The bat's head and ear movements are similar to other species that use active sensing -- like the ear movements of a cat on alert, the head tilt of an owl, or the movements of a human's eyes, which are all used to attend to important information.
To do this, the researchers went out and caught a few big brown bats, brought them into the lab, and taught them how to sit on a platform while tracking moving prey with their head and ears. They didn't want the bat to fly to its prey, but rather watch it from a stationary position.
So they built a circular pulley system with tasty meal worms attached to fishing line. The scientists would then crank the pulley, turn the line and watch as the bats sent out sounds clicks to track the location of the rotating tasty morsels.
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To track the movements, they affixed pieces of reflective tape on several parts of the bats' ears and head, and then captured the whole scene on a 3-D motion-capture video camera.
"You can move the insect back and forth in front of the animal and train the bat to follow it," Wohlgemuth said. "What we didn't realize is how tightly coordinated the bats sonar vocalizations are with the movements of the head and the ears."
The researcher said the study may help unlock secrets to other animals' hearing mechanisms as well.
"Never before has anybody characterized the head waggles," Wohlgemuth said. "Plus the movements of the ears haven't been seen before. The tight temporal coordination is amazing."
James Simmons, professor of biology at Brown University and an expert in echolocation, said that although the behavior of moving the ears with the sonar sounds has been observed before, the Johns Hopkins research study provided some new insights.
"This PLoS paper provides actual data from behaving bats to assess how bats may be exploiting changes in the receiving organ (the external ear) to somehow make sonar perception better," Simmons said in an e-mail to Discovery News. "The question now is what dimensions of the bat's perceptions are being enhanced, and by how much."
A journal article detailing the team's experiments will be published Thursday in the journal PLOS Biology, and includes senior author Cynthia Moss, professor of neuroscience at Hopkins and Ninad B. Kothari, a Johns Hopkins graduate student.
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