Nothing is free in nature and this includes wind power. A particular concern with wind turbines is their effects on bats, which may often be found darting among treetops en masse while on the hunt for bugs to eat. When those treetops turn out to be spinning turbine blades, bad things happen: a bat might be hit directly, or it might wind up with bleeding lungs courtesy of abrupt changes in air pressure around turbines. Dozens of bats may be killed in a single night, only to be found the next morning littered underneath 30-foot turbine blades spinning at up to 80 miles per hour.
The global standard for predicting such impacts from wind farms—and impacts from energy projects, generally—is the ecological impact assessment (EIA). In North America and Europe, bats are protected species (by the Endangered Species Act and EUROBATS, respectively), which means that such assessments are taken very seriously and are prepared at often great cost to wind farm developers. And, given this cost, we would hope that wind farm EIAs are actually doing something to protect bat populations. Alas, this does not seem to be the case, according to a study published Monday in Current Biology from the University of Exeter in the UK. Simply, the perception of risk revealed in the EIA process was not enough to predict actual bat casualties following construction of wind turbines. Bats are just too random.
"Given that EIAs are undertaken globally, are extremely expensive, and are enshrined in legislation, their place in evidence-based decision making deserves evaluation," write Fiona Mathews and colleagues. "Here we assess how well EIAs of wind-farm developments protect bats. We found they do not predict the risks to bats accurately, and even in those cases where high risk was correctly identified, the mitigation deployed did not avert the risk. Given that the primary purpose of an EIA is to make planning decisions evidence-based, our results indicate that EIA mitigation strategies used to date have been ineffective in protecting bats."
Mathews' conclusions are based on surveys of 46 wind farms across the UK over a one-month period. Because dead bats are hard to find, the researchers employed search dogs (below) and audio analyses. Most bat species are pretty tiny, averaging around 5 grams, and this, according to Mathews, is a large part of why existing wind farms don't report the bat fatalities or report "no problem."
Bat activity and bat fatalities at each site were compared to EIA predictions for 29 of the sites (the remaining EIAs were not made available from wind farm developers or public sources). 18 of the assessments concluded that further field-based observations of bat activity were not neccessary because planned turbines were unlikely to overlap with the sorts of features likely to be frequented by bats.
It's basically like saying that because we think bat impacts are unlikely we don't have to study bat activity to see if bat impacts are likely. It wouldn't be that unusual in the world of environmental assessments, but I digress.
"However, during our post-construction surveys we found that half of these  sites contained casualties (ranging from one to 64 fatalities per month during the July–October survey period), and 97 percent had evidence of bat activity (ranging from one to 236 passes per night)," the new study reports. "The perception of risk to bats during EIAs was not significant in predicting either bat casualty rates or activity levels post-construction." So: a lot of dead bats where there shouldn't be any.
Though Mathews puts it rather more delicately, the conclusion is that energy firms are spending a lot of money for PR rather than bat protection. "The precautionary principle indicates that sites perceived to contain little collision threat to bats should be treated with caution until there is a greater understanding of how to identify risk factors to bats," she writes. "On occasions when mitigation is currently deemed unnecessary, post-construction surveys should still be conducted (e.g. carcass searches) to ensure that the predictions are accurate and bat behaviour has not altered from pre-construction levels."
Simply, we need to apply science to bats and wind farms, which means evaluating hypotheses. We spend loads of money on impact assessments, and it seems silly not to follow through to see what the actual environmental impact of a project winds up being. Otherwise, that money really is all just for show—not science.