"Certain bats can deform the shapes of their ears in a way that changes the animal's ultrasonic hearing pattern. Within just one tenth of a second, these bats are able to change their outer ear shapes from one extreme configuration to another," said Rolf Müller, associate professor of mechanical engineering at Virginia Tech.
Bats are flying mammals most well known for their abilities to navigate and pursue their prey in complete darkness. By emitting ultrasonic pulses and listing to the returning echoes, the animals are able to obtain detailed information on their surroundings. Horseshoe bats, in particular, can use their sonar systems to maneuver swiftly through dense vegetation and identify insect prey under difficult conditions.
Acting as biosonar receiving antennas, the ears of bats perform a critical function in bringing about these ultrasonic sensing capabilities.
Using a combination of methods that included high-speed stereo vision and high-resolution tomography, researchers from Virginia Tech and Shandong University have been able to reconstruct the three-dimensional geometries of the outer ears from live horseshoe bats as they deform in these short time intervals.
Their paper appears in Physical Review Letters. Müller explained the significance of their work, saying, "In about 100 milliseconds, this type of bat can alter his ear shape significantly in ways that would suit different acoustic sensing tasks." By comparison, "a human blink of an eye takes two to three times as long. As a result of these shape changes, the shape of the animals' spatial hearing sensitivity also undergoes a qualitative change."
"This photo shows a bat with the landmarks on the ear and a high-speed video camera pointed at it in the laboratory of Rolf Mueller, Virginia Tech associate professor of mechanical engineering.(Photo Credit: Virginia Tech)
Using computer analysis of the deforming shapes, the researchers found that the ultrasonic hearing spotlights associated with the different ear configurations could suit different hearing tasks performed by the animals. Hence, the ear deformation in horseshoe bats could be a substrate for adapting the spatial hearing of the animals on a very short time scale.
The research piggybacks earlier work led by Müller and reported in Bioinspiration and Biometrics. That study provided insights into the various shapes of bat ears among the different species, and illustrated how the differences could affect how their navigation systems worked.
This photo shows a sequence of deforming ears on the bat, taken in the laboratory of Rolf Mueller, Virginia Tech associate professor of mechanical engineering. (Photo Credit: Virginia Tech)