High-speed cameras reveal how bats land upside down

Bats, in order to roost upside down on cave ceilings or tree limbs, use their heavy wings to perform an acrobatic maneuver that allows them to change direction quickly. To determine how this is possible, a team of researchers from Brown University have utilized a special flight enclosure, high-speed cameras, and computer modeling to study the bats in motion.

"Bats land in a unique way," said Sharon Swartz, a biologist at Brown University who was a senior author of the new research along with Kenny Breuer from Brown’s School of Engineering in a press release. "They have to go from flying with their heads forward to executing an acrobatic maneuver that puts them head down and feet up. No other flying animal lands the same way as bats do."

How these bats were able to determine the necessary motion and forces to perform such maneuvers hadn’t been clear, however, according to Breuer.

"When they come in to land they’re not moving very fast, which makes it hard to generate the aerodynamic forces needed to reorient themselves," said Breuer. "So the question is, how do bats get themselves in position to land?"

In the study, Seba’s short-tailed bats, Carollia perspicillata (three individuals), and Lesser dog-faced fruit bats, Cynopterus brachyotis (two individuals), were used. The bats were encouraged to land repeatedly in a single location in view of three high-speed cameras by covering the ceiling and walls of a flight corridor with plastic sheets and heavy-duty paper, except for a small, square landing pad made out of white mesh. The cameras used were FASTCAM 1024 PCI cameras from Photron, which feature a 1024 x 1024 10-bit ADC (Bayer system color) CMOS image sensor with a 17 µm pixel size. The sensor can achieve frame rates up to 109,500 fps.

Through training, the bats regularly landed on the pad, but to elicit "failed landing" maneuvers, the team modified the landing experiment by removing the pads. When they did this, bats would attempt to grasp the missing landing pad and on failure would begin to fall, quickly reorient, and fly out of the test area. The cameras—which were equipped with 50 mm lenses—were placed orthogonally and were used to record wing and body kinematics of the bats. All videos were recorded at 1,000 fps, which allowed the team to acquire between 500 and 1,500 frames per maneuver, or approximately 125-175 frames per wing beat. The scene was lit using diffused white light and to increase the lighting and contrast, the team covered the walls across from each camera with heavy-duty white paper.

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