How Bats Master the Art of Drinking Water While in Flight

While humans often pride themselves on multitasking, bats may surpass us in this skill. Numerous bat species can fly and drink water simultaneously without ever crashing. New research now sheds light on the physics that enable these extraordinary feats of coordination.

Sunghwan Jung, a biophysicist at Cornell University and lead author of the study published recently in the Journal of the Royal Society Interface, explains that although the mechanics are complex, the broader goal is understanding how animals accomplish multiple tasks at once. "Animals lead busy lives just like humans, and being able to multitask increases their chances of survival," he said.

Among the world’s roughly 1,400 bat species, "skimming the wing" is the most common strategy for taking a drink, according to Rolf Müller, a mechanical engineer at Virginia Tech and co-author of the study.

This behavior likely evolved as a survival tactic to keep bats off the ground and away from predators. Although water is essential, these sources can be hazardous environments for animals, Jung added.

Some bats drink by directly licking water with their tongues while flying over a water body. Others, such as flying foxes, employ a different technique: wetting their fur and then licking the water off, a method known as “belly dipping.”

The recent study focused exclusively on bats that lick water during flight: Pratt’s leaf-nosed bats from Asia and the greater horseshoe bats found across Europe, Africa, and Asia. Both species are insectivorous.

Researchers placed the bats in a large flight enclosure and deprived them of water for six hours before introducing a water source. Multiple cameras positioned around the water captured stereoscopic images that tracked specific points on the bats’ bodies as they swooped down to drink. Combining data from these angles allowed creation of a three-dimensional representation of the bats’ movements through space.

Similar to how humans slow down when multitasking, the bats reduced their flight speed as they approached the water. This slowdown may result partly from the challenge of performing two tasks simultaneously and partly from the physical constraints of flying close to the water surface. To avoid their wings touching the water, bats decreased their wingbeat amplitude by about half and used a larger wing stroke angle to counteract the drag caused by their downward-tilted heads.

At the same time, bats exhibited precise tongue control to gently sip water. This accuracy is crucial to prevent water from splashing into their noses. Since many bat species echolocate by emitting high-frequency sounds through their nostrils, water entering the nasal passages could temporarily impair their navigation.

Ulmar Grafe, a bat specialist from Brunei Darussalam University not involved in the study, praised the work as "admirable." He noted that drinking while flying is an important but understudied behavior, largely because it is difficult to observe in laboratory settings. Though the study examined only a small number of bats from two species, it reveals the impressive skill and complexity of bat flight maneuvers.

Kenny Breuer, an engineer at Brown University who also did not participate in the research, called the study "a wonderful blend of detailed observations, careful characterization, and rigorous modeling of some of nature’s most remarkable fliers."

Jung and his team plan to extend their research to other multitasking behaviors in animals, such as swallows that skim water surfaces to drink and dragonflies performing acrobatic mating maneuvers while airborne.

Additionally, the findings could inform the design of bio-inspired flying robots, a project already underway by Jung and his collaborators.

"The approach taken by the researchers highlights the unexpected benefits of basic scientific investigation, enhancing our understanding of the environment and inspiring innovative engineering designs," Breuer concluded.