This February, researchers at Virginia Tech made progress in their quest of making Small Flying Vehicles with Flapping Wings, Known as “Micro Air Vehicles”, by studying Movement of Fruit Bats’ Wings. While scientists are learning from bats in advancing robots, bats population has been ravaged by White Nose Syndrome which cave biologist feared would wipe out entire population. Two recent observations from Nature Conservancy and the Pennsylvania Game Commission seems to show the bat population is stabilizing, and scientists studying bats for robotics can relax a little on this good news.
The wings of bats—digits connected by a flexible and tough membrane—are a distinctive and remarkable feature. Evolved as a result of modification to the forelimbs of their ancestors, the wing membrane is an extension of the skin of the body, made up of external epidermis and an internal layer of dermis. The curvature of the wing in flight is controlled by the muscle in the dermis layer, enabling the agility and high maneuverability bats need to capture mid-flight prey. For a long time, the understanding of how bats control their wings to manipulate the air around them is limited, due to the complexity of both the measurements on their wing movements and related computer analysis.
Professor Kamal Viswanath and colleagues in Virginia Tech recently took the challenge to crack these complexities and published Straight-line Climbing Flight Aerodynamics of a Fruit Bat in the journal of Physics of Fluids. A fruit bat weighs about 30 grams, which is the weight of a CD, or an AA battery. Researchers were most surprised to find that bats manipulated their wing motion with correct timing to maximize the force generated by their wing, as the wing shape and size changing continuously during flapping. To materialize a bat-inspired flying robot, the next step for this group is to break down the complex movements into simpler ones that are realistic for robots, and to study different bat wing motions other than straight-line flight.
White Nose Syndrome (WNS) first appeared in U.S. in 2006 in a cave in New York. Caused by the fungus Pseudogymnoascus destructans, WNS has led to severe bat mortality across the eastern United States during the past five years. The devastation is considered to be the most precipitous wildlife decline in the past century in U.S. Although fruit bat in Virginia Tech’s study is not one of the 11 species which are documented to have WNS, all bats across North America are at imminent risk according to Bat Conservation International. Any news showing the decline of the bat population is slowing down or stabilizing is good news for everyone including robots scientists studying bats—they can relax that their source of inspiration will be around for more discoveries.
WNS kills bats by forcing them out of hibernation and burning through fat reserves. The fungus irritates their skin enough to wake the bats up, and then the bats have to burn fat to warm up for about one hour before they can move to groom themselves. Bats usually have enough fat to do this once or twice, but if the fungus wakes them up more, they have to leave to find food. Therefore, bats with WNS are usually starving or freezing to death in the winter.
In Pennsylvania, the Nature Conservancy’s Aitkin cave had 41 bats this year, which is two more than its count in 2012; in Hartman’s Cave had 11 bats while 10 were found in 2012. The heyday of these two caves held 4,000 and 200 bats, respectively. The Game Commission monitors a total of 10 caves and each of them had the number of bats no lesser than previous count. This seemingly stabilized bat population generated cautious optimism among scientists.
The biologists are not sure what made the difference between life and death in bats. It is possible the survivors have a genetic resistance or some physiological adaptation. They did notice fatter little brown bats have larger chances to survive the fungus infection, probably because the extra fat packed reduced their needs to fly out for food during winter.
Besides the latest “micro air vehicles,” bats have inspired many other robotic development such as sensing technology imitating their bio sonar mechanism. Whether the bat populations are indeed stabilizing may need further confirmation from other caves in larger areas, but this cautious optimism is welcomed after frustrating loss of bat population for years. More bats inspired robotics development may be expected as there are over 1,000 species in bat family. Scientists have a lot more to learn from bats to make better robots, and they can relax knowing a stabilizing bat population will sustain their creativity, as well as the health of the ecosystem relying on bats.
By Tina Zhang