Bats: efficient hunters

It is understandable why Count Dracula would change into the form of a bat. Bats are cooler than cool. A new study from the University of Maryland's bat-flight room helps explain why bats are such awesome creatures.

Unlike most humans and visually guided animals, bats rely on hearing, rather than vision, to fly and forage in darkness. They perform split-second aerial acrobatics, guided entirely by sound, to catch small insect prey. What is known is that bats "see" by sending out beams of sound into the environment and listening for the echoes that are returned from objects like bugs and trees. The bat uses these echoes to maneuver past the trees and to catch bugs. What has not been known, however, is if bats convert what they hear into what they do in the same way that humans convert vision into action. The bat's use of sound to capture insects takes place so quickly, it's not possible to observe its behavior in real time, or with standard equipment. Now, with a unique combination of high-speed infrared cameras and ultrasonic microphones, University of Maryland professor Cynthia Moss and doctoral student Kaushik Ghose have been able to see how exactly a bat moves in response to sound. They found that there is a strong and predictable connection between where a bat "looks" with its sonar beam - its acoustic gaze -- and how it flies. snip In their study, which appears in the February 8 issue of the Journal of Neuroscience, Moss and Ghose report that a bat directs its beams of sound ahead of its flight, like a flashlight. If it directs its beam to the left, about a tenth of a second later it turns to the left. By adjusting how sharply it follows its beam, the bat is able to adapt between "looking around" in a search mode and "homing in" in attack mode. "The findings add a significant piece of information to understanding how bats function," says Moss, professor of psychology and director of the university's Neuroscience and Cognitive Science graduate program. "Previous work on humans and other visually guided animals have suggested that we 'look' where we go. But it was not known if there was a similar relationship between the bat's acoustic gaze and its flight motion. "The discovery that the bat adjusts how sharply it turns in flight to follow its sonar beam is also remarkable. Such an adjustable linkage between vision and locomotion hasn't been found yet in sighted animals." snip Technology was the key to the team's insight into the bat's blazingly fast skills. Moss's is the only lab in the world with a bat flight-room equipped with high-speed infrared cameras. The cameras allowed the researchers to record the bat's behavior, then slow it to analyze the moves frame by frame, like a baseball coach studying a play. The microphone array, designed by Ghose for his doctoral thesis, revealed the beams of sound the bat put out as it flew and captured insects. Arranged around the flight room, the microphones recorded the directional patterns of sound emitted by the bat, which show where the bat is "looking." snip The slow motion video and audio showed that when the bat is flying along, just scanning its surroundings for prey, it makes more gentle turns toward the direction of its gaze -- like window-shopping in the mall. "When the bat is just searching," Ghose says, "it puts out about 10 calls per second. In this stage, the bat could be directing its sonar beam far off to the side, but it turns only leisurely toward that direction." But when the bat has located a bug with its sound beam, it begins to call more rapidly, putting out 100-150 calls a second. In this state, the bat follows its beam much more precisely, making abrupt turns to follow the direction of its acoustic gaze. "The bat switches to attack mode when it senses the bug," says Ghose."It uses rapid maneuvers to align its flight path and to intersect with the unfortunate insect."

Video of a bat in action on the site.