Insects hoping to outsmart their bat predators would do best to hide under a rock. New research shows that even in complex surroundings--where prey is closely interspersed with its environment--bats use a series of rapid calls to break through the clutter and find their quarry.
When hunting or navigating, bats send out high-frequency chirps that bounce back from nearby objects, revealing their size and location. Not all of these "echolocating" chirps are the same, however. A bat flying out in the open will emit loud chirps separated by relatively long pauses (100 milliseconds) as it waits for something interesting to bounce back. If that bounce comes from an insect, the bat will focus its calls in the bug's direction and accelerate its chirps as it closes in.
But what if the insect is near another object? Psychologist and bat expert Cynthia Moss of the University of Maryland, College Park, wondered if the overlapping echoes would confuse the bat. To find out, she and colleagues recorded the calls and flight patterns of big brown bats (Eptesicus fuscus) in a closed room, called the Batlab. In one set of trials, the bats took just a few seconds to find and capture a worm suspended by string from the ceiling. But when the researchers hung a plant 10 centimeters from the worm, the bats only went for the snack half of the time--taking an average of a minute and a half to do so, the team reports online today in PLoS Biology. The bats fared better when the worm and plant were separated by 20 centimeters or more.
Audio and video recordings revealed that the bats more often let out a rapid succession of chirps followed by a short pause when confronted with closely packed objects. Moss hypothesizes that these repetitive, strobelike snapshots "sharpen up the image" of a complicated setting, much like we might stare intently to pick out an object in a busy scene.
Strobing had been noticed in the field with other bat species, but this is the first time it has been measured in detail, says neuroscientist James Simmons of Brown University. He and Moss have separate plans to study the behavior further by putting bats through other types of obstacle courses.
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