Certain types of bats may be losing their lives after approaching wind turbines they've mistaken for trees, according to a new study conducted by researchers from the United States Geological Survey.

Findings from the work, published in the Proceedings of the National Academy of Sciences, were based on data collected by video surveillance cameras utilized to monitor bats for several months, while they flew at at night near experimentally-manipulated wind turbines.

The observations revealed that tree-roosting bats, or "tree bats," seemed to approach and interact with wind turbines in consistent and predictable ways.

"If we can understand why bats approach wind turbines, we may be able to turn them away," Paul Cryan, a USGS research scientist and the study's lead author, said in a news release. "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."

According to the USGS, bats are long-lived, slow-breeding mammals that serve as the main predators of night flying insects like moths and beetles.

In fact, insect-eating bats are estimated to save U.S. farmers billions of dollars yearly by providing natural pest control.

Fatal collisions between bats and tall, human-made structures have historically been rarely observed, but the rate of those fatal encounters rose dramatically with the installation of large, industrial wind turbines throughout the country -- reaching upwards of tens to hundreds of thousands of bat deaths every year.

An apparent result of interacting with the moving blades of wind turbines, most of the killed tree bats are found dead beneath turbines, for some unknown seasonal reason, in late summer and autumn.

The USGS research team, using thermal cameras that image heat instead of light, logged several months of surveillance footage at three wind turbines in Indiana.

The team also covered the nighttime airspace around turbines with near-infrared security cameras, radar and machines that record the ultrasonic calls of bats.

Over the period of the study, bats were seen on video near turbines more than 900 times, typically approaching individual turbines one or more times instead of simply flying past.

It was noted they often flew very close to the turbine monopoles, nacelles (machinery boxes at top of monopoles) and sometimes approached stationary or slow-moving blades. Meanwhile, radar imaging showed that hundreds of night-migrating birds also flew above and around the turbines nightly, but not as closely as the bats.

The authors of the research concluded from the way bats approached the turbines that they might be following airflow paths around the tree-like structures, but may not be able to tell a tree from a wind turbine with slow or stopped blades.

"The way bats approach turbines suggests they follow air currents and use their dim-adapted vision to find and closely investigate tall things shaped like trees," said Marcos Gorresen, an author of the study and scientist with the University of Hawaii at Hilo. "We see these behaviors less often on darker nights and when fast-moving turbine blades are creating chaotic downwind turbulence. This may be because bats are less likely to mistake turbines for trees and approach them in those conditions."

Previous studies indicated that bat fatalities at wind turbines might occur more often on nights with low average wind speeds.

Although these new findings revealed bats closely investigating most parts of the turbines, the study could not determine their reasons for doing so.

"It might be possible to efficiently further reduce fatalities with this method by accounting for sporadic gusts of wind during low-wind periods when bats might be hanging around turbines," said Cris Hein, an author of the study and scientist with Bat Conservation International.

The authors concluded that increasing people's understanding of the ways that bats perceive and approach wind turbines will ultimately help in the search for ways to reduce the risk such an important energy source poses to such an important natural resource.