do to solve them.

Bottom line: Bats navigate in groups of hundreds of thousands, and still don’t collide with each other. How do they do it? We finally know!

Source: Onboard recordings reveal how bats maneuver under severe acoustic interference

Via Max Planck Institute of Animal Behavior

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