From University of Washington, Conservation Magazine
The first clue that bats were dying due to a case of mistaken identity was that the dead were mostly tree-roosting species. Wind turbines are killing the tiny flying mammals in record numbers, but the cave dwelling varieties were largely unaffected. Dead bats have turned up at wind turbine facilities on multiple continents, with death totals ranging from tens to hundreds of thousands. Bats are fighting a war on two fronts: one against wind farms, the other against white nose syndrome.
The puzzling part is that bat collisions with tall man-made structures aren’t all that common; they’re mostly limited to wind farms. There must be something unique about wind turbines with their massive spinning blades of doom that actively attracts bats to their eventual demise. At least, that’s what a group of researchers led by Paul M. Cryan of the US Geological Survey’s Fort Collins Science Center, suspected.
Like any good ecological detective, Cryan began by putting together all the clues.
One, three quarters of bats killed by turbines were ones that roosted in trees, at least in North America and Europe.
Two, most fatalities at Northern Hemisphere sites occurred during the late summer and autumn, with a smaller peak in the spring.
Three, while multiple tree-dwelling species were affected by turbine-based mortality, what they had in common was certain behavioral traits. That suggested that bat behavior would play a key role in solving the mystery.
Four, fatalities were more likely when wind speeds were lower than 5-6 meters per second. Early research suggested that bats could be saved if the turbine blades were prevented from turning until winds grew faster than that speed. The problem is that there are financial incentives to keep the turbines spinning even in those lower speeds, despite the tremendous costs to bat populations.
Learn more here: http://conservationmagazine.org/2014/10/bats-get-confused-by-wind-turbines-pretending-to-be-trees/
Also, from the USGS
The study, led by U.S. Geological Survey scientist Paul Cryan, was the first to use video surveillance cameras to watch bats for several months flying at night near experimentally manipulated wind turbines and led to the discovery that tree-roosting bats, or “tree bats,” may approach and interact with wind turbines in consistent and predictable ways.
Bats are long-lived, slow-breeding mammals that serve as the main predators of night flying insects, such as moths and beetles. Insect-eating bats are estimated to save farmers billions of dollars each year in the United States by providing natural pest control. Historically, fatal collisions of bats and tall, human-made structures were rarely observed, but something changed with the construction of large, industrial wind turbines. It is now estimated that tens to hundreds of thousands of bats die each year after interacting with the moving blades of wind turbines. Most tree bats are found dead beneath turbines in late summer and autumn, yet reasons for this seasonal susceptibility remain a mystery – unknown behaviors of bats may play a role.
"If we can understand why bats approach wind turbines, we may be able to turn them away," said Paul Cryan, a USGS research scientist and the study’s lead author. "Advances in technology helped us overcome the difficulties of watching small bats flying in the dark around the 40-story heights of wind turbines. The new behaviors we saw are useful clues in the quest to know how bats perceive wind turbines and why they approach them."
The researchers used ‘thermal’ cameras that image heat instead of light, and they recorded surveillance imagery of bats for several months at three wind turbines in Indiana. The team also monitored the nighttime airspace around turbines with near-infrared security cameras, radar and machines that record the ultrasonic calls of bats, as well as developed computer code for automatically finding bats in the hundreds of hours of recorded video imagery. Over the period of the study, bats were seen on video near turbines more than 900 times.
Bats typically approached turbines one or more times rather than just flying past, and bats often flew very close to the turbine monopoles, nacelles (machinery boxes at top of monopoles) and sometimes approached stationary or slow-moving blades. At the same time, radar indicated that hundreds of night-migrating birds were flying above and around the turbines nightly, but not closely approaching like bats.
Learn more here: http://www.usgs.gov/newsroom/article.asp?ID=4016&from=rss&utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+UsgsNewsroom+%28Newsroom+-+National+Releases%29
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