Some humans like to think of themselves as good multitaskers, but bats may do it better. Many bat species have the ability to fly while simultaneously drinking water — but unlike people who try similar multitasking, such as driving while texting, the bats never crash. Now, new research reveals the physics behind this feat of coordination.
“The technical details of how bats do this are very complex, but what we’re ultimately trying to understand is how animals multitask,” said Sunghwan Jung, a biophysicist at Cornell University and an author of the study published Wednesday in the Journal of the Royal Society Interface. “Animals have very busy lives, like humans, and if they can do two tasks at the same time, they have a better chance at survival.”
Of the world’s approximately 1,400 bat species, “skim drinking on the wing” is the most prevalent strategy for taking a sip of water, said Rolf Müller, a mechanical engineer at Virginia Tech and an author of the study.
This behavior likely evolved to keep bats off the ground and away from predators. Although finding water is a necessity, sources of water can be dangerous places for animals, Dr. Jung said.
Some bats drink directly by lapping water with their tongues as they fly over a water source. Others, such as flying foxes, drink indirectly by wetting their fur and then licking it — a strategy known as “belly-dipping.”
The new study focused on the tongue-lappers only: Two Pratt’s roundleaf bats, which live around Asia, and four greater horseshoe bats common in Europe, Africa and Asia, both of which are insectivorous species.
In a laboratory enclosure large enough for the bats to fly around in, the researchers deprived the animals of water for six hours and then introduced a drinking source. They positioned several cameras at different angles near the water and used stereoscopic imaging to track specific points on the bats’ bodies as they swooped down to drink. They combined data for the different cameras to produce a 3-D rendering of the bats as they moved through the space.
Like humans who tend to slow down when multitasking, the researchers found that the bats reduced their flight speed as they approached the water. They suspect this may be partly a result of the challenge of performing two tasks simultaneously, as well as because of the physical constraints of flying so close to the water surface. To avoid touching the water with their wings, the bats lessened the scope of their wing stroke by about half. They also used a higher angle flapping motion to counterbalance the drag caused by their heads leaning down.
At the same time, the bats precisely controlled their tongues as they delicately scooped water into their mouths. Precision is key, Dr. Jung said, to keep a splash of water out of the bats’ noses. Bats navigate using echolocation, which entails emitting a high-frequency sound and then using the bounce-back of the sound waves to gather information about objects in the environment. Counterintuitively, though, some bat species emit echolocation calls through their nostrils rather than their mouths. So getting water up their noses would effectively cause them to go temporarily blind.
Ulmar Grafe, a biologist at Universiti Brunei Darussalam who specializes in bats and was not involved in the research, said the paper is “impressive.”
“Drinking on the wing is important to bats but has not received the necessary attention, because it is very hard to get bats to perform this behavior in the lab,” he said. While the study involved a small number of bats of two species, he said it “reveals the remarkable ability and complexity of bat flight maneuvers.”
Kenny Breuer, an engineer at Brown University who was not involved in the research, added that the study is “a wonderful combination of detailed observations, careful characterization and rigorous modeling of some of nature’s most impressive fliers.”
Dr. Jung and his colleagues plan to carry out further studies of other animals’ multitasking behaviors, from swallows that glide across the surface of water to drink, to dragonflies that perform aerobatic mating contortions mid-flight.
The findings that come out of such studies could also inform bio-inspired flying robots, Dr. Jung added — something he and his colleagues are already working on.
“The entire approach that the authors have taken highlights the unexpected benefits that we can find from this kind of basic scientific research for improving our understanding of the environment and inspiring new engineering designs,” Dr. Breuer said.
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