Scientists solve the mystery of “cocktail party” of bat echolocation

Every night, bats appear in large quantities, creating what scientists call “cocktail party nightmare” separated by conflicting echoes.

No one knows how bats manage this serious sensory challenge. Now, scientists from Tel Aviv University and the Max Planck Institute for Animal Behavior (MPI-AB) have tracked thousands of bats to find out: When bats first come out of their habitat, they increase distance from the center of the group and safely adjust their echo volume in areas with the highest bat density. The study was published on March 31 in the Proceedings of the National Academy of Sciences.

Aya Goldshtein, Omer Mazar and Yossi Yovel spent many nights outside the Bat Cave. Even so, it was shocked to see thousands of bats erupting from a cave until late at night, sometimes at such a high density of liquids. But until recently, bat biologists were confused by what they didn’t see. “Bats don’t touch each other, even in thousands of bat colonies, all bats fly out of a small opening,” said Goldshtein of MPI-AB.

“Nightmare” cocktail party

Every night, when they are foraging from caves, the bats don’t fall deadly, which is a scientific mystery. Echo bats mostly sense their world through echoes: they make calls and listen to the echoes reflected, which in turn allows them to “see” what is around them. But if many bats echo immediately (for example, when the entire colony emerges from a few minutes of caves, the call from others should flood the important echo information needed by the bat. Scientists call this loss of acoustic information “interference” and they hope the bats collide as a result.

However, aerial accidents outside the cave are so rare, “You are almost excited when you witness an event,” Goldshtein said.

For decades, scientists have tried to figure out how bats solve this “cocktail nightmare”, where ambient chat shocks you at the sound you need to hear. For example, they examined how bats grouped echoes. In the lab, scientists observed that individual bats in the group were amusing at slightly different frequencies, which should theoretically reduce barriers. Is this the solution?

Research like this in the past was an important stepping stone, but because of missing key pieces, they did not provide compelling answers to the mystery of cocktail parties. “From the perspective of a single bat during the advent, no one has seen this. If we don’t study behavior in action, how can we understand behavior?”

Walk into the bat cave

Goldshtein and colleagues collected data from wild bats from dusk caves for the first time. They combined a combination of high-resolution tracking developed by Ran Nathan and Sivan Toledo, ultrasound recording and sensorimotor computer modeling – all of which allowed researchers to enter the sensory world of bats as animals squeezed out of caves and flew past the landscape.

The team, led by scientists from Tel Aviv University, studied the larger rat-tailed bats in the Hula Valley of Israel. Over two years, they marked dozens of bats with a lightweight tracker, recording their locations every second. Some of these tags also include ultrasonic microphones that record auditory scenes from the perspective of a single bat. Each year, data is collected on the same day as the bats are marked.

Warning: The marked bats are released outside the cave and enter emerging colonies, which means that when the density is highest, real data is missing on the cave opening. The team filled this gap with the computing model developed by Omer Mazar and simulations. The model incorporates data collected by the tracker and microphone to reproduce the complete sequence of behavior starting from the entrance of the cave and ends after the bat crosses the valley two kilometers. “The simulation allows us to verify assumptions about how bats solve this complex task during their emergence,” Mazar said.

Avoid the dilemma of sound

The pictures appearing are amazing. When leaving the cave, the bats experience a harsh call, with 94% of the echoes being blocked. However, within five seconds of leaving the cave, the bat greatly reduced the echolocation interference. They also made two important behavioral changes: First, they emanate from dense colony cores while maintaining the group structure. Second, they make shorter and weaker calls at higher frequencies.

Researchers suspect that bats will reduce clogging by quickly dispersing from the cave. But why do bats locate their echoes higher at a higher frequency? Will calling more calls increase interference problems and therefore collision risk? To understand the results, the author must approach the scene from the perspective of the bat.

“Imagine you’re a bat, walking through a messy space. The most important object you need to know is a bat directly in front. So, you should be in a way that only provides the most detailed information about that bat. Of course, you might miss most of the information available because of the squeeze, but you just need enough details to avoid getting into that bat.”

In other words, bats change the way they echo to get detailed information about their nearest neighbors, and the strategy ultimately helps them successfully manipulate and avoid collisions.

The authors emphasize that by studying bats in the natural environment while performing relevant tasks, this unexpected result of how bats solve the cocktail party dilemma is possible. “Past theoretical and laboratory research has allowed us to imagine these possibilities,” Goldshtein said. “But we can understand the challenges they face and what they do to solve them by putting ourselves in the shoes of animals as much as possible.”