Wing Hairs Turn Bats Into Aerial Aces

Whether flying upside down, changing direction in a split second, or hovering, bats are truly the acrobatic experts of the sky. Their airborne skills are so good that some engineers want to design planes that mimic bats instead of birds. Now, thanks to new research revealing how bat wings sense airflow, engineers are one step closer to doing so.

Scientists suspected that short hairs found on bat wings played a role in their flight. The hairs are unusual in several ways. They're very sparse, so they're unlikely used for warmth or waterproofing. Moreover, researchers cutting into the skin where the hair protrudes have found sensory receptors not usually associated with hair. All these features suggest that these hairs are somehow important for flight, but the hypothesis had never been directly tested.

Neuroscientist Susanne Sterbing-D'Angelo of the University of Maryland, College Park, and her colleagues studied the function of the wing hairs in big brown bats and short-tailed fruit bats. When the researchers blew a stream of air across the hairs, simulating flying, neurons in a sensory area of the brain were activated. When the airflow blew in the reverse direction across the wing—suggesting drafts that could upset flight—the neurons were even more active, leading the researchers to hypothesize that the sensors tell the bat when it's flying in unusual winds, so it can adjust its flying technique.

Watch out! A slow-motion video shot with an infrared camera shows a big brown bat maneuvering through an obstacle course in the dark.
Credit: Batlab, University of Maryland

The researchers next trained bats to fly through an obstacle course in the lab, lit only by dim red light to simulate the nighttime conditions during which bats are active. The big brown bats flew through a roomful of artificial trees, and short-tailed fruit bats were trained in a roomful of nets. When the team removed the wing hairs from the trained bats (using a hair-removal cream), the animals flew through the course less efficiently. In particular, the bats didn't turn as sharply or fly as fast; their average speed decreased from 3.5 to 2.5 meters per second. The study, published today in Proceedings of the National Academy of Sciences, concludes that the wing hairs translate airflow information for flight behavior.

"Solving this problem of how bats fly, and how we can learn from it, has been a really great collaboration between biologists and engineers," says Belinda Batten of Oregon State University in Corvallis. A mechanical engineer herself, Batten led the team that first used modeling to hint at the capabilities that bat hairs could have for airflow sensing and says the potential for engineers to learn from these bat sensors is huge. "If one were to develop artificial sensors that mimic these sensors on bats, we could improve the flight capabilities of planes," she says. Planes equipped with such sensors could better predict changes in airflow that could lead to sudden drops, a problem aviation technology has struggled to solve.

The next step, Batten says, is to make the leap from the biological sensors on bats to synthetic, engineered sensors. And that means more questions for the biologists—once bats have sensed a change in airflow, how do they use that information to stay stable? Sterbing-D'Angelo's team is currently looking for answers.