Why migrating, tree-roosting bats are more susceptible to being killed by wind turbines has been a mystery. In a recent issue of the Proceedings of the National Academies of Science (PNAS), US Geological Survey scientist Paul Cryan offers an explanation: under certain wind conditions, the air currents around turbines is similar enough to the air currents around trees to confuse the bats into thinking the turbines are big trees.

The paper says that the bats congregate on the downwind side of trees to feast on the flying insects that congregate there. The paper doesn’t make this comparison, but it’s a lot like trout hanging out in an eddy, waiting for insects and other edibles to join them.

The problem, of course, is that spinning blades and barotrauma are not kind to bats that hang around wind turbines.

Two of the take-aways from the paper are that turbine operators can put bat deterrents on the downwind side of the turbines, and that changing the operating parameters of the turbines could help save bats, such as preventing the blades from turning in a sudden gust on an otherwise calm night.

Read the PNAS paper, here.
Read a Washington Post paper on the study and the white nose syndrome threat, here. (But note that it never mentions that one group of bat speices is more vulnerable to white nose syndrome, while a different group of bats is more vulnerable to wind turbines.)
A summary of the paper in the Discover Magazine blog is here.
A different summary of the paper in the Popular Science blog is here.
And just for good luck, here is the write-up from Conservation Magazine.

Photo: Instead of going with a generic bat photo, since I don’t seem to have any of common migrating bats, I went with a generic wind farm photo. This is not the wind farm that was studied in the Cryan paper. Lovely photo by by Joshua Winchell.