'Zen' Bats Hit Their Target by Not Aiming at It

ScienceDaily (Feb. 5, 2010) — New research conducted at the University of Maryland's bat lab shows Egyptian fruit bats find a target by NOT aiming their guiding sonar directly at it. Instead, they alternately point the sound beam to either side of the target. The new findings by researchers from Maryland and the Weizmann Institute of Science in Israel suggest that this strategy optimizes the bats' ability to pinpoint the location of a target, but also makes it harder for them to detect a target in the first place.

"We think that this tradeoff between detecting a object and determining its location is fundamental to any process that involves tracking an object whether done by a bat, a dog or a human, and whether accomplished through hearing, smell or sight," said coauthor Cynthia Moss, a University of Maryland professor of psychology, who directs interdisciplinary bat echolocation research in the university's Auditory Neuroethology Lab, better known as the bat lab.

Moss, colleagues Nachum Ulanovsky and Yossi Yovel of the Weizmann Institute, and Ben Falk, a graduate student of Moss's in Maryland's Neuroscience and Cognitive Science Program, published their findings in the journal Science. Ulanovsky, the paper's corresponding author, was a Maryland postdoctoral student under Moss.

For this research, Ulanovsky and Yossi trained fruit bats to land on a spherical target while relying exclusively on their sonar. Trained in Israel, the bats were then brought to Maryland to be studied in Moss's specialized lab. High speed infrared cameras recorded the bats movement in flight while the shape and direction of their sonar beam patterns was measured with a sensitive arrangement of 20 microphones positioned around the large room. These bats emit paired clicking sounds and the researchers found that the sonar beam created by each click alternated to the left and right of a target. This alternating pattern effectively directed the inside edge, or maximum slope, of each sonar beam onto the target. As a result, any change in the relative position of the target to the bat reflected that large sonar edge back at the bat, delivering the largest possible change in echo intensity.

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