We've got many different kinds of bats in Pennsylvania but only one can stop a windmill.  We've got big brown bats, little brown bats, tri-colored bats, hoary bats, small-footed bats, silver-haired bats, northern long ear bats, red bats, evening bats, and an occasional seminole bat.  But none of those bats can stop a windmill.

The only bat in Pennsylvania capable of stopping a windmill is this little guy

It is the rarely seen Indiana bat (Myotis sodalis).   It's a whopping 3 inches long and weighs in at less than half an ounce.  It likes to hibernate in clusters of 250 bats per square foot on the ceilings and side walls of caves.  Although 97 percent of Indiana bats are found in Missouri, Kentucky, Indiana and Illinois, Pennsylvania is on the edge of its habitat range. 

The thing that distinguishes the Indiana bat from all other bats is that this little guy is the only bat in Pennsylvania that is on the federal endangered species list.  That means, when you are siting a wind farm in western Pennsylvania, the US Fish & Wildlife Service will want a pre-construction impact assessment of wind development on bats.  Depending on the project, they can ask the project developer to conduct mist-net and cave and mine opening surveys for the Indiana bat.  The Pennsylvania Game Commission gets developers to sign Wind Energy Voluntary Cooperation Agreements that include monitoring of post-construction bat mortality.  And if dead bats are found, and they turn out to be Indiana bats, you can expect both the US Fish & Wildlife Service and the PA Game Commission will be looking to the project developer to mitigate adverse impacts on the bats.

And this is not a hypothetical situation.  It just happened at a 35 turbine wind farm in Cambria and Blair Counties.  According to a news report , a bat carcass was discovered by a technician on September 26 and was brought into the office as per standard monitoring protocol.  When it was determined to be an Indiana bat (sometimes Indiana bats are mistaken for little brown or northern long ear bats), the power company operating the wind farm immediately curtailed nighttime operations of the turbines and reported the incident to the PA Game Commission and the US Fish & Wildlife Service.  At this time, the wind turbines are being turned off 30 minutes before dusk until 30 minutes after dawn every night.  The expectation is that the wind farm will be able to be put back into full operation in mid-November, when the migratory season for bats ends and they begin their winter hibernation.

So, how many bats does it take to stop a windmill?  Just one.  If it's a dead Indiana bat .