image: Great roundleaf bat (Hipposideros armiger), with colors indicating the speed of the ear surface (left), angle between ear motion and ultrasound echo propagation (center), and magnitude of the resulting Doppler shift (right). view more
Credit: Image courtesy of Phat Nguyen and Thomas Tucker (Virginia Tech School of Visual Arts, Blacksburg, VA).
A study explores how the rapid ear motions of certain bat species enhance sensing and navigation. Doppler shifts are changes in the frequency of a signal caused by the relative motion of the source and the detector. Xiaoyan Yin and Rolf Müller tested a hypothesis that the ear motions of some bat species generate functionally relevant Doppler shifts in echolocation signals. In experimental measurements of ear motions in three bat species, the authors found that the pinna--the external portion of the ear--moved rapidly to create Doppler shifts of up to 383 Hz, well above the bats' perception threshold. The motion of the fastest parts of the pinna was parallel to the direction of echo propagation, suggesting an evolutionary adaptation to maximize Doppler shift. Fast pinna motions and large Doppler shifts coincided with echo reception. Experiments using a biomimetic model of the bat pinna revealed that Doppler-shifted signals entered the ear canal, and that these signals varied with direction such that they could provide information on the direction of the echo source. These bat species have been known to detect Doppler shifts from prey motions, but the use of self-generated Doppler shifts has not been previously reported and could lead to new principles for sensory systems, according to the authors.
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Article #19-01120: "Fast-moving bat ears create informative Doppler shifts," by Xiaoyan Yin and Rolf Müller.
MEDIA CONTACT: Rolf Müller, Virginia Tech, Blacksburg, VA; tel: 540-231-6005; e-mail: rolf.mueller@vt.edu
Journal
Proceedings of the National Academy of Sciences