It started when a researcher noticed the bats he studies cock their heads to the side, just like his pet dog.
“It’s an adorable behavior, and I was curious about the purpose,” says neuroscientist Melville J. Wohlgemuth, a postdoctoral fellow in psychological and brain sciences at Johns Hopkins University. “I wanted to know when bats were doing this and why. It seemed to occur as bats were targeting prey, and that turns out to be the case.”
Turns out that bats’ fetching head waggles and ear wiggles synch with vocalizations, helping them locate the echoes and zero in on its dinner.
The finding demonstrates how movement can enhance signals used by senses like sight and hearing—not just in bats, but also in dogs, cats, and even in humans.
Bats use sonar-like echolocation—chirping and listening for the echo—to detect, track, and catch prey; that is well-documented. But the new study is the first to show how rapid, subtle repositioning of the head and ears factor into the hunt.
For the study, published in PLOS Biology, researchers took an innovative approach to studying the head waggles and ear movements of the big brown bat, a common species that in the wild hunts in flight, in both open and cluttered spaces.
First, the scientists trained bats to sit on a platform while tracking moving prey—mealworms attached to a fishing line. Once a bat was trained, the researchers attached reflective markers to the top of its head and both ears. The markers allowed the team to precisely measure the head and ear positions as bats tracked worms moving in various directions.
They found that head waggles, about one per second, occurred when the insect prey changed direction or moved erratically. The ear movements, a flattening and perking imperceptible to the naked eye, happened as the worm grew closer. Though very tiny, the ear twitches help the bat discern the precise direction the echoes come from, and track and capture the prey.
Most notably, these head and ear movements coordinated with the bat’s vocalizations, on a millisecond time scale, allowing the animal to pinpoint prey with considerably more accuracy.
Other studies on how animals and humans localize sound sources missed the importance of head waggles and ear movements, because laboratories typically observe the subject with a fixed head position. That’s not at all how bats or other animals operate in the real world, when their heads are free to move, not restrained, says coauthor Cynthia F. Moss, professor and neuroscientist.
She compared the bat’s head and ear movements to the behavior of other species that use active sensing—like the ear movements of a cat on alert, the head tilt of an owl, or the movements of a human’s eyes, all used to attend to important information.
“By studying these movements, we as humans can get insight into how movement helps animals sense their environment.”
Source: Johns Hopkins University