Bat echolocation and wind turbines

After reading the article on the decimation of bat populations in North America, that was the subject of my previous entry, I wanted to learn more about these incredible flying mammals. There is actually a whole website called Bat Web dedicated to the understanding of bats where you can watch a video presented by John O. Whitaker at Indiana State University on just how amazing bats are.

Perhaps the most intriguing aspect of bats is their ability to echolocate while simultaneously hunting prey. To find out more about how the brains of bats process sounds, I read a press release from The American Physiological Society, which discussed a study that was conducted at The University of Wyoming. An area of the brain called the auditory cortex is responsible for receiving and processing auditory (sound) signals. Unlike some species of bats that use echolocation for orientation and location of potential prey, pallid bats use echolocation to determine their orientation but use passive listening to find prey. Therefore, these bats must somehow separate these auditory cues to make sense of their surroundings. By mapping the brains of these animals, Khaleel Razak and Zoltan Fuzessery have shown that the auditory cortex of these bats appears to be able to enhance the contrast between multiple incoming signals that may vary in spectrum, time, and space allowing them to segregate the various incoming stimuli. There is a neat website where you can listen to various bat sounds and see an animation of echolocation from the Oakland Museum of California.

Despite their ability to echolocate moving objects so well, bats seem to have another foe with which to contend to survive: wind turbines. Unlike the many bird deaths observed at wind turbines, according to a recent study, only about half of bats found dead near turbines died from direct contact with the blades. Instead, researchers Baerwald, D'Amours, Klug and Barclay found evidence of barotrauma (trauma caused by rapidly changing air pressures) in the lungs of 90% of bats near turbines. This means that the majority of bat deaths near turbines were associated with trauma caused by the rapid lowering of air pressure near the turbine blades. The researchers further suggest that the unique anatomy of the respiratory system of birds helps to protect them from barotrauma-induced injuries in comparison to mammals, although it does not protect them from direct contact with the blades.

Researchers Baerwald, Edworthy, Holder and Barclay went on to conduct an experiment published in the Journal of Wildlife Management to try to reduce bat fatalities at wind turbines. By simply adjusting the speed at which wind turbines begin to turn or changing the angle of the blades to reduce the speed, they were able to ensure that the turbine blades were "near motionless" in low-wind conditions. With this simple intervention, they were able to demonstrate a reduction in bat deaths by about 60%...finally some good news for bats! This intervention may help to reduce the number of birds that collide with the turbine blades in low-wind conditions as well.

Photo Credit: Brazilian Free-tailed Bat © Merlin D. Tuttle, Bat
Conservation International.