Sep 142016

Bats enhance their hearing by waggling their heads, say scientists

New research shows that bats cock their heads from side to side – like tiny, flying puppies – to better track insects.

by Joseph Dussault, Christian Science Monitor Staff
September 11, 2016

To those who don’t already think bats are adorable, this may change your mind.

New research shows that bats waggle their heads from side to side – like tiny, flying puppies – when they’re listening. This behavior, according to a study published Thursday in the journal PLOS Biology, may help bats locate prey more easily while echolocating.

“The sound is going to be hitting the ears in different ways throughout that dynamic process, and it’s those differences the bats exploit,” study author Melville Wohlgemuth, a postdoctoral researcher at Johns Hopkins University, told Live Science.

Wohlgemuth, a behavioral neuroscientist specializing in echolocation, naturally spends a lot of time with bats. Over several acoustic studies, he began to notice a strange routine: When hunting, some bats would cock their heads left and right, squeaking during the breaks. Suddenly reminded of his dog, Wohlgemuth set out to understand the purpose of the odd behavior.

But first, he had to teach his subjects to be lazy. Big brown bats, or Eptesicus fuscus, are normally dynamic hunters. Able to reach speeds of up to 40 mph, these animals can be difficult to study in flight. So researchers trained a group of bats to sit on a platform and wait for food, which would be delivered via fishing wire. Using high speed cameras and reflective markers on each ear, Wohlgemuth and colleagues could later reconstruct the bats’ head movements.

In some trials, researchers would move the food in simple patterns. In others, they would deliver the food over complex paths and at changing speeds. When the prey moved more erratically or changed directions suddenly, the bats would waggle more frequently.

Wohlgemuth and colleagues conclude that bats waggle to enhance their sensory perception. Most true bats use sonar to hunt, which means they’re receiving constant auditory feedback from all directions. By changing the orientation of their ears, they can better localize those sounds.

“They have to be able to find that tiny little echo of the insect against all the other clutter echoes of the background,” Wohlgemuth told The Washington Post. “So bats have these very robust and very dramatic behaviors.”

It’s an unusually simple answer, but recent research suggests that bat sonar may be just that: simple. Last year, scientists at the University of Antwerp and the University of Bristol found that bat flight maneuvers were based on a simple left-right binary. When an object is close, the corresponding echo is louder. So when a bat receives a comparatively loud signal in its left ear, it will respond by turning right to avoid the object, and vice-versa.

The new finding, researchers say, draws new connections between physical movement and sensory processing in animals. Dogs, cats and even humans exhibit similar, though subtler, behaviors. The study also highlights parallels between echolocation and vision. Just as our eyes do, bats’ ears provide spatial perception through movement.

“You almost get a different snapshot of the sound coming in,” Wohlgemuth said. “Sort of like how you might move your eyes around to get better views of the world.”

Published 9-11-16 at the Christian Science Monitor website.