Weird & Wild

How Do Swarming Bats Avoid Crashing Into Each Other?

The mammals obey "traffic rules," using their built-in sonar to track each others' positions in the air, a new study says.

 

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A Daubenton's bat (Myotis daubentonii) swoops down to catch prey in Venray, the Netherlands.

 

Under the cover of darkness, swarms of fast-flying bats take to the skies in their nightly quest to find food. But how the mammals manage to maneuver without crashing into each other has been up in the air—until now. (See "6 Bat Myths Busted: Are They Really Blind?")

A new study finds that the nocturnal creatures follow a few simple "traffic rules" to avoid midair collisions: The bats first home in on the positions of other bats using their built-in sonar, then follow the flight path of a leader bat—or wingman, as it were.

In new experiments conducted in the United Kingdom, scientists observed the flight patterns of wild Daubenton's bats (Myotis daubentonii), an insectivore that weighs about as much as an AAA battery and ranges from the British Isles to Japan.

The critters fly low over lakes and other bodies of water to pick off midges, moths, and other insects, often plucking the bugs off the water's surface with their feet, like an eagle catching a fish.

To the naked eye, all this flitting may look chaotic. But after logging 70,000 pieces of data on flying bats, scientists found some "surprisingly rich" coordination behind the mammals' flights, says study co-author Marc Holderied, a behavioral biologist at the U.K.'s University of Bristol.

"Sometimes they avoided collision by one of them speeding up and the other slowing down," said Holderied, whose study appeared March 26 in the journal PLOS Computational Biology.

Dances in the Dark

Many bat species echolocate, or emit rapid, high-pitched noises and listen to echoes of those sound waves bouncing off potential prey. (Also see "When It Comes to Echolocation, Some Bats Just Wing It.")

After observing the bats' flight patterns, Holderied and his team took this data and put it into a model that simulated how the animals would have used their built-in sonar while flying. This model gave the team a glimpse into how the flying bats see the world around them.

In doing so, the team discovered the Daubenton's bat uses echolocation for another purpose: keeping track of other bats flying in its airspace.

These ultrasonic skills allow the bats to both avoid collisions and zero in on a leader bat to follow.

Once a bat choses a leader, it will then start mimicking the leader bat's turns and dives. And thanks to a reaction time of about 500 milliseconds—or about the time it takes you to blink—the two bats' movements appear almost perfectly synchronized. (See National Geographic's best bat pictures.)

Interestingly, some bat pairs appeared to trade the role of leader multiple times in a single flight. And because echolocation can provide information from 360 degrees around, the "lead" bat was not always the one flying in front.   

In other words, it is possible to lead from behind.

Why the Imitation Game?

The researchers admit that although they have developed a sophisticated model to explain how bats can zig and zag without going zonk, the question of why they do so remains unknown.

One possibility is that the second bat gains some advantage by following, perhaps picking off insects missed by the leader. It's also possible that tandem flights benefit both bats since eavesdropping on the other bat's hunting signals would allow both to scour more territory than either could alone. (See "Bats Make Calls to Jam Rivals' Sonar—First Time Ever Found.")

Watch a video of the long-eared bat hunting for food.

Finally, the authors note "it's not entirely impossible" that they had witnessed training flights between a mother and her young.

Overall, there's a lot more to discover about bat-flight maneuvers.

For instance, understanding how hundreds of thousands of bats fly simultaneously when streaming out of the mouth of a cave?

"That is the holy grail of swarm robotics," he says.  

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