Bats use leaves as mirrors to detect prey

Aug. 1 (UPI) — Bats see by hearing. In a bat’s world, mirrors are surfaces that reflect sound waves, not light.

According to a new study, a leaf is one of the best mirrors in the natural world, and these tree-grown mirrors help bats detect acoustically camouflaged prey.

“For many years it was thought to be a sensory impossibility for bats to find silent, motionless prey resting on leaves by echolocation alone,” Inga Geipel, a postdoctoral fellow at the Smithsonian Tropical Research Institute, said in a news release.

Scientists used a biosonar device and high-speed cameras to investigate how bats use their echolocation to find motionless prey in total darkness.

As they fly, bats emit sound waves and listen for their reflections off surrounding objects. Using their unique ability to analyze these reflected sound waves and their shifting frequencies, bats can construct a 3D image of their surroundings.

But their echolocation abilities aren’t perfect — bigger objects and moving objects are easiest to detect. Small, motionless objects are more difficult to locate, especially when echoes are bouncing loudly off the leaves in a dense forest. Among trees rich with leaves, the sound waves bounced off the back of a tiny insect are easily drowned out.

Before scientists observed bats targeting small, motionless insects, they blasted test leaves with sound waves from 500 different positions, with and without insects, and recorded the echoes of five different frequencies that are picked up by bat ears.

Echoes reflected back at angles of 30 degrees and less were too loud. The insects remained acoustically camouflaged.

But at bigger, oblique angles, the leaf acts like a lake reflecting the surrounding treeline at dusk or dawn — the sun no longer directly overhead. Most of the sound waves are reflected off the leaf and away from where they came, allowing the waves bouncing back off the insect to be picked up by the bat.

Researchers predicted that their film footage would reveal bats approaching leaves from angles between 42 and 78 degrees. Sure enough, that’s what they saw.

The scientists shared their findings this week in the journal Current Biology.

“This study changes our understanding of the potential uses of echolocation,” Geipel said. “It has important implications for the study of predator-prey interactions and for the fields of sensory ecology and evolution.”





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