Photo/IllutrationA miniature radio microphone is fixed on the back of a bentwinged bat for the experiment. The photo was taken on May 1. (Provided by Kazuma Hase)

KYOTO--Researchers here have finally figured out why swarms of bats don't collide with each other when flying in total darkness.

Although it was well known that bats have inbuilt sonar to guide them at night and in caves, how that mechanism worked was not fully understood.

It emerges that each bat is able to modulate self-generated acoustic signals to scan their environment without signal interference.

A team at Doshisha University published its findings in Communications Biology, a journal affiliated with the British scientific magazine Nature, on May 3 in a paper titled, “Bats enhance their call identities to solve the cocktail party problem.”

The cocktail party problem refers to acoustic communication that occurs among a large group of individuals in a complex auditory scene, such as a boisterous party with multiple sounds. In the case of humans, this might involve loud music and talking.

A similar situation can occur when multiple individuals of a species use active sensing emit signals to scan the surrounding environment.

Under such circumstances, bats need to extract biologically relevant sounds from other noise and process them to avoid obstacles or to capture food, for example, in a cave. This amounts to jamming out other noise.

Bats tend to form colonies numbering hundreds and thousands. Darkness is their call to fly out into the night and forage for insects.

But they never collide with each other.

During flight, each bat emits a distinctive frequency to scan obstacles and echolocate the distance between themselves and other objects. Until now, it was not understood why their signals do not entangle.

Kazuma Hase, a graduate student at the university, and other researchers fixed a miniature radio microphone on the backs of four captive bentwinged bats to capture acoustic waves.

They found that when a single bat flies, it emits a changeless frequency. When four bats fly simultaneously, each bat emits a different frequency.

The team said the secrets of bat behavior could be applied to the development of robots being controlled en masse at the same time.

“This innate skill could be a reference in finding ways to stop robots from colliding with each other,” said Shizuko Hiryu, a professor of animal physiology and behavior at the university.