On moonless nights in a tropical forest, bats slice through the inky darkness, snatching up insects resting silently on leaves–a seemingly impossible feat. New experiments at the Smithsonian Tropical Research Institute (STRI) show that by changing their approach angle, the echolocating leaf-nosed bats can use this sixth sense to find acoustically camouflaged prey. These new findings, published in Current Biology, have exciting implications for the evolution of predator-prey interactions.

“For many years it was thought to be a sensory impossibility for bats to find silent, motionless prey resting on leaves by echolocation alone,” said Inga Geipel, Tupper Postdoctoral Fellow at STRI. Geipel’s team discovered how the bats achieve the impossible. By combining evidence from experiments using a biosonar device to create and measure artificial signals, with evidence from high-speed video observations of bats as they approach prey, the importance of the approach angle was revealed.

Bats have a superpower humans do not share: they flood an area with sound waves and then use information from the returning echoes to navigate through the environment. Leaves reflect echolocation signals strongly, masking the weaker echoes from resting insects. So in the thick foliage of a tropical forest, echoes from the leaves may act as a natural cloaking mechanism for the insects, known as acoustic camouflage.

To understand how bats overcome acoustic camouflage and seize their prey, the researchers aimed sound waves at a leaf with and without an insect from more than 500 positions in order to create a full, three-dimensional representation of the echoes. At each position, they calculated the intensity of the echoes for five different frequencies of sound that represent the frequencies of a bat’s call.[…]

Source: Bats use leaves as mirrors to find prey in the dark – ScienceBlog.com