Witchcraft, black magic, vampires: Dark things come to mind when you think of bats. It all falls apart, though, when you watch how adorable they look waggling their heads.
Head waggling and ear wiggling is something that cats and dogs do as they zoom in on a target or just listen to you. That’s what Melville Wohlgemuth, a neuroscientist at Johns Hopkins, noticed in his pug. He then saw that the bats he studied, too, cocked their heads from side to side.
“I have a pug, and any time I would talk to him he would do this head-tilting behavior. When I saw it in my bats I thought, ‘What is this funny little thing that they do?’” Wohlgemuth said. “After more investigation I realized that of course, there’s a purpose to it.”
It turns out the bats cock their heads to the side when they are targeting prey. The movements of the head are synched with the bat’s vocalization and improves the precision with which they localize their target, according to the findings published Thursday in PLOS Biology.
“The main way any animal with two ears figures out where a sound is coming from is by looking at the difference in the way one sound hits the two ears,” Wohlgemuth said.
The sound of a car approaching from your right side, for example, is louder to your right ear and arrives at it a bit earlier than it hits the left ear. Though the tiny time difference is imperceptible, the brain can still calculate it to locate and track the car.
Moving the head (which moves the ears) would accentuate these acoustic cues that are used to determine where the source of a sound is, Wohlgemuth said.
Bats are experts in auditory localization, and so are great models for neuroscience research, Wohlgemuth said. To figure out where everything is in a cluttered environment, bats produce sounds, and calculate the whereabouts of objects based on what they hear in the reflecting echo. They also use this information to change their vocalization, their flight and movements of their head and ears.
Most research on bats has looked at the animals in laboratory settings in which the scientists try to keep the animals and their heads stationary. Wohlgemuth and his colleagues, Cynthia Moss and Ninad Kothari, decided to create a setting in which bats could move their heads like they would under natural conditions.
But since it is hard to track head movements in a flying bat, they trained the bats to keep still, and catch worms that researchers moved toward them by a computer-controlled hook.
“So instead of a bat flying to an insect, the insect flew to the bat,” Wohlgemuth said. This allowed researchers to measure the timing of head waggles and the respective location of insect prey to the bats’ ears.
The bats waggled their heads about once per second as they tracked the movement of the insect prey. The waggles also matched the bats’ vocalizations, showing that body movement plays a role in bats’ auditory localization.
These findings in bats could apply, to some extent, to cats, dogs and humans, Wohlgemuth said.
“Everybody has some impression of their pet doing these kind of things,” he said. “These behaviors are likely consistent across essentially any animal that uses two ears to hear.”