January 2007, Volume 5, Issue 1

Bats in the News

Wrinkles of Echolocation

The deep wrinkles and grooves that carve the faces of some bats apparently help them focus the biological sonar system that lets them navigate in the dark, scientists in China told the online LiveScience of Yahoo! News.

Bats maneuver and hunt by emitting echolocation calls and analyzing the echoes that bounce off objects in their paths. Most bats emit the calls from their mouths, but about 300 species use their noses. These bats typically have an upraised “noseleaf” around their nostrils, and often faces adorned with grooves and spikes.
LiveScience said scientists have long speculated that the noseleaves might help shape bat sonar, but had not been able to confirm it. Biologist-turned-physicist Rolf Müller of Shandong University in Jinan, China, and doctoral student Qiao Zhuang say they have demonstrated precisely how at least one bat species exploits its wrinkles.
The researchers used X-ray scans to generate three-dimensional computer models of the noseleaves of the rufous horseshoe bat of southern Asia, LiveScience said. Then they simulated how the bats’ ultrasound pulses interact with the noseleaves.
Computer simulations showed that horizontal furrows along the top of the noseleaves behaved as cavities that resonate strongly with certain frequencies of sound, causing different frequencies to focus in different ways. Müller told the LiveScience that 60-kilohertz sound gets spread vertically, while the 80-kilohertz frequency continues to be focused straight ahead.
The furrows help shape how the lower-frequency sounds “illuminate” the environment, while other frequencies are unchanged and can scan the world in different ways.
The complexity the noseleaves add to the bat ultrasound beams could help “in performing difficult sonar tasks like navigating in complex environments such as dense forests or doing several things at once, such as looking for prey and avoiding obstacles,” Müller speculated.
The goal of this research is to not only better understand how bat echolocation works, Müller told LiveScience, but to apply the principles to improving antenna technology for use in sonar, scanners and wireless communication.

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