Big-eared bats are unusual among bats, said Inga Geipel, the study’s lead author and a fellow with the Smithsonian Tropical Research Institute. They specialize in hunting comparatively larger prey such as dragonflies and lizards. And they bring insects back to their babies for as long as five months after their pups are weaned
“I have been working with this species for over 12 years now and they surprise me over and over again,” Geipel said.
Geipel first observed the bat’s amazing echolocation in a 2013 study. For the latest paper, researchers tried to understand how they manage this feat.
“Previously it was thought to be a sensory impossibility to find silent and motionless insects resting on leaves just by using echolocation as the weaker prey echoes would be masked by the stronger echoes of the leaves,” Geipel said.
The little bats can hover like a hummingbird as they scan their environment. High-speed video revealed how the bats approach the target leaf from below and gradually ascend like a drone rising over a tree. They had no trouble finding the meal, plucking the tasty insect from the leaf and carrying it off to devour.
The high-frequency bat chirps strike the leaf’s surface at different angles. The pulses deflect off the leaf and bounce off the unwitting prey, reflecting back an echo to the bats that something besides the leaf is there. Scientists call this “specular reflection.”
“We found that the bat approached the insects in a stereotypical way, coming up from the ground,” he said. “And it uses the mirror effect. When you call against a flat surface, most of the echo bounces away from you. But if there is an insect there, it creates a reflector and you start to get an echo back. It’s an adaptive behavior to separate the background, which is conspicuous, from the prey.”