How bats navigate rush hour without crashing into each other

Every evening, as the sun dips below the horizon, thousands of bats surge out of caves and take to the skies. For those who have watched it up close, the spectacle is unforgettable – dark wings blur together in motion that is so dense, it can seem fluid.

Yet amidst this chaos, one mystery remains: how do they all manage to avoid collisions? Despite emerging in massive numbers from tight spaces, bats almost never crash.

“The bats don’t run into each other,” noted Aya Goldshtein from the Max Planck Institute of Animal Behavior. “Even in colonies of hundreds of thousands of bats all flying out of a small opening.”

Goldshtein, along with colleagues Omer Mazar and Yossi Yovel, explored this question in a new study that was led by scientists from Tel Aviv University.

The mystery of mid-air traffic control

Bats rely heavily on echolocation to navigate. They emit high-frequency calls and interpret the returning echoes to “see” the world around them.

But when thousands of bats are calling at the same time, those signals should interfere with each other. This phenomenon, known as “jamming,” should make it nearly impossible to distinguish useful echoes from noise.

It’s like trying to have a conversation at a crowded party where everyone is shouting at once – a problem that researchers refer to as the “cocktail party nightmare.”

And yet, despite the chaos, accidents between bats are almost nonexistent. “You’re almost excited when you witness one,” said Goldshtein.

Past studies offered a few clues. In the lab, scientists noticed that bats flying in small groups shifted their call frequencies slightly. This seemed to help avoid jamming, but didn’t fully explain how large colonies manage to avoid mid-air collisions, night after night.

According to Yovel, the missing piece was a real-world perspective. “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?”

Tracking bats as they navigate

To address this, the team collected data directly from wild bats as they emerged from a cave in Israel’s Hula Valley.

Using a mix of high-resolution location tracking, ultrasonic recording, and computer modeling, the researchers recreated the experience of a single bat as it navigated the crowd.

Over the course of two years, they tagged multiple greater mouse-tailed bats with tiny trackers that recorded their position every second.

Some trackers included microphones to record echolocation calls and ambient sound from the bat’s perspective. All data collection took place on the same nights that the bats were released.

One challenge remained. The tagged bats were released just outside the cave, so the team lacked data from the exact moment the bats exited the cave – where crowding is at its peak.

To fill in this gap, Mazar developed a computer model that simulated the initial emergence. The simulation drew on the real tracking and audio data to map each bat’s path for two kilometers across the landscape.

“The simulation allows us to verify our assumptions of how bats solve this complex task during emergence,” said Mazar.

How bats beat the noise

What the team found was surprising. In the first seconds after exiting the cave, 94 percent of echolocation calls were jammed.

But by five seconds in, that number dropped significantly. The bats weren’t just spreading out – they were also adjusting how they echolocated.

First, they moved out of the densest part of the group, giving themselves more space while still staying within the broader colony. Second, they changed their calls to be shorter, softer, and at higher frequencies.

This shift in behavior raised another question. Wouldn’t increasing the number of calls just add to the noise? Not necessarily, said the team – especially when you look at it from the bat’s perspective.

“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. So you should echolocate in such a way that gives you the most detailed information about only that bat,” explained Mazar.

“Sure, you might miss most of the information available because of jamming, but it doesn’t matter because you only need enough detail to avoid crashing into that bat.”

In other words, bats aren’t trying to hear everything. They’re focused on gathering just enough information to make it safely past the bat that is right ahead of them.

Bats adapt to avoid crashes

The researchers believe the key to these findings was observing bats in their natural environment – not in the lab.

“Theoretical and lab studies of the past have allowed us to imagine the possibilities,” said Goldshtein. “But only by putting ourselves, as close 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.”

This study shows how bats overcome intense auditory clutter and avoid crashes with fine-tuned behavior, which they adapt in real-time.

It’s not about cutting through all the noise – it’s about focusing on just enough of the right noise to stay safe.

The full study was published in the journal Proceedings of the National Academy of Sciences.

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